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1
Coquillat, Sylvain, Véronique Pont, Mickaël Pardé, Michaël Kreitz, Dominique Lambert, Ronan Houel, Didier Ricard, Eric Gonneau, Pierre de Guibert, and Serge Prieur. "Découverte d'une anomalie électrique dans des orages méditerranéens." La Météorologie, no. 120 (2023): 046. http://dx.doi.org/10.37053/lameteorologie-2023-0016.
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L'analyse de 561 jours d'orage sur 6 années de données de l'imageur d'éclair 3D Saetta a permis d'identifier des nuages convectifs en région Corse présentant une structure électrique anormale et apparaissant par flux de sud de poussières désertiques africaines. L'explication physique des processus électriques apporte les bases pour comprendre ce que l'imageur permet de déduire sur la structure électrique des cellules orageuses. Des hypothèses microphysiques et radiatives conduisant à un faible contenu en gouttelettes d'eau surfondue à l'origine de cette électrisation anormale sont explorées en s'appuyant sur l'analyse du contexte en aérosols et des conditions météorologiques environnantes. The analysis of 561 days of thunderstorms over 6 years of data from the 3D lightning imager Saetta has allowed to identify convective clouds in Corsica region with an abnormal electrical structure and appearing by southern flow of African desert dust. The physical explanation of the electrical processes brings the basis to understand what the imager allows to deduce about the electrical structure of thunderstorm cells. Microphysical and radiative hypotheses leading to a low content of supercooled droplets at the origin of this abnormal electrification are explored by relying on the analysis of the aerosol context and the surrounding meteorological conditions.
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Anders, Evan H., Adam S. Jermyn, Daniel Lecoanet, J. R. Fuentes, Lydia Korre, Benjamin P. Brown, and Jeffrey S. Oishi. "Convective Boundary Mixing Processes." Research Notes of the AAS 6, no. 2 (February 28, 2022): 41. http://dx.doi.org/10.3847/2515-5172/ac5892.
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Abstract Convective motions extend beyond the nominal boundaries of a convection zone. These motions mix fluid through multiple mechanisms collectively called “convective boundary mixing.” In this note, we discuss three distinct fluid dynamical processes: convective overshoot, entrainment, and penetrative convection. We describe the structure of a convective boundary that these processes create. To resolve discrepancies between models and observations, the stellar astrophysics community should distinguish between these processes and parameterize each of them separately in 1D evolutionary models.
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Bouffard, Damien, and Alfred Wüest. "Convection in Lakes." Annual Review of Fluid Mechanics 51, no. 1 (January 5, 2019): 189–215. http://dx.doi.org/10.1146/annurev-fluid-010518-040506.
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Lakes and other confined water bodies are not exposed to tides, and their wind forcing is usually much weaker compared to ocean basins and estuaries. Hence, convective processes are often the dominant drivers for shaping mixing and stratification structures in inland waters. Due to the diverse environments of lakes—defined by local morphological, geochemical, and meteorological conditions, among others—a fascinating variety of convective processes can develop with remarkably unique signatures. Whereas the classical cooling-induced and shear-induced convections are well-known phenomena due to their dominant roles in ocean basins, other convective processes are specific to lakes and often overlooked, for example, sidearm, under-ice, and double-diffusive convection or thermobaric instability and bioconvection. Additionally, the peculiar properties of the density function at low salinities/temperatures leave distinctive traces. In this review, we present these various processes and connect observations with theories and model results.
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Zheng, Zhang, Liu, Liu, and Che. "A Study of Vertical Structures and Microphysical Characteristics of Different Convective Cloud–Precipitation Types Using Ka-Band Millimeter Wave Radar Measurements." Remote Sensing 11, no. 15 (August 1, 2019): 1810. http://dx.doi.org/10.3390/rs11151810.
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Millimeter wave cloud radar (MMCR) is one of the primary instruments employed to observe cloud–precipitation. With appropriate data processing, measurements of the Doppler spectra, spectral moments, and retrievals can be used to study the physical processes of cloud–precipitation. This study mainly analyzed the vertical structures and microphysical characteristics of different kinds of convective cloud–precipitation in South China during the pre-flood season using a vertical pointing Ka-band MMCR. Four kinds of convection, namely, multi-cell, isolated-cell, convective–stratiform mixed, and warm-cell convection, are discussed herein. The results show that the multi-cell and convective–stratiform mixed convections had similar vertical structures, and experienced nearly the same microphysical processes in terms of particle phase change, particle size distribution, hydrometeor growth, and breaking. A forward pattern was proposed to specifically characterize the vertical structure and provide radar spectra models reflecting the different microphysical and dynamic features and variations in different parts of the cloud body. Vertical air motion played key roles in the microphysical processes of the isolated- and warm-cell convections, and deeply affected the ground rainfall properties. Stronger, thicker, and slanted updrafts caused heavier showers with stronger rain rates and groups of larger raindrops. The microphysical parameters for the warm-cell cloud–precipitation were retrieved from the radar data and further compared with the ground-measured results from a disdrometer. The comparisons indicated that the radar retrievals were basically reliable; however, the radar signal weakening caused biases to some extent, especially for the particle number concentration. Note that the differences in sensitivity and detectable height of the two instruments also contributed to the compared deviation.
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Tulich, Stefan N., and Brian E. Mapes. "Multiscale Convective Wave Disturbances in the Tropics: Insights from a Two-Dimensional Cloud-Resolving Model." Journal of the Atmospheric Sciences 65, no. 1 (January 1, 2008): 140–55. http://dx.doi.org/10.1175/2007jas2353.1.
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Abstract Multiscale convective wave disturbances with structures broadly resembling observed tropical waves are found to emerge spontaneously in a nonrotating, two-dimensional cloud model forced by uniform cooling. To articulate the dynamics of these waves, model outputs are objectively analyzed in a discrete truncated space consisting of three cloud types (shallow convective, deep convective, and stratiform) and three dynamical vertical wavelength bands. Model experiments confirm that diabatic processes in deep convective and stratiform regions are essential to the formation of multiscale convective wave patterns. Specifically, upper-level heating (together with low-level cooling) serves to preferentially excite discrete horizontally propagating wave packets with roughly a full-wavelength structure in troposphere and “dry” phase speeds cn in the range 16–18 m s−1. These wave packets enhance the triggering of new deep convective cloud systems, via low-level destabilization. The new convection in turn causes additional heating over cooling, through delayed development of high-based deep convective cells with persistent stratiform anvils. This delayed forcing leads to an intensification and then widening of the low-level cold phases of wave packets as they move through convecting regions. Additional widening occurs when slower-moving (∼8 m s−1) “gust front” wave packets excited by cooling just above the boundary layer trigger additional deep convection in the vicinity of earlier convection. Shallow convection, meanwhile, provides positive forcing that reduces convective wave speeds and destroys relatively small-amplitude-sized waves. Experiments with prescribed modal wind damping establish the critical role of short vertical wavelengths in setting the equivalent depth of the waves. However, damping of deep vertical wavelengths prevents the clustering of mesoscale convective wave disturbances into larger-scale envelopes, so these circulations are important as well.
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Deng, Liping, and Xiaoqing Wu. "Effects of Convective Processes on GCM Simulations of the Madden–Julian Oscillation." Journal of Climate 23, no. 2 (January 15, 2010): 352–77. http://dx.doi.org/10.1175/2009jcli3114.1.
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Abstract Weak temporal variability in tropical climates such as the Madden–Julian oscillation (MJO) is one of major deficiencies in general circulation models (GCMs). The uncertainties in the representation of convection and cloud processes are responsible for these deficiencies. With the improvement made to the convection scheme, the Iowa State University (ISU) GCM, which is based on a version of the NCAR Community Climate Model, is able to simulate many features of MJO as revealed by observations. In this study, four 10-yr (1979–88) ISU GCM simulations with observed sea surface temperatures are analyzed and compared to examine the effects of the revised convection closure, convection trigger condition, and convective momentum transport (CMT) on the MJO simulations. The modifications made in the convection scheme improve the simulations of amplitude, spatial distribution, eastward propagation, and horizontal and vertical structures, especially for the coherent feature of eastward-propagating convection and the precursor sign of convective center. The revised convection closure plays a key role in the improvement of the eastward propagation of MJO. The convection trigger helps produce less frequent but more vigorous moist convection and enhance the amplitude of the MJO signal. The inclusion of CMT results in a more coherent structure for the MJO deep convective center and its corresponding atmospheric variances.
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Palotai, Csaba, Shawn Brueshaber, Ramanakumar Sankar, and Kunio Sayanagi. "Moist Convection in the Giant Planet Atmospheres." Remote Sensing 15, no. 1 (December 30, 2022): 219. http://dx.doi.org/10.3390/rs15010219.
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The outer planets of our Solar System display a myriad of interesting cloud features, of different colors and sizes. The differences between the types of observed clouds suggest a complex interplay between the dynamics and chemistry at play in these atmospheres. Particularly, the stark difference between the banded structures of Jupiter and Saturn vs. the sporadic clouds on the ice giants highlights the varieties in dynamic, chemical and thermal processes that shape these atmospheres. Since the early explorations of these planets by spacecrafts, such as Voyager and Voyager 2, there are many outstanding questions about the long-term stability of the observed features. One hypothesis is that the internal heat generated during the formation of these planets is transported to the upper atmosphere through latent heat release from convecting clouds (i.e., moist convection). In this review, we present evidence of moist convective activity in the gas giant atmospheres of our Solar System from remote sensing data, both from ground- and space-based observations. We detail the processes that drive moist convective activity, both in terms of the dynamics as well as the microphysical processes that shape the resulting clouds. Finally, we also discuss the effects of moist convection on shaping the large-scale dynamics (such as jet structures on these planets).
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Hirt, Mirjam, Stephan Rasp, Ulrich Blahak, and George C. Craig. "Stochastic Parameterization of Processes Leading to Convective Initiation in Kilometer-Scale Models." Monthly Weather Review 147, no. 11 (October 11, 2019): 3917–34. http://dx.doi.org/10.1175/mwr-d-19-0060.1.
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Abstract Kilometer-scale models allow for an explicit simulation of deep convective overturning but many subgrid processes that are crucial for convective initiation are still poorly represented. This leads to biases such as insufficient convection triggering and late peak of summertime convection. A physically based stochastic perturbation scheme (PSP) for subgrid processes has been proposed (Kober and Craig) that targets the coupling between subgrid turbulence and resolved convection. The first part of this study presents four modifications to this PSP scheme for subgrid turbulence: an autoregressive, continuously evolving random field; a limitation of the perturbations to the boundary layer that removes artificial convection at night; a mask that turns off perturbations in precipitating columns to retain coherent structures; and nondivergent wind perturbations that drastically increase the effectiveness of the vertical velocity perturbations. In a revised version, PSP2, the combined modifications retain the physically based coupling to the boundary layer scheme of the original scheme while removing undesirable side effects. This has the potential to improve predictions of convective initiation in kilometer-scale models while minimizing other biases. The second part of the study focuses on perturbations to account for convective initiation by subgrid orography. Here the mechanical lifting effect is modeled by introducing vertical and horizontal wind perturbations of an orographically induced gravity wave. The resulting perturbations lead to enhanced convective initiation over mountainous terrain. However, the total benefit of this scheme is unclear and we do not adopt the scheme in our revised configuration.
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Huang, Yipeng, Murong Zhang, Yuchun Zhao, Ben Jong-Dao Jou, Hui Zheng, Changrong Luo, and Dehua Chen. "Inter-Zone Differences of Convective Development in a Convection Outbreak Event over Southeastern Coast of China: An Observational Analysis." Remote Sensing 14, no. 1 (December 29, 2021): 131. http://dx.doi.org/10.3390/rs14010131.
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Among the densely-populated coastal areas of China, the southeastern coast has received less attention in convective development despite having been suffering from significantly increasing thunderstorm activities. The convective complexity under such a region with extremely complex underlying and convective conditions deserves in-depth observational surveys. This present study examined a high-impact convection outbreak event with over 40 hail reports in the southeastern coast of China on 6 May 2020 by focusing on contrasting the convective development (from convective initiation to supercell occurrences) among three adjacent convection-active zones (north (N), middle (M), and south (S)). The areas from N to S featured overall flatter terrain, higher levels of free convection, lower relative humidity, larger convective inhibition, more convective available potential energy, and greater vertical wind shears. With these mesoscale environmental variations, distinct inter-zone differences in the convective development were observed with the region’s surveillance radar network and the Himawari-8 geostationary satellite. Convection initiated in succession from N to S and began with more warm-rain processes in N and M and more ice-phase processes in S. The subsequent convection underwent more vigorous vertical growth from N to S. The extremely deep convection in S was characterized by the considerably strong precipitation above the freezing level, echo tops of up to 18 km, and a great amount of deep (even overshooting) and thick convective clouds with significant cloud-top glaciation. Horizontal anvil expansion in convective clouds was uniquely apparent over S. From N to S, more pronounced mesocyclone and weak-echo region signatures indicated high risks of severe supercell hailstorms. These results demonstrate the strong linkage between the occurrence likelihood of severe convection and associated weather (such as supercells and hailstones) and the early-stage convective development that can be well-captured by high-resolution observations and may facilitate fine-scale convection nowcasting.
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Zakharov N.S., Pokusaev B.G., Vyazmin A.V., Nekrasov D.A., Sulyagina O.A., and Moshin A.A. "Research of heat transfer processes in hydrogels by holographic interferometry and gradient thermometry." Technical Physics Letters 48, no. 5 (2022): 7. http://dx.doi.org/10.21883/tpl.2022.05.53551.19058.
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The study of natural convection in structured optically transparent materials using pure and combined agarose-gelatin gels was carried out by optical holography. The article presents data on visualization of the occurrence and development of convective flows in such gels with non-stationary conductive heating from below. The similarities and differences of the conditions of heat transfer and the occurrence of convection in structured materials and droplet liquids are analyzed. For the first time experimentally obtained data on the effect of two interpenetrating and interacting structured media on the transition from conductive to convective heat transfer. Keywords: natural convection in gels, optical holography, hydrogels, three-dimensional bioprinting.
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Schulz, Hauke, and Bjorn Stevens. "Observing the Tropical Atmosphere in Moisture Space." Journal of the Atmospheric Sciences 75, no. 10 (October 2018): 3313–30. http://dx.doi.org/10.1175/jas-d-17-0375.1.
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Measurements from the Barbados Cloud Observatory are analyzed to identify the processes influencing the distribution of moist static energy and the large-scale organization of tropical convection. Five years of water vapor and cloud profiles from a Raman lidar and cloud radar are composed to construct the structure of the observed atmosphere in moisture space. The large-scale structure of the atmosphere is similar to that now familiar from idealized studies of convective self-aggregation, with shallow clouds prevailing over a moist marine layer in regions of low-rank humidity, and deep convection in a nearly saturated atmosphere in regions of high-rank humidity. With supplementary reanalysis datasets the overall circulation pattern is reconstructed in moisture space, and shows evidence of a substantial lower-tropospheric component to the circulation. This shallow component of the circulation helps support the differentiation between the moist and dry columns, similar to what is found in simulations of convective self-aggregation. Radiative calculations show that clear-sky radiative differences can explain a substantial part of this circulation, with further contributions expected from cloud radiative effects. The shallow component appears to be important for maintaining the low gross moist stability of the convecting column. A positive feedback between a shallow circulation driven by differential radiative cooling and the low-level moisture gradients that help support it is hypothesized to play an important role in conditioning the atmosphere for deep convection. The analysis suggests that the radiatively driven shallow circulations identified by modeling studies as contributing to the self-aggregation of convection in radiative–convective equilibrium similarly play a role in shaping the intertropical convergence zone and, hence, the large-scale structure of the tropical atmosphere.
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Bell, Michael M., and Michael T. Montgomery. "Mesoscale Processes during the Genesis of Hurricane Karl (2010)." Journal of the Atmospheric Sciences 76, no. 8 (July 11, 2019): 2235–55. http://dx.doi.org/10.1175/jas-d-18-0161.1.
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Abstract Observations from the Pre-Depression Investigation of Cloud Systems in the Tropics (PREDICT), Genesis and Rapid Intensification Processes (GRIP), and Intensity Forecast Experiment (IFEX) field campaigns are analyzed to investigate the mesoscale processes leading to the tropical cyclogenesis of Hurricane Karl (2010). Research aircraft missions provided Doppler radar, in situ flight level, and dropsonde data documenting the structural changes of the predepression disturbance. Following the pre-Karl wave pouch, variational analyses at the meso-β and meso-α scales suggest that the convective cycle in Karl alternately built the low- and midlevel circulations leading to genesis episodically rather than through a sustained lowering of the convective mass flux from increased stabilization. Convective bursts that erupt in the vorticity-rich environment of the recirculating pouch region enhance the low-level meso-β- and meso-α-scale circulation through vortex stretching. As the convection wanes, the resulting stratiform precipitation strengthens the midlevel circulation through convergence associated with ice microphysical processes, protecting the disturbance from the intrusion of dry environmental air. Once the column saturation fraction returns to a critical value, a subsequent convective burst below the midlevel circulation further enhances the low-level circulation, and the convective cycle repeats. The analyses suggest that the onset of deep convection and associated low-level spinup were closely related to the coupling of the vorticity and moisture fields at low and midlevels. Our interpretation of the observational analysis presented in this study reaffirms a primary role of deep convection in the genesis process and provides a hypothesis for the supporting role of stratiform precipitation and the midlevel vortex.
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Heavens, Nicholas G., David M. Kass, James H. Shirley, Sylvain Piqueux, and Bruce A. Cantor. "An Observational Overview of Dusty Deep Convection in Martian Dust Storms." Journal of the Atmospheric Sciences 76, no. 11 (October 16, 2019): 3299–326. http://dx.doi.org/10.1175/jas-d-19-0042.1.
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Abstract Deep convection, as used in meteorology, refers to the rapid ascent of air parcels in Earth’s troposphere driven by the buoyancy generated by phase change in water. Deep convection undergirds some of Earth’s most important and violent weather phenomena and is responsible for many aspects of the observed distribution of energy, momentum, and constituents (particularly water) in Earth’s atmosphere. Deep convection driven by buoyancy generated by the radiative heating of atmospheric dust may be similarly important in the atmosphere of Mars but lacks a systematic description. Here we propose a comprehensive framework for this phenomenon of dusty deep convection (DDC) that is supported by energetic calculations and observations of the vertical dust distribution and exemplary dusty deep convective structures within local, regional, and global dust storm activity. In this framework, DDC is distinct from a spectrum of weaker dusty convective activity because DDC originates from preexisting or concurrently forming mesoscale circulations that generate high surface dust fluxes, oppose large-scale horizontal advective–diffusive processes, and are thus able to maintain higher dust concentrations than typically simulated. DDC takes two distinctive forms. Mesoscale circulations that form near Mars’s highest volcanoes in dust storms of all scales can transport dust to the base of the upper atmosphere in as little as 2 h. In the second distinctive form, mesoscale circulations at low elevations within regional and global dust storm activity generate freely convecting streamers of dust that are sheared into the middle atmosphere over the diurnal cycle.
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Schumacher, Russ S., and Richard H. Johnson. "Mesoscale Processes Contributing to Extreme Rainfall in a Midlatitude Warm-Season Flash Flood." Monthly Weather Review 136, no. 10 (October 2008): 3964–86. http://dx.doi.org/10.1175/2008mwr2471.1.
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Observations and numerical simulations are used to investigate the atmospheric processes that led to extreme rainfall and resultant destructive flash flooding in eastern Missouri on 6–7 May 2000. In this event, a quasi-stationary mesoscale convective system (MCS) developed near a preexisting mesoscale convective vortex (MCV) in a very moist environment that included a strong low-level jet (LLJ). This nocturnal MCS produced in excess of 300 mm of rain in a small area to the southwest of St. Louis, Missouri. Operational model forecasts and simulations using a convective parameterization scheme failed to produce the observed rainfall totals for this event. However, convection-permitting simulations using the Weather Research and Forecasting Model were successful in reproducing the quasi-stationary organization and evolution of this MCS. In both observations and simulations, scattered elevated convective cells were repeatedly initiated 50–75 km upstream before merging into the mature MCS and contributing to the heavy rainfall. Lifting provided by the interaction between the LLJ and the MCV assisted in initiating and maintaining the convection. Simulations indicate that the MCS was long lived despite the lack of a convectively generated cold pool at the surface. Instead, a nearly stationary low-level gravity wave helped to organize the convection into a quasi-linear system that was conducive to extreme local rainfall amounts. Idealized simulations of convection in a similar environment show that such a low-level gravity wave is a response to diabatic heating and that the vertical wind profile featuring a strong reversal of the wind shear with height is responsible for keeping the wave nearly stationary. In addition, the convective system acted to reintensify the midlevel MCV and also caused a distinct surface low pressure center to develop in both the observed and simulated system.
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Grandpeix, Jean-Yves, and Jean-Philippe Lafore. "A Density Current Parameterization Coupled with Emanuel’s Convection Scheme. Part I: The Models." Journal of the Atmospheric Sciences 67, no. 4 (April 1, 2010): 881–97. http://dx.doi.org/10.1175/2009jas3044.1.
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Abstract The aim of the present series of papers is to develop a density current parameterization for global circulation models. This first paper is devoted to the presentation of this new wake parameterization coupled with Emanuel’s convective scheme. The model represents a population of identical circular cold pools (the wakes) with vertical frontiers. The wakes are cooled by the precipitating downdrafts while the outside area is warmed by the subsidence induced by the saturated drafts. The budget equations for mass, energy, and water yield evolution equations for the prognostic variables (the vertical profiles of the temperature and humidity differences between the wakes and their exterior). They also provide additional terms for the equations of the mean variables. The driving terms of the wake equations are the differential heating and drying due to convective drafts. The action of the convection on the wakes is implemented by splitting the convective tendency and attributing the effect of the precipitating downdrafts to the wake region and the effect of the saturated drafts to their exterior. Conversely, the action of the wakes on convection is implemented by introducing two new variables representing the convergence at the leading edge of the wakes. The available lifting energy (ALE) determines the triggers of deep convection: convection occurs when ALE exceeds the convective inhibition. The available lifting power (ALP) determines the intensity of convection; it is equal to the power input into the system by the collapse of the wakes. The ALE/ALP closure, together with the splitting of the convective heating and drying, implements the full coupling between wake and convection. The coupled wake–convection scheme thus created makes it possible to represent the moist convective processes more realistically, to prepare the coupling of convection with boundary layer and orographic processes, and to consider simulating the propagation of convective systems.
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Zhang, Guang J., and Xiaoliang Song. "Parameterization of Microphysical Processes in Convective Clouds in Global Climate Models." Meteorological Monographs 56 (April 1, 2016): 12.1–12.18. http://dx.doi.org/10.1175/amsmonographs-d-15-0015.1.
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Abstract The microphysical processes inside convective clouds play an important role in climate. They directly control the amount of detrainment of cloud hydrometeor and water vapor from updrafts. The detrained water substance in turn affects the anvil cloud formation, upper-tropospheric water vapor distribution, and thus the atmospheric radiation budget. In global climate models, convective parameterization schemes have not explicitly represented microphysics processes in updrafts until recently. In this paper, the authors provide a review of existing schemes for convective microphysics parameterization. These schemes are broadly divided into three groups: tuning-parameter-based schemes (simplest), single-moment schemes, and two-moment schemes (most comprehensive). Common weaknesses of the tuning-parameter-based and single-moment schemes are outlined. Examples are presented from one of the two-moment schemes to demonstrate the performance of the scheme in simulating the hydrometeor distribution in convection and its representation of the effect of aerosols on convection.
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Rowe, Angela K., Steven A. Rutledge, and Timothy J. Lang. "Investigation of Microphysical Processes Occurring in Organized Convection during NAME." Monthly Weather Review 140, no. 7 (July 1, 2012): 2168–87. http://dx.doi.org/10.1175/mwr-d-11-00124.1.
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Abstract A major objective of the North American Monsoon Experiment (NAME) was to quantify microphysical processes within convection occurring near the steep topography of northwestern Mexico. A previous study compared examples of isolated convection using polarimetric radar data and noted a dependence on mixed-phase processes via drop freezing and subsequent riming growth along the coastal plain and western slopes, with an even greater role of melting ice in rainfall production over the highest terrain. Despite the higher frequency of these isolated cells compared to organized convective systems, the latter were responsible for 75% of rainfall. Therefore, this study seeks to evaluate the role of mesoscale organization on microphysical processes and describes the evolution of these systems as a function of topography. Similar to isolated convection, both warm-rain and ice-based processes played important roles in producing intense rainfall in organized convection. Although similarities existed between cell types, organized convection was typically deeper and contained greater ice mass, which melted and contributed to the development of outflow boundaries. As convection organized along the slopes, these boundaries spread over the lower terrain, converging with diurnally driven upslope flow, thus allowing for the generation of new convection and propagation toward the coast. Once over lower elevations, additional warm-cloud depth contributed to intense rainfall and allowed for continued ice production. This, along with the development of rear inflow in the trailing stratiform region, led to further development of convective outflow, similar to organized systems in the tropics and midlatitudes.
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Emanuel, Kerry. "Inferences from Simple Models of Slow, Convectively Coupled Processes." Journal of the Atmospheric Sciences 76, no. 1 (January 1, 2019): 195–208. http://dx.doi.org/10.1175/jas-d-18-0090.1.
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Abstract A framework for conceptual understanding of slow, convectively coupled disturbances is developed and applied to several canonical tropical problems, including the water vapor content of an atmosphere in radiative–convective equilibrium, the relationship between convective precipitation and column water vapor, Walker-like circulations, self-aggregation of convection, and the Madden–Julian oscillation. The framework is a synthesis of previous work that developed four key approximations: boundary layer energy quasi equilibrium, conservation of free-tropospheric moist and dry static energies, and the weak temperature gradient approximation. It is demonstrated that essential features of slow, convectively coupled processes can be understood without reference to complex turbulent and microphysical processes, even though accounting for such complexity is essential to quantitatively accurate modeling. In particular, we demonstrate that the robust relationship between column water vapor and precipitation observed over tropical oceans does not necessarily imply direct sensitivity of convection to free-tropospheric moisture. We also show that to destabilize the radiative–convective equilibrium state, feedbacks between radiation and clouds and water vapor must be sufficiently strong relative to the gross moist stability.
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Barros, Sheila Santana De, and Marcos Daisuke Oyama. "Sistemas meteorológicos associados à ocorrência de precipitação no centro de lançamento de Alcântara." Revista Brasileira de Meteorologia 25, no. 3 (September 2010): 333–44. http://dx.doi.org/10.1590/s0102-77862010000300005.
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O Centro de Lançamento de Alcântara (CLA; 2° 22'S, 44º 23'W) tem papel importante para as atividades aeroespaciais no Brasil, sendo de interesse estudar os sistemas precipitantes atuantes sobre a região. O trabalho teve como objetivo caracterizar os sistemas associados aos eventos de precipitação ocorridos no CLA entre 2005 e 2006, utilizando totais horários de precipitação, dados de Reanálise do NCEP/NCAR, temperatura de brilho do satélite GOES-12 e radiação de onda longa emergente. Para tal, definiram-se critérios para identificar os sistemas meteorológicos de grande, meso e de escala local associados à precipitação no CLA. Os resultados apontaram que 40% dos eventos de precipitação estiveram associados a fatores de grande escala, destacando-se a Zona de Convergência Intertropical. Verificou-se que 60% (40%) dos eventos de precipitação se devem a processos estratiformes (convectivos). Os sistemas convectivos apresentaram as seguintes características: áreas entre 10(4) km² e 25x10(4) km², chuva posicionada na porção convectiva do sistema, intensificação por convecção diurna, inclusão em um sistema de escala maior e origem preferencial de sudeste ou nordeste. Os sistemas formados por processos estratiformes se subdividiram quase igualmente em dois grupos: resquícios de sistemas convectivos anteriormente atuantes no CLA e sistemas que não estão associados a nenhum processo convectivo.
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Zhang, Gang, and Ronald B. Smith. "Numerical Study of Physical Processes Controlling Summer Precipitation over the Western Ghats Region." Journal of Climate 31, no. 8 (March 20, 2018): 3099–115. http://dx.doi.org/10.1175/jcli-d-17-0002.1.
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Abstract Summer precipitation over the Western Ghats and its adjacent Arabian Sea is an important component of the Indian monsoon. To advance understanding of the physical processes controlling this regional precipitation, a series of high-resolution convection-permitting simulations were conducted using the Weather Research and Forecasting (WRF) Model. Convection simulated in the WRF Model agrees with TRMM and MODIS satellite estimates. Sensitivity simulations are conducted, by altering topography, latent heating, and sea surface temperature (SST), to quantify the effects of different physical forcing factors. It is helpful to put India’s west coast rainfall systems into three categories with different causes and characteristics. 1) Offshore rainfall is controlled by incoming convective available potential energy (CAPE), the entrainment of midtropospheric dry layer in the monsoon westerlies, and the latent heat flux and SST of the Arabian Sea. It is not triggered by the Western Ghats. When offshore convection is present, it reduces both CAPE and the downwind coastal rainfall. Strong (weak) offshore rainfall is associated with high (low) SSTs in the Arabian Sea, suggested by both observations and sensitivity simulations. 2) Coastal convective rainfall is forced by the coastline roughness, diurnal heating, and the Western Ghats topography. This localized convective rainfall ends abruptly beyond the Western Ghats, producing a rain shadow to the east of the mountains. This deep convection with mixed phase microphysics is the biggest overall rain producer. 3) Orographic stratiform warm rain and drizzle dominate the local precipitation on the crest of the Western Ghats.
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Zahn, J. P. "Theory of Transport Processes." International Astronomical Union Colloquium 121 (1990): 425–36. http://dx.doi.org/10.1017/s0252921100068111.
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AbstractThis review focuses on the transport of matter and angular momentum in the radiative zones of stellar interiors. The two main causes of such transport are the convective overshooting in the vicinity of convection zones, and the slow motions (meridional circulation and turbulence) due to the rotation of the star. In addition, momentum can be transfered through waves (generated by the motions above) and through magnetic stresses. The characteristics of those processes are examined, with special emphasis on turbulent diffusion.
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Anderson, Daniel M., and Peter Guba. "Convective Phenomena in Mushy Layers." Annual Review of Fluid Mechanics 52, no. 1 (January 5, 2020): 93–119. http://dx.doi.org/10.1146/annurev-fluid-010719-060332.
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Since the Annual Review of Fluid Mechanics review of mushy layers by Worster (1997) , there have been significant advances in the understanding of convective processes in mushy layers. These advances have come in the areas of ( a) more detailed analysis, computation, and understanding of convective instabilities and chimney convection in binary alloys; ( b) investigations of diffusive and convective transport processes in ternary alloys; and ( c) applications of mushy layer theory in materials science, sea ice, and polar climate modeling, as well as other geophysical applications such as the convective dynamics of the Earth's core. Our objective for this review is to provide an updated account of the understanding of mushy layer convection and related applications and, in doing so, to provide a new resource to the fluid dynamics research community interested in these complex systems.
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Bellenger, H., Y. N. Takayabu, T. Ushiyama, and K. Yoneyama. "Role of Diurnal Warm Layers in the Diurnal Cycle of Convection over the Tropical Indian Ocean during MISMO." Monthly Weather Review 138, no. 6 (June 1, 2010): 2426–33. http://dx.doi.org/10.1175/2010mwr3249.1.
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Abstract The role of air–sea interaction in the diurnal variations of convective activity during the suppressed and developing stages of an intraseasonal convective event is analyzed using in situ observations from the Mirai Indian Ocean cruise for the Study of the Madden–Julian oscillation (MJO)-convection Onset (MISMO) experiment. For the whole period, convection shows a clear average diurnal cycle with a primary maximum in the early morning and a secondary one in the afternoon. Episodes of large diurnal sea surface temperature (SST) variations are observed because of diurnal warm layer (DWL) formation. When no DWL is observed, convection exhibits a diurnal cycle characterized by a maximum in the early morning, whereas when DWL forms, convection increases around noon and peaks in the afternoon. Boundary layer processes are found to control the diurnal evolution of convection. In particular, when DWL forms, the change in surface heat fluxes can explain the decrease of convective inhibition and the intensification of the convection during the early afternoon.
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Sumi, Yukari, and Hirohiko Masunaga. "A Moist Static Energy Budget Analysis of Quasi-2-Day Waves Using Satellite and Reanalysis Data." Journal of the Atmospheric Sciences 73, no. 2 (February 1, 2016): 743–59. http://dx.doi.org/10.1175/jas-d-15-0098.1.
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Abstract A moist static energy (MSE) budget analysis is applied to quasi-2-day waves to examine the effects of thermodynamic processes on the wave propagation mechanism. The 2-day waves are defined as westward inertia–gravity (WIG) modes identified with filtered geostationary infrared measurements, and the thermodynamic parameters and MSE budget variables computed from reanalysis data are composited with respect to the WIG peaks. The composite horizontal and vertical MSE structures are overall as theoretically expected from WIG wave dynamics. A prominent horizontal MSE advection is found to exist, although the wave dynamics is mainly regulated by vertical advection. The vertical advection decreases MSE around the times of the convective peak, plausibly resulting from the first baroclinic mode associated with deep convection. Normalized gross moist stability (NGMS) is used to examine the thermodynamic processes involving the large-scale dynamics and convective heating. NGMS gradually decreases to zero before deep convection and reaches a maximum after the convection peak, where low (high) NGMS leads (lags) deep convection. The decrease in NGMS toward zero before the occurrence of active convection suggests an increasingly efficient conversion from convective heating to large-scale dynamics as the wave comes in, while the increase afterward signifies that this linkage swiftly dies out after the peak.
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Russo, M. R., V. Marécal, C. R. Hoyle, J. Arteta, C. Chemel, M. P. Chipperfield, O. Dessens, et al. "Tropical deep convection and its impact on composition in global and mesoscale models - Part 1: Meteorology and comparison with observations." Atmospheric Chemistry and Physics Discussions 10, no. 8 (August 19, 2010): 19469–514. http://dx.doi.org/10.5194/acpd-10-19469-2010.
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Abstract. Tropical convection is a very important atmospheric process acting on the water cycle, radiative budget of the atmosphere and air composition of the upper troposphere and lower stratosphere (UTLS), and it affects a broad range of spatial and temporal scales. The fast vertical transport in convective plumes can efficiently redistribute water vapour and pollutants up to the Tropical Tropopause Layer (TTL), and therefore affect the composition of the lower stratosphere. Chemistry Climate Models and Chemistry Transport Models are routinely used to study chemical processes in the atmosphere. In these models convection and convective transport of tracers are parameterised, and due to the interplay of chemical and dynamical processes, it has proven difficult to evaluate the convective transport of chemical species by comparison with observed chemical fields. In this work we investigate different characteristics of tropical convection by using convective proxies from many independent observational datasets (including surface precipitation rates, cloud top pressure and OLR). We use observations to analyse the seasonal cycle and geographical preferences of convection, and its impact on water vapour. Using highly temporally resolved cloud top data we calculate the frequency distribution of high clouds in three tropical regions. The observational data is used as a benchmark for a number of numerical models, with a view to assess the ability of models to reproduce the seasonality, preferential location and vertical extent of tropical convection. Finally we discuss the implications of our findings on modelling the composition of the upper troposphere and lower stratosphere.
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Feng, Tao, Jia-Yuh Yu, Xiu-Qun Yang, and Ronghui Huang. "Convective Coupling in Tropical-Depression-Type Waves. Part II: Moisture and Moist Static Energy Budgets." Journal of the Atmospheric Sciences 77, no. 10 (October 1, 2020): 3423–40. http://dx.doi.org/10.1175/jas-d-19-0173.1.
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AbstractThe companion of this paper, Part I, discovered the characteristics of the rainfall progression in tropical-depression (TD)-type waves over the western North Pacific. In Part II, the large-scale controls on the convective rainfall progression have been investigated using the ERA-Interim data and the TRMM 3B42 precipitation-rate data during June–October from 1998 to 2013 through budgets of moist static energy (MSE) and moisture. A buildup of column-integrated MSE occurs in advance of deep convection, and an export of MSE occurs following deep convection, which is consistent with the MSE recharge–discharge paradigm. The MSE recharge–discharge is controlled by horizontal processes, whereby horizontal moisture advection causes net MSE import prior to deep convection. Such moistening by horizontal advection creates a moist midtroposphere, which helps destabilize the atmospheric column, leading to the development of deep convective rainfall. Following the heaviest rainfall, negative horizontal moisture advection dries the troposphere, inhibiting convection. Such moistening and drying processes explain why deep convection can develop without preceding shallow convection. The advection of moisture anomalies by the mean horizontal flow controls the tropospheric moistening and drying processes. As the TD-type waves propagate northwestward in coincidence with the northwestward environmental flow, the moisture, or convective rainfall, is phase locked to the waves. The critical role of the MSE import by horizontal advection in modulating the rainfall progression is supported by the anomalous gross moist stability (AGMS), where the lowest AGMS corresponds to the quickest increase in the precipitation rate prior to the rainfall maximum.
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de Vries, Andries Jan, Franziska Aemisegger, Stephan Pfahl, and Heini Wernli. "Stable water isotope signals in tropical ice clouds in the West African monsoon simulated with a regional convection-permitting model." Atmospheric Chemistry and Physics 22, no. 13 (July 11, 2022): 8863–95. http://dx.doi.org/10.5194/acp-22-8863-2022.
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Abstract. Tropical ice clouds have an important influence on the Earth's radiative balance. They often form as a result of tropical deep convection, which strongly affects the water budget of the tropical tropopause layer. Ice cloud formation involves complex interactions on various scales. These processes are not yet fully understood and lead to large uncertainties in climate projections. In this study, we investigate the formation of tropical ice clouds related to deep convection in the West African monsoon, using stable water isotopes as tracers of moist atmospheric processes. We perform convection-permitting simulations with the regional Consortium for Small-Scale Modelling isotope-enabled (COSMOiso) model for the period from June to July 2016. First, we evaluate our model simulations using space-borne observations of mid-tropospheric water vapour isotopes, monthly station data of precipitation isotopes, and satellite-based precipitation estimates. Next, we explore the isotope signatures of tropical deep convection in atmospheric water vapour and ice based on a case study of a mesoscale convective system (MCS) and a statistical analysis of a 1-month period. The following five key processes related to tropical ice clouds can be distinguished based on isotope information: (1) convective lofting of enriched ice into the upper troposphere, (2) cirrus clouds that form in situ from ambient vapour under equilibrium fractionation, (3) sedimentation and sublimation of ice in the mixed-phase cloud layer in the vicinity of convective systems and underneath cirrus shields, (4) sublimation of ice in convective downdraughts that enriches the environmental vapour, and (5) the freezing of liquid water just above the 0 ∘C isotherm in convective updraughts. Importantly, we note large variations in the isotopic composition of water vapour in the upper troposphere and lower tropical tropopause layer, ranging from below −800 ‰ to over −400 ‰, which are strongly related to vertical motion and the moist processes that take place in convective updraughts and downdraughts. In convective updraughts, the vapour is depleted by the preferential condensation and deposition of heavy isotopes, whereas the non-fractionating sublimation of ice in convective downdraughts enriches the environmental vapour. An opposite vapour isotope signature emerges in thin-cirrus cloud regions where the direct transport of enriched (depleted) vapour prevails in large-scale ascent (descent). Overall, this study demonstrates that isotopes can serve as useful tracers to disentangle the role of different processes in the West African monsoon water cycle, including convective transport, the formation of ice clouds, and their impact on the tropical tropopause layer.
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Bellenger, H., K. Yoneyama, M. Katsumata, T. Nishizawa, K. Yasunaga, and R. Shirooka. "Observation of Moisture Tendencies Related to Shallow Convection." Journal of the Atmospheric Sciences 72, no. 2 (February 1, 2015): 641–59. http://dx.doi.org/10.1175/jas-d-14-0042.1.
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Abstract Tropospheric moisture is a key factor controlling the global climate and its variability. For instance, moistening of the lower troposphere is necessary to trigger the convective phase of a Madden–Julian oscillation (MJO). However, the relative importance of the processes controlling this moistening has yet to be quantified. Among these processes, the importance of the moistening by shallow convection is still debated. The authors use high-frequency observations of humidity and convection from the Research Vessel (R/V) Mirai that was located in the Indian Ocean ITCZ during the Cooperative Indian Ocean Experiment on Intraseasonal Variability/Dynamics of the MJO (CINDY/DYNAMO) campaign. This study is an initial attempt to directly link shallow convection to moisture variations within the lowest 4 km of the atmosphere from the convective scale to the mesoscale. Within a few tens of minutes and near shallow convection occurrences, moisture anomalies of 0.25–0.5 g kg−1 that correspond to tendencies on the order of 10–20 g kg−1 day−1 between 1 and 4 km are observed and are attributed to shallow convective clouds. On the scale of a few hours, shallow convection is associated with anomalies of 0.5–1 g kg−1 that correspond to tendencies on the order of 1–4 g kg−1 day−1 according to two independent datasets: lidar and soundings. This can be interpreted as the resultant mesoscale effect of the population of shallow convective clouds. Large-scale advective tendencies can be stronger than the moistening by shallow convection; however, the latter is a steady moisture supply whose importance can increase with the time scale. This evaluation of the moistening tendency related to shallow convection is ultimately important to develop and constrain numerical models.
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Zhang, Guang J., Jeffrey T. Kiehl, and Philip J. Rasch. "Response of Climate Simulation to a New Convective Parameterization in the National Center for Atmospheric Research Community Climate Model (CCM3)*." Journal of Climate 11, no. 8 (August 1, 1998): 2097–115. http://dx.doi.org/10.1175/1520-0442-11.8.2097.
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Abstract This study examines the response of the climate simulation by the National Center for Atmospheric Research Community Climate Model (CCM3) to the introduction of the Zhang and McFarlane convective parameterization in the model. It is shown that in the CCM3 the simulated surface climate in the tropical convective regimes, especially in the western Pacific warm pool, is markedly improved, yielding a much better agreement with the recent observations. The systematic bias in the surface evaporation, surface wind stress over the tropical Pacific Ocean in previous model simulations is significantly reduced, owing to the better simulation of the surface flow. Experiments using identical initial and boundary conditions, but different convection schemes, are performed to isolate the role of the convection schemes and to understand the interaction between convection and the large-scale circulation in a convecting atmosphere. The comparison of the results from these experiments in the western Pacific warm pool suggests that use of the Zhang and McFarlane scheme makes a significant contribution to the improved climate simulation in CCM3. The simulated atmosphere using the Zhang and McFarlane scheme exhibits a quasi-equilibrium between convection and the large-scale processes. When this scheme is removed from the CCM3, such a quasi-equilibrium is no longer observed. In addition, the simulated thermodynamic structures, the surface evaporation, and surface winds in the Pacific warm pool become very similar to those in the CCM2 climate. Examination of the temporal evolution of the various fields demonstrates that the stabilization of the atmosphere using the new convection scheme takes place during the transition from nonequilibrium to quasi equilibrium at the beginning of the time integration. After quasi equilibrium is reached, the atmosphere is warmer and more stable compared to the run without the new scheme. Associated with the more stable stratification, the atmospheric circulation becomes weaker, thus the surface winds and evaporation are weaker because of the coupling between thermodynamics and dynamics in the tropical troposphere.
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Cai, Zhongyin, and Lide Tian. "Processes Governing Water Vapor Isotope Composition in the Indo-Pacific Region: Convection and Water Vapor Transport." Journal of Climate 29, no. 23 (November 15, 2016): 8535–46. http://dx.doi.org/10.1175/jcli-d-16-0297.1.
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Abstract In an effort to understand the mechanisms controlling water vapor isotope composition in the Indo-Pacific region, encompassing southeastern Asia, this study investigates the spatial and interannual patterns in summer [June–September (JJAS)] water vapor isotopologues retrieved from the Tropospheric Emission Spectrometer (TES), especially those patterns associated with convection and water vapor transport. Both precipitation and water vapor isotope values exhibit a V-shaped longitudinal pattern in their spatial variations, reflecting the gradual rainout and increase in convective intensity along water vapor transport routes. On the temporal scale, compared with the 2006–10 JJAS mean conditions, TES water vapor δD over the eastern Indian Ocean and southeastern Asia (R_W120; 10°S–30°N, 80°–120°E) is higher in the 2009 JJAS El Niño event when convective activity is reduced and lower in the 2010 JJAS La Niña event when convective activity is enhanced. This is consistent with the direct response of water vapor δD to deep convection. In contrast, TES water vapor δD over the western Pacific (R_WP; 10°S–30°N, 120°–140°E) is higher in the La Niña year than in the El Niño year, although convective activity in R_WP varies in the same manner as in R_W120. A comparison of water vapor δD values with convection and water vapor transport suggests that the westward transport of water vapor–isotopic anomalies and changes in the flux of water vapor transported from the central to the western Pacific lead to such an opposite response in the R_WP. These findings help interpret what causes the interannual variations recorded by Indo-Pacific water isotopologues.
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Tomassini, Lorenzo. "The Interaction between Moist Convection and the Atmospheric Circulation in the Tropics." Bulletin of the American Meteorological Society 101, no. 8 (August 1, 2020): E1378—E1396. http://dx.doi.org/10.1175/bams-d-19-0180.1.
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Abstract Theories of the interaction between moist convection and the atmospheric circulation in the tropics are reviewed. Two main schools of thought are highlighted: (i) one that emphasizes the lower-level control of convection through moisture convergence and variations in convective inhibition, and (ii) one that sees convection as an adjustment process in reaction to larger-scale instabilities, referred to as convective quasi-equilibrium theory. Conceptually the two views consider moist convection to have fundamentally different roles in the tropical circulation. In one case the presence of low-level inhibition and the conditional nature of the atmospheric instability allows for convective vertical motion and latent heating to drive and reinforce synoptic-scale disturbances and overturning circulations; in the other case, because low-level inhibition is not acknowledged to be a widespread controlling barrier, convection is believed to balance and dampen vertical instabilities at the rate they are created by larger-scale processes over the vertical extent of the atmosphere. More recently, investigations of the moisture dynamics surrounding organized convective structures have led to an emerging consensus on the theory of convection–circulation coupling in the tropics that acknowledges the important role of lower- to midtropospheric moisture variations, and the significance of moist convection and convective clouds for initiating and establishing circulations. However, the implementation of these new insights in numerical models lags behind. This is exemplified by the apparent inadequacy of climate models to correctly represent decadal variability in the tropical Pacific, a fact that potentially has implications for the confidence in climate change projections based on such models.
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White, B. A., A. M. Buchanan, C. E. Birch, P. Stier, and K. J. Pearson. "Quantifying the Effects of Horizontal Grid Length and Parameterized Convection on the Degree of Convective Organization Using a Metric of the Potential for Convective Interaction." Journal of the Atmospheric Sciences 75, no. 2 (January 24, 2018): 425–50. http://dx.doi.org/10.1175/jas-d-16-0307.1.
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Abstract The organization of deep convection and its misrepresentation in many global models is the focus of much current interest. A new method is presented for quantifying convective organization based on the identification of convective objects and subsequent derivation of object numbers, areas, and separation distances to describe the degree of convective organization. These parameters are combined into a “convection organization potential” based on the physical principle of an interaction potential between pairs of convective objects. This technique is applied to simulated and observed fields of outgoing longwave radiation (OLR) over the West African monsoon region using data from Met Office Unified Model simulations and satellite observations made by the Geostationary Earth Radiation Budget (GERB) instrument. The method is evaluated by using it to quantify differences between models with different horizontal grid lengths and representations of convection. Distributions of OLR, precipitation and organization parameters, the diurnal cycle of convection, and relationships between the meteorology in different states of organization are compared. Switching from a configuration with parameterized convection to one that allows the model to resolve convective processes at the model grid scale is the leading-order factor improving some aspects of model performance, while increased model resolution is the dominant factor for others. However, no single model configuration performs best compared to observations, indicating underlying deficiencies in both model scaling and process understanding.
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Han, Ji-Young, So-Young Kim, In-Jin Choi, and Emilia Jin. "Effects of the Convective Triggering Process in a Cumulus Parameterization Scheme on the Diurnal Variation of Precipitation over East Asia." Atmosphere 10, no. 1 (January 12, 2019): 28. http://dx.doi.org/10.3390/atmos10010028.
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Effects of the convective triggering process in a cumulus parameterization scheme on the diurnal variation of precipitation over East Asia are examined using a regional climate model. Based on a cloud-resolving simulation showing the irrelevance of convective inhibition once convection is initiated and the sensitivity experiments to trigger conditions, the triggering process in the simplified Arakawa-Schubert (SAS) convection scheme is modified to use different convective initiation and termination conditions. The diurnal variation of precipitation frequency with the modified triggering process becomes in phase with the observed one, leading to a delayed afternoon peak in precipitation rate that is in better agreement with the observation. However, the bias in the phase of precipitation intensity is not resolved and the bias of excessive precipitation increases, indicating that adequate representation of not only the triggering process but also other moist convective processes that determine the strength of convection is required for further improvement in the simulation of the diurnal variation of precipitation.
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Belikov, D. A., S. Maksyutov, M. Krol, A. Fraser, M. Rigby, H. Bian, A. Agusti-Panareda, et al. "Off-line algorithm for calculation of vertical tracer transport in the troposphere due to deep convection." Atmospheric Chemistry and Physics Discussions 12, no. 8 (August 14, 2012): 20239–89. http://dx.doi.org/10.5194/acpd-12-20239-2012.
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Abstract. A modified cumulus convection parametrisation scheme is presented. This scheme computes the mass of air transported upward in a cumulus cell using conservation of moisture and a detailed distribution of convective precipitation provided by a reanalysis dataset. The representation of vertical transport within the scheme includes entrainment and detrainment processes in convective updrafts and downdrafts. Output from the proposed parametrisation scheme is employed in the National Institute for Environmental Studies (NIES) global chemical transport model driven by JRA-25/JCDAS reanalysis. The simulated convective precipitation rate and mass fluxes are compared with observations and reanalysis data. A simulation of the short-lived tracer 222Rn is used to further evaluate the performance of the cumulus convection scheme. Simulated distributions of 222Rn are validated against observations at the surface and in the free troposphere, and compared with output from models that participated in the TransCom-CH4 Transport Model Intercomparison. From this comparison, we demonstrate that the proposed convective scheme can successfully reproduce deep cloud convection.
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Rogers, Robert F., Paul D. Reasor, Jonathan A. Zawislak, and Leon T. Nguyen. "Precipitation Processes and Vortex Alignment during the Intensification of a Weak Tropical Cyclone in Moderate Vertical Shear." Monthly Weather Review 148, no. 5 (April 14, 2020): 1899–929. http://dx.doi.org/10.1175/mwr-d-19-0315.1.
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Abstract The mechanisms underlying the development of a deep, aligned vortex, and the role of convection and vertical shear in this process, are explored by examining airborne Doppler radar and deep-layer dropsonde observations of the intensification of Hurricane Hermine (2016), a long-lived tropical depression that intensified to hurricane strength in the presence of moderate vertical wind shear. During Hermine’s intensification the low-level circulation appeared to shift toward locations of deep convection that occurred primarily downshear. Hermine began to steadily intensify once a compact low-level vortex developed within a region of deep convection in close proximity to a midlevel circulation, causing vorticity to amplify in the lower troposphere primarily through stretching and tilting from the deep convection. A notable transition of the vertical mass flux profile downshear of the low-level vortex to a bottom-heavy profile also occurred at this time. The transition in the mass flux profile was associated with more widespread moderate convection and a change in the structure of the deep convection to a bottom-heavy mass flux profile, resulting in greater stretching of vorticity in the lower troposphere of the downshear environment. These structural changes in the convection were related to a moistening in the midtroposphere downshear, a stabilization in the lower troposphere, and the development of a mid- to upper-level warm anomaly associated with the developing midlevel circulation. The evolution of precipitation structure shown here suggests a multiscale cooperative interaction across the convective and mesoscale that facilitates an aligned vortex that persists beyond convective time scales, allowing Hermine to steadily intensify to hurricane strength.
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Piriou, Jean-Marcel, Jean-Luc Redelsperger, Jean-François Geleyn, Jean-Philippe Lafore, and Françoise Guichard. "An Approach for Convective Parameterization with Memory: Separating Microphysics and Transport in Grid-Scale Equations." Journal of the Atmospheric Sciences 64, no. 11 (November 1, 2007): 4127–39. http://dx.doi.org/10.1175/2007jas2144.1.
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Abstract An approach for convective parameterization is presented here, in which grid-scale budget equations of parameterization use separate microphysics and transport terms. This separation is used both as a way to introduce into the parameterization a more explicit causal link between all involved processes and as a vehicle for an easier representation of the memory of convective cells. The equations of parameterization become closer to those of convection-resolving models [cloud-system-resolving models (CSRMs) and large-eddy simulations (LESs)], facilitating parameterization development and validation processes versus a detailed budget of these high-resolution models. The new Microphysics and Transport Convective Scheme (MTCS) equations are presented and discussed. A first version of a convective scheme based on these equations is tested within a single-column framework. The results obtained with the new scheme are close to those of traditional ones in very moist convective cases [like the Global Atmospheric Research Programme (GARP) Atlantic Tropical Experiment (GATE) Phase III, 1974]. The simulation of more difficult drier situations [European Cloud Systems Study/Global Energy and Water Cycle Experiment (GEWEX) Cloud System Studies (EUROCS/GCSS)] is improved through more memory due to higher sensitivity of simulated convection to dry midtropospheric layers; a prognostic relation between cloudy entrainment and precipitation evaporation dramatically improves the prediction of the phase lag of the convective diurnal cycle over land with respect to surface heat forcing. The present proposal contains both a relatively general equation set, which can deal continuously with dry, moist, and deep precipitating convection, and separate—and still crude—explicit moist microphysics. In the future, when increasing the complexity of microphysical computations, such an approach may help to unify dry, moist, and deep precipitating convection inside a single parameterization, as well as facilitate global climate model (GCM) and limited-area model (LAM) parameterizations in sharing the same formulation of explicit microphysics with CSRMs.
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Sui, C.-H., X. Li, and K.-M. Lau. "Radiative–Convective Processes in Simulated Diurnal Variations ofTropical Oceanic Convection." Journal of the Atmospheric Sciences 55, no. 13 (July 1998): 2345–57. http://dx.doi.org/10.1175/1520-0469(1998)055<2345:rcpisd>2.0.co;2.
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Stechmann, Samuel N., and Andrew J. Majda. "Gravity Waves in Shear and Implications for Organized Convection." Journal of the Atmospheric Sciences 66, no. 9 (September 1, 2009): 2579–99. http://dx.doi.org/10.1175/2009jas2976.1.
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Abstract It is known that gravity waves in the troposphere, which are often excited by preexisting convection, can favor or suppress the formation of new convection. Here it is shown that in the presence of wind shear or barotropic wind, the gravity waves can create a more favorable environment on one side of preexisting convection than the other side. Both the nonlinear and linear analytic models developed here show that the greatest difference in favorability between the two sides is created by jet shears, and little or no difference in favorability is created by wind profiles with shear at low levels and no shear in the upper troposphere. A nonzero barotropic wind (or, equivalently, a propagating heat source) is shown to also affect the favorability on each side of the preexisting convection. It is shown that these main features are captured by linear theory, and advection by the background wind is the main physical mechanism at work. These processes should play an important role in the organization of wave trains of convective systems (i.e., convectively coupled waves); if one side of preexisting convection is repeatedly more favorable in a particular background wind shear, then this should determine the preferred propagation direction of convectively coupled waves in this wind shear. In addition, these processes are also relevant to individual convective systems: it is shown that a barotropic wind can lead to near-resonant forcing that amplifies the strength of upstream gravity waves, which are known to trigger new convective cells within a single convective system. The barotropic wind is also important in confining the upstream waves to the vicinity of the source, which can help ensure that any new convective cells triggered by the upstream waves are able to merge with the convective system. All of these effects are captured in a two-dimensional model that is further simplified by including only the first two vertical baroclinic modes. Numerical results are shown with a nonlinear model, and linear theory results are in good agreement with the nonlinear model for most cases.
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Penny, Andrew B., Patrick A. Harr, and James D. Doyle. "Sensitivity to the Representation of Microphysical Processes in Numerical Simulations during Tropical Storm Formation." Monthly Weather Review 144, no. 10 (October 2016): 3611–30. http://dx.doi.org/10.1175/mwr-d-15-0259.1.
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An analysis of in situ observations from the nondeveloping tropical disturbance named TCS025 revealed that a combination of unfavorable system-scale and environmental factors limited further development. In this study, a multiphysics ensemble of high-resolution simulations of TCS025 are analyzed and compared. A simulation that overdeveloped the TCS025 disturbance is compared with one that correctly simulated nondevelopment and reveals that convection was stronger and diabatic heating rates were larger in the developing simulation. This led to continued spinup of the low-level circulation primarily through vorticity stretching. In contrast, convection was much weaker in the nondeveloping simulation, and after an initial period of deep convection, average vorticity tendencies from stretching became weakly negative, which allowed for the frictional spindown of the low-level circulation. Convective-scale differences identified early in the simulations appear to have resulted from the explicit representation of graupel in the developing simulation. The net impacts resulting from these differences in convection are manifest in the average diabatic heating profiles that are important for determining the developmental outcome. Additional simulations are conducted whereby the diabatic heating rates are artificially adjusted. Relatively small changes in the diabatic heating rate led to significantly different outcomes with respect to storm development, and the degree of overdevelopment is largely dictated by the diabatic heating rate. These findings suggest the correct representation of convective processes and associated diabatic heating are necessary to adequately forecast tropical cyclogenesis, especially for systems near a threshold of development like TCS025.
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Minamide, Masashi, and Derek J. Posselt. "Using Ensemble Data Assimilation to Explore the Environmental Controls on the Initiation and Predictability of Moist Convection." Journal of the Atmospheric Sciences 79, no. 4 (April 2022): 1151–69. http://dx.doi.org/10.1175/jas-d-21-0140.1.
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Abstract Atmospheric deep moist convection has emerged as one of the most challenging topics for numerical weather prediction, due to its chaotic process of development and multiscale physical interactions. This study examines the dynamics and predictability of a weakly organized linear convective system using convection permitting EnKF analysis and forecasts with assimilating all-sky satellite radiances from a water vapor sensitive band of the Advanced Baseline Imager on GOES-16. The case chosen occurred over the Gulf of Mexico on 11 June 2017 during the NASA Convective Processes Experiment (CPEX) field campaign. Analysis of the water vapor and dynamic ensemble covariance structures revealed that meso-α-scale (2000–200 km) and meso-β-scale (200–20 km) initial features helped to constrain the general location of convection with a few hours of lead time, contributing to enhancing convective activity, but meso-γ-scale (20–2 km) or even-smaller-scale features with less than 30-min lead time were identified to be essential for capturing individual convective storms. The impacts of meso-α-scale initial features on the prediction of particular individual convective cells were found to be classified into two regimes; in a relatively dry regime, the meso-α-scale environment needs to be moist enough to support the development of the convection of interest, but in a relatively wet regime, a drier meso-α-scale environment is preferable to suppress the surrounding convective activity. This study highlights the importance of high-resolution initialization of moisture fields for the prediction of a quasi-linear tropical convective system, as well as demonstrating the accuracy that may be necessary to predict convection exactly when and where it occurs.
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Xue, Ming, and William J. Martin. "A High-Resolution Modeling Study of the 24 May 2002 Dryline Case during IHOP. Part I: Numerical Simulation and General Evolution of the Dryline and Convection." Monthly Weather Review 134, no. 1 (January 1, 2006): 149–71. http://dx.doi.org/10.1175/mwr3071.1.
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Abstract Results from a high-resolution numerical simulation of the 24 May 2002 dryline convective initiation (CI) case are presented. The simulation uses a 400 km × 700 km domain with a 1-km horizontal resolution grid nested inside a 3-km domain and starts from an assimilated initial condition at 1800 UTC. Routine as well as special upper-air and surface observations collected during the International H2O Project (IHOP_2002) are assimilated into the initial condition. The initiation of convective storms at around 2015 UTC along a section of the dryline south of the Texas panhandle is correctly predicted, as is the noninitiation of convection at a cold-front–dryline intersection (triple point) located farther north. The timing and location of predicted CI are accurate to within 20 min and 25 km, respectively. The general evolution of the predicted convective line up to 6 h of model time also verifies well. Mesoscale convergence associated with the confluent flow around the dryline is shown to produce an upward moisture bulge, while surface heating and boundary layer mixing are responsible for the general deepening of the boundary layer. These processes produce favorable conditions for convection but the actual triggering of deep moist convection at specific locations along the dryline depends on localized forcing. Interaction of the primary dryline convergence boundary with horizontal convective rolls on its west side provides such localized forcing, while convective eddies on the immediate east side are suppressed by a downward mesoscale dryline circulation. A companion paper analyzes in detail the exact processes of convective initiation along this dryline.
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Lane, Todd P., and Fuqing Zhang. "Coupling between Gravity Waves and Tropical Convection at Mesoscales." Journal of the Atmospheric Sciences 68, no. 11 (November 1, 2011): 2582–98. http://dx.doi.org/10.1175/2011jas3577.1.
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Abstract An idealized cloud-system-resolving model simulation is used to examine the coupling between a tropical cloud population and the mesoscale gravity waves that it generates. Spectral analyses of the cloud and gravity wave fields identify a clear signal of coupling between the clouds and a deep tropospheric gravity wave mode with a vertical wavelength that matches the depth of the convection, which is about two-thirds of the tropospheric depth. This vertical wavelength and the period of the waves, defined by a characteristic convective time scale, means that the horizontal wavelength is constrained through the dispersion relation. Indeed, the wave–convection coupling manifests at the appropriate wavelength, with the emergence of quasi-regular cloud-system spacing of order 100 km. It is shown that cloud systems at this spacing achieve a quasi-resonant state, at least for a few convective life cycles. Such regular spacing is a key component of cloud organization and is likely a contributor to the processes controlling the upscale growth of convective systems. Other gravity wave processes are also elucidated, including their apparent role in the maintenance of convective systems by providing a mechanism for renewed convective activity and system longevity.
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Rybka, H., and H. Tost. "Uncertainties in future climate predictions due to convection parameterisations." Atmospheric Chemistry and Physics Discussions 13, no. 10 (October 16, 2013): 26893–931. http://dx.doi.org/10.5194/acpd-13-26893-2013.
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Abstract. In the last decades several convection parameterisations have been developed to consider the impact of small-scale unresolved processes in Earth System Models associated with convective clouds. Global model simulations, which have been performed under current climate conditions with different convection schemes, significantly differ among each other in the simulated transport of trace gases and precipitation patterns due to the parameterisation assumptions and formulations, e.g. the simplified treatment of the cloud microphysics. Here we address sensitivity studies comparing four different convection schemes under alternative climate conditions (doubling of the CO2 concentrations) to identify uncertainties related to convective processes. The increase in surface temperature reveals regional differences up to 4 K dependent on the chosen convection parameterisation. The increase in upper tropospheric temperature affects the amount of water vapour transported to the lower stratosphere. Furthermore, the change in transporting short-lived pollutants within the atmosphere is highly ambiguous for the lower and upper troposphere. Finally, cloud radiative effects have been analysed uncovering a shift in different cloud types in the tropics.
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Lane, Todd P., and Mitchell W. Moncrieff. "Characterization of Momentum Transport Associated with Organized Moist Convection and Gravity Waves." Journal of the Atmospheric Sciences 67, no. 10 (October 1, 2010): 3208–25. http://dx.doi.org/10.1175/2010jas3418.1.
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Abstract Tropical convection is inherently multiscalar, involving complex fields of clouds and various regimes of convective organization ranging from small disorganized cumulus up to large organized convective clusters. In addition to being a crucial component of the atmospheric water cycle and the global heat budget, tropical convection induces vertical fluxes of horizontal momentum. There are two main contributions to the momentum transport. The first resides entirely in the troposphere and is due to ascent, descent, and organized circulations associated with precipitating convective systems. The second resides in the troposphere, stratosphere, and farther aloft and is caused by vertically propagating gravity waves. Both the convective momentum transport and the gravity wave momentum flux must be parameterized in general circulation models; yet in existing parameterizations, these two processes are treated independently. This paper examines the relationship between the convective momentum transport and convectively generated gravity wave momentum flux by utilizing idealized simulations of multiscale tropical convection in different wind shear conditions. The simulations produce convective systems with a variety of regimes of convective organization and therefore different convective momentum transport properties and gravity wave spectra. A number of important connections are identified, including a consistency in the sign of the momentum transports in the lower troposphere and stratosphere that is linked to the generation of gravity waves by tilted convective structures. These results elucidate important relationships between the convective momentum transport and the gravity wave momentum flux that will be useful for interlinking their parameterization in the future.
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Vreugdenhil, Catherine A., and Bishakhdatta Gayen. "Ocean Convection." Fluids 6, no. 10 (October 12, 2021): 360. http://dx.doi.org/10.3390/fluids6100360.
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Ocean convection is a key mechanism that regulates heat uptake, water-mass transformation, CO2 exchange, and nutrient transport with crucial implications for ocean dynamics and climate change. Both cooling to the atmosphere and salinification, from evaporation or sea-ice formation, cause surface waters to become dense and down-well as turbulent convective plumes. The upper mixed layer in the ocean is significantly deepened and sustained by convection. In the tropics and subtropics, night-time cooling is a main driver of mixed layer convection, while in the mid- and high-latitude regions, winter cooling is key to mixed layer convection. Additionally, at higher latitudes, and particularly in the sub-polar North Atlantic Ocean, the extensive surface heat loss during winter drives open-ocean convection that can reach thousands of meters in depth. On the Antarctic continental shelf, polynya convection regulates the formation of dense bottom slope currents. These strong convection events help to drive the immense water-mass transport of the globally-spanning meridional overturning circulation (MOC). However, convection is often highly localised in time and space, making it extremely difficult to accurately measure in field observations. Ocean models such as global circulation models (GCMs) are unable to resolve convection and turbulence and, instead, rely on simple convective parameterizations that result in a poor representation of convective processes and their impact on ocean circulation, air–sea exchange, and ocean biology. In the past few decades there has been markedly more observations, advancements in high-resolution numerical simulations, continued innovation in laboratory experiments and improvement of theory for ocean convection. The impacts of anthropogenic climate change on ocean convection are beginning to be observed, but key questions remain regarding future climate scenarios. Here, we review the current knowledge and future direction of ocean convection arising from sea–surface interactions, with a focus on mixed layer, open-ocean, and polynya convection.
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de Szoeke, Simon P. "Variations of the Moist Static Energy Budget of the Tropical Indian Ocean Atmospheric Boundary Layer." Journal of the Atmospheric Sciences 75, no. 5 (May 2018): 1545–51. http://dx.doi.org/10.1175/jas-d-17-0345.1.
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The atmospheric circulation depends on poorly understood interactions between the tropical atmospheric boundary layer (BL) and convection. The surface moist static energy (MSE) source (130 W m−2, of which 120 W m−2 is evaporation) to the tropical marine BL is balanced by upward MSE flux at the BL top that is the source for deep convection. Important for modeling tropical convection and circulation is whether MSE enters the free troposphere by dry turbulent processes originating within the boundary layer or by motions generated by moist deep convection in the free troposphere. Here, highly resolved observations of the BL quantify the MSE fluxes in approximate agreement with recent cloud-resolving models, but the fluxes depend on convective conditions. In convectively suppressed (weak precipitation) conditions, entrainment and downdraft fluxes export equal shares (60 W m−2) of MSE from the BL. Downdraft fluxes are found to increase 50%, and entrainment to decrease, under strongly convective conditions. Variable entrainment and downdraft MSE fluxes between the BL and convective clouds must both be considered for modeling the climate.
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Tomassini, Lorenzo. "Mesoscale Circulations and Organized Convection in African Easterly Waves." Journal of the Atmospheric Sciences 75, no. 12 (December 1, 2018): 4357–81. http://dx.doi.org/10.1175/jas-d-18-0183.1.
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Abstract Global convection-permitting model simulations and remote sensing observations are used to investigate the interaction between organized convection, both moist and dry, and the atmospheric circulation in the case of an African easterly wave (AEW). The wave disturbance is associated with a quadrupole structure of divergence, with two convergence centers slightly ahead of the trough. Moisture transport from southeast of the trough to the area in front and lower midtropospheric moisture convergence precondition and organize convection. The main inflow into the squall-line cluster is from behind. The moisture-abundant inflow collides at the low level with monsoon air with high moist static energy and establishes a frontal line of updrafts at the leading edge of the propagating mesoscale convective system. A mantle of moisture surrounds the convective core. A potential vorticity budget analysis reveals that convective latent heating is driving the evolution of the wave but not in a quasi-steady way. The wave propagation includes a succession of convective bursts and subsequent dynamic adjustment processes. Dry convection associated with the Saharan air layer (SAL) and SAL intrusions into the wave trough together with vorticity advection can play a role in intensifying AEWs dynamically as they move from the West African coast across the Atlantic Ocean. Our analysis demonstrates that the synoptic-scale wave and convection are interlinked through mesoscale circulations on a continuum of scales. This implies that the relation between organized convection and the atmospheric circulation is intrinsically dynamic, which poses a particular challenge to subgrid convection parameterizations in numerical models.
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Vergara-Temprado, Jesús, Nikolina Ban, Davide Panosetti, Linda Schlemmer, and Christoph Schär. "Climate Models Permit Convection at Much Coarser Resolutions Than Previously Considered." Journal of Climate 33, no. 5 (March 1, 2020): 1915–33. http://dx.doi.org/10.1175/jcli-d-19-0286.1.
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AbstractThe “gray zone” of convection is defined as the range of horizontal grid-space resolutions at which convective processes are partially but not fully resolved explicitly by the model dynamics (typically estimated from a few kilometers to a few hundred meters). The representation of convection at these scales is challenging, as both parameterizing convective processes or relying on the model dynamics to resolve them might cause systematic model biases. Here, a regional climate model over a large European domain is used to study model biases when either using parameterizations of deep and shallow convection or representing convection explicitly. For this purpose, year-long simulations at horizontal resolutions between 50- and 2.2-km grid spacing are performed and evaluated with datasets of precipitation, surface temperature, and top-of-the-atmosphere radiation over Europe. While simulations with parameterized convection seem more favorable than using explicit convection at around 50-km resolution, at higher resolutions (grid spacing ≤ 25 km) models tend to perform similarly or even better for certain model skills when deep convection is turned off. At these finer scales, the representation of deep convection has a larger effect in model performance than changes in resolution when looking at hourly precipitation statistics and the representation of the diurnal cycle, especially over nonorographic regions. The shortwave net radiative balance at the top of the atmosphere is the variable most strongly affected by resolution changes, due to the better representation of cloud dynamical processes at higher resolutions. These results suggest that an explicit representation of convection may be beneficial in representing some aspects of climate over Europe at much coarser resolutions than previously thought, thereby reducing some of the uncertainties derived from parameterizing deep convection.
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Zhang, Zhe, Youcun Qi, Donghuan Li, Ziwei Zhu, Meilin Yang, Nan Wang, Yin Yang, and Qiyuan Hu. "A Real-Time Algorithm to Identify Convective Precipitation Adjacent to or within the Bright Band in the Radar Scan Domain." Journal of Hydrometeorology 22, no. 5 (May 2021): 1139–51. http://dx.doi.org/10.1175/jhm-d-20-0005.1.
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AbstractHydrological hazards usually occur after heavy precipitation, especially during strong convection. Therefore, accurately identifying convective precipitation is very helpful for hydrological warning and forecasting. However, separating the convective, bright band (BB), and stratiform precipitation is found to be challenging when the convection is adjacent to or within the BB region. A new convection/BB/stratiform precipitation segregation algorithm is proposed in this study to resolve this challenging issue. This algorithm is applicable for a single radar volume scan data in native (polar) coordinates and consists of four processes: 1) check the freezing (0°C) level to roughly assess whether convection is occurring or not; 2) identify the convective cores through analyzing composite reflectivity (maximum reflectivity for a given range gate among all the sweeps), vertically integrated liquid water (VIL), VIL horizontal gradient, and reflectivity at the levels of 0°, −10°, and above −10°C; 3) delineate the whole convective region through the seeded region growing method by taking account of the microphysical differences between the BB and convective regions; and 4) delineate BB features in the stratiform region. The proposed algorithm utilizes the physical characteristics of different precipitation types for precisely segregating the convective, BB, and stratiform precipitation. This algorithm has been tested with radar data of different precipitation events and evaluated with three months of rain gauge data. The results show that the proposed algorithm performs consistently well for challenging precipitation events with the convection adjacent to or within a strong BB. Furthermore, the proposed algorithm could be used to improve the vertical profile of reflectivity (VPR) correction and reduce the overestimation of rainfall in the BB precipitation region.
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Suselj, Kay, Marcin J. Kurowski, and João Teixeira. "On the Factors Controlling the Development of Shallow Convection in Eddy-Diffusivity/Mass-Flux Models." Journal of the Atmospheric Sciences 76, no. 2 (January 28, 2019): 433–56. http://dx.doi.org/10.1175/jas-d-18-0121.1.
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Abstract This study addresses key aspects of shallow moist convection, as simulated by a multiplume eddy-diffusivity/mass-flux (EDMF) model. Two factors suggested in the literature to be essential for the development of convective plumes are investigated: surface conditions and lateral entrainment. The model consistently decomposes the subgrid vertical mixing into convective plumes and the nonconvective environment. The modeled convection shows low sensitivity to the surface plume area. The results indicate that plume development in the subcloud layer is controlled by both surface conditions and lateral entrainment. Their impact significantly changes in the cloud layer where the surface conditions are no longer important. The development of shallow convection is dominated by the interactions between the plumes and the large-scale field and is sensitive to the representation of the variability of thermodynamic properties between the plumes. A simple two-layer model of steady-state convection is proposed to help understand the role of these processes in shaping the properties of moist convection.