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Journal articles on the topic 'Cloud structure'
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Yu, Haixiao, Jinji Ma, Safura Ahmad, Erchang Sun, Chao Li, Zhengqiang Li, and Jin Hong. "Three-Dimensional Cloud Structure Reconstruction from the Directional Polarimetric Camera." Remote Sensing 11, no. 24 (December 4, 2019): 2894. http://dx.doi.org/10.3390/rs11242894.
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Clouds affect radiation transmission through the atmosphere, which impacts the Earth’ s energy balance and climate. Currently, the study of clouds is mostly based on a two-dimensional (2-D) plane rather than a three-dimensional (3-D) space. However, 3-D cloud reconstruction is playing an important role not only in a radiation transmission calculation but in forecasting climate change as well. Currently, the study of clouds is mostly based on 2-D single angle satellite observation data while the importance of a 3-D structure of clouds in atmospheric radiation transmission is ignored. 3-D structure reconstruction would improve the radiation transmission accuracy of the cloudy atmosphere based on multi-angle observations data. Characterizing the 3-D structure of clouds is crucial for an extensive study of this complex intermediate medium in the atmosphere. In addition, it is also a great carrier for visualization of its parameters. Special attributes and the shape of clouds can be clearly illustrated in a 3-D cloud while these are difficult to describe in a 2-D plane. It provides a more intuitive expression for the study of complex cloud systems. In order to reconstruct a 3-D cloud structure, we develop and explore a ray casting algorithm applied to data from the Directional Polarimetric Camera (DPC), which is onboard the GF-5 satellite. In this paper, we use DPC with characteristics of imaging multiple angles of the same target, and characterize observations of clouds from different angles in 3-D space. This feature allows us to reconstruct 3-D clouds from different angles of observations. In terms of verification, we use cloud profile data provided by the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) to compare with the results of reconstructed 3-D clouds based on DPC data. This shows that the reconstruction method has good accuracy and effectiveness. This 3-D cloud reconstruction method would lay a scientific reference for future analysis on the role of clouds in the atmosphere and for the construction of 3-D structures of aerosols.
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Lines, S., N. J. Mayne, J. Manners, I. A. Boutle, B. Drummond, T. Mikal-Evans, K. Kohary, and D. K. Sing. "Overcast on Osiris: 3D radiative-hydrodynamical simulations of a cloudy hot Jupiter using the parametrized, phase-equilibrium cloud formation code EddySed." Monthly Notices of the Royal Astronomical Society 488, no. 1 (July 1, 2019): 1332–55. http://dx.doi.org/10.1093/mnras/stz1788.
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ABSTRACT We present results from 3D radiative-hydrodynamical simulations of HD 209458b with a fully coupled treatment of clouds using the EddySed code, critically, including cloud radiative feedback via absorption and scattering. We demonstrate that the thermal and optical structure of the simulated atmosphere is markedly different, for the majority of our simulations, when including cloud radiative effects, suggesting this important mechanism cannot be neglected. Additionally, we further demonstrate that the cloud structure is sensitive to not only the cloud sedimentation efficiency (termed fsed in EddySed), but also the temperature–pressure profile of the deeper atmosphere. We briefly discuss the large difference between the resolved cloud structures of this work, adopting a phase-equilibrium and parametrized cloud model, and our previous work incorporating a cloud microphysical model, although a fairer comparison where, for example, the same list of constituent condensates is included in both treatments is reserved for a future work. Our results underline the importance of further study into the potential condensate size distributions and vertical structures, as both strongly influence the radiative impact of clouds on the atmosphere. Finally, we present synthetic observations from our simulations reporting an improved match, over our previous cloud-free simulations, to the observed transmission, HST WFC3 emission, and 4.5 μm Spitzer phase curve of HD 209458b. Additionally, we find all our cloudy simulations have an apparent albedo consistent with observations.
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Alves, João, Marco Lombardi, and Charles Lada. "Insights on molecular cloud structure." Proceedings of the International Astronomical Union 6, S270 (May 2010): 99–102. http://dx.doi.org/10.1017/s1743921311000238.
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AbstractStars form in the densest regions of clouds of cold molecular hydrogen. Measuring structure in these clouds is far from trivial as 99% of the mass of a molecular cloud is inaccessible to direct observation. Over the last decade we have been developing an alternative, more robust density tracer technique based on dust extinction measurements towards background starlight. The new technique does not suffer from the complications plaguing the more conventional molecular line and dust emission techniques, and when used with these can provide unique views on cloud chemistry and dust grain properties in molecular clouds. In this brief communication we summarize the main results achieved so far using this technique.
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Lan, Ji Ming, Shu Jie Lu, and Li Ming Zhang. "Research of Distributional Ecology Cloud-Structure." Advanced Materials Research 760-762 (September 2013): 1758–61. http://dx.doi.org/10.4028/www.scientific.net/amr.760-762.1758.
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Proposed that idea of cloud computing ecology development, supports and guiding cloud model deployment, the cloud service management and Clouds protocols observes the purification of mix cloud environment. Has designed the multiple dimension data saving structure and real-time mass-data processing of model as well as the asynchronous overall construction distributional ecology cloud structure. It has been shown that this ecology cloud structure is healthy.
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Sotiropoulou, G., J. Sedlar, M. Tjernström, M. D. Shupe, I. M. Brooks, and P. O. G. Persson. "The thermodynamic structure of summer Arctic stratocumulus and the dynamic coupling to the surface." Atmospheric Chemistry and Physics Discussions 14, no. 3 (February 11, 2014): 3815–74. http://dx.doi.org/10.5194/acpd-14-3815-2014.
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Abstract. The vertical structure of Arctic low-level clouds and Arctic boundary layer is studied, using observations from ASCOS (Arctic Summer Cloud Ocean Study), in the central Arctic, in late summer 2008. Two general types of cloud structures are examined: the "neutrally-stratified" and "stably-stratified" clouds. Neutrally-stratified are mixed-phase clouds where radiative-cooling near cloud top produces turbulence that creates a cloud-driven mixed layer. When this layer mixes with the surface-generated turbulence, the cloud layer is coupled to the surface, whereas when such an interaction does not occur, it remains decoupled; the latter state is most frequently observed. The decoupled clouds are usually higher compared to the coupled; differences in thickness or cloud water properties between the two cases are however not found. The surface fluxes are also very similar for both states. The decoupled clouds exhibit a bimodal thermodynamic structure, depending on the depth of the sub-cloud mixed layer (SML): clouds with shallower SMLs are disconnected from the surface by weak inversions, whereas those that lay over a deeper SML are associated with stronger inversions at the decoupling height. Neutrally-stratified clouds generally precipitate; the evaporation/sublimation of precipitation often enhances the decoupling state. Finally, stably-stratified clouds are usually lower, geometrically and optically thinner, non-precipitating liquid-water clouds, not containing enough liquid to drive efficient mixing through cloud-top cooling.
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Sotiropoulou, G., J. Sedlar, M. Tjernström, M. D. Shupe, I. M. Brooks, and P. O. G. Persson. "The thermodynamic structure of summer Arctic stratocumulus and the dynamic coupling to the surface." Atmospheric Chemistry and Physics 14, no. 22 (November 28, 2014): 12573–92. http://dx.doi.org/10.5194/acp-14-12573-2014.
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Abstract. The vertical structure of Arctic low-level clouds and Arctic boundary layer is studied, using observations from ASCOS (Arctic Summer Cloud Ocean Study), in the central Arctic, in late summer 2008. Two general types of cloud structures are examined: the "neutrally stratified" and "stably stratified" clouds. Neutrally stratified are mixed-phase clouds where radiative-cooling near cloud top produces turbulence that generates a cloud-driven mixed layer. When this layer mixes with the surface-generated turbulence, the cloud layer is coupled to the surface, whereas when such an interaction does not occur, it remains decoupled; the latter state is most frequently observed. The decoupled clouds are usually higher compared to the coupled; differences in thickness or cloud water properties between the two cases are however not found. The surface fluxes are also very similar for both states. The decoupled clouds exhibit a bimodal thermodynamic structure, depending on the depth of the sub-cloud mixed layer (SCML): clouds with shallower SCMLs are disconnected from the surface by weak inversions, whereas those that lay over a deeper SCML are associated with stronger inversions at the decoupling height. Neutrally stratified clouds generally precipitate; the evaporation/sublimation of precipitation often enhances the decoupling state. Finally, stably stratified clouds are usually lower, geometrically and optically thinner, non-precipitating liquid-water clouds, not containing enough liquid to drive efficient mixing through cloud-top cooling.
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Cesana, G., D. E. Waliser, D. Henderson, T. S. L’Ecuyer, X. Jiang, and J. L. F. Li. "The Vertical Structure of Radiative Heating Rates: A Multimodel Evaluation Using A-Train Satellite Observations." Journal of Climate 32, no. 5 (February 7, 2019): 1573–90. http://dx.doi.org/10.1175/jcli-d-17-0136.1.
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Abstract We assess the vertical distribution of radiative heating rates (RHRs) in climate models using a multimodel experiment and A-Train satellite observations, for the first time. As RHRs rely on the representation of cloud amount and properties, we first compare the modeled vertical distribution of clouds directly against lidar–radar combined cloud observations (i.e., without simulators). On a near-global scale (50°S–50°N), two systematic differences arise: an excess of high-level clouds around 200 hPa in the tropics, and a general lack of mid- and low-level clouds compared to the observations. Then, using RHR profiles calculated with constraints from A-Train and reanalysis data, along with their associated maximum uncertainty estimates, we show that the excess clouds and ice water content in the upper troposphere result in excess infrared heating in the vicinity of and below the clouds as well as a lack of solar heating below the clouds. In the lower troposphere, the smaller cloud amount and the underestimation of cloud-top height is coincident with a shift of the infrared cooling to lower levels, substantially reducing the greenhouse effect, which is slightly compensated by an erroneous excess absorption of solar radiation. Clear-sky RHR differences between the observations and the models mitigate cloudy RHR biases in the low levels while they enhance them in the high levels. Finally, our results indicate that a better agreement between observed and modeled cloud profiles could substantially improve the RHR profiles. However, more work is needed to precisely quantify modeled cloud errors and their subsequent effect on RHRs.
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Tamura, M., T. Nagata, S. Sato, M. Tanaka, N. Kaifu, J. Hough, I. McLean, I. Gatley, R. Garden, and M. McCaughrean. "Magnetic Field Structure in Dark Clouds." Symposium - International Astronomical Union 115 (1987): 48–50. http://dx.doi.org/10.1017/s0074180900094808.
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The magnetic field geometry in the central regions of two dark clouds has been mapped by measuring the polarization at 2.2 μm of background stars and of stars embedded in the clouds. The observations were done with the Kyoto polarimeter on the Agematsu 1m IR telescope in December 1984 for Heiles Cloud 2 in the Taurus dark cloud complex, and on the UKIRT 3.8m in May and July 1985 for the ρ Ophiuchus dark cloud core. The main results are: i)Most of the stars in both regions show polarization and their maxima are 2.7% in Heiles Cloud 2 and 7.6% in ρ Oph, respectively. There are similar positive relations between polarization degree and extinct ion Av's.ii)The distribution of position angles for Heiles Cloud 2 shows a single mode at about 50° and that for ρ Oph shows a bimode, at about 50° and 150°.iii)The magnetic fields, as delineated by the infrared polarization, appear perpendicular to the flattened elongations of the molecular clouds.
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Kikuch, Katsuhiro, Masaharu Fujii, Ryuichi Shirooka, and Susumu Yoshida. "The Cloud Base Structure of Stratocumulus Clouds." Journal of the Meteorological Society of Japan. Ser. II 69, no. 6 (1991): 701–8. http://dx.doi.org/10.2151/jmsj1965.69.6_701.
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Matheou, Georgios, Anthony B. Davis, and João Teixeira. "The Spiderweb Structure of Stratocumulus Clouds." Atmosphere 11, no. 7 (July 8, 2020): 730. http://dx.doi.org/10.3390/atmos11070730.
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Stratocumulus clouds have a distinctive structure composed of a combination of lumpy cellular structures and thin elongated regions, resembling canyons or slits. The elongated slits are referred to as “spiderweb” structure to emphasize their interconnected nature. Using very high resolution large-eddy simulations (LES), it is shown that the spiderweb structure is generated by cloud-top evaporative cooling. Analysis of liquid water path (LWP) and cloud liquid water content shows that cloud-top evaporative cooling generates relatively shallow slits near the cloud top. Most of liquid water mass is concentrated near the cloud top, thus cloud-top slits of clear air have a large impact on the entire-column LWP. When evaporative cooling is suppressed in the LES, LWP exhibits cellular lumpy structure without the elongated low-LWP regions. Even though the spiderweb signature on the LWP distribution is negligible, the cloud-top evaporative cooling process significantly affects integral boundary layer quantities, such as the vertically integrated turbulent kinetic energy, mean liquid water path, and entrainment rate. In a pair of simulations driven only by cloud-top radiative cooling, evaporative cooling nearly doubles the entrainment rate.
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Balmes, Kelly, and Qiang Fu. "An Investigation of Optically Very Thin Ice Clouds from Ground-Based ARM Raman Lidars." Atmosphere 9, no. 11 (November 14, 2018): 445. http://dx.doi.org/10.3390/atmos9110445.
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Optically very thin ice clouds from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and ground-based Raman lidars (RL) at the atmospheric radiation measurement (ARM) sites of the Southern Great Plains (SGP) and Tropical Western Pacific (TWP) are analyzed. The optically very thin ice clouds, with ice cloud column optical depths below 0.01, are about 23% of the transparent ice-cloudy profiles from the RL, compared to 4–7% from CALIPSO. The majority (66–76%) of optically very thin ice clouds from the RLs are found to be adjacent to ice clouds with ice cloud column optical depths greater than 0.01. The temporal structure of RL-observed optically very thin ice clouds indicates a clear sky–cloud continuum. Global cloudiness estimates from CALIPSO observations leveraged with high-sensitivity RL observations suggest that CALIPSO may underestimate the global cloud fraction when considering optically very thin ice clouds.
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Biondi, R., W. J. Randel, S. P. Ho, T. Neubert, and S. Syndergaard. "Thermal structure of intense convective clouds derived from GPS radio occultations." Atmospheric Chemistry and Physics Discussions 11, no. 10 (October 27, 2011): 29093–116. http://dx.doi.org/10.5194/acpd-11-29093-2011.
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Abstract. Thermal structure associated with deep convective clouds is investigated using Global Positioning System (GPS) radio occultation measurements. GPS data are insensitive to the presence of clouds, and provide high vertical resolution and high accuracy measurements to identify associated temperature behavior. Deep convective systems are identified using International Satellite Cloud Climatology Project (ISCCP) satellite data, and cloud tops are accurately measured using Cloud-Aerosol Lidar with Orthogonal Polarization (CALIPSO) lidar observations; we focus on 53 cases of near-coincident GPS occultations with CALIPSO profiles over deep convection. Results show a sharp spike in GPS bending angle highly correlated to the top of the clouds, corresponding to anomalously cold temperatures within the clouds. Above the clouds the temperatures return to background conditions, and there is a strong inversion at cloud top. For cloud tops below 14 km, the temperature lapse rate within the cloud often approaches a moist adiabat, consistent with rapid undiluted ascent within the convective systems.
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Biondi, R., W. J. Randel, S. P. Ho, T. Neubert, and S. Syndergaard. "Thermal structure of intense convective clouds derived from GPS radio occultations." Atmospheric Chemistry and Physics 12, no. 12 (June 18, 2012): 5309–18. http://dx.doi.org/10.5194/acp-12-5309-2012.
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Abstract. Thermal structure associated with deep convective clouds is investigated using Global Positioning System (GPS) radio occultation measurements. GPS data are insensitive to the presence of clouds, and provide high vertical resolution and high accuracy measurements to identify associated temperature behavior. Deep convective systems are identified using International Satellite Cloud Climatology Project (ISCCP) satellite data, and cloud tops are accurately measured using Cloud-Aerosol Lidar with Orthogonal Polarization (CALIPSO) lidar observations; we focus on 53 cases of near-coincident GPS occultations with CALIPSO profiles over deep convection. Results show a sharp spike in GPS bending angle highly correlated to the top of the clouds, corresponding to anomalously cold temperatures within the clouds. Above the clouds the temperatures return to background conditions, and there is a strong inversion at cloud top. For cloud tops below 14 km, the temperature lapse rate within the cloud often approaches a moist adiabat, consistent with rapid undiluted ascent within the convective systems.
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Narendra Reddy, Nelli, Madineni Venkat Ratnam, Ghouse Basha, and Varaha Ravikiran. "Cloud vertical structure over a tropical station obtained using long-term high-resolution radiosonde measurements." Atmospheric Chemistry and Physics 18, no. 16 (August 17, 2018): 11709–27. http://dx.doi.org/10.5194/acp-18-11709-2018.
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Abstract. Cloud vertical structure, including top and base altitudes, thickness of cloud layers, and the vertical distribution of multilayer clouds, affects large-scale atmosphere circulation by altering gradients in the total diabatic heating and cooling and latent heat release. In this study, long-term (11 years) observations of high-vertical-resolution radiosondes are used to obtain the cloud vertical structure over a tropical station at Gadanki (13.5∘ N, 79.2∘ E), India. The detected cloud layers are verified with independent observations using cloud particle sensor (CPS) sonde launched from the same station. High-level clouds account for 69.05 %, 58.49 %, 55.5 %, and 58.6 % of all clouds during the pre-monsoon, monsoon, post-monsoon, and winter seasons, respectively. The average cloud base (cloud top) altitudes for low-level, middle-level, high-level, and deep convective clouds are 1.74 km (3.16 km), 3.59 km (5.55 km), 8.79 km (10.49 km), and 1.22 km (11.45 km), respectively. Single-layer, two-layer, and three-layer clouds account for 40.80 %, 30.71 %, and 19.68 % of all cloud configurations, respectively. Multilayer clouds occurred more frequently during the monsoon with 34.58 %. Maximum cloud top altitude and cloud thickness occurred during the monsoon season for single-layer clouds and the uppermost layer of multiple-layer cloud configurations. In multilayer cloud configurations, diurnal variations in the thickness of upper-layer clouds are larger than those of lower-layer clouds. Heating and cooling in the troposphere and lower stratosphere due to these cloud layers are also investigated and peak cooling (peak warming) is found below (above) the cold-point tropopause (CPT) altitude. The magnitude of cooling (warming) increases from single-layer to four- or more-layer cloud occurrence. Further, the vertical structure of clouds is also studied with respect to the arrival date of the Indian summer monsoon over Gadanki.
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Mason, Shannon, Christian Jakob, Alain Protat, and Julien Delanoë. "Characterizing Observed Midtopped Cloud Regimes Associated with Southern Ocean Shortwave Radiation Biases." Journal of Climate 27, no. 16 (August 7, 2014): 6189–203. http://dx.doi.org/10.1175/jcli-d-14-00139.1.
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Abstract Clouds strongly affect the absorption and reflection of shortwave and longwave radiation in the atmosphere. A key bias in climate models is related to excess absorbed shortwave radiation in the high-latitude Southern Ocean. Model evaluation studies attribute these biases in part to midtopped clouds, and observations confirm significant midtopped clouds in the zone of interest. However, it is not yet clear what cloud properties can be attributed to the deficit in modeled clouds. Present approaches using observed cloud regimes do not sufficiently differentiate between potentially distinct types of midtopped clouds and their meteorological contexts. This study presents a refined set of midtopped cloud subregimes for the high-latitude Southern Ocean, which are distinct in their dynamical and thermodynamic background states. Active satellite observations from CloudSat and Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) are used to study the macrophysical structure and microphysical properties of the new cloud regimes. The subgrid-scale variability of cloud structure and microphysics is quantified within the cloud regimes by identifying representative physical cloud profiles at high resolution from the radar–lidar (DARDAR) cloud classification mask. The midtopped cloud subregimes distinguish between stratiform clouds under a high inversion and moderate subsidence; an optically thin cold-air advection cloud regime occurring under weak subsidence and including altostratus over low clouds; optically thick clouds with frequent deep structures under weak ascent and warm midlevel anomalies; and a midlevel convective cloud regime associated with strong ascent and warm advection. The new midtopped cloud regimes for the high-latitude Southern Ocean will provide a refined tool for model evaluation and the attribution of shortwave radiation biases to distinct cloud processes and properties.
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Li, Pak Shing, and Richard I. Klein. "Magnetized interstellar molecular clouds – II. The large-scale structure and dynamics of filamentary molecular clouds." Monthly Notices of the Royal Astronomical Society 485, no. 4 (March 27, 2019): 4509–28. http://dx.doi.org/10.1093/mnras/stz653.
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Abstract We perform ideal magnetohydrodynamics high-resolution adaptive mesh refinement simulations with driven turbulence and self-gravity and find that long filamentary molecular clouds are formed at the converging locations of large-scale turbulence flows and the filaments are bounded by gravity. The magnetic field helps shape and reinforce the long filamentary structures. The main filamentary cloud has a length of ∼4.4 pc. Instead of a monolithic cylindrical structure, the main cloud is shown to be a collection of fibre/web-like substructures similar to filamentary clouds such as L1495. Unless the line-of-sight is close to the mean field direction, the large-scale magnetic field and striations in the simulation are found roughly perpendicular to the long axis of the main cloud, similar to L1495. This provides strong support for a large-scale moderately strong magnetic field surrounding L1495. We find that the projection effect from observations can lead to incorrect interpretations of the true three-dimensional physical shape, size, and velocity structure of the clouds. Helical magnetic field structures found around filamentary clouds that are interpreted from Zeeman observations can be explained by a simple bending of the magnetic field that pierces through the cloud. We demonstrate that two dark clouds form a T-shaped configuration that is strikingly similar to the infrared dark cloud SDC13, leading to the interpretation that SDC13 results from a collision of two long filamentary clouds. We show that a moderately strong magnetic field (${{\cal M}_{\rm A}}\sim 1$) is crucial for maintaining a long and slender filamentary cloud for a long period of time ∼0.5 Myr.
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Mazin, I. P. "Cloud Phase Structure: Experimental Data Analysis and Parameterization." Journal of the Atmospheric Sciences 63, no. 2 (February 1, 2006): 667–81. http://dx.doi.org/10.1175/jas3660.1.
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Abstract In this article, the data collected over 6 yr of daily observations at a network of aircraft sounding (31 stations) in the former Soviet Union, and the data collected by Canadian researchers in field campaigns in the 1990s, are reanalyzed and compared with each other. To describe the cloud phase structure (CPS), the notion of the cloud phase index (CPI)3 is used; that is, the local mass fraction of the ice particles in the total (water + ice) water content. It is concluded that the average distribution of the (CPI)3 values in clouds depends mainly on the temperature, the cloud types, and the scale of averaging. If these characteristics remain unchanged the geographic and seasonal variations of the phase structure are small. It is shown that for averaging scales of the order of 100 m, the frequency of occurrence of liquid clouds [(CPI)3 = 0] varies from approximately 60% at 0°C to 5% at −35°C, and that of the ice clouds from about 5% to 60%. The frequency of occurrence of the mixed clouds only weakly depends on temperature, varying within 30%–40%. The dependence of the cumulative (CPI)3 distribution on temperature in the interval 0.1 < (CPI)3 < 0.7 is close to linear. For stratiform clouds (without going into further details) the coefficients of the linear parameterization are found as a function of temperature. Knowing the (CPI)3 distribution allows one to also estimate the humidity in clouds. The most urgent challenges for the experimental studies of the cloud phase structure are formulated.
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Stubenrauch, C. J., S. Cros, A. Guignard, and N. Lamquin. "A 6-year global cloud climatology from the Atmospheric InfraRed Sounder AIRS and a statistical analysis in synergy with CALIPSO and CloudSat." Atmospheric Chemistry and Physics Discussions 10, no. 3 (March 30, 2010): 8247–96. http://dx.doi.org/10.5194/acpd-10-8247-2010.
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Abstract. We present a six-year global climatology of cloud properties, obtained from observations of the Atmospheric Infrared Sounder (AIRS) onboard the NASA Aqua satellite. Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) combined with CloudSat observations, both missions launched as part of the A-Train in 2006, provide a unique opportunity to evaluate the retrieved AIRS cloud properties such as cloud amount and height as well as to explore the vertical structure of different cloud types. AIRS-LMD cloud detection agrees with CALIPSO about 85% over ocean and about 75% over land. Global cloud amount has been estimated as about 66% to 74%, depending on the weighting of not cloudy AIRS footprints by partial cloud cover (0 or 0.3). 40% of all clouds are high clouds, and about 44% of all clouds are single layer low-level clouds. The "radiative" cloud height determined by the AIRS-LMD retrieval corresponds well to the height of the maximum backscatter signal and of the "apparent middle" of the cloud. Whereas the real cloud thickness of high opaque clouds often fills the whole troposphere, their "apparent" cloud thickness (at which optical depth reaches about 5) is on average only 2.5 km. The real geometrical thickness of optically thin cirrus as identified by AIRS-LMD is identical to the "apparent" cloud thickness with an average of about 2.5 km in the tropics and midlatitudes. High clouds in the tropics have slightly more diffusive cloud tops than at higher latitudes. In general, the depth of the maximum backscatter signal increases nearly linearly with increasing "apparent" cloud thickness. For the same "apparent" cloud thickness optically thin cirrus show a maximum backscatter about 10% deeper inside the cloud than optically thicker clouds. We also show that only the geometrically thickest opaque clouds and (the probably surrounding anvil) cirrus penetrate the stratosphere in the tropics.
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Stubenrauch, C. J., S. Cros, A. Guignard, and N. Lamquin. "A 6-year global cloud climatology from the Atmospheric InfraRed Sounder AIRS and a statistical analysis in synergy with CALIPSO and CloudSat." Atmospheric Chemistry and Physics 10, no. 15 (August 6, 2010): 7197–214. http://dx.doi.org/10.5194/acp-10-7197-2010.
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Abstract. We present a six-year global climatology of cloud properties, obtained from observations of the Atmospheric Infrared Sounder (AIRS) onboard the NASA Aqua satellite. Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) combined with CloudSat observations, both missions launched as part of the A-Train in 2006, provide a unique opportunity to evaluate the retrieved AIRS cloud properties such as cloud amount and height. In addition, they permit to explore the vertical structure of different cloud types. AIRS-LMD cloud detection agrees with CALIPSO about 85% over ocean and about 75% over land. Global cloud amount has been estimated from 66% to 74%, depending on the weighting of not cloudy AIRS footprints by partial cloud cover from 0 to 0.3. 42% of all clouds are high clouds, and about 42% of all clouds are single layer low-level clouds. The "radiative" cloud height determined by the AIRS-LMD retrieval corresponds well to the height of the maximum backscatter signal and of the "apparent middle" of the cloud. Whereas the real cloud thickness of high opaque clouds often fills the whole troposphere, their "apparent" cloud thickness (at which optical depth reaches about 5) is on average only 2.5 km. The real geometrical thickness of optically thin cirrus as identified by AIRS-LMD is identical to the "apparent" cloud thickness with an average of about 2.5 km in the tropics and midlatitudes. High clouds in the tropics have slightly more diffusive cloud tops than at higher latitudes. In general, the depth of the maximum backscatter signal increases nearly linearly with increasing "apparent" cloud thickness. For the same "apparent" cloud thickness optically thin cirrus show a maximum backscatter about 10% deeper inside the cloud than optically thicker clouds. We also show that only the geometrically thickest opaque clouds and (the probably surrounding anvil) cirrus penetrate the stratosphere in the tropics.
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Creamean, Jessie M., Gijs de Boer, Hagen Telg, Fan Mei, Darielle Dexheimer, Matthew D. Shupe, Amy Solomon, and Allison McComiskey. "Assessing the vertical structure of Arctic aerosols using balloon-borne measurements." Atmospheric Chemistry and Physics 21, no. 3 (February 9, 2021): 1737–57. http://dx.doi.org/10.5194/acp-21-1737-2021.
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Abstract. The rapidly warming Arctic is sensitive to perturbations in the surface energy budget, which can be caused by clouds and aerosols. However, the interactions between clouds and aerosols are poorly quantified in the Arctic, in part due to (1) limited observations of vertical structure of aerosols relative to clouds and (2) ground-based observations often being inadequate for assessing aerosol impacts on cloud formation in the characteristically stratified Arctic atmosphere. Here, we present a novel evaluation of Arctic aerosol vertical distributions using almost 3 years' worth of tethered balloon system (TBS) measurements spanning multiple seasons. The TBS was deployed at the U.S. Department of Energy Atmospheric Radiation Measurement Program's facility at Oliktok Point, Alaska. Aerosols were examined in tandem with atmospheric stability and ground-based remote sensing of cloud macrophysical properties to specifically address the representativeness of near-surface aerosols to those at cloud base. Based on a statistical analysis of the TBS profiles, ground-based aerosol number concentrations were unequal to those at cloud base 86 % of the time. Intermittent aerosol layers were observed 63 % of the time due to poorly mixed below-cloud environments, mostly found in the spring, causing a decoupling of the surface from the cloud layer. A uniform distribution of aerosol below cloud was observed only 14 % of the time due to a well-mixed below-cloud environment, mostly during the fall. The equivalent potential temperature profiles of the below-cloud environment reflected the aerosol profile 89 % of the time, whereby a mixed or stratified below-cloud environment was observed during a uniform or layered aerosol profile, respectively. In general, a combination of aerosol sources, thermodynamic structure, and wet removal processes from clouds and precipitation likely played a key role in establishing observed aerosol vertical structures. Results such as these could be used to improve future parameterizations of aerosols and their impacts on Arctic cloud formation and radiative properties.
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Forsythe, John M., Jason B. Dodson, Philip T. Partain, Stanley Q. Kidder, and Thomas H. Vonder Haar. "How Total Precipitable Water Vapor Anomalies Relate to Cloud Vertical Structure." Journal of Hydrometeorology 13, no. 2 (April 1, 2012): 709–21. http://dx.doi.org/10.1175/jhm-d-11-049.1.
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Abstract The NOAA operational total precipitable water (TPW) anomaly product is available to forecasters to display percentage of normal TPW in real time for applications like heavy precipitation forecasts. In this work, the TPW anomaly is compared to multilayer cloud frequency and vertical structure. The hypothesis is tested that the TPW anomaly is reflective of changes in cloud vertical distribution, and that anomalously moist atmospheres have more and deeper clouds, while dry atmospheres have fewer and thinner clouds. Cloud vertical occurrence profiles from the CloudSat 94-GHz radar and the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) are composited according to TPW anomaly for summer and winter from 2007 to 2010. Three geographic regions are examined: the North Pacific (NPAC), the tropical east Pacific (Niño), and the Mississippi Valley (MSVL), which is a land-only region. Cloud likelihood increases as TPW anomaly values increase beyond 100% over MSVL and Niño. Over NPAC, shallow boundary layer cloud occurrence is not a function of TPW anomaly, while high clouds and deep clouds throughout the troposphere are more likely at higher TPW anomalies. In the Niño region, boundary layer clouds grow vertically as the TPW anomaly increases, and the anomaly range is smaller than in the midlatitudes. In summer, the MSVL region resembles Niño, but boundary layer clouds are observed less frequently than expected. The wintertime MSVL results do not show any compelling relationship, perhaps because of the difficulties in computing TPW anomaly in a very dry atmosphere.
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Stein, T. H. M., C. E. Holloway, I. Tobin, and S. Bony. "Observed Relationships between Cloud Vertical Structure and Convective Aggregation over Tropical Ocean." Journal of Climate 30, no. 6 (March 6, 2017): 2187–207. http://dx.doi.org/10.1175/jcli-d-16-0125.1.
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Abstract Using the satellite-infrared-based Simple Convective Aggregation Index (SCAI) to determine the degree of aggregation, 5 years of CloudSat–CALIPSO cloud profiles are composited at a spatial scale of 10 degrees to study the relationship between cloud vertical structure and aggregation. For a given large-scale vertical motion and domain-averaged precipitation rate, there is a large decrease in anvil cloud (and in cloudiness as a whole) and an increase in clear sky and low cloud as aggregation increases. The changes in thick anvil cloud are proportional to the changes in total areal cover of brightness temperatures below 240 K [cold cloud area (CCA)], which is negatively correlated with SCAI. Optically thin anvil cover decreases significantly when aggregation increases, even for a fixed CCA, supporting previous findings of a higher precipitation efficiency for aggregated convection. Cirrus, congestus, and midlevel clouds do not display a consistent relationship with the degree of aggregation. Lidar-observed low-level cloud cover (where the lidar is not attenuated) is presented herein as the best estimate of the true low-level cloud cover, and it is shown that it increases as aggregation increases. Qualitatively, the relationships between cloud distribution and SCAI do not change with sea surface temperature, while cirrus clouds are more abundant and low-level clouds less at higher sea surface temperatures. For the observed regimes, the vertical cloud profile varies more evidently with SCAI than with mean precipitation rate. These results confirm that convective scenes with similar vertical motion and rainfall can be associated with vastly different cloudiness (both high and low cloud) and humidity depending on the degree of convective aggregation.
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Hultgren, K., J. Gumbel, D. A. Degenstein, A. E. Bourassa, and N. D. Lloyd. "Application of tomographic algorithms to Polar Mesospheric Cloud observations by Odin/OSIRIS." Atmospheric Measurement Techniques Discussions 5, no. 3 (May 25, 2012): 3693–716. http://dx.doi.org/10.5194/amtd-5-3693-2012.
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Abstract. Limb-scanning satellites can provide global information about the vertical structure of Polar Mesospheric Clouds. However, information about horizontal structures usually remains limited. This is due to both a long line of sight and a long scan duration. On eighteen days during the Northern Hemisphere summers 2010–2011 and the Southern Hemisphere summer 2011/2012, the Swedish-led Odin satellite was operated in a special mesospheric mode with short limb scans limited to the altitude range of Polar Mesospheric Clouds. For Odin's Optical Spectrograph and InfraRed Imager System (OSIRIS) this provides multiple views through a given cloud volume and, thus, a basis for tomographic analysis of the vertical/horizontal cloud structure. Here we present algorithms for tomographic analysis of mesospheric clouds based on maximum probability techniques. We also present results of simulating OSIRIS tomography and retrieved cloud structures from the special tomographic periods.
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Rossow, William B., and Yuanchong Zhang. "Evaluation of a Statistical Model of Cloud Vertical Structure Using Combined CloudSat and CALIPSO Cloud Layer Profiles." Journal of Climate 23, no. 24 (December 15, 2010): 6641–53. http://dx.doi.org/10.1175/2010jcli3734.1.
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Abstract A model of the three-dimensional distribution of clouds was developed from the statistics of cloud layer occurrence from the International Satellite Cloud Climatology Project (ISCCP) and the statistics of cloud vertical structure (CVS) from an analysis of radiosonde humidity profiles. The CVS model associates each cloud type, defined by cloud-top pressure of the topmost cloud layer and total column optical thickness, with a particular CVS. The advent of satellite cloud radar (CloudSat) and lidar [Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO)] measurements (together C&C) of CVS allows for a quantitative evaluation of this statistical model. The zonal monthly-mean cloud layer distribution from the ISCCP CVS agrees with that from C&C to within 10% (when normalized to the same total cloud amount). The largest differences are an overestimate of middle-level cloudiness in winter polar regions, an overestimate of cloud-top pressures of the highest-level clouds, especially in the tropics, and an underestimate of low-level cloud amounts over southern midlatitude oceans. A more severe test of the hypothesized relationship is made by comparing CVS for individual satellite pixels. The agreement of CVS is good for isolated low-level clouds and reasonably good when the uppermost cloud layer is a high-level cloud; however, the agreement is not good when the uppermost cloud layer is a middle-level cloud, even when ISCCP correctly locates cloud top. An improved CVS model combining C&C and ISCCP may require classification at spatial scales larger than individual satellite pixels.
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Coley, P. F., and P. R. Jonas. "The influence of cloud structure and droplet concentration on the reflectance of shortwave radiation." Annales Geophysicae 14, no. 8 (August 31, 1996): 845–52. http://dx.doi.org/10.1007/s00585-996-0845-5.
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Abstract. The effects of cloud shadowing, channelling, cloud side illumination and droplet concentration are investigated with regard to the reflection of shortwave solar radiation. Using simple geometric clouds, coupled with a Monte Carlo model the transmission properties of idealized cloud layers are found. The clouds are illuminated with direct solar radiation from above. The main conclusion reached is that the distribution of the cloud has a very large influence on the reflectivity of a cloud layer. In particular, if the cloud contains vertical gaps through the cloud layer in which the liquid water content is zero, then, smaller more numerous gaps are more influential on the radiation than fewer, larger gaps with equal cloud fraction. At very low solar zenith angles channelling of the radiation reduces the reflection expected on the basis of the percentage cloud cover. At high solar zenith angles the illumination of the cloud edges significantly increases the reflection despite the shadowing of one cloud by another when the width of the gaps is small. The impact of droplet concentration upon the reflection of cloud layers is also investigated. It is found that at low solar zenith angles where channelling is important, the lower concentrations increase the transmission. Conversely, when cloud edge illumination is dominant the cloud distribution is found to be more important for the higher concentrations.
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Li, P. S., C. F. McKee, and R. I. Klein. "Structure and Dynamics of Magnetized Dark Molecular Clouds." Proceedings of the International Astronomical Union 10, H16 (August 2012): 386. http://dx.doi.org/10.1017/s1743921314011557.
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Massive infrared dark clouds (IRDCs) are believed to be the precursors to star clusters and massive stars (e.g. Bergin & Tafalla 2007). The supersonic, turbulent nature of molecular clouds in the presence of magnetic fields poses a great challenge in understanding the structure and dynamics of magnetized molecular clouds and the star formation therein. Using the high-order radiation-magneto-hydrodynamic adaptive mesh refinement (AMR) code ORION2 (Li et al. 2012), we perform a large-scale driven-turbulence simulation to reveal the 3D filamentary structure and dynamical state of a highly supersonic (thermal Mach number = 10) and strongly magnetized (plasma β=0.02) massive infrared dark molecular cloud. With the high resolution afforded by AMR, we follow the dynamical evolution of the cloud in order to understand the roles of strong magnetic fields, turbulence, and self-gravity in shaping the cloud and in the formation of dense cores.
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Sedlar, Joseph, Matthew D. Shupe, and Michael Tjernström. "On the Relationship between Thermodynamic Structure and Cloud Top, and Its Climate Significance in the Arctic." Journal of Climate 25, no. 7 (March 28, 2012): 2374–93. http://dx.doi.org/10.1175/jcli-d-11-00186.1.
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Abstract Cloud and thermodynamic characteristics from three Arctic observation sites are investigated to understand the collocation between low-level clouds and temperature inversions. A regime where cloud top was 100–200 m above the inversion base [cloud inside inversion (CII)] was frequently observed at central Arctic Ocean sites, while observations from Barrow, Alaska, indicate that cloud tops were more frequently constrained to inversion base height [cloud capped by inversion (CCI)]. Cloud base and top heights were lower, and temperature inversions were also stronger and deeper, during CII cases. Both cloud regimes were often decoupled from the surface except for CCI over Barrow. In-cloud lapse rates differ and suggest increased cloud-mixing potential for CII cases. Specific humidity inversions were collocated with temperature inversions for more than 60% of the CCI and more than 85% of the CII regimes. Horizontal advection of heat and moisture is hypothesized as an important process controlling thermodynamic structure and efficiency of cloud-generated motions. The portion of CII clouds above the inversion contains cloud radar signatures consistent with cloud droplets. The authors test the longwave radiative impact of cloud liquid above the inversion through hypothetical liquid water distributions. Optically thin CII clouds alter the effective cloud emission temperature and can lead to an increase in surface flux on the order of 1.5 W m−2 relative to the same cloud but whose top does not extend above the inversion base. The top of atmosphere impact is even larger, increasing outgoing longwave radiation up to 10 W m−2. These results suggest a potentially significant longwave radiative forcing via simple liquid redistributions for a distinctly dominant cloud regime over sea ice.
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Liu, Lei, Xuejin Sun, Feng Chen, Shijun Zhao, and Taichang Gao. "Cloud Classification Based on Structure Features of Infrared Images." Journal of Atmospheric and Oceanic Technology 28, no. 3 (March 1, 2011): 410–17. http://dx.doi.org/10.1175/2010jtecha1385.1.
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Abstract Some cloud structure features that can be extracted from infrared images of the sky are suggested for cloud classification. Both the features and the classifier are developed over zenithal images taken by the whole-sky infrared cloud-measuring system (WSIRCMS), which is placed in Nanjing, China. Before feature extraction, the original infrared image was smoothed to suppress noise. Then, the image was enhanced using top-hat transformation and a high-pass filtering. Edges are detected from the enhanced image after adaptive optimization threshold segmentation and morphological edge detection. Several structural features are extracted from the segment image and edge image, such as cloud gray mean value (ME), cloud fraction (ECF), edge sharpness (ES), and cloud mass and gap distribution parameters, including very small-sized cloud mass and gaps (SMG), middle-sized cloud gaps (MG), medium–small-sized cloud gaps (MSG), and main cloud mass (MM). It is found that these features are useful for distinguishing cirriform, cumuliform, and waveform clouds. A simple but efficient supervised classifier called the rectangle method is used to do cloud classification. The performance of the classifier is assessed with an a priori classification carried out by visual inspection of 277 images. The index of agreement is 90.97%.
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Pudritz, Ralph E. "Formation of structure in star-forming clouds." Canadian Journal of Physics 68, no. 9 (September 1, 1990): 808–23. http://dx.doi.org/10.1139/p90-118.
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Star formation occurs in massive, dense, molecular clouds in the interstellar medium. These clouds have a rich substructure consisting of dense clumps and extended filaments. Since stars only form within these dense clumps, any fundamental theory of star formation must predict their physical properties. This review focusses on the physics of molecular clouds and discusses in this context a particular mechanism for the formation of structure that is well supported by the observations. Strong hydromagnetic waves are likely to be excited in molecular clouds since it is observed that cloud magnetic fields have energy densities close to gravity. These waves support the cloud against global gravitational collapse by providing an effective wave "pressure". This review also shows that waves may control the formation of structure in molecular clouds.
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Dib, Sami, Sylvain Bontemps, Nicola Schneider, Davide Elia, Volker Ossenkopf-Okada, Mohsen Shadmehri, Doris Arzoumanian, et al. "The structure and characteristic scales of molecular clouds." Astronomy & Astrophysics 642 (October 2020): A177. http://dx.doi.org/10.1051/0004-6361/202038849.
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The structure of molecular clouds holds important clues regarding the physical processes that lead to their formation and subsequent dynamical evolution. While it is well established that turbulence imprints a self-similar structure onto the clouds, other processes, such as gravity and stellar feedback, can break their scale-free nature. The break of self-similarity can manifest itself in the existence of characteristic scales that stand out from the underlying structure generated by turbulent motions. In this work, we investigate the structure of the Cygnus-X North and Polaris Flare molecular clouds, which represent two extremes in terms of their star formation activity. We characterize the structure of the clouds using the delta-variance (Δ-variance) spectrum. In the Polaris Flare, the structure of the cloud is self-similar over more than one order of magnitude in spatial scales. In contrast, the Δ-variance spectrum of Cygnus-X North exhibits an excess and a plateau on physical scales of ≈0.5−1.2 pc. In order to explain the observations for Cygnus-X North, we use synthetic maps where we overlay populations of discrete structures on top of a fractal Brownian motion (fBm) image. The properties of these structures, such as their major axis sizes, aspect ratios, and column density contrasts with the fBm image, are randomly drawn from parameterized distribution functions. We are able to show that, under plausible assumptions, it is possible to reproduce a Δ-variance spectrum that resembles that of the Cygnus-X North region. We also use a “reverse engineering” approach in which we extract the compact structures in the Cygnus-X North cloud and reinject them onto an fBm map. Using this approach, the calculated Δ-variance spectrum deviates from the observations and is an indication that the range of characteristic scales (≈0.5−1.2 pc) observed in Cygnus-X North is not only due to the existence of compact sources, but is a signature of the whole population of structures that exist in the cloud, including more extended and elongated structures.
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Miyazaki, Ryuji, Makoto Yamamoto, and Koichi Harada. "Line-Based Planar Structure Extraction from a Point Cloud with an Anisotropic Distribution." International Journal of Automation Technology 11, no. 4 (June 29, 2017): 657–65. http://dx.doi.org/10.20965/ijat.2017.p0657.
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We propose a line-based region growing method for extracting planar regions with precise boundaries from a point cloud with an anisotropic distribution. Planar structure extraction from point clouds is an important process in many applications, such as maintenance of infrastructure components including roads and curbstones, because most artificial structures consist of planar surfaces. A mobile mapping system (MMS) is able to obtain a large number of points while traveling at a standard speed. However, if a high-end laser scanning system is equipped, the point cloud has an anisotropic distribution. In traditional point-based methods, this causes problems when calculating geometric information using neighboring points. In the proposed method, the precise boundary of a planar structure is maintained by appropriately creating line segments from an input point cloud. Furthermore, a normal vector at a line segment is precisely estimated for the region growing process. An experiment using the point cloud from an MMS simulation indicates that the proposed method extracts planar regions accurately. Additionally, we apply the proposed method to several real point clouds and evaluate its effectiveness via visual inspection.
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Gong, J., D. L. Wu, and V. Limpasuvan. "Meridionally-tilted ice cloud structures in the tropical Upper Troposphere as seen by CloudSat." Atmospheric Chemistry and Physics Discussions 14, no. 17 (September 26, 2014): 24915–42. http://dx.doi.org/10.5194/acpd-14-24915-2014.
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Abstract. It remains challenging to quantify global cloud properties and uncertainties associated with their impacts on climate change because of our poor understanding of cloud three-dimensional (3-D) structures from observations and unrealistic/unconsidered characterization of 3-D cloud effects in Global Climate Models (GCMs). In this study we find cloud 3-D effects can cause significant error in cloud ice and radiation measurements if it is not taken into account appropriately. One of the cloud 3-D complexities, the slantwise tilt structure, has not received much attention in research and even little report is given on its global perspective. A novel approach is presented here to analyze the ice cloud water content (IWC) profiles retrieved from CloudSat and a joint radar-lidar product (DARDAR). By integrating IWC along different tilt angles, we find that Upper-Troposphere (UT) ice cloud mass between 11 and 17 km is tilted poleward from active convection centers in the tropics. This systematic tilt in cloud mass structure is expected from the mass conservation principle of the Hadley circulation with the divergent flow of each individual convection/convective system from down below, and its existence is further confirmed from cloud-resolving scale Weather Research and Forecasting (WRF) model simulations. Thus, additive effects of tilted cloud structures can induce 5–20% variability by nature or an error in satellite cloud/hydrometeor ice retrievals if simply converting it from slant to nadir column. A surprising finding is the equatorward tilt in middle tropospheric (5–11 km) ice clouds, which is also evident in high-resolution model simulations but not in coarse-resolution simulations with cumulus parameterization. The observed cloud tilt structures are intrinsic properties of tropical clouds, producing synoptic distributions around the ITCZ. These findings imply that current interpretations based on over-simplified cloud vertical structures could lead to substantial cloud measurement errors and induce subsequent impact on understanding cloud radiative, dynamical and hydrological properties.
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Gong, J., D. L. Wu, and V. Limpasuvan. "Meridionally tilted ice cloud structures in the tropical upper troposphere as seen by CloudSat." Atmospheric Chemistry and Physics 15, no. 11 (June 9, 2015): 6271–81. http://dx.doi.org/10.5194/acp-15-6271-2015.
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Abstract. It remains challenging to quantify global cloud properties and uncertainties associated with their impacts on climate change because of our poor understanding of cloud three-dimensional (3-D) structures from observations and unrealistic characterization of 3-D cloud effects in global climate models (GCMs). In this study we find cloud 3-D effects can cause significant error in cloud ice and radiation measurements if it is not taken into account appropriately. One of the cloud 3-D complexities, the slantwise tilt structure, has not received much attention in research and even less has been reported considering a global perspective. A novel approach is presented here to analyze the ice cloud water content (IWC) profiles retrieved from CloudSat and a joint radar–lidar product (DARDAR). By integrating IWC profiles along different tilt angles, we find that upper-troposphere (UT) ice cloud mass between 11 and 17 km is tilted poleward from active convection centers in the tropics [30° S, 30° N]. This systematic tilt in cloud mass structure is expected from the mass conservation principle of the Hadley circulation with the divergent flow of each individual convection/convective system from down below, and its existence is further confirmed from cloud-resolving-scale Weather Research and Forecasting (WRF) model simulations. Thus, additive effects of tilted cloud structures can introduce 5–20% variability by its nature or produce errors to satellite cloud/hydrometeor ice retrievals if simply converting it from slant to nadir column. A surprising finding is the equatorward tilt in middle tropospheric (5–11 km) ice clouds, which is also evident in high-resolution model simulations but not in coarse-resolution simulations with cumulus parameterization. The observed cloud tilt structures are intrinsic properties of tropical clouds, producing synoptic distributions around the Intertropical Convergence Zone (ITCZ). These findings imply that current interpretations based on over-simplified cloud vertical structures could lead to considerable cloud measurement errors and have a subsequent impact on understanding cloud radiative, dynamical and hydrological properties.
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Westerlund, B. E. "An overview of the structure and kinematics of the Magellanic Clouds." Symposium - International Astronomical Union 148 (1991): 15–23. http://dx.doi.org/10.1017/s0074180900199942.
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A vast amount of observational data concerning the structure and kinematics of the Magellanic Clouds is now available. Many basic quantities (e.g. distances and geometry) are, however, not yet sufficiently well determined. Interactions between the Small Magellanic Cloud (SMC), the Large Magellanic Cloud (LMC) and our Galaxy have dominated the evolution of the Clouds, causing bursts of star formation which, together with stochastic self-propagating star formation, produced the observed structures. In the youngest generation in the LMC it is seen as an intricate pattern imitating a fragmented spiral structure. In the SMC much of the fragmentation is along the line of sight complicating the reconstruction of its history. The violent events in the past are also recognizable in complex velocity patterns which make the analysis of the kinematics of the Clouds difficult.
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Chatterjee, Kamalika, Rahul Kashyap, and Jaywant H. Arakeri. "Experimental Study of Cloud Formation." Applied Mechanics and Materials 110-116 (October 2011): 2570–76. http://dx.doi.org/10.4028/www.scientific.net/amm.110-116.2570.
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Cloud formation is a ubiquitous process and modeling it as a simplified experimental set-up may be an interesting and fruitful task. In this study different flow and thermal processes and fluid structures during cloud formation (especially Cumulus clouds) are investigated through an experimental setup. Vapor coming out of a 20cm×20cm water surface at temperature 60-800C interacts inside a square plexiglas tube of vertical height 60cm with dry, cold air passing from above the tube. An air conditioner is used to supply cold air at temperature 180C over the plexiglas tube. Various parameters like rate of evaporation, speed of cold air are regulated as per requirements. Turbulent plume structure is observed through a sheet of light. Optical visualization method is adopted for observing the condensed water droplets. Movies of vertical and horizontal views of plume structure are taken. Observation of this entrainment process reveals the turbulent nature of convection related to it and the gradual growth of cloud (aggregation of condensed water particles) with drop of temperature as clouds move up. Our present study is also important for prediction of type of Cumulus cloud formed for known environmental conditions.
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Smedsmo, Jamie L., Efi Foufoula-Georgiou, Venugopal Vuruputur, Fanyou Kong, and Kelvin Droegemeier. "On the Vertical Structure of Modeled and Observed Deep Convective Storms: Insights for Precipitation Retrieval and Microphysical Parameterization." Journal of Applied Meteorology 44, no. 12 (December 1, 2005): 1866–84. http://dx.doi.org/10.1175/jam2306.1.
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Abstract An understanding of the vertical structure of clouds is important for remote sensing of precipitation from space and for the parameterization of cloud microphysics in numerical weather prediction (NWP) models. The representation of cloud hydrometeor profiles in high-resolution NWP models has direct applications in inversion-type precipitation retrieval algorithms [e.g., the Goddard profiling (GPROF) algorithm used for retrieval of precipitation from passive microwave sensors] and in quantitative precipitation forecasting. This study seeks to understand how the vertical structure of hydrometeors (liquid and frozen water droplets in a cloud) produced by high-resolution NWP models with explicit microphysics, henceforth referred to as cloud-resolving models (CRMs), compares to observations. Although direct observations of 3D hydrometeor fields are not available, comparisons of modeled and observed radar echoes can provide some insight into the vertical structure of hydrometeors and, in turn, into the ability of CRMs to produce precipitation structures that are consistent with observations. Significant differences are revealed between the vertical structure of observed and modeled clouds of a severe midlatitude storm over Texas for which the surface precipitation is reasonably well captured. Possible reasons for this discrepancy are presented, and the need for future research is highlighted.
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Wood, R. "Drizzle in Stratiform Boundary Layer Clouds. Part I: Vertical and Horizontal Structure." Journal of the Atmospheric Sciences 62, no. 9 (September 1, 2005): 3011–33. http://dx.doi.org/10.1175/jas3529.1.
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Abstract Detailed observations of stratiform boundary layer clouds on 12 days are examined with specific reference to drizzle formation processes. The clouds differ considerably in mean thickness, liquid water path (LWP), and droplet concentration. Cloud-base precipitation rates differ by a factor of 20 between cases. The lowest precipitation rate is found in the case with the highest droplet concentration even though this case had by far the highest LWP, suggesting that drizzle can be severely suppressed in polluted clouds. The vertical and horizontal structure of cloud and drizzle liquid water and bulk microphysical parameters are examined in detail. In general, the highest concentration of r > 20 μm drizzle drops is found toward the top of the cloud, and the mean volume radius of the drizzle drops increases monotonically from cloud top to base. The resulting precipitation rates are largest at the cloud base but decrease markedly only in the upper third of the cloud. Below cloud, precipitation rates decrease markedly with distance below base due to evaporation, and are broadly consistent in most cases with the results from a simple sedimentation–evaporation model. Evidence is presented that suggests evaporating drizzle is cooling regions of the subcloud layer, which could result in dynamical feedbacks. A composite power spectrum of the horizontal spatial series of precipitation rate is found to exhibit a power-law scaling from the smallest observable scales to close to the maximum observable scale (∼30 km). The exponent is considerably lower (1.1–1.2) than corresponding exponents for LWP variability obtained in other studies (∼1.5–2), demonstrating that there is relatively more variability of drizzle on small scales. Singular measures analysis shows that drizzle fields are much more intermittent than the cloud liquid water content fields, consistent with a drizzle production process that depends strongly upon liquid water content. The adiabaticity of the clouds, which can be modeled as a simple balance between drizzle loss and turbulent replenishment, is found to decrease if the time scale for drizzle loss is shorter than roughly 5–10 eddy turnover time scales. Finally, the data are compared with three simple scalings derived from recent observations of drizzle in subtropical stratocumulus clouds.
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Rossow, William B., Yuanchong Zhang, and Junhong Wang. "A Statistical Model of Cloud Vertical Structure Based on Reconciling Cloud Layer Amounts Inferred from Satellites and Radiosonde Humidity Profiles." Journal of Climate 18, no. 17 (September 1, 2005): 3587–605. http://dx.doi.org/10.1175/jcli3479.1.
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Abstract To diagnose how cloud processes feed back on weather- and climate-scale variations of the atmosphere requires determining the changes that clouds produce in the atmospheric diabatic heating by radiation and precipitation at the same scales of variation. In particular, not only the magnitude of these changes must be quantified but also their correlation with atmospheric temperature variations; hence, the space–time resolution of the cloud perturbations must be sufficient to account for the majority of these variations. Although extensive new global cloud and radiative flux datasets have recently become available, the vertical profiles of clouds and consequent radiative flux divergence have not been systematically measured covering weather-scale variations from about 100 km, 3 h up to climate-scale variations of 10 000 km, decadal inclusive. By combining the statistics of cloud layer occurrence from the International Satellite Cloud Climatology Project (ISCCP) and an analysis of radiosonde humidity profiles, a statistical model has been developed that associates each cloud type, recognizable from satellite measurements, with a particular cloud vertical structure. Application of this model to the ISCCP cloud layer amounts produces estimates of low-level cloud amounts and average cloud-base pressures that are quantitatively closer to observations based on surface weather observations, capturing the variations with latitude and season and land and ocean (results are less good in the polar regions). The main advantage of this statistical model is that the correlations of cloud vertical structure with meteorology are qualitatively similar to “classical” information relating cloud properties to weather. These results can be evaluated and improved with the advent of satellites that can directly probe cloud vertical structures over the globe, providing statistics with changing meteorological conditions.
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Viviana Vlăduţescu, Daniela, Stephen E. Schwartz, and Dong Huang. "Optical instruments synergy in determination of optical depth of thin clouds." EPJ Web of Conferences 176 (2018): 08008. http://dx.doi.org/10.1051/epjconf/201817608008.
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Optically thin clouds have a strong radiative effect and need to be represented accurately in climate models. Cloud optical depth of thin clouds was retrieved using high resolution digital photography, lidar, and a radiative transfer model. The Doppler Lidar was operated at 1.5 μm, minimizing return from Rayleigh scattering, emphasizing return from aerosols and clouds. This approach examined cloud structure on scales 3 to 5 orders of magnitude finer than satellite products, opening new avenues for examination of cloud structure and evolution.
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Miville-Deschênes, M. A., Q. Salomé, P. G. Martin, G. Joncas, K. Blagrave, K. Dassas, A. Abergel, et al. "Structure formation in a colliding flow: The Herschel view of the Draco nebula." Astronomy & Astrophysics 599 (March 2017): A109. http://dx.doi.org/10.1051/0004-6361/201628289.
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Context. The Draco nebula is a high Galactic latitude interstellar cloud observed at velocities corresponding to the intermediate velocity cloud regime. This nebula shows unusually strong CO emission and remarkably high-contrast small-scale structures for such a diffuse high Galactic latitude cloud. The 21 cm emission of the Draco nebula reveals that it is likely to have been formed by the collision of a cloud entering the disk of the Milky Way. Such physical conditions are ideal to study the formation of cold and dense gas in colliding flows of diffuse and warm gas. Aims. The objective of this study is to better understand the process of structure formation in a colliding flow and to describe the effects of matter entering the disk on the interstellar medium. Methods. We conducted Herschel-SPIRE observations of the Draco nebula. The clumpfind algorithm was used to identify and characterize the small-scale structures of the cloud. Results. The high-resolution SPIRE map reveals the fragmented structure of the interface between the infalling cloud and the Galactic layer. This front is characterized by a Rayleigh-Taylor (RT) instability structure. From the determination of the typical length of the periodic structure (2.2 pc) we estimated the gas kinematic viscosity. This allowed us to estimate the dissipation scale of the warm neutral medium (0.1 pc), which was found to be compatible with that expected if ambipolar diffusion were the main mechanism of turbulent energy dissipation. The statistical properties of the small-scale structures identified with clumpfind are found to be typical of that seen in molecular clouds and hydrodynamical turbulence in general. The density of the gas has a log-normal distribution with an average value of 103 cm-3. The typical size of the structures is 0.1−0.2 pc, but this estimate is limited by the resolution of the observations. The mass of these structures ranges from 0.2 to 20 M⊙ and the distribution of the more massive structures follows a power-law dN/ dlog (M) ~ M-1.4. We identify a mass-size relation with the same exponent as that found in molecular clouds (M ~ L2.3). On the other hand, we found that only 15% of the mass of the cloud is in gravitationally bound structures. Conclusions. We conclude that the collision of diffuse gas from the Galactic halo with the diffuse interstellar medium of the outer layer of the disk is an efficient mechanism for producing dense structures. The increase of pressure induced by the collision is strong enough to trigger the formation of cold neutral medium out of the warm gas. It is likely that ambipolar diffusion is the mechanism dominating the turbulent energy dissipation. In that case the cold structures are a few times larger than the energy dissipation scale. The dense structures of Draco are the result of the interplay between magnetohydrodynamical turbulence and thermal instability as self-gravity is not dominating the dynamics. Interestingly they have properties typical of those found in more classical molecular clouds.
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Li, Ying, and David W. J. Thompson. "Observed Signatures of the Barotropic and Baroclinic Annular Modes in Cloud Vertical Structure and Cloud Radiative Effects." Journal of Climate 29, no. 13 (June 14, 2016): 4723–40. http://dx.doi.org/10.1175/jcli-d-15-0692.1.
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Abstract The signatures of large-scale annular variability on the vertical structure of clouds and cloud radiative effects are examined in vertically resolved CloudSat and other satellite and reanalysis data products. The northern and southern “barotropic” annular modes (the NAM and SAM) have a complex vertical structure. Both are associated with a meridional dipole in clouds between subpolar and middle latitudes, but the sign of the anomalies changes between upper, middle, and lower tropospheric levels. In contrast, the northern and southern baroclinic annular modes have a much simpler vertical structure. Both are linked to same-signed anomalies in clouds extending throughout the troposphere at middle to high latitudes. The changes in cloud incidence associated with both the barotropic and baroclinic annular modes are consistent with dynamical forcing by the attendant changes in static stability and/or vertical motion. The results also provide the first observational estimates of the vertically resolved atmospheric cloud radiative effects associated with hemispheric-scale extratropical variability. In general, the anomalies in atmospheric cloud radiative effects associated with the annular modes peak in the middle to upper troposphere, and are consistent with the anomalous trapping of longwave radiation by variations in upper tropospheric clouds. The southern baroclinic annular mode gives rise to periodic behavior in longwave cloud radiative effects at the top of the atmosphere averaged over Southern Hemisphere midlatitudes.
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Durden, Stephen L., Simone Tanelli, and Gregg Dobrowalski. "CloudSat and A-Train Observations of Tropical Cyclones." Open Atmospheric Science Journal 3, no. 1 (March 27, 2009): 80–92. http://dx.doi.org/10.2174/1874282300903010080.
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The CloudSat 94-GHz Cloud Profiling Radar was designed to provide global information on the vertical structure of clouds. It was launched in April 2006, joining the A-Train of earth science satellites. Although primarily focused on clouds and climate, the CloudSat radar also provides a unique view of the vertical structure of clouds in tropical cyclones. The authors use data from CloudSat and other A-Train satellite constellation missions to examine tropical cyclone cloud properties. They consider several case studies and then examine cloud statistics based on seventeen tropical cyclone overpasses. In addition to the new qualitative view of cloud structure provided by CloudSat, the CloudSat and other ATrain products also contain quantitative estimates of cloud properties. Although the accuracy of these products in tropical cyclones is not validated by direct comparison, the authors do find reasonable agreement with previous in situ measurements.
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Scheirer, R., and S. Schmidt. "CLABAUTAIR: a new algorithm for retrieving three-dimensional cloud structure from airborne microphysical measurements." Atmospheric Chemistry and Physics 5, no. 9 (September 8, 2005): 2333–40. http://dx.doi.org/10.5194/acp-5-2333-2005.
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Abstract. A new algorithm is presented to reproduce the three-dimensional structure of clouds from airborne measurements of microphysical parameters. Data from individual flight legs are scanned for characteristic patterns, and the autocorrelation functions for several directions are used to extrapolate the observations along the flight path to a full three-dimensional distribution of the cloud field. Thereby, the mean measured profiles of microphysical parameters are imposed to the cloud field by mapping the measured probability density functions onto the model layers. The algorithm was tested by simulating flight legs through synthetic clouds (by means of Large Eddy Simulations (LES)) and applied to a stratocumulus cloud case measured during the first field experiment of the EC project INSPECTRO (INfluence of clouds on the SPECtral actinic flux in the lower TROposphere) in East Anglia, UK. The number and position of the flight tracks determine the quality of the retrieved cloud field. If they provide a representative sample of the entire field, the derived pattern closely resembles the statistical properties of the real cloud field.
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Scheirer, R., and S. Schmidt. "CLABAUTAIR: a new algorithm for retrieving three-dimensional cloud structure from airborne microphysical measurements." Atmospheric Chemistry and Physics Discussions 4, no. 6 (December 23, 2004): 8609–25. http://dx.doi.org/10.5194/acpd-4-8609-2004.
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Abstract. A new algorithm is presented to retrieve the three-dimensional structure of clouds from airborne measurements of microphysical parameters. Data from individual flight legs are scanned for characteristic patterns, and the autocorrelation functions for several directions are used to extrapolate the observations along the flight path to a full three-dimensional distribution of the cloud field. Thereby, the mean measured profiles of microphysical parameters are imposed to the cloud field by mapping the measured probability density functions onto the model layers. The algorithm was tested by simulating flight legs through synthetic clouds (by means of Large Eddy Simulations (LES)) and applied to a stratocumulus cloud case measured during the first field experiment of the EC project INSPECTRO (INfluence of clouds on the SPECtral actinic flux in the lower TROposphere) in East Anglia, UK. The number and position of the flight tracks determine the quality of the retrieved cloud field. If they provide a representative sample of the entire field, the derived pattern closely resembles the statistical properties of the real cloud field.
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Deiss, B. M., and A. Just. "A Hydromagnetic Model for the Hierarchical Structure of Molecular Clouds." Symposium - International Astronomical Union 169 (1996): 609–10. http://dx.doi.org/10.1017/s0074180900230416.
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We propose a physical model of molecular clouds which is based on the idea that the back reaction of substructures of a cloud on the ambient medium maintains and stabilizes the cloud on larger scales: clumps, which are assumed to carry a magnetic moment, are coupled to the ambient medium by magnetic forces, hence continually inducing velocity fluctuations due to their random motion. The energy source is then the gravitational binding energy of the clumps in the global potential of the whole cloud.
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REISMAN, G. E., Y. C. WANG, and C. E. BRENNEN. "Observations of shock waves in cloud cavitation." Journal of Fluid Mechanics 355 (January 25, 1998): 255–83. http://dx.doi.org/10.1017/s0022112097007830.
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This paper describes an investigation of the dynamics and acoustics of cloud cavitation, the structures which are often formed by the periodic breakup and collapse of a sheet or vortex cavity. This form of cavitation frequently causes severe noise and damage, though the precise mechanism responsible for the enhancement of these adverse effects is not fully understood. In this paper, we investigate the large impulsive surface pressures generated by this type of cavitation and correlate these with the images from high-speed motion pictures. This reveals that several types of propagating structures (shock waves) are formed in a collapsing cloud and dictate the dynamics and acoustics of collapse. One type of shock wave structure is associated with the coherent collapse of a well-defined and separate cloud when it is convected into a region of higher pressure. This type of global structure causes the largest impulsive pressures and radiated noise. But two other types of structure, termed ‘crescent-shaped regions’ and ‘leading-edge structures’ occur during the less-coherent collapse of clouds. These local events are smaller and therefore produce less radiated noise but the interior pressure pulse magnitudes are almost as large as those produced by the global events.The ubiquity and severity of these propagating shock wave structures provides a new perspective on the mechanisms reponsible for noise and damage in cavitating flows involving clouds of bubbles. It would appear that shock wave dynamics rather than the collapse dynamics of single bubbles determine the damage and noise in many cavitating flows.
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Beckman, J. E., J. Trapero, J. R. Álamo, R. Génova, and I. Lundstrom. "Structure Within the Local Bubble: Properties of Individual Clouds." International Astronomical Union Colloquium 166 (1997): 191–94. http://dx.doi.org/10.1017/s0252921100070962.
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Starting from the casual observation that neighbouring lines of sight to stars at similar distances in the LISM show abruptly varying column densities, we developed a technique for measuring properties of single clouds. Fig.l shows an idealized version of this. The steps (Trapero et al. 1992, 1995) are: –Correct for extinction the distances to local stars used, via B-V (where available), or our own measured Nal or KI absorptions.–Measure diametral column density towards A from Nal or KI equivalent width and convert to hydrogen: N(H) [cm−2].–Measure cloud diameter, between E and E’.–Estimate the number density, n(H) = N(H)/d [cm−3].–Use a canonical thermal pressure, nT = 3500 K cmThis at least gives the decision cool (<100K) or warm (>5000K).–Estimate the cloud mass by integrating n(H) over the estimated volume.Following up, cool cores within warm clouds, or warm envelopes around cool clouds can be identified using distance and velocity as tags. We have found empirical rules of thumb to guide us: –The KI resonance at 7699Å is ideal for finding cool clouds; it is too weak to show up in warm clouds.–NaI D doublet lines weaker than 5mÅ typify warm clouds. There are too many of these, by a factor 50, to come from cool cloud edges. This is confirmed by the “low velocity Routly-Spitzer effect” (see below).
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Schäfer, Michael, Katharina Loewe, André Ehrlich, Corinna Hoose, and Manfred Wendisch. "Simulated and observed horizontal inhomogeneities of optical thickness of Arctic stratus." Atmospheric Chemistry and Physics 18, no. 17 (September 12, 2018): 13115–33. http://dx.doi.org/10.5194/acp-18-13115-2018.
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Abstract. Two-dimensional horizontal fields of cloud optical thickness τ derived from airborne measurements of solar spectral, cloud-reflected radiance are compared with semi-idealized large eddy simulations (LESs) of Arctic stratus performed with the Consortium for Small-scale Modeling (COSMO) atmospheric model. The measurements were collected during the Vertical Distribution of Ice in Arctic Clouds (VERDI) campaign carried out in Inuvik, Canada, in April/May 2012. The input for the LESs is obtained from collocated airborne dropsonde observations of a persistent Arctic stratus above the sea-ice-free Beaufort Sea. Simulations are performed for spatial resolutions of 50 m (1.6 km × 1.6 km domain) and 100 m (6.4 km × 6.4 km domain). Macrophysical cloud properties, such as cloud top altitude and vertical extent, are well captured by the COSMO simulations. However, COSMO produces rather homogeneous clouds compared to the measurements, in particular for the simulations with coarser spatial resolution. For both spatial resolutions, the directional structure of the cloud inhomogeneity is well represented by the model. Differences between the individual cases are mainly associated with the wind shear near cloud top and the vertical structure of the atmospheric boundary layer. A sensitivity study changing the wind velocity in COSMO by a vertically constant scaling factor shows that the directional, small-scale cloud inhomogeneity structures can range from 250 to 800 m, depending on the mean wind speed, if the simulated domain is large enough to capture also large-scale structures, which then influence the small-scale structures. For those cases, a threshold wind velocity is identified, which determines when the cloud inhomogeneity stops increasing with increasing wind velocity.
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Degünther, M., and R. Meerkötter. "Effect of remote clouds on surface UV irradiance." Annales Geophysicae 18, no. 6 (June 30, 2000): 679–86. http://dx.doi.org/10.1007/s00585-000-0679-5.
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Abstract. Clouds affect local surface UV irradiance, even if the horizontal distance from the radiation observation site amounts to several kilometers. In order to investigate this effect, which we call remote clouds effect, a 3-dimensional radiative transfer model is applied. Assuming the atmosphere is subdivided into a quadratic based sector and its surrounding, we quantify the influence of changing cloud coverage within this surrounding from 0% to 100% on surface UV irradiance at the sector center. To work out this remote clouds influence as a function of sector base size, we made some calculations for different sizes between 10 km × 10 km and 100 km × 100 km. It appears that in the case of small sectors (base size < 20 km × 20 km) the remote clouds effect is highly variable: Depending on cloud structure, solar zenith angle and wavelength, the surface UV irradiance may be enhanced up to 15% as well as reduced by more than 50%. In contrast, for larger sectors it is always the case that enhancements become smaller by 5% if sector base size exceeds 60 km × 60 km. However, these values are upper estimates of the remote cloud effects and they are found only for special cloud structures. Since these structures might occur but cannot be regarded as typical, different satellite observed cloud formations (horizontal resolution about 1 km × 1 km) have also been investigated. For these more common cloud distributions we find remote cloud effects to be distinctly smaller than the corresponding upper estimates, e.g., for a sector with base size of 25 km × 25 km the surface UV irradiance error due to ignoring the actual remote clouds and replacing their influence with periodic horizontal boundary conditions is less than 3%, whereas the upper estimate of remote clouds effect would suggest an error close to 10%.Key words: Atmospheric composition and structure (transmission and scattering of radiation) - Meteorology and atmospheric dynamics (radiative process)
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Miller, Steven D., John M. Forsythe, Philip T. Partain, John M. Haynes, Richard L. Bankert, Manajit Sengupta, Cristian Mitrescu, Jeffrey D. Hawkins, and Thomas H. Vonder Haar. "Estimating Three-Dimensional Cloud Structure via Statistically Blended Satellite Observations." Journal of Applied Meteorology and Climatology 53, no. 2 (February 2014): 437–55. http://dx.doi.org/10.1175/jamc-d-13-070.1.
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AbstractThe launch of the NASA CloudSat in April 2006 enabled the first satellite-based global observation of vertically resolved cloud information. However, CloudSat’s nonscanning W-band (94 GHz) Cloud Profiling Radar (CPR) provides only a nadir cross section, or “curtain,” of the atmosphere along the satellite ground track, precluding a full three-dimensional (3D) characterization and thus limiting its utility for certain model verification and cloud-process studies. This paper details an algorithm for extending a limited set of vertically resolved cloud observations to form regional 3D cloud structure. Predicated on the assumption that clouds of the same type (e.g., cirrus, cumulus, and stratocumulus) often share geometric and microphysical properties as well, the algorithm identifies cloud-type-dependent correlations and uses them to estimate cloud-base height and liquid/ice water content vertical structure. These estimates, when combined with conventional retrievals of cloud-top height, result in a 3D structure for the topmost cloud layer. The technique was developed on multiyear CloudSat data and applied to Moderate Resolution Imaging Spectroradiometer (MODIS) swath data from the NASA Aqua satellite. Data-exclusion experiments along the CloudSat ground track show improved predictive skill over both climatology and type-independent nearest-neighbor estimates. More important, the statistical methods, which employ a dynamic range-dependent weighting scheme, were also found to outperform type-dependent near-neighbor estimates. Application to the 3D cloud rendering of a tropical cyclone is demonstrated.