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1
Kim, So-Young, and Song-You Hong. "The Use of Partial Cloudiness in a Bulk Cloud Microphysics Scheme: Concept and 2D Results." Journal of the Atmospheric Sciences 75, no. 8 (August 2018): 2711–19. http://dx.doi.org/10.1175/jas-d-17-0234.1.
Повний текст джерелаАнотація:
The source and sink terms of microphysical processes vary nonlinearly with cloud condensate amount. Therefore, partial cloudiness is one of the important factors to be considered in a cloud microphysics scheme given that in-cloud condensate amount depends on the cloud fraction of the grid box. An alternative concept to represent the partial cloudiness effect on the microphysical processes of a bulk microphysics scheme is proposed. Based on the statistical relationship between cloud condensate and cloudiness, all hydrometeors in the microphysical processes are treated after converting them to in-cloud values by dividing the amount by estimated cloudiness and multiplying it after the computation of all microphysics terms. The underlying assumption is that all the microphysical processes occur in a cloudy part of the grid box. In a 2D idealized storm case, the Weather Research and Forecasting (WRF) single-moment 5-class (WSM5) microphysics scheme with the proposed approach increases the amount of snow and rain through enhanced autoconversion/accretion and increases precipitation reaching the surface.
2
Gettelman, A. "Putting the clouds back in aerosol-cloud interactions." Atmospheric Chemistry and Physics Discussions 15, no. 15 (August 3, 2015): 20775–810. http://dx.doi.org/10.5194/acpd-15-20775-2015.
Повний текст джерелаАнотація:
Abstract. Aerosol Cloud Interactions (ACI) are the consequence of perturbed aerosols affecting cloud drop and crystal number, with corresponding microphysical and radiative effects. ACI are sensitive to both cloud microphysical processes (the "C" in ACI) and aerosol emissions and processes (the "A" in ACI). This work highlights the importance of cloud microphysical processes, using idealized and global tests of a cloud microphysics scheme used for global climate prediction. Uncertainties in cloud microphysical processes cause uncertainties of up to −35 to +50 % in ACI, stronger than uncertainties due to natural aerosol emissions (−20 to +30 %). The different dimensions and sensitivities of ACI to microphysical processes are analyzed in detail, showing that precipitation processes are critical for understanding ACI and that uncertain cloud lifetime effects are 1/3 of simulated ACI. Buffering of different processes is important, as is the mixed phase and coupling of the microphysics to the condensation and turbulence schemes in the model.
3
Gettelman, A. "Putting the clouds back in aerosol–cloud interactions." Atmospheric Chemistry and Physics 15, no. 21 (November 9, 2015): 12397–411. http://dx.doi.org/10.5194/acp-15-12397-2015.
Повний текст джерелаАнотація:
Abstract. Aerosol–cloud interactions (ACI) are the consequence of perturbed aerosols affecting cloud drop and crystal number, with corresponding microphysical and radiative effects. ACI are sensitive to both cloud microphysical processes (the "C" in ACI) and aerosol emissions and processes (the "A" in ACI). This work highlights the importance of cloud microphysical processes, using idealized and global tests of a cloud microphysics scheme used for global climate prediction. Uncertainties in key cloud microphysical processes examined with sensitivity tests cause uncertainties of nearly −30 to +60 % in ACI, similar to or stronger than uncertainties identified due to natural aerosol emissions (−30 to +30 %). The different dimensions and sensitivities of ACI to microphysical processes identified in previous work are analyzed in detail, showing that precipitation processes are critical for understanding ACI and that uncertain cloud lifetime effects are nearly one-third of simulated ACI. Buffering of different processes is important, as is the mixed phase and coupling of the microphysics to the condensation and turbulence schemes in the model.
4
Heikenfeld, Max, Bethan White, Laurent Labbouz, and Philip Stier. "Aerosol effects on deep convection: the propagation of aerosol perturbations through convective cloud microphysics." Atmospheric Chemistry and Physics 19, no. 4 (February 28, 2019): 2601–27. http://dx.doi.org/10.5194/acp-19-2601-2019.
Повний текст джерелаАнотація:
Abstract. The impact of aerosols on ice- and mixed-phase processes in deep convective clouds remains highly uncertain, and the wide range of interacting microphysical processes is still poorly understood. To understand these processes, we analyse diagnostic output of all individual microphysical process rates for two bulk microphysics schemes in the Weather and Research Forecasting model (WRF). We investigate the response of individual processes to changes in aerosol conditions and the propagation of perturbations through the microphysics all the way to the macrophysical development of the convective clouds. We perform simulations for two different cases of idealised supercells using two double-moment bulk microphysics schemes and a bin microphysics scheme. The simulations cover a comprehensive range of values for cloud droplet number concentration (CDNC) and cloud condensation nuclei (CCN) concentration as a proxy for aerosol effects on convective clouds. We have developed a new cloud tracking algorithm to analyse the morphology and time evolution of individually tracked convective cells in the simulations and their response to the aerosol perturbations. This analysis confirms an expected decrease in warm rain formation processes due to autoconversion and accretion for more polluted conditions. There is no evidence of a significant increase in the total amount of latent heat, as changes to the individual components of the integrated latent heating in the cloud compensate each other. The latent heating from freezing and riming processes is shifted to a higher altitude in the cloud, but there is no significant change to the integrated latent heat from freezing. Different choices in the treatment of deposition and sublimation processes between the microphysics schemes lead to strong differences including feedbacks onto condensation and evaporation. These changes in the microphysical processes explain some of the response in cloud mass and the altitude of the cloud centre of gravity. However, there remain some contrasts in the development of the bulk cloud parameters between the microphysics schemes and the two simulated cases.
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Cox, Christopher J., David D. Turner, Penny M. Rowe, Matthew D. Shupe, and Von P. Walden. "Cloud Microphysical Properties Retrieved from Downwelling Infrared Radiance Measurements Made at Eureka, Nunavut, Canada (2006–09)." Journal of Applied Meteorology and Climatology 53, no. 3 (March 2014): 772–91. http://dx.doi.org/10.1175/jamc-d-13-0113.1.
Повний текст джерелаАнотація:
AbstractThe radiative properties of clouds are related to cloud microphysical and optical properties, including water path, optical depth, particle size, and thermodynamic phase. Ground-based observations from remote sensors provide high-quality, long-term, continuous measurements that can be used to obtain these properties. In the Arctic, a more comprehensive understanding of cloud microphysics is important because of the sensitivity of the Arctic climate to changes in radiation. Eureka, Nunavut (80°N, 86°25′W, 10 m), Canada, is a research station located on Ellesmere Island. A large suite of ground-based remote sensors at Eureka provides the opportunity to make measurements of cloud microphysics using multiple instruments and methodologies. In this paper, cloud microphysical properties are presented using a retrieval method that utilizes infrared radiances obtained from an infrared spectrometer at Eureka between March 2006 and April 2009. These retrievals provide a characterization of the microphysics of ice and liquid in clouds with visible optical depths between 0.25 and 6, which are a class of clouds whose radiative properties depend greatly on their microphysical properties. The results are compared with other studies that use different methodologies at Eureka, providing context for multimethod perspectives. The authors’ findings are supportive of previous studies, including seasonal cycles in phase and liquid particle size, weak temperature–phase dependencies, and frequent occurrences of supercooled water. Differences in microphysics are found between mixed-phase and single-phase clouds for both ice and liquid. The Eureka results are compared with those obtained using a similar retrieval technique during the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment.
6
Song, Xiaoliang, Guang J. Zhang, and J. L. F. Li. "Evaluation of Microphysics Parameterization for Convective Clouds in the NCAR Community Atmosphere Model CAM5." Journal of Climate 25, no. 24 (December 15, 2012): 8568–90. http://dx.doi.org/10.1175/jcli-d-11-00563.1.
Повний текст джерелаАнотація:
Abstract A physically based two-moment microphysics parameterization scheme for convective clouds is implemented in the NCAR Community Atmosphere Model version 5 (CAM5) to improve the representation of convective clouds and their interaction with large-scale clouds and aerosols. The explicit treatment of mass mixing ratio and number concentration of cloud and precipitation particles enables the scheme to account for the impact of aerosols on convection. The scheme is linked to aerosols through cloud droplet activation and ice nucleation processes and to stratiform cloud parameterization through convective detrainment of cloud liquid/ice water content (LWC/IWC) and droplet/crystal number concentration (DNC/CNC). A 5-yr simulation with the new convective microphysics scheme shows that both cloud LWC/IWC and DNC/CNC are in good agreement with observations, indicating the scheme describes microphysical processes in convection well. Moreover, the microphysics scheme is able to represent the aerosol effects on convective clouds such as the suppression of warm rain formation and enhancement of freezing when aerosol loading is increased. With more realistic simulations of convective cloud microphysical properties and their detrainment, the mid- and low-level cloud fraction is increased significantly over the ITCZ–southern Pacific convergence zone (SPCZ) and subtropical oceans, making it much closer to the observations. Correspondingly, the serious negative bias in cloud liquid water path over subtropical oceans observed in the standard CAM5 is reduced markedly. The large-scale precipitation is increased and precipitation distribution is improved as well. The long-standing precipitation bias in the western Pacific is significantly alleviated because of microphysics–thermodynamics feedbacks.
7
Vanderlei Martins, J., A. Marshak, L. A. Remer, D. Rosenfeld, Y. J. Kaufman, R. Fernandez-Borda, I. Koren, V. Zubko, and P. Artaxo. "Remote sensing the vertical profile of cloud droplet effective radius, thermodynamic phase, and temperature." Atmospheric Chemistry and Physics Discussions 7, no. 2 (March 30, 2007): 4481–519. http://dx.doi.org/10.5194/acpd-7-4481-2007.
Повний текст джерелаАнотація:
Abstract. Cloud-aerosol interaction is no longer simply a radiative problem, but one affecting the water cycle, the weather, and the total energy balance including the spatial and temporal distribution of latent heat release. Information on the vertical distribution of cloud droplet microphysics and thermodynamic phase as a function of temperature or height, can be correlated with details of the aerosol field to provide insight on how these particles are affecting cloud properties and its consequences to cloud lifetime, precipitation, water cycle, and general energy balance. Unfortunately, today's experimental methods still lack the observational tools that can characterize the true evolution of the cloud microphysical, spatial and temporal structure in the cloud droplet scale, and then link these characteristics to environmental factors and properties of the cloud condensation nuclei. Here we propose and demonstrate a new experimental approach (the cloud scanner instrument) that provides the microphysical information missed in current experiments and remote sensing options. Cloud scanner measurements can be performed from aircraft, ground, or satellite by scanning the side of the clouds from the base to the top, providing us with the unique opportunity of obtaining snapshots of the cloud droplet microphysical and thermodynamic states as a function of height and brightness temperature in clouds at several development stages. The brightness temperature profile of the cloud side can be directly associated with the thermodynamic phase of the droplets to provide information on the glaciation temperature as a function of different ambient conditions, aerosol concentration, and type. An aircraft prototype of the cloud scanner was built and flew in a field campaign in Brazil. The CLAIM-3D (3-Dimensional Cloud Aerosol Interaction Mission) satellite concept proposed here combines several techniques to simultaneously measure the vertical profile of cloud microphysics, thermodynamic phase, brightness temperature, and aerosol amount and type in the neighborhood of the clouds. The wide wavelength range, and the use of mutli-angle polarization measurements proposed for this mission allow us to estimate the availability and characteristics of aerosol particles acting as cloud condensation nuclei, and their effects on the cloud microphysical structure. These results can provide unprecedented details on the response of cloud droplet microphysics to natural and anthropogenic aerosols in the size scale where the interaction really happens.
8
Martins, J. V., A. Marshak, L. A. Remer, D. Rosenfeld, Y. J. Kaufman, R. Fernandez-Borda, I. Koren, A. L. Correia, V. Zubko, and P. Artaxo. "Remote sensing the vertical profile of cloud droplet effective radius, thermodynamic phase, and temperature." Atmospheric Chemistry and Physics 11, no. 18 (September 16, 2011): 9485–501. http://dx.doi.org/10.5194/acp-11-9485-2011.
Повний текст джерелаАнотація:
Abstract. Cloud-aerosol interaction is a key issue in the climate system, affecting the water cycle, the weather, and the total energy balance including the spatial and temporal distribution of latent heat release. Information on the vertical distribution of cloud droplet microphysics and thermodynamic phase as a function of temperature or height, can be correlated with details of the aerosol field to provide insight on how these particles are affecting cloud properties and their consequences to cloud lifetime, precipitation, water cycle, and general energy balance. Unfortunately, today's experimental methods still lack the observational tools that can characterize the true evolution of the cloud microphysical, spatial and temporal structure in the cloud droplet scale, and then link these characteristics to environmental factors and properties of the cloud condensation nuclei. Here we propose and demonstrate a new experimental approach (the cloud scanner instrument) that provides the microphysical information missed in current experiments and remote sensing options. Cloud scanner measurements can be performed from aircraft, ground, or satellite by scanning the side of the clouds from the base to the top, providing us with the unique opportunity of obtaining snapshots of the cloud droplet microphysical and thermodynamic states as a function of height and brightness temperature in clouds at several development stages. The brightness temperature profile of the cloud side can be directly associated with the thermodynamic phase of the droplets to provide information on the glaciation temperature as a function of different ambient conditions, aerosol concentration, and type. An aircraft prototype of the cloud scanner was built and flew in a field campaign in Brazil. The CLAIM-3D (3-Dimensional Cloud Aerosol Interaction Mission) satellite concept proposed here combines several techniques to simultaneously measure the vertical profile of cloud microphysics, thermodynamic phase, brightness temperature, and aerosol amount and type in the neighborhood of the clouds. The wide wavelength range, and the use of multi-angle polarization measurements proposed for this mission allow us to estimate the availability and characteristics of aerosol particles acting as cloud condensation nuclei, and their effects on the cloud microphysical structure. These results can provide unprecedented details on the response of cloud droplet microphysics to natural and anthropogenic aerosols in the size scale where the interaction really happens.
9
Rosenfeld, D., G. Liu, X. Yu, Y. Zhu, J. Dai, X. Xu, and Z. Yue. "High resolution (375 m) cloud microstructure as seen from the NPP/VIIRS Satellite imager." Atmospheric Chemistry and Physics Discussions 13, no. 11 (November 13, 2013): 29845–94. http://dx.doi.org/10.5194/acpd-13-29845-2013.
Повний текст джерелаАнотація:
Abstract. The VIIRS (Visible Infrared Imaging Radiometer Suite) onboard the Suomi NPP (National Polar-Orbiting Partnership) satellite has improved resolution of 750 m with respect to 1000 m of the MODerate-resolution Imaging Spectroradiometer, for the channels that allow retrieving cloud microphysical parameters such as cloud drop effective radius (re). The VIIRS has also an imager with 5 channels of double resolution of 375 m, which was not designed for retrieving cloud products. A methodology for a high resolution retrieval of re and microphysical presentation of the cloud field based on the VIIRS imager was developed and evaluated with respect to MODIS in this study. The tripled microphysical resolution with respect to MODIS allows obtaining new insights for cloud aerosol interactions, especially at the smallest cloud scales, because the VIIRS imager can resolve the small convective elements that are sub-pixel for MODIS cloud products. Examples are given for new insights on ship tracks in marine stratocumulus, pollution tracks from point and diffused sources in stratocumulus and cumulus clouds over land, deep tropical convection in pristine air mass over ocean and land, tropical clouds that develop in smoke from forest fires and in heavy pollution haze over densely populated regions in southeast Asia, and for pyro-cumulonimbus clouds. It is found that the VIIRS imager provides more robust physical interpretation and refined information for cloud and aerosol microphysics as compared to MODIS, especially in the initial stage of cloud formation. VIIRS is found to identify much more full-cloudy pixels when small boundary layer convective elements are present. This, in turn, allows a better quantification of cloud aerosol interactions and impacts on precipitation forming processes.
10
Rosenfeld, D., G. Liu, X. Yu, Y. Zhu, J. Dai, X. Xu, and Z. Yue. "High-resolution (375 m) cloud microstructure as seen from the NPP/VIIRS satellite imager." Atmospheric Chemistry and Physics 14, no. 5 (March 10, 2014): 2479–96. http://dx.doi.org/10.5194/acp-14-2479-2014.
Повний текст джерелаАнотація:
Abstract. VIIRS (Visible Infrared Imaging Radiometer Suite), onboard the Suomi NPP (National Polar-orbiting Partnership) satellite, has an improved resolution of 750 m with respect to the 1000 m of the Moderate Resolution Imaging Spectroradiometer for the channels that allow retrieving cloud microphysical parameters such as cloud drop effective radius (re). VIIRS also has an imager with five channels of double resolution of 375 m, which was not designed for retrieving cloud products. A methodology for a high-resolution retrieval of re and microphysical presentation of the cloud field based on the VIIRS imager was developed and evaluated with respect to MODIS in this study. The tripled microphysical resolution with respect to MODIS allows obtaining new insights for cloud–aerosol interactions, especially at the smallest cloud scales, because the VIIRS imager can resolve the small convective elements that are sub-pixel for MODIS cloud products. Examples are given for new insights into ship tracks in marine stratocumulus, pollution tracks from point and diffused sources in stratocumulus and cumulus clouds over land, deep tropical convection in pristine air mass over ocean and land, tropical clouds that develop in smoke from forest fires and in heavy pollution haze over densely populated regions in southeastern Asia, and for pyro-cumulonimbus clouds. It is found that the VIIRS imager provides more robust physical interpretation and refined information for cloud and aerosol microphysics as compared to MODIS, especially in the initial stage of cloud formation. VIIRS is found to identify significantly more fully cloudy pixels when small boundary layer convective elements are present. This, in turn, allows for a better quantification of cloud–aerosol interactions and impacts on precipitation-forming processes.
11
Jarecka, D., H. Pawlowska, W. W. Grabowski, and A. A. Wyszogrodzki. "Modeling microphysical effects of entrainment in clouds observed during EUCAARI-IMPACT field campaign." Atmospheric Chemistry and Physics Discussions 13, no. 1 (January 15, 2013): 1489–526. http://dx.doi.org/10.5194/acpd-13-1489-2013.
Повний текст джерелаАнотація:
Abstract. This paper discusses aircraft observations and large-eddy simulation (LES) of the 15 May 2008, North Sea boundary-layer clouds from the EUCAARI-IMPACT field campaign. These clouds were advected from the north-east by the prevailing lower-tropspheric winds, and featured stratocumulus-over-cumulus cloud formations. Almost-solid stratocumulus deck in the upper part of the relatively deep weakly decoupled marine boundary layer overlaid a field of small cumuli with a cloud fraction of ~10%. The two cloud formations featured distinct microphysical characteristics that were in general agreement with numerous past observations of strongly-diluted shallow cumuli on the one hand and solid marine boundary-layer stratocumulus on the other. Macrophysical and microphysical cloud properties were reproduced well by the double-moment warm-rain microphysics large-eddy simulation. A novel feature of the model is its capability to locally predict homogeneity of the subgrid-scale mixing between the cloud and its cloud-free environment. In the double-moment warm-rain microphysics scheme, the homogeneity is controlled by a single parameter α, that ranges from 0 to 1 and limiting values representing the homogeneous and the extremely inhomogeneous mixing scenarios, respectively. Parameter α depends on the characteristic time scales of the droplet evaporation and of the turbulent homogenization. In the model, these scales are derived locally based on the subgrid-scale turbulent kinetic energy, spatial scale of cloudy filaments, the mean cloud droplet radius, and the humidity of the cloud-free air entrained into the cloud. Simulated mixing is on average quite inhomogeneous, with the mean parameter α around 0.7 across the entire depth of the cloud field, but with local variations across almost the entire range, especially near the base and the top of the cloud field.
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Muhlbauer, A., T. Hashino, L. Xue, A. Teller, U. Lohmann, R. M. Rasmussen, I. Geresdi, and Z. Pan. "Intercomparison of aerosol-cloud-precipitation interactions in stratiform orographic mixed-phase clouds." Atmospheric Chemistry and Physics 10, no. 17 (September 2, 2010): 8173–96. http://dx.doi.org/10.5194/acp-10-8173-2010.
Повний текст джерелаАнотація:
Abstract. Anthropogenic aerosols serve as a source of both cloud condensation nuclei (CCN) and ice nuclei (IN) and affect microphysical properties of clouds. Increasing aerosol number concentrations is hypothesized to retard the cloud droplet coalescence and the riming in mixed-phase clouds, thereby decreasing orographic precipitation. This study presents results from a model intercomparison of 2-D simulations of aerosol-cloud-precipitation interactions in stratiform orographic mixed-phase clouds. The sensitivity of orographic precipitation to changes in the aerosol number concentrations is analysed and compared for various dynamical and thermodynamical situations. Furthermore, the sensitivities of microphysical processes such as coalescence, aggregation, riming and diffusional growth to changes in the aerosol number concentrations are evaluated and compared. The participating numerical models are the model from the Consortium for Small-Scale Modeling (COSMO) with bulk microphysics, the Weather Research and Forecasting (WRF) model with bin microphysics and the University of Wisconsin modeling system (UWNMS) with a spectral ice habit prediction microphysics scheme. All models are operated on a cloud-resolving scale with 2 km horizontal grid spacing. The results of the model intercomparison suggest that the sensitivity of orographic precipitation to aerosol modifications varies greatly from case to case and from model to model. Neither a precipitation decrease nor a precipitation increase is found robustly in all simulations. Qualitative robust results can only be found for a subset of the simulations but even then quantitative agreement is scarce. Estimates of the aerosol effect on orographic precipitation are found to range from −19% to 0% depending on the simulated case and the model. Similarly, riming is shown to decrease in some cases and models whereas it increases in others, which implies that a decrease in riming with increasing aerosol load is not a robust result. Furthermore, it is found that neither a decrease in cloud droplet coalescence nor a decrease in riming necessarily implies a decrease in precipitation due to compensation effects by other microphysical pathways. The simulations suggest that mixed-phase conditions play an important role in buffering the effect of aerosol perturbations on cloud microphysics and reducing the overall susceptibility of clouds and precipitation to changes in the aerosol number concentrations. As a consequence the aerosol effect on precipitation is suggested to be less pronounced or even inverted in regions with high terrain (e.g., the Alps or Rocky Mountains) or in regions where mixed-phase microphysics is important for the climatology of orographic precipitation.
13
Gayatri, K., S. Patade, and T. V. Prabha. "Aerosol–Cloud Interaction in Deep Convective Clouds over the Indian Peninsula Using Spectral (Bin) Microphysics." Journal of the Atmospheric Sciences 74, no. 10 (September 13, 2017): 3145–66. http://dx.doi.org/10.1175/jas-d-17-0034.1.
Повний текст джерелаАнотація:
Abstract The Weather Research and Forecasting (WRF) Model coupled with a spectral bin microphysics (SBM) scheme is used to investigate aerosol effects on cloud microphysics and precipitation over the Indian peninsular region. The main emphasis of the study is in comparing simulated cloud microphysical structure with in situ aircraft observations from the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX). Aerosol–cloud interaction over the rain-shadow region is investigated with observed and simulated size distribution spectra of cloud droplets and ice particles in monsoon clouds. It is shown that size distributions as well as other microphysical characteristics obtained from simulations such as liquid water content, cloud droplet effective radius, cloud droplet number concentration, and thermodynamic parameters are in good agreement with the observations. It is seen that in clouds with high cloud condensation nuclei (CCN) concentrations, snow and graupel size distribution spectra were broader compared to clouds with low concentrations of CCN, mainly because of enhanced riming in the presence of a large number of droplets with a diameter of 10–30 μm. The Hallett–Mossop ice multiplication process is illustrated to have an impact on snow and graupel mass. The changes in CCN concentrations have a strong effect on cloud properties over the domain, amounts of cloud water, and the glaciation of the clouds, but the effects on surface precipitation are small when averaged over a large area. Overall enhancement of cold-phase cloud processes in the high-CCN case contributed to slight enhancement (5%) in domain-averaged surface precipitation.
14
Ilotoviz, Eyal, and Alexander Khain. "Application of a new scheme of cloud base droplet nucleation in a spectral (bin) microphysics cloud model: sensitivity to aerosol size distribution." Atmospheric Chemistry and Physics 16, no. 22 (November 17, 2016): 14317–29. http://dx.doi.org/10.5194/acp-16-14317-2016.
Повний текст джерелаАнотація:
Abstract. A new scheme of droplet nucleation at cloud base is implemented into the Hebrew University Cloud Model (HUCM) with spectral (bin) microphysics. In this scheme, supersaturation maximum Smax near cloud base is calculated using theoretical results according to which Smax ∼ w3∕4Nd−1∕2, where w is the vertical velocity at cloud base and Nd is droplet concentration. Microphysical cloud structure obtained in the simulations of a midlatitude hail storm using the new scheme is compared with that obtained in the standard approach, in which droplet nucleation is calculated using supersaturation calculated in grid points. The simulations were performed with different concentrations of cloud condensational nuclei (CCN) and with different shapes of CCN size spectra. It is shown that the new nucleation scheme substantially improves the vertical profile of droplet concentration shifting the concentration maximum to cloud base. It is shown that the effect of the CCN size distribution shape on cloud microphysics is not less important than the effect of the total CCN concentration. It is shown that the smallest CCN with diameters less than about 0.015 µm have a substantial effect on mixed-phase and ice microphysics of deep convective clouds. Such CCN are not measured by standard CCN probes, which hinders understanding of cold microphysical processes.
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Wyszogrodzki, A. A., W. W. Grabowski, L. P. Wang, and O. Ayala. "Turbulent collision-coalescence in maritime shallow convection." Atmospheric Chemistry and Physics 13, no. 16 (August 27, 2013): 8471–87. http://dx.doi.org/10.5194/acp-13-8471-2013.
Повний текст джерелаАнотація:
Abstract. This paper discusses cloud simulations aiming at quantitative assessment of the effects of cloud turbulence on rain development in shallow ice-free convective clouds. Cloud fields from large-eddy simulations (LES) applying bin microphysics with the collection kernel enhanced by cloud turbulence are compared to those with the standard gravitational collection kernel. Simulations for a range of cloud condensation nuclei (CCN) concentrations are contrasted. Details on how the parameterized turbulent collection kernel is used in LES simulations are presented. Because of the disparity in spatial scales between the bottom-up numerical studies guiding the turbulent kernel development and the top-down LES simulations of cloud dynamics, we address the consequence of the turbulence intermittency in the unresolved range of scales on the mean collection kernel applied in LES. We show that intermittency effects are unlikely to play an important role in the current simulations. Highly-idealized single-cloud simulations are used to illustrate two mechanisms that operate in cloud field simulations. First, the microphysical enhancement leads to earlier formation of drizzle through faster autoconversion of cloud water into drizzle, as suggested by previous studies. Second, more efficient removal of condensed water from cloudy volumes when a turbulent collection kernel is used leads to an increased cloud buoyancy and enables clouds to reach higher levels. This is the dynamical enhancement. Both mechanisms operate in the cloud field simulations. The microphysical enhancement leads to the increased drizzle and rain inside clouds in simulations with high CCN. In low-CCN simulations with significant surface rainfall, dynamical enhancement leads to a larger contribution of deeper clouds to the entire cloud population, and results in a dramatically increased mean surface rain accumulation. These results call for future modeling and observational studies to corroborate the findings.
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Grabowski, Wojciech W. "Indirect Impact of Atmospheric Aerosols in Idealized Simulations of Convective–Radiative Quasi Equilibrium." Journal of Climate 19, no. 18 (September 15, 2006): 4664–82. http://dx.doi.org/10.1175/jcli3857.1.
Повний текст джерелаАнотація:
Abstract This paper discusses a cloud-resolving modeling study concerning the impact of warm-rain microphysics on convective–radiative quasi equilibrium with fixed surface characteristics and prescribed solar input, both mimicking the mean conditions on earth. Two limits of the concentration of cloud droplets, either 100 cm−3 (referred to as “pristine”) or 1000 cm−3 (referred to as “polluted”), are considered. In addition, three formulations of the effective radius of water droplets in diluted cloudy volumes are used, corresponding to the homogeneous, intermediate, and extremely inhomogeneous mixing scenarios. The assumed concentration of cloud droplets, together with the assumed mixing scenario, affects the local value of the effective radius of cloud droplets (the first indirect aerosol effect, also known as the Twomey effect) and the transfer of cloud water into drizzle and rain, which can affect the mean cloudiness and the hydrologic cycle (the second indirect effect). The convective–radiative quasi equilibrium mimics the estimates of globally and annually averaged water and energy fluxes across the earth’s atmosphere to within less than 10 W m−2. As on earth, the model cloudiness is dominated by shallow convection. It is found that the impact of warm microphysics is dominated by the first indirect effect, whereas the second indirect effect has a smaller impact. The assumed droplet concentration and mixing scenario impact the mean “planetary” albedo and, thus, the amount of solar energy reaching the surface, with all other components of atmospheric energy and water budgets virtually the same in all simulations. The weak second indirect effect highlights the difference between the impact of cloud microphysics on a single cloud and the impact on an ensemble of clouds, with only the latter including the feedbacks between clouds and their environment. The formulation of the effective radius in the diluted cloudy volumes turns out to be of critical importance, with the amount of solar energy reaching the surface being the same in the pristine case assuming the homogeneous mixing scenario and in the polluted case with the extremely inhomogeneous mixing. This result emphasizes the essential role of poorly understood microphysical transformations within diluted convective clouds, which strongly impact the magnitude of the first indirect (Twomey) effect. Implications for future research in this area are discussed.
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Larsen, H., J. F. Gayet, G. Febvre, H. Chepfer, and G. Brogniez. "Measurement errors in cirrus cloud microphysical properties." Annales Geophysicae 16, no. 2 (February 28, 1998): 266–76. http://dx.doi.org/10.1007/s00585-998-0266-8.
Повний текст джерелаАнотація:
Abstract. The limited accuracy of current cloud microphysics sensors used in cirrus cloud studies imposes limitations on the use of the data to examine the cloud's broadband radiative behaviour, an important element of the global energy balance. We review the limitations of the instruments, PMS probes, most widely used for measuring the microphysical structure of cirrus clouds and show the effect of these limitations on descriptions of the cloud radiative properties. The analysis is applied to measurements made as part of the European Cloud and Radiation Experiment (EUCREX) to determine mid-latitude cirrus microphysical and radiative properties.Key words. Atmospheric composition and structure (cloud physics and chemistry) · Meteorology and atmospheric dynamics · Radiative processes · Instruments and techniques
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Jarecka, Dorota, Wojciech W. Grabowski, and Hanna Pawlowska. "Modeling of Subgrid-Scale Mixing in Large-Eddy Simulation of Shallow Convection." Journal of the Atmospheric Sciences 66, no. 7 (July 1, 2009): 2125–33. http://dx.doi.org/10.1175/2009jas2929.1.
Повний текст джерелаАнотація:
Abstract This paper discusses an extension of the approach proposed previously to represent the delay of cloud water evaporation and buoyancy reversal due to the cloud–environment mixing in bulk microphysics large-eddy simulation of clouds. In the original approach, an additional equation for the mean spatial scale of cloudy filaments was introduced to represent the progress toward microscale homogenization of a volume undergoing turbulent cloud–environment mixing, with the evaporation of cloud water allowed only when the filament scale approached the Kolmogorov microscale. Here, it is shown through a posteriori analysis of model simulations that one should also predict the volume fraction of the cloudy air that was diagnosed in the original approach. The resulting model of turbulent mixing and homogenization, referred to as the λ–β model, is applied in a series of shallow convection simulations using various spatial resolutions and compared to the traditional bulk model. This work represents an intermediate step in the development of a modeling framework to simulate characteristics of microphysical transformations during entrainment and subgrid-scale turbulent mixing.
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Wyszogrodzki, A. A., W. W. Grabowski, L. P. Wang, and O. Ayala. "Turbulent collision-coalescence in maritime shallow convection." Atmospheric Chemistry and Physics Discussions 13, no. 4 (April 8, 2013): 9217–65. http://dx.doi.org/10.5194/acpd-13-9217-2013.
Повний текст джерелаАнотація:
Abstract. This paper discusses cloud simulations aiming at quantitative assessment of the effects of cloud turbulence on rain development in shallow ice-free convective clouds. Cloud fields from large-eddy simulations (LES) applying the bin microphysics with the collision kernel enhanced by cloud turbulence are compared to those with the standard gravitational collision kernel. Simulations for a range of cloud condensation nuclei (CCN) concentrations are contrasted. Details of the turbulent kernel and how it is used in LES simulations are presented. Because of the disparity in spatial scales between the bottom-up numerical studies guiding the turbulent kernel development and the top-down LES simulations of cloud dynamics, we address the consequence of the turbulence intermittency in the unresolved range of scales on the mean collision kernel applied in LES. We show that intermittency effects are unlikely to play an important role in the current simulations. Highly-idealized single-cloud simulations are used to illustrate two mechanisms that operate in cloud field simulations. First, the microphysical enhancement leads to earlier formation of drizzle through faster autoconversion of cloud water into drizzle, as suggested by previous studies. Second, more efficient removal of condensed water from cloudy volumes when a turbulent collection kernel is used leads to an increased cloud buoyancy and enables clouds to reach higher levels. This is the dynamical enhancement. Both mechanisms seem to operate in the cloud field simulations. The microphysical enhancement leads to the increased drizzle and rain inside clouds in simulations with high CCN. In low-CCN simulations with significant surface rainfall, dynamical enhancement allows maintenance of the cloud water path despite significant increase of the precipitation water path and dramatically increased mean surface rain accumulation. These results call for future modeling and observational studies to corroborate the findings.
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Dubuisson, Philippe, Vincent Giraud, Jacques Pelon, Bertrand Cadet, and Ping Yang. "Sensitivity of Thermal Infrared Radiation at the Top of the Atmosphere and the Surface to Ice Cloud Microphysics." Journal of Applied Meteorology and Climatology 47, no. 10 (October 1, 2008): 2545–60. http://dx.doi.org/10.1175/2008jamc1805.1.
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Abstract This paper reports on the sensitivity of the brightness temperatures associated with radiances at the surface and the top of the atmosphere, simulated for the Imaging Infrared Radiometer (IIR) 8.7-, 10.6-, and 12-μm channels under ice cloudy conditions, to the optical and microphysical properties of ice clouds. The 10.6- and 12-μm channels allow simultaneous retrieval of ice cloud optical thickness and effective particle size (Deff) less than 100 μm. It is illustrated that the particle shape and size distributions of ice crystals have noticeable effects on the brightness temperatures. Using the split window technique based on the 10.6- and 12-μm channels in conjunction with cloud properties assumed a priori, the authors show that the influence of the cloud microphysical properties can lead to differences on the order of ±10% and ±25% in retrieved effective particle sizes for small (Deff < 20 μm) and large particles (Deff > 40 μm), respectively. The impact of cloud model on retrieved optical thickness is on the order of ±10%. Different particle habits may lead to ±25% differences in ice water path (IWP). Theoretically, the use of an additional channel (i.e., 8.7 μm) can give a stronger constraint on cloud model and improve the retrieval of Deff and IWP. The present simulations have confirmed that cloud microphysics has a significant impact on the 8.7-μm brightness temperatures mainly because of particle shape. This impact is larger than the errors of the IIR measurements for cloud optical thicknesses (at 12 μm) ranging from 0.3 to 8. Furthermore, it is shown that the characterization of optical and microphysical properties of ice clouds from ground-based measurements is quite challenging. Especially, water vapor in the atmosphere has an important impact on ground-based cloud retrievals. Observation stations at higher altitudes or airborne measurements would minimize the atmospheric effect.
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Formenton, M., G. Panegrossi, D. Casella, S. Dietrich, A. Mugnai, P. Sanò, F. Di Paola, H. D. Betz, C. Price, and Y. Yair. "Using a cloud electrification model to study relationships between lightning activity and cloud microphysical structure." Natural Hazards and Earth System Sciences 13, no. 4 (April 24, 2013): 1085–104. http://dx.doi.org/10.5194/nhess-13-1085-2013.
Повний текст джерелаАнотація:
Abstract. In this study a one-dimensional numerical cloud electrification model, called the Explicit Microphysics Thunderstorm Model (EMTM), is used to find quantitative relationships between the simulated electrical activity and microphysical properties in convective clouds. The model, based on an explicit microphysics scheme coupled to an ice–ice noninductive electrification scheme, allows us to interpret the connection of cloud microphysical structure with charge density distribution within the cloud, and to study the full evolution of the lightning activity (intracloud and cloud-to-ground) in relation to different environmental conditions. Thus, we apply the model to a series of different case studies over continental Europe and the Mediterranean region. We first compare, for selected case studies, the simulated lightning activity with the data provided by the ground-based Lightning Detection Network (LINET) in order to verify the reliability of the model and its limitations, and to assess its ability to reproduce electrical activity consistent with the observations. Then, using all simulations, we find a correlation between some key microphysical properties and cloud electrification, and derive quantitative relationships relating simulated flash rates to minimum thresholds of graupel mass content and updrafts. Finally, we provide outlooks on the use of such relationships and comments on the future development of this study.
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Muhlbauer, A., T. Hashino, L. Xue, A. Teller, U. Lohmann, R. M. Rasmussen, I. Geresdi, and Z. Pan. "Intercomparison of aerosol-cloud-precipitation interactions in stratiform orographic mixed-phase clouds." Atmospheric Chemistry and Physics Discussions 10, no. 4 (April 21, 2010): 10487–550. http://dx.doi.org/10.5194/acpd-10-10487-2010.
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Abstract. Anthropogenic aerosols serve as a source of both cloud condensation nuclei (CCN) and ice nuclei (IN) and affect microphysical properties of clouds. Increasing aerosol number concentrations is hypothesized to retard the cloud droplet collision/coalescence and the riming in mixed-phase clouds, thereby decreasing orographic precipitation. This study presents results from a model intercomparison of 2-D simulations of aerosol-cloud-precipitation interactions in stratiform orographic mixed-phase clouds. The sensitivity of orographic precipitation to changes in the aerosol number concentrations is analyzed and compared for various dynamical and thermodynamical situations. Furthermore, the sensitivities of microphysical processes such as collision/coalescence, aggregation and riming to changes in the aerosol number concentrations are evaluated and compared. The participating models are the Consortium for Small-Scale Modeling's (COSMO) model with bulk-microphysics, the Weather Research and Forecasting (WRF) model with bin-microphysics and the University of Wisconsin modeling system (UWNMS) with a spectral ice-habit prediction microphysics scheme. All models are operated on a cloud-resolving scale with 2 km horizontal grid spacing. The results of the model intercomparison suggest that the sensitivity of orographic precipitation to aerosol modifications varies greatly from case to case and from model to model. Neither a precipitation decrease nor a precipitation increase is found robustly in all simulations. Qualitative robust results can only be found for a subset of the simulations but even then quantitative agreement is scarce. Estimates of the second indirect aerosol effect on orographic precipitation are found to range from –19% to 0% depending on the simulated case and the model. Similarly, riming is shown to decrease in some cases and models whereas it increases in others which implies that a decrease in riming with increasing aerosol load is not a robust result. Furthermore, it is found that neither a decrease in cloud droplet coalescence nor a decrease in riming necessarily implies a decrease in precipitation due to compensation effects by other microphysical pathways. The simulations suggest that mixed-phase conditions play an important role in reducing the overall susceptibility of clouds and precipitation with respect to changes in the aerosols number concentrations. As a consequence the indirect aerosol effect on precipitation is suggested to be less pronounced or even inverted in regions with high terrain (e.g., the Alps or Rocky Mountains) or in regions where mixed-phase microphysics climatologically plays an important role for orographic precipitation.
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CALCAN, Andreea, Sabina STEFAN, Sorin Nicolae VAJAIAC, and Denisa MOACA. "Airborne measurements in different clouds." INCAS BULLETIN 13, no. 1 (March 5, 2021): 19–28. http://dx.doi.org/10.13111/2066-8201.2021.13.1.3.
Повний текст джерелаАнотація:
The aim of this paper is to analyze different aspects of microphysical properties of mixed phase clouds, considering also the processes that are contributing to their formation. ATMOSLAB airborne laboratory, equipped with CAPS – Cloud, Aerosol and Precipitation Spectrometer sensors system was exploited to perform three flight research missions focused on cloud microphysics. For this purpose, there was analyzed the variation of 4 major parameters with high influence the cold clouds lifecycle (temperature, pressure, number concentration, effective diameter and 2D images of droplets and ice crystals) and was highlighted the occurrence of nucleation, accretion and droplet coalescence in cirrus and cirrostratus clouds.
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Grabowski, Wojciech W., and Hugh Morrison. "Untangling Microphysical Impacts on Deep Convection Applying a Novel Modeling Methodology. Part II: Double-Moment Microphysics." Journal of the Atmospheric Sciences 73, no. 9 (September 1, 2016): 3749–70. http://dx.doi.org/10.1175/jas-d-15-0367.1.
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Abstract The suggested impact of pollution on deep convection dynamics, referred to as the convective invigoration, is investigated in simulations applying microphysical piggybacking and a comprehensive double-moment bulk microphysics scheme. The setup follows the case of daytime convective development over land based on observations during the Large-Scale Biosphere–Atmosphere (LBA) experiment in Amazonia. In contrast to previous simulations with single-moment microphysics schemes and in agreement with results from bin microphysics simulations by others, the impact of pollution simulated by the double-moment scheme is large for the upper-tropospheric convective anvils that feature higher cloud fractions in polluted conditions. The increase comes from purely microphysical considerations: namely, the increased cloud droplet concentrations in polluted conditions leading to the increased ice crystal concentrations and, consequently, smaller fall velocities and longer residence times. There is no impact on convective dynamics above the freezing level and thus no convective invigoration. Polluted deep convective clouds precipitate about 10% more than their pristine counterparts. The small enhancement comes from smaller supersaturations below the freezing level and higher buoyancies inside polluted convective updrafts with velocities between 5 and 10 m s−1. The simulated supersaturations are large, up to several percent in both pristine and polluted conditions, and they call into question results from deep convection simulations applying microphysical schemes with saturation adjustment. Sensitivity simulations show that the maximum supersaturations and the upper-tropospheric anvil cloud fractions strongly depend on the details of small cloud condensation nuclei (CCN) that can be activated in strong updrafts above the cloud base.
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Barahona, D., A. Molod, J. Bacmeister, A. Nenes, A. Gettelman, H. Morrison, V. Phillips, and A. Eichmann. "Development of two-moment cloud microphysics for liquid and ice within the NASA Goddard earth observing system model (GEOS-5)." Geoscientific Model Development Discussions 6, no. 4 (October 29, 2013): 5289–373. http://dx.doi.org/10.5194/gmdd-6-5289-2013.
Повний текст джерелаАнотація:
Abstract. This work presents the development of a two-moment cloud microphysics scheme within the version 5 of the NASA Goddard Earth Observing System (GEOS-5). The scheme includes the implementation of a comprehensive stratiform microphysics module, a new cloud coverage scheme that allows ice supersaturation and a new microphysics module embedded within the moist convection parameterization of GEOS-5. Comprehensive physically-based descriptions of ice nucleation, including homogeneous and heterogeneous freezing, and liquid droplet activation are implemented to describe the formation of cloud particles in stratiform clouds and convective cumulus. The effect of preexisting ice crystals on the formation of cirrus clouds is also accounted for. A new parameterization of the subgrid scale vertical velocity distribution accounting for turbulence and gravity wave motion is developed. The implementation of the new microphysics significantly improves the representation of liquid water and ice in GEOS-5. Evaluation of the model shows agreement of the simulated droplet and ice crystal effective and volumetric radius with satellite retrievals and in situ observations. The simulated global distribution of supersaturation is also in agreement with observations. It was found that when using the new microphysics the fraction of condensate that remains as liquid follows a sigmoidal increase with temperature which differs from the linear increase assumed in most models and is in better agreement with available observations. The performance of the new microphysics in reproducing the observed total cloud fraction, longwave and shortwave cloud forcing, and total precipitation is similar to the operational version of GEOS-5 and in agreement with satellite retrievals. However the new microphysics tends to underestimate the coverage of persistent low level stratocumulus. Sensitivity studies showed that the simulated cloud properties are robust to moderate variation in cloud microphysical parameters. However significant sensitivity in ice cloud properties was found to variation in the dispersion of the ice crystal size distribution and the critical size for ice autoconversion. The implementation of the new microphysics leads to a more realistic representation of cloud processes in GEOS-5 and allows the linkage of cloud properties to aerosol emissions.
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Jarecka, D., H. Pawlowska, W. W. Grabowski, and A. A. Wyszogrodzki. "Modeling microphysical effects of entrainment in clouds observed during EUCAARI-IMPACT field campaign." Atmospheric Chemistry and Physics 13, no. 16 (August 27, 2013): 8489–503. http://dx.doi.org/10.5194/acp-13-8489-2013.
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Abstract. This paper discusses aircraft observations and large-eddy simulation (LES) modeling of 15 May 2008, North Sea boundary-layer clouds from the EUCAARI-IMPACT field campaign. These clouds are advected from the northeast by the prevailing lower-tropospheric winds and featured stratocumulus-over-cumulus cloud formations. An almost-solid stratocumulus deck in the upper part of the relatively deep, weakly decoupled marine boundary layer overlays a field of small cumuli. The two cloud formations have distinct microphysical characteristics that are in general agreement with numerous past observations of strongly diluted shallow cumuli on one hand and solid marine stratocumulus on the other. Based on the available observations, a LES model setup is developed and applied in simulations using a novel LES model. The model features a double-moment warm-rain bulk microphysics scheme combined with a sophisticated subgrid-scale scheme allowing local prediction of the homogeneity of the subgrid-scale turbulent mixing. The homogeneity depends on the characteristic time scales for the droplet evaporation and for the turbulent homogenization. In the model, these scales are derived locally based on the subgrid-scale turbulent kinetic energy, spatial scale of cloudy filaments, mean cloud droplet radius, and humidity of the cloud-free air entrained into a cloud, all predicted by the LES model. The model reproduces contrasting macrophysical and microphysical characteristics of the cumulus and stratocumulus cloud layers. Simulated subgrid-scale turbulent mixing within the cumulus layer and near the stratocumulus top is on average quite inhomogeneous, but varies significantly depending on the local conditions.
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Carey, Lawrence D., Jianguo Niu, Ping Yang, J. Adam Kankiewicz, Vincent E. Larson, and Thomas H. Vonder Haar. "The Vertical Profile of Liquid and Ice Water Content in Midlatitude Mixed-Phase Altocumulus Clouds." Journal of Applied Meteorology and Climatology 47, no. 9 (September 1, 2008): 2487–95. http://dx.doi.org/10.1175/2008jamc1885.1.
Повний текст джерелаАнотація:
Abstract The microphysical properties of mixed-phase altocumulus clouds are investigated using in situ airborne measurements acquired during the ninth Cloud Layer Experiment (CLEX-9) over a midlatitude location. Approximately ⅔ of the sampled profiles are supercooled liquid–topped altocumulus clouds characterized by mixed-phase conditions. The coexistence of measurable liquid water droplets and ice crystals begins at or within tens of meters of cloud top and extends down to cloud base. Ice virga is found below cloud base. Peak liquid water contents occur at or near cloud top while peak ice water contents occur in the lower half of the cloud or in virga. The estimation of ice water content from particle size data requires that an assumption be made regarding the particle mass–dimensional relation, resulting in potential error on the order of tens of percent. The highest proportion of liquid is typically found in the coldest (top) part of the cloud profile. This feature of the microphysical structure for the midlatitude mixed-phase altocumulus clouds is similar to that reported for mixed-phase clouds over the Arctic region. The results obtained for limited cases of midlatitude mixed-phase clouds observed during CLEX-9 may have an implication for the study of mixed-phase cloud microphysics, satellite remote sensing applications, and the parameterization of mixed-phase cloud radiative properties in climate models.
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Barahona, D., A. Molod, J. Bacmeister, A. Nenes, A. Gettelman, H. Morrison, V. Phillips, and A. Eichmann. "Development of two-moment cloud microphysics for liquid and ice within the NASA Goddard Earth Observing System Model (GEOS-5)." Geoscientific Model Development 7, no. 4 (August 20, 2014): 1733–66. http://dx.doi.org/10.5194/gmd-7-1733-2014.
Повний текст джерелаАнотація:
Abstract. This work presents the development of a two-moment cloud microphysics scheme within version 5 of the NASA Goddard Earth Observing System (GEOS-5). The scheme includes the implementation of a comprehensive stratiform microphysics module, a new cloud coverage scheme that allows ice supersaturation, and a new microphysics module embedded within the moist convection parameterization of GEOS-5. Comprehensive physically based descriptions of ice nucleation, including homogeneous and heterogeneous freezing, and liquid droplet activation are implemented to describe the formation of cloud particles in stratiform clouds and convective cumulus. The effect of preexisting ice crystals on the formation of cirrus clouds is also accounted for. A new parameterization of the subgrid-scale vertical velocity distribution accounting for turbulence and gravity wave motion is also implemented. The new microphysics significantly improves the representation of liquid water and ice in GEOS-5. Evaluation of the model against satellite retrievals and in situ observations shows agreement of the simulated droplet and ice crystal effective radius, the ice mass mixing ratio and number concentration, and the relative humidity with respect to ice. When using the new microphysics, the fraction of condensate that remains as liquid follows a sigmoidal dependency with temperature, which is in agreement with observations and which fundamentally differs from the linear increase assumed in most models. The performance of the new microphysics in reproducing the observed total cloud fraction, longwave and shortwave cloud forcing, and total precipitation is similar to the operational version of GEOS-5 and in agreement with satellite retrievals. The new microphysics tends to underestimate the coverage of persistent low-level stratocumulus. Sensitivity studies showed that the simulated cloud properties are robust to moderate variation in cloud microphysical parameters. Significant sensitivity remains to variation in the dispersion of the ice crystal size distribution and the critical size for ice autoconversion. Despite these issues, the implementation of the new microphysics leads to a considerably improved and more realistic representation of cloud processes in GEOS-5, and allows the linkage of cloud properties to aerosol emissions.
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Krueger, Steven K., Qiang Fu, K. N. Liou, and Hung-Neng S. Chin. "Improvements of an Ice-Phase Microphysics Parameterization for Use in Numerical Simulations of Tropical Convection." Journal of Applied Meteorology 34, no. 1 (January 1, 1995): 281–87. http://dx.doi.org/10.1175/1520-0450-34.1.281.
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Abstract It is important to properly simulate the extent and ice water content of tropical anvil clouds in numerical models that explicitly include cloud formation because of the significant effects that these clouds have on the radiation budget. For this reason, a commonly used bulk ice-phase microphysics parameterization was modified to more realistically simulate some of the microphysical processes that occur in tropical anvil clouds. Cloud ice growth by the Bergeron process and the associated formation of snow were revised. The characteristics of graupel were also modified in accord with a previous study. Numerical simulations of a tropical squall line demonstrate that the amount of cloud ice and the extent of anvil clouds are increased to more realistic values by the first two changes.
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Klinger, Carolin, Graham Feingold, and Takanobu Yamaguchi. "Cloud droplet growth in shallow cumulus clouds considering 1-D and 3-D thermal radiative effects." Atmospheric Chemistry and Physics 19, no. 9 (May 14, 2019): 6295–313. http://dx.doi.org/10.5194/acp-19-6295-2019.
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Abstract. The effect of 1-D and 3-D thermal radiation on cloud droplet growth in shallow cumulus clouds is investigated using large eddy simulations with size-resolved cloud microphysics. A two-step approach is used for separating microphysical effects from dynamical feedbacks. In step one, an offline parcel model is used to describe the onset of rain. The growth of cloud droplets to raindrops is simulated with bin-resolved microphysics along previously recorded Lagrangian trajectories. It is shown that thermal heating and cooling rates can enhance droplet growth and raindrop production. Droplets grow to larger size bins in the 10–30 µm radius range. The main effect in terms of raindrop production arises from recirculating parcels, where a small number of droplets are exposed to strong thermal cooling at cloud edge. These recirculating parcels, comprising about 6 %–7 % of all parcels investigated, make up 45 % of the rain for the no-radiation simulation and up to 60 % when 3-D radiative effects are considered. The effect of 3-D thermal radiation on rain production is stronger than that of 1-D thermal radiation. Three-dimensional thermal radiation can enhance the rain amount up to 40 % compared to standard droplet growth without radiative effects in this idealized framework. In the second stage, fully coupled large eddy simulations show that dynamical effects are stronger than microphysical effects, as far as the production of rain is concerned. Three-dimensional thermal radiative effects again exceed one-dimensional thermal radiative effects. Small amounts of rain are produced in more clouds (over a larger area of the domain) when thermal radiation is applied to microphysics. The dynamical feedback is shown to be an enhanced cloud circulation with stronger subsiding shells at the cloud edges due to thermal cooling and stronger updraft velocities in the cloud center. It is shown that an evaporation–circulation feedback reduces the amount of rain produced in simulations where 3-D thermal radiation is applied to microphysics and dynamics, in comparison to where 3-D thermal radiation is only applied to dynamics.
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Marinou, Eleni, Kalliopi Artemis Voudouri, Ioanna Tsikoudi, Eleni Drakaki, Alexandra Tsekeri, Marco Rosoldi, Dragos Ene, et al. "Geometrical and Microphysical Properties of Clouds Formed in the Presence of Dust above the Eastern Mediterranean." Remote Sensing 13, no. 24 (December 9, 2021): 5001. http://dx.doi.org/10.3390/rs13245001.
Повний текст джерелаАнотація:
In this work, collocated lidar–radar observations are used to retrieve the vertical profiles of cloud properties above the Eastern Mediterranean. Measurements were performed in the framework of the PRE-TECT experiment during April 2017 at the Greek atmospheric observatory of Finokalia, Crete. Cloud geometrical and microphysical properties at different altitudes were derived using the Cloudnet target classification algorithm. We found that the variable atmospheric conditions that prevailed above the region during April 2017 resulted in complex cloud structures. Mid-level clouds were observed in 38% of the cases, high or convective clouds in 58% of the cases, and low-level clouds in 2% of the cases. From the observations of cloudy profiles, pure ice phase occurred in 94% of the cases, mixed-phase clouds were observed in 27% of the cases, and liquid clouds were observed in 8.7% of the cases, while Drizzle or rain occurred in 12% of the cases. The significant presence of Mixed-Phase Clouds was observed in all the clouds formed at the top of a dust layer, with three times higher abundance than the mean conditions (26% abundance at −15 °C). The low-level clouds were formed in the presence of sea salt and continental particles with ice abundance below 30%. The derived statistics on clouds’ high-resolution vertical distributions and thermodynamic phase can be combined with Cloudnet cloud products and lidar-retrieved aerosol properties to study aerosol-cloud interactions in this understudied region and evaluate microphysics parameterizations in numerical weather prediction and global climate models.
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Gettelman, A., H. Morrison, C. R. Terai, and R. Wood. "Microphysical process rates and global aerosol–cloud interactions." Atmospheric Chemistry and Physics 13, no. 19 (October 7, 2013): 9855–67. http://dx.doi.org/10.5194/acp-13-9855-2013.
Повний текст джерелаАнотація:
Abstract. Cloud microphysical process rates control the amount of condensed water in clouds and impact the susceptibility of precipitation to cloud-drop number and aerosols. The relative importance of different microphysical processes in a climate model is analyzed, and the autoconversion and accretion processes are found to be critical to the condensate budget in most regions. A simple steady-state model of warm rain formation is used to illustrate that the diagnostic rain formulations typical of climate models may result in excessive contributions from autoconversion, compared to observations and large eddy simulation models with explicit bin-resolved microphysics and rain formation processes. The behavior does not appear to be caused by the bulk process rate formulations themselves, because the steady-state model with the same bulk accretion and autoconversion has reduced contributions from autoconversion. Sensitivity tests are conducted to analyze how perturbations to the precipitation microphysics for stratiform clouds impact process rates, precipitation susceptibility and aerosol–cloud interactions (ACI). With similar liquid water path, corrections for the diagnostic rain assumptions in the GCM based on the steady-state model to boost accretion indicate that the radiative effects of ACI may decrease by 20% in the GCM. Links between process rates, susceptibility and ACI are not always clear in the GCM. Better representation of the precipitation process, for example by prognosticating precipitation mass and number, may help better constrain these effects in global models with bulk microphysics schemes.
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Cintineo, Rebecca, Jason A. Otkin, Ming Xue, and Fanyou Kong. "Evaluating the Performance of Planetary Boundary Layer and Cloud Microphysical Parameterization Schemes in Convection-Permitting Ensemble Forecasts Using Synthetic GOES-13 Satellite Observations." Monthly Weather Review 142, no. 1 (January 1, 2014): 163–82. http://dx.doi.org/10.1175/mwr-d-13-00143.1.
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Abstract In this study, the ability of several cloud microphysical and planetary boundary layer parameterization schemes to accurately simulate cloud characteristics within 4-km grid-spacing ensemble forecasts over the contiguous United States was evaluated through comparison of synthetic Geostationary Operational Environmental Satellite (GOES) infrared brightness temperatures with observations. Four double-moment microphysics schemes and five planetary boundary layer (PBL) schemes were evaluated. Large differences were found in the simulated cloud cover, especially in the upper troposphere, when using different microphysics schemes. Overall, the results revealed that the Milbrandt–Yau and Morrison microphysics schemes tended to produce too much upper-level cloud cover, whereas the Thompson and the Weather Research and Forecasting Model (WRF) double-moment 6-class (WDM6) microphysics schemes did not contain enough high clouds. Smaller differences occurred in the cloud fields when using different PBL schemes, with the greatest spread in the ensemble statistics occurring during and after daily peak heating hours. Results varied somewhat depending upon the verification method employed, which indicates the importance of using a suite of verification tools when evaluating high-resolution model performance. Finally, large differences between the various microphysics and PBL schemes indicate that large uncertainties remain in how these schemes represent subgrid-scale processes.
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Reutter, P., J. Trentmann, A. Seifert, P. Neis, H. Su, M. Herzog, H. Wernli, M. O. Andreae, and U. Pöschl. "3-D model simulations of dynamical and microphysical interactions in pyro-convective clouds under idealized conditions." Atmospheric Chemistry and Physics Discussions 13, no. 7 (July 23, 2013): 19527–57. http://dx.doi.org/10.5194/acpd-13-19527-2013.
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Abstract. Pyro-convective clouds, i.e. convective clouds forming over wildland fires due to high sensible heat, play an important role for the transport of aerosol particles and trace gases into the upper troposphere and lower stratosphere. Additionally, due to the emission of a large number of aerosol particles from forest fires, the microphysical structure of a pyro-convective cloud is clearly different from that of ordinary convective clouds. A crucial step in the microphysical evolution of a (pyro-) convective cloud is the activation of aerosol particles to form cloud droplets. The activation process affects the initial number and size of cloud droplets and can thus influence the evolution of the convective cloud and the formation of precipitation. Building upon a realistic parameterization of CCN activation, the model ATHAM is used to investigate the dynamical and microphysical processes of idealized three-dimensional pyro-convective clouds in mid-latitudes. A state-of-the-art two-moment microphysical scheme has been implemented in order to study the influence of the aerosol concentration on the cloud development. The results show that the aerosol concentration influences the formation of precipitation. For low aerosol concentrations (NCN=1000 cm−3), rain droplets are rapidly formed by autoconversion of cloud droplets. This also triggers the formation of large graupel and hail particles resulting in an early and strong onset of precipitation. With increasing aerosol concentration (NCN=20 000 cm−3 and NCN=60 000 cm−3) the formation of rain droplets is delayed due to more but smaller cloud droplets. Therefore, the formation of ice crystals and snowflakes becomes more important for the eventual formation of graupel and hail. However, this causes a delay of the onset of precipitation and its intensity for increasing aerosol concentration. This work shows the first detailed investigation of the interaction between cloud microphysics and dynamics of a pyro-convective cloud using the combination of a high resolution atmospheric model and a detailed microphysical scheme.
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Shupe, Matthew D., Pavlos Kollias, P. Ola G. Persson, and Greg M. McFarquhar. "Vertical Motions in Arctic Mixed-Phase Stratiform Clouds." Journal of the Atmospheric Sciences 65, no. 4 (April 1, 2008): 1304–22. http://dx.doi.org/10.1175/2007jas2479.1.
Повний текст джерелаАнотація:
Abstract The characteristics of Arctic mixed-phase stratiform clouds and their relation to vertical air motions are examined using ground-based observations during the Mixed-Phase Arctic Cloud Experiment (MPACE) in Barrow, Alaska, during fall 2004. The cloud macrophysical, microphysical, and dynamical properties are derived from a suite of active and passive remote sensors. Low-level, single-layer, mixed-phase stratiform clouds are typically topped by a 400–700-m-deep liquid water layer from which ice crystals precipitate. These clouds are strongly dominated (85% by mass) by liquid water. On average, an in-cloud updraft of 0.4 m s−1 sustains the clouds, although cloud-scale circulations lead to a variability of up to ±2 m s−1 from the average. Dominant scales-of-variability in both vertical air motions and cloud microphysical properties retrieved by this analysis occur at 0.5–10-km wavelengths. In updrafts, both cloud liquid and ice mass grow, although the net liquid mass growth is usually largest. Between updrafts, nearly all ice falls out and/or sublimates while the cloud liquid diminishes but does not completely evaporate. The persistence of liquid water throughout these cloud cycles suggests that ice-forming nuclei, and thus ice crystal, concentrations must be limited and that water vapor is plentiful. These details are brought together within the context of a conceptual model relating cloud-scale dynamics and microphysics.
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Ping, Fan, Zhexian Luo, and Xiaofan Li. "Microphysical and Radiative Effects of Ice Clouds on Tropical Equilibrium States: A Two-Dimensional Cloud-Resolving Modeling Study." Monthly Weather Review 135, no. 7 (July 1, 2007): 2794–802. http://dx.doi.org/10.1175/mwr3419.1.
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Abstract The microphysical and radiative effects of ice clouds on tropical equilibrium states are investigated based on three two-dimensional cloud-resolving simulations imposed by zero vertical velocity and time-invariant zonal wind and sea surface temperature. An experiment without ice microphysics (ice microphysical and radiative effects; C00), another experiment without ice radiative effects (CI0), and the control experiment (CIR) are carried out. The model with cyclic lateral boundaries is integrated for 40 days to reach equilibrium states in all experiments. CI0 produces a colder and drier equilibrium state than CIR and C00 do through generating a larger IR cooling, a larger vapor condensation rate, and consuming a larger amount of water vapor. A larger surface rain rate occurs in CI0 than in CIR and C00. The ice radiative effects on thermodynamic equilibrium states are stronger than the ice microphysical effects so that the exclusion of ice microphysics yields a colder and drier equilibrium state in C00 than in CIR. The ice radiative effects and the ice microphysical effects on surface rainfall processes are largely offset, which leads to similar zonal-mean surface rain rates in C00 and CIR.
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Andrejczuk, Miroslaw, Wojciech W. Grabowski, Szymon P. Malinowski, and Piotr K. Smolarkiewicz. "Numerical Simulation of Cloud–Clear Air Interfacial Mixing: Effects on Cloud Microphysics." Journal of the Atmospheric Sciences 63, no. 12 (December 2006): 3204–25. http://dx.doi.org/10.1175/jas3813.1.
Повний текст джерелаАнотація:
This paper extends the previously published numerical study of Andrejczuk et al. on microscale cloud–clear air mixing. Herein, the primary interest is on microphysical transformations. First, a convergence study is performed—with well-resolved direct numerical simulation of the interfacial mixing in the limit—to optimize the design of a large series of simulations with varying physical parameters. The principal result is that all conclusions drawn from earlier low-resolution (Δx = 10−2 m) simulations are corroborated by the high-resolution (Δx = 0.25 × 10−2 m) calculations, including the development of turbulent kinetic energy (TKE) and the evolution of microphysical properties. This justifies the use of low resolution in a large set of sensitivity simulations, where microphysical transformations are investigated in response to variations of the initial volume fraction of cloudy air, TKE input, liquid water mixing ratio in cloudy filaments, relative humidity (RH) of clear air, and size of cloud droplets. The simulations demonstrate that regardless of the initial conditions the evolutions of the number of cloud droplets and the mean volume radius follow a universal path dictated by the TKE input, RH of clear air filaments, and the mean size of cloud droplets. The resulting evolution path only weakly depends on the progress of the homogenization. This is an important conclusion because it implies that a relatively simple rule can be developed for representing the droplet-spectrum evolution in cloud models that apply parameterized microphysics. For the low-TKE input, when most of the TKE is generated by droplet evaporation during mixing and homogenization, an inhomogeneous scenario is observed with approximately equal changes in the dimensionless droplet number and mean volume radius cubed. Consistent with elementary scale analysis, higher-TKE inputs, higher RH of cloud-free filaments, and larger cloud droplets enhance the homogeneity of mixing. These results are discussed in the context of observations of entrainment and mixing in natural clouds.
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Storer, Rachel L., Guang J. Zhang, and Xiaoliang Song. "Effects of Convective Microphysics Parameterization on Large-Scale Cloud Hydrological Cycle and Radiative Budget in Tropical and Midlatitude Convective Regions." Journal of Climate 28, no. 23 (December 1, 2015): 9277–97. http://dx.doi.org/10.1175/jcli-d-15-0064.1.
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Abstract A two-moment microphysics scheme for deep convection was previously implemented in the NCAR Community Atmosphere Model version 5 (CAM5) by Song et al. The new scheme improved hydrometeor profiles in deep convective clouds and increased deep convective detrainment, reducing the negative biases in low and midlevel cloud fraction and liquid water path compared to observations. Here, the authors examine in more detail the impacts of this improved microphysical representation on regional-scale water and radiation budgets. As a primary source of cloud water for stratiform clouds is detrainment from deep and shallow convection, the enhanced detrainment leads to larger stratiform cloud fractions, higher cloud water content, and more stratiform precipitation over the ocean, particularly in the subtropics where convective frequency is also increased. This leads to increased net cloud radiative forcing. Over land regions, cloud amounts are reduced as a result of lower relative humidity, leading to weaker cloud forcing and increased OLR. Comparing the water budgets to cloud-resolving model simulations shows improvement in the partitioning between convective and stratiform precipitation, though the deep convection is still too active in the GCM. The addition of convective microphysics leads to an overall improvement in the regional cloud water budgets.
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Gettelman, A., H. Morrison, and S. J. Ghan. "A New Two-Moment Bulk Stratiform Cloud Microphysics Scheme in the Community Atmosphere Model, Version 3 (CAM3). Part II: Single-Column and Global Results." Journal of Climate 21, no. 15 (August 1, 2008): 3660–79. http://dx.doi.org/10.1175/2008jcli2116.1.
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Abstract The global performance of a new two-moment cloud microphysics scheme for a general circulation model (GCM) is presented and evaluated relative to observations. The scheme produces reasonable representations of cloud particle size and number concentration when compared to observations, and it represents expected and observed spatial variations in cloud microphysical quantities. The scheme has smaller particles and higher number concentrations over land than the standard bulk microphysics in the GCM and is able to balance the top-of-atmosphere radiation budget with 60% the liquid water of the standard scheme, in better agreement with retrieved values. The new scheme diagnostically treats both the mixing ratio and number concentration of rain and snow, and it is therefore able to differentiate the two key regimes, consisting of drizzle in shallow, warm clouds and larger rain drops in deeper cloud systems. The modeled rain and snow size distributions are consistent with observations.
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MOACA, Denisa, Andreea CALCAN, and Sorin Nicolae VAJAIAC. "Numerical simulation and analysis of pressure distribution and airflow speed around an airborne cloud microphysics measurements instrument." INCAS BULLETIN 12, no. 4 (December 4, 2020): 127–33. http://dx.doi.org/10.13111/2066-8201.2020.12.4.11.
Повний текст джерелаАнотація:
Clouds have an important impact on Earth’s energetic balance, so measuring accurately the microphysical parameters and using them in research has become one important step in atmospheric studies. Regarding the fact that light scattering probes convert the flow rate to concentration, any wrong assumption or measurement of the flow rate can lead to incorrect results. Applying numerical simulation to an airborne cloud microphysics measurements instrument can provide information that can be measured in any point of the sampling volume, and further used in determination of microphysics parameters, providing more accurate data. Taking this into consideration, in this paper are presented the results of numerical simulation applied to Cloud Aerosol and Precipitation Spectrometer and the comparison with results reported in literature.
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Dietlicher, Remo, David Neubauer, and Ulrike Lohmann. "Elucidating ice formation pathways in the aerosol–climate model ECHAM6-HAM2." Atmospheric Chemistry and Physics 19, no. 14 (July 17, 2019): 9061–80. http://dx.doi.org/10.5194/acp-19-9061-2019.
Повний текст джерелаАнотація:
Abstract. Cloud microphysics schemes in global climate models have long suffered from a lack of reliable satellite observations of cloud ice. At the same time there is a broad consensus that the correct simulation of cloud phase is imperative for a reliable assessment of Earth's climate sensitivity. At the core of this problem is understanding the causes for the inter-model spread of the predicted cloud phase partitioning. This work introduces a new method to build a sound cause-and-effect relation between the microphysical parameterizations employed in our model and the resulting cloud field by analysing ice formation pathways. We find that freezing processes in supercooled liquid clouds only dominate ice formation in roughly 6 % of the simulated clouds, a small fraction compared to roughly 63 % of the clouds governed by freezing in the cirrus temperature regime below −35 ∘C. This pathway analysis further reveals that even in the mixed-phase temperature regime between −35 and 0 ∘C, the dominant source of ice is the sedimentation of ice crystals that originated in the cirrus regime. The simulated fraction of ice cloud to total cloud amount in our model is lower than that reported by the CALIPSO-GOCCP satellite product. This is most likely caused by structural differences of the cloud and aerosol fields in our model rather than the microphysical parametrizations employed.
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Khain, Pavel, Reuven Heiblum, Ulrich Blahak, Yoav Levi, Harel Muskatel, Elyakom Vadislavsky, Orit Altaratz, et al. "Parameterization of Vertical Profiles of Governing Microphysical Parameters of Shallow Cumulus Cloud Ensembles Using LES with Bin Microphysics." Journal of the Atmospheric Sciences 76, no. 2 (February 1, 2019): 533–60. http://dx.doi.org/10.1175/jas-d-18-0046.1.
Повний текст джерелаАнотація:
Abstract Shallow convection is a subgrid process in cloud-resolving models for which their grid box is larger than the size of small cumulus clouds (Cu). At the same time such Cu substantially affect radiation properties and thermodynamic parameters of the low atmosphere. The main microphysical parameters used for calculation of radiative properties of Cu in cloud-resolving models are liquid water content (LWC), effective droplet radius, and cloud fraction (CF). In this study, these parameters of fields of small, warm Cu are calculated using large-eddy simulations (LESs) performed using the System for Atmospheric Modeling (SAM) with spectral bin microphysics. Despite the complexity of microphysical processes, several fundamental properties of Cu were found. First, despite the high variability of LWC and droplet concentration within clouds and between different clouds, the volume mean and effective radii per specific level vary only slightly. Second, the values of effective radius are close to those forming during adiabatic ascent of air parcels from cloud base. These findings allow for characterization of a cloud field by specific vertical profiles of effective radius and of mean liquid water content, which can be calculated using the theoretical profile of adiabatic liquid water content and the droplet concentration at cloud base. Using the results of these LESs, a simple parameterization of cloud-field-averaged vertical profiles of effective radius and of liquid water content is proposed for different aerosol and thermodynamic conditions. These profiles can be used for calculation of radiation properties of Cu fields in large-scale models. The role of adiabatic processes in the formation of microstructure of Cu is discussed.
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Wood, Robert, Terence L. Kubar, and Dennis L. Hartmann. "Understanding the Importance of Microphysics and Macrophysics for Warm Rain in Marine Low Clouds. Part II: Heuristic Models of Rain Formation." Journal of the Atmospheric Sciences 66, no. 10 (October 1, 2009): 2973–90. http://dx.doi.org/10.1175/2009jas3072.1.
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Abstract Two simple heuristic model formulations for warm rain formation are introduced and their behavior explored. The first, which is primarily aimed at representing warm rain formation in shallow convective clouds, is a continuous collection model that uses an assumed cloud droplet size distribution consistent with observations as the source of embryonic drizzle drops that are then allowed to fall through a fixed cloud, accreting cloud droplets. The second, which is applicable to steady-state precipitation formation in stratocumulus, is a simple two-moment bulk autoconversion and accretion model in which cloud liquid water is removed by drizzle formation and replenished on a externally specified time scale that reflects the efficacy of turbulent overturning that characterizes stratocumulus. The models’ behavior is shown to be broadly consistent with observations from the A-Train constellation of satellites, allowing the authors to explore reasons for changing model sensitivity to microphysical and macrophysical cloud properties. The models are consistent with one another, and with the observations, in that they demonstrate that the sensitivity of rain rate to cloud droplet concentration Nd (which here represents microphysical influence) is greatest for weakly precipitating clouds (i.e., for low cloud liquid water path and/or high Nd). For the steady-state model, microphysical sensitivity is shown to strongly decrease with the ratio of replenishment to drizzle time scales. Thus, rain from strongly drizzling and/or weakly replenished clouds shows low sensitivity to microphysics. This is essentially because most precipitation in these clouds is forming via accretion rather than autoconversion. For the continuous-collection model, as cloud liquid water content increases, the precipitation rate becomes more strongly controlled by the availability of cloud liquid water than by the initial embryo size or by the cloud droplet size. The models help to explain why warm rain in marine stratocumulus clouds is sensitive to Nd but why precipitation from thicker cumulus clouds appears to be less so.
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Gettelman, A., H. Morrison, C. R. Terai, and R. Wood. "Microphysical process rates and global aerosol-cloud interactions." Atmospheric Chemistry and Physics Discussions 13, no. 5 (May 3, 2013): 11789–825. http://dx.doi.org/10.5194/acpd-13-11789-2013.
Повний текст джерелаАнотація:
Abstract. Cloud microphysical process rates control the amount of condensed water in clouds and impact the susceptibility of precipitation to drop number and aerosols. The relative importance of different microphysical processes in a climate model is analyzed, and the autoconversion and accretion processes are found to be critical to the condensate budget in most regions. A simple steady-state model of warm rain formation is used to illustrate that the diagnostic rain formulations typical of climate models may result in excessive contributions from autoconversion, compared to observations and large eddy simulation models with explicit bin-resolved microphysics and rain formation processes. The behavior does not appear to be caused by the bulk process rate formulations themselves, because the steady state model with bulk accretion and autoconversion has reduced contributions from autoconversion. Sensitivity tests are conducted to analyze how perturbations to the precipitation microphysics for stratiform clouds impact process rates, precipitation susceptibility and aerosol-cloud interactions (ACI). With similar liquid water path, corrections for the diagnostic rain assumptions in the GCM based on the steady state model to boost accretion over autoconversion indicate that the radiative effects of ACI may decrease by 20% in the GCM for the same mean liquid water path. Links between process rates, susceptibility and ACI are not always clear in the GCM. Better representation of the precipitation process, for example by prognosing precipitation mass and number, may help better constrain these effects in global models with bulk microphysics schemes.
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Posselt, Derek J. "A Bayesian Examination of Deep Convective Squall-Line Sensitivity to Changes in Cloud Microphysical Parameters." Journal of the Atmospheric Sciences 73, no. 2 (February 1, 2016): 637–65. http://dx.doi.org/10.1175/jas-d-15-0159.1.
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Abstract Deep convective cloud content, precipitation distribution and rate, dynamics, and radiative fluxes are known to be sensitive to the details of liquid- and ice-phase cloud microphysical processes. Previous studies have explored the multivariate convective response to changes in cloud microphysical parameter values in a framework that isolated the cloud and radiation schemes from the thermodynamic and dynamic environment. This study uses a Bayesian Markov chain Monte Carlo (MCMC) algorithm to generate sets of cloud microphysical parameters consistent with a specific storm environment in a three-dimensional cloud-system-resolving model. These parameter sets, and the corresponding large ensemble of model simulations, contain information about the univariate model sensitivity, as well as parameter–state and parameter–parameter interactions. Examination of the relationships between cloud parameters and in-cloud vertical motion and latent heat release provides information about the influence of microphysical processes on the in-cloud environment. Exploration of the joint dependence of microphysical properties and clear-air relative humidity and temperature allows an assessment of the influence of cloud microphysics on the near-cloud environment. Analysis of the MCMC results indicates the model output is sensitive to a small subset of the parameters. In addition, constraint of cloud microphysics using bulk observations of the hydrologic cycle and TOA radiative fluxes uniquely constrains vertical velocity, latent heat release, and the environmental temperature and relative humidity.
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Harshvardhan, Guang Guo, Robert N. Green, Zheng Qu, and Takashi Y. Nakajima. "Remotely Sensed Microphysical and Thermodynamic Properties of Nonuniform Water Cloud Fields." Journal of the Atmospheric Sciences 61, no. 21 (November 1, 2004): 2574–87. http://dx.doi.org/10.1175/jas3301.1.
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Abstract Visible and near-infrared reflected radiances have been used to estimate the cloud optical depth and effective radius of cloud-filled global area coverage (GAC) pixels from the Advanced Very High Resolution Radiometer (AVHRR) for two cases in the North Atlantic Ocean. One is representative of clouds having low concentrations of cloud condensation nuclei (CCN), while the other is an example of maritime clouds forming in continental air, in this case, intruding from Europe around a cutoff low pressure system. It is shown that an estimate of the cloud drop concentration can be obtained from remotely sensed cloud radiative properties and standard meteorological analyses. These concentrations show very clearly the influence of enhanced CCN on cloud microphysics. However, conclusions regarding the indirect radiative effect of aerosol on cloud must wait for the development of a framework for analyzing changes in cloud liquid water path (LWP). It is shown that estimates of LWP are greatly influenced by the scheme that is used to identify cloudy pixels at the AVHRR GAC resolution. Application of a very strict thermal channel spatial coherence criterion for identifying cloud-filled pixels yields mean LWP estimates for cloudy pixels alone that are 40%–75% higher than mean LWP estimates for the much larger sample of possibly cloudy pixels identified by a reflectance threshold criterion.
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Mielikainen, J., B. Huang, H. L. A. Huang, M. D. Goldberg, and A. Mehta. "Speeding Up the Computation of WRF Double-Moment 6-Class Microphysics Scheme with GPU." Journal of Atmospheric and Oceanic Technology 30, no. 12 (December 1, 2013): 2896–906. http://dx.doi.org/10.1175/jtech-d-12-00218.1.
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Abstract The Weather Research and Forecasting model (WRF) double-moment 6-class microphysics scheme (WDM6) implements a double-moment bulk microphysical parameterization of clouds and precipitation and is applicable in mesoscale and general circulation models. WDM6 extends the WRF single-moment 6-class microphysics scheme (WSM6) by incorporating the number concentrations for cloud and rainwater along with a prognostic variable of cloud condensation nuclei (CCN) number concentration. Moreover, it predicts the mixing ratios of six water species (water vapor, cloud droplets, cloud ice, snow, rain, and graupel), similar to WSM6. This paper describes improving the computational performance of WDM6 by exploiting its inherent fine-grained parallelism using the NVIDIA graphics processing unit (GPU). Compared to the single-threaded CPU, a single GPU implementation of WDM6 obtains a speedup of 150× with the input/output (I/O) transfer and 206× without the I/O transfer. Using four GPUs, the speedup reaches 347× and 715×, respectively.
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Ryzhkov, Alexander V., Jeffrey Snyder, Jacob T. Carlin, Alexander Khain, and Mark Pinsky. "What Polarimetric Weather Radars Offer to Cloud Modelers: Forward Radar Operators and Microphysical/Thermodynamic Retrievals." Atmosphere 11, no. 4 (April 8, 2020): 362. http://dx.doi.org/10.3390/atmos11040362.
Повний текст джерелаАнотація:
The utilization of polarimetric weather radars for optimizing cloud models is a next frontier of research. It is widely understood that inadequacies in microphysical parameterization schemes in numerical weather prediction (NWP) models is a primary cause of forecast uncertainties. Due to its ability to distinguish between hydrometeors with different microphysical habits and to identify “polarimetric fingerprints” of various microphysical processes, polarimetric radar emerges as a primary source of needed information. There are two approaches to leverage this information for NWP models: (1) radar microphysical and thermodynamic retrievals and (2) forward radar operators for converting the model outputs into the fields of polarimetric radar variables. In this paper, we will provide an overview of both. Polarimetric measurements can be combined with cloud models of varying complexity, including ones with bulk and spectral bin microphysics, as well as simplified Lagrangian models focused on a particular microphysical process. Combining polarimetric measurements with cloud modeling can reveal the impact of important microphysical agents such as aerosols or supercooled cloud water invisible to the radar on cloud and precipitation formation. Some pertinent results obtained from models with spectral bin microphysics, including the Hebrew University cloud model (HUCM) and 1D models of melting hail and snow coupled with the NSSL forward radar operator, are illustrated in the paper.
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Grabowski, Wojciech W., and Dorota Jarecka. "Modeling Condensation in Shallow Nonprecipitating Convection." Journal of the Atmospheric Sciences 72, no. 12 (November 20, 2015): 4661–79. http://dx.doi.org/10.1175/jas-d-15-0091.1.
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Abstract Two schemes for modeling condensation in warm nonprecipitating clouds are compared. The first one is the efficient bulk condensation scheme where cloudy volumes are always at saturation and cloud water evaporates instantaneously to maintain saturation. The second one is the comprehensive bin condensation scheme that predicts the evolution of the cloud droplet spectrum and allows sub- and supersaturations in cloudy volumes. The emphasis is on the impact of the two schemes on cloud dynamics. Theoretical considerations show that the bulk condensation scheme provides more buoyancy than the bin scheme, but the effect is small, with the potential density temperature difference around 0.1 K for 1% supersaturation. The 1D advection–condensation tests document the high-vertical-resolution requirement for the bin scheme to resolve the cloud-base supersaturation maximum and CCN activation, which is difficult to employ in 3D cloud simulations. Simulations of shallow convection cloud fields are executed applying bulk and bin schemes, with the mean droplet concentrations in the bin scheme covering a wide range, from about 5 to over 4000 cm−3. Simulations employ the microphysical piggybacking methodology to extract impacts with high confidence. They show that the differences in cloud fields simulated with bulk and bin schemes come not from small differences in the condensation but from more significant differences in the evaporation of cloud water near cloud edges as a result of entrainment and mixing with the environment. The latter makes the impact of cloud microphysics on simulated macroscopic cloud field properties even more difficult to assess because of highly uncertain subgrid-scale parameterizations.
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Lee, Seoung Soo, Zhanqing Li, Yuwei Zhang, Hyelim Yoo, Seungbum Kim, Byung-Gon Kim, Yong-Sang Choi, et al. "Effects of model resolution and parameterizations on the simulations of clouds, precipitation, and their interactions with aerosols." Atmospheric Chemistry and Physics 18, no. 1 (January 3, 2018): 13–29. http://dx.doi.org/10.5194/acp-18-13-2018.
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Abstract. This study investigates the roles played by model resolution and microphysics parameterizations in the well-known uncertainties or errors in simulations of clouds, precipitation, and their interactions with aerosols by the numerical weather prediction (NWP) models. For this investigation, we used cloud-system-resolving model (CSRM) simulations as benchmark simulations that adopt high-resolution and full-fledged microphysical processes. These simulations were evaluated against observations, and this evaluation demonstrated that the CSRM simulations can function as benchmark simulations. Comparisons between the CSRM simulations and the simulations at the coarse resolutions that are generally adopted by current NWP models indicate that the use of coarse resolutions as in the NWP models can lower not only updrafts and other cloud variables (e.g., cloud mass, condensation, deposition, and evaporation) but also their sensitivity to increasing aerosol concentration. The parameterization of the saturation process plays an important role in the sensitivity of cloud variables to aerosol concentrations. while the parameterization of the sedimentation process has a substantial impact on how cloud variables are distributed vertically. The variation in cloud variables with resolution is much greater than what happens with varying microphysics parameterizations, which suggests that the uncertainties in the NWP simulations are associated with resolution much more than microphysics parameterizations.