Entrainment and droplet spectral characteristics in convective clouds during transition to monsoon

Bera, Sudarsan; Pandithurai, G.; Prabha, Thara V.

doi:10.1002/asl.657

Cited by 27 publications

(17 citation statements)

References 35 publications

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“…Thus, mixing of a cloud parcel with more diluted ones leads to proportional changes in the DSD shape. Such similarity in the DSD shapes at different droplet concentrations was reported in observations of stratocumulus (Bower & Choularton, ; Martin et al, ) and cumulus clouds (Bera, Pandithurai, & Bera, ; Bera, Prabha, & Grabowski, ; Korolev et al, ; Paluch, ).…”

Section: Analysis Of Scattering Diagramssupporting

confidence: 78%

“…This pronounced similarity of the DSD in different zones indicates high linear correlation between the droplet concentration and LWC within a wide variation range of these quantities. The similarity of DSD at different LWCs, as well as an increase in the peak radius with increasing LWC at small LWC values, was observed in in situ measurements in nonprecipitating clouds (Bera, Pandithurai, & Prabha, ; Bera, Prabha, & Grabowski, ; Paluch, ).…”

Section: Analysis Of Scattering Diagramssupporting

confidence: 58%

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Physical Interpretation of Mixing Diagrams

2018

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Type of mixing at cloud edges is often determined by means of mixing diagrams showing the dependence of normalized cube of the mean volume radius on the dilution level. The mixing diagrams correspond to the final equilibrium state of mixing between two air volumes. While interpreting in situ measurements, scattering diagrams are plotted in which normalized droplet concentration is used instead of dilution level. Utilization of such scattering diagrams for interpretation of in situ observations faces significant difficulties and often leads to misinterpretation of the mixing process and to uncertain conclusions concerning the mixing type. In this study we analyze the scattering diagrams obtained by means of a Lagrangian‐Eulerian model of a stratocumulus cloud. The model consists of 2,000 interacting Largangian parcels which mix with their neighbors during their motion in the atmospheric boundary layer. In the diagram, each parcel is denoted by a point. Changes of microphysical parameters of the parcel are represented by movements of the point in the scattering diagram. The method of plotting the scattering diagrams using the model is in many aspects similar to that used in in situ measurements. It is shown that a scattering diagram shows snapshots of a transient mixing process. The location of points in the scattering diagrams reflects largely the history and the origin of air parcels. Location of points on scattering diagram characterizes intensity of entrainment, and different parameters of droplet size distributions (DSDs) like concentration, mean volume (or effective) radius, and DSD width.

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Section: Analysis Of Scattering Diagramssupporting

confidence: 78%

Section: Analysis Of Scattering Diagramssupporting

confidence: 58%

Physical Interpretation of Mixing Diagrams

2018

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“…Two flight observations (16 June for PRE and 22 June for MON, 2009) during this transition are analyzed here with special attention given to the differences in microphysical properties of convective clouds resulting from different thermodynamic conditions. These two case studies are representing the general characteristics of PRE and MON environment and have been used in many previous studies [e.g., Prabha et al ., ; Bera et al ., ]. The 16 June cloud was growing in a more polluted environment than the 22 June case.…”

Section: Resultsmentioning

confidence: 99%

“…This is indicated in Figure b that shows a significant deviation of the effective radius from the mean radius after reaching 12 µm. The latter is considered a threshold for drizzle/rain initiation in ice‐free clouds [ Pruppacher and Klett , ; Kulkarni et al ., ; Khain et al ., ; Bera et al ., ]. Drizzle/rain drop formation at lower levels in a monsoon cloud makes the relationship between the r m and r e steeper due to production of larger (>12 µm) droplets and spectral broadening (the larger steepness is mainly due to larger droplet production above 4 km).…”

Section: Resultsmentioning

confidence: 99%

Observations of monsoon convective cloud microphysics over India and role of entrainment‐mixing

2016

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Microphysical characteristics of premonsoon and monsoon deep cumuli over India observed by an instrumented aircraft are contrasted focusing on influences of environmental conditions and entrainment‐mixing processes. Differences in the lower tropospheric temperature and moisture profiles lead to contrasting undiluted cloud buoyancy profiles around the cloud base, larger in the premonsoon case. It is argued that this affects the variation of the mean and maximum cloud droplet number concentrations and the droplet radius within the lowest several hundred meters above the cloud base. The conserved‐variable thermodynamic diagram analysis suggests that entrained parcels originate from levels close to the observational level. Mixing processes and their impact on the droplet size distribution (DSD) are investigated contrasting 1 Hz and 10 Hz observations. Inhomogeneous‐type mixing, likely because of unresolved small‐scale structures associated with active turbulent stirring, is noted at cloud edge volumes where dilution is significant and DSDs shift toward smaller sizes with reduced droplet number concentrations due to complete evaporation of smaller droplets and partial evaporation of larger droplets. DSDs within cloud core volumes suggest that the largest droplets are formed in the least diluted volumes where raindrops can form at higher levels; no superadiabatic droplet growth is observed. The typical diluted parcel size is approximately 100–200 m for cloud edge volumes, and it is much smaller, 10–20 m, for cloud core volumes. Time scale analysis indicates the possibility of inhomogeneous type mixing within the diluted cloud edge volumes at spatial scales of a 100 m or more.

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“…Entrainment rate, a key quantity in the convective parameterization, can be measured from the difference of moist conserved parameters inside the cloud and for the environment (as suggested by Betts, 1975). Entrainment in cumulus clouds has been widely investigated using in situ aircraft and satellite-based observations (Bera, Pandithurai, & Prabha, 2016;Bera, Prabha, & Grabowski, 2016;Bera et al, 2019;Gerber et al, 2008;Luo et al, 2010;Paluch, 1979;Raga et al, 1990;Squires, 1958). However, detrainment that is conjugate of the entrainment is less documented as pointed out by Böing et al (2013).…”

Section: Introductionmentioning

confidence: 99%

Parameterization of Entrainment Rate and Mass Flux in Continental Cumulus Clouds: Inference From Large Eddy Simulation

Bera

Prabha

2019

JGR Atmospheres

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Large eddy simulation with contrasting environmental humidity is used to study entrainment and detrainment rates and convective mass flux during the development stages of continental deep cumulus clouds. The cumulus clouds studied here are deeper than marine shallow cumulus or stratocumulus in the published literature. The main objective of the study is to parameterize the entrainment and detrainment rates in monsoon clouds during the break monsoon periods over land, useful for the large‐scale atmospheric models. A systematic decrease in cloud liquid water path is noted in drier environments as clouds become shallower due to the reduction of positive buoyancy in the cloud core. Updraft and downdraft velocities in the subcloud layers are strengthened in the drier environments, which are found to affect in‐cloud updraft strength. A most important finding of the present study is the effect of environmental humidity on the entrainment (and detrainment) rates and the convective mass flux. Many previous studies on this topic reported opposite results. The present study found that decreasing environmental humidity leads to a decrease in both the entrainment rate and the convective mass flux but an increase in the detrainment rate. The relationship of the entrainment parameters with the environmental relative humidity can be used for parameterization in the large‐scale models. The physical mechanism responsible for such response is identified as the strengthening of the subcloud updrafts compensated by the enhanced downdraft into the boundary layer in the drier environments, and this mechanism subsequently led to higher in‐cloud updraft velocity, resulting in lower entrainment rate.

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Entrainment and droplet spectral characteristics in convective clouds during transition to monsoon

Cited by 27 publications

References 35 publications

Physical Interpretation of Mixing Diagrams

Physical Interpretation of Mixing Diagrams

Observations of monsoon convective cloud microphysics over India and role of entrainment‐mixing

Parameterization of Entrainment Rate and Mass Flux in Continental Cumulus Clouds: Inference From Large Eddy Simulation

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