Cloud‐edge mixing: Direct numerical simulation and observations in Indian Monsoon clouds
Abstract A direct numerical simulation (DNS) with the decaying turbulence setup has been carried out to study cloud‐edge mixing and its impact on the droplet size distribution (DSD) applying thermodynamic conditions observed in monsoon convective clouds over Indian subcontinent during the Cloud Aero...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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American Geophysical Union (AGU)
2017-03-01
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| Series: | Journal of Advances in Modeling Earth Systems |
| Subjects: | |
| Online Access: | https://doi.org/10.1002/2016MS000731 |
| _version_ | 1797735984332275712 |
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| author | Bipin Kumar Sudarsan Bera Thara V. Prabha Wojceich W. Grabowski |
| author_facet | Bipin Kumar Sudarsan Bera Thara V. Prabha Wojceich W. Grabowski |
| author_sort | Bipin Kumar |
| collection | DOAJ |
| description | Abstract A direct numerical simulation (DNS) with the decaying turbulence setup has been carried out to study cloud‐edge mixing and its impact on the droplet size distribution (DSD) applying thermodynamic conditions observed in monsoon convective clouds over Indian subcontinent during the Cloud Aerosol Interaction and Precipitation Enhancement EXperiment (CAIPEEX). Evaporation at the cloud‐edges initiates mixing at small scale and gradually introduces larger‐scale fluctuations of the temperature, moisture, and vertical velocity due to droplet evaporation. Our focus is on early evolution of simulated fields that show intriguing similarities to the CAIPEEX cloud observations. A strong dilution at the cloud edge, accompanied by significant spatial variations of the droplet concentration, mean radius, and spectral width, are found in both the DNS and in observations. In DNS, fluctuations of the mean radius and spectral width come from the impact of small‐scale turbulence on the motion and evaporation of inertial droplets. These fluctuations decrease with the increase of the volume over which DNS data are averaged, as one might expect. In cloud observations, these fluctuations also come from other processes, such as entrainment/mixing below the observation level, secondary CCN activation, or variations of CCN activation at the cloud base. Despite large differences in the spatial and temporal scales, the mixing diagram often used in entrainment/mixing studies with aircraft data is remarkably similar for both DNS and cloud observations. We argue that the similarity questions applicability of heuristic ideas based on mixing between two air parcels (that the mixing diagram is designed to properly represent) to the evolution of microphysical properties during turbulent mixing between a cloud and its environment. |
| first_indexed | 2024-03-12T13:07:00Z |
| format | Article |
| id | doaj.art-0d63fe66ab074a4398f7219612b01e79 |
| institution | Directory Open Access Journal |
| issn | 1942-2466 |
| language | English |
| last_indexed | 2024-03-12T13:07:00Z |
| publishDate | 2017-03-01 |
| publisher | American Geophysical Union (AGU) |
| record_format | Article |
| series | Journal of Advances in Modeling Earth Systems |
| spelling | doaj.art-0d63fe66ab074a4398f7219612b01e792023-08-28T13:36:50ZengAmerican Geophysical Union (AGU)Journal of Advances in Modeling Earth Systems1942-24662017-03-019133235310.1002/2016MS000731Cloud‐edge mixing: Direct numerical simulation and observations in Indian Monsoon cloudsBipin Kumar0Sudarsan Bera1Thara V. Prabha2Wojceich W. Grabowski3High Performance Computing SystemsIndian Institute of Tropical MeteorologyPune IndiaPhysics and Dynamics of Tropical CloudIndian Institute of Tropical MeteorologyPune IndiaPhysics and Dynamics of Tropical CloudIndian Institute of Tropical MeteorologyPune IndiaMesoscale and Microscale Meteorology LaboratoryNational Center for Atmospheric ResearchBoulder Colorado USAAbstract A direct numerical simulation (DNS) with the decaying turbulence setup has been carried out to study cloud‐edge mixing and its impact on the droplet size distribution (DSD) applying thermodynamic conditions observed in monsoon convective clouds over Indian subcontinent during the Cloud Aerosol Interaction and Precipitation Enhancement EXperiment (CAIPEEX). Evaporation at the cloud‐edges initiates mixing at small scale and gradually introduces larger‐scale fluctuations of the temperature, moisture, and vertical velocity due to droplet evaporation. Our focus is on early evolution of simulated fields that show intriguing similarities to the CAIPEEX cloud observations. A strong dilution at the cloud edge, accompanied by significant spatial variations of the droplet concentration, mean radius, and spectral width, are found in both the DNS and in observations. In DNS, fluctuations of the mean radius and spectral width come from the impact of small‐scale turbulence on the motion and evaporation of inertial droplets. These fluctuations decrease with the increase of the volume over which DNS data are averaged, as one might expect. In cloud observations, these fluctuations also come from other processes, such as entrainment/mixing below the observation level, secondary CCN activation, or variations of CCN activation at the cloud base. Despite large differences in the spatial and temporal scales, the mixing diagram often used in entrainment/mixing studies with aircraft data is remarkably similar for both DNS and cloud observations. We argue that the similarity questions applicability of heuristic ideas based on mixing between two air parcels (that the mixing diagram is designed to properly represent) to the evolution of microphysical properties during turbulent mixing between a cloud and its environment.https://doi.org/10.1002/2016MS000731DNScloud‐edge mixingentrainmentdroplet size distributionmixing diagram |
| spellingShingle | Bipin Kumar Sudarsan Bera Thara V. Prabha Wojceich W. Grabowski Cloud‐edge mixing: Direct numerical simulation and observations in Indian Monsoon clouds Journal of Advances in Modeling Earth Systems DNS cloud‐edge mixing entrainment droplet size distribution mixing diagram |
| title | Cloud‐edge mixing: Direct numerical simulation and observations in Indian Monsoon clouds |
| title_full | Cloud‐edge mixing: Direct numerical simulation and observations in Indian Monsoon clouds |
| title_fullStr | Cloud‐edge mixing: Direct numerical simulation and observations in Indian Monsoon clouds |
| title_full_unstemmed | Cloud‐edge mixing: Direct numerical simulation and observations in Indian Monsoon clouds |
| title_short | Cloud‐edge mixing: Direct numerical simulation and observations in Indian Monsoon clouds |
| title_sort | cloud edge mixing direct numerical simulation and observations in indian monsoon clouds |
| topic | DNS cloud‐edge mixing entrainment droplet size distribution mixing diagram |
| url | https://doi.org/10.1002/2016MS000731 |
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