Simulation of Mesoscale Cellular Convection in Marine Stratocumulus: 2. Nondrizzling Conditions
Abstract This is the second of two large‐eddy simulation studies on the mechanisms of mesoscale cellular organization in drizzling (open cells) and nondrizzling marine stratocumulus (closed cells). This study uses a hard nudging approach which maintains fixed horizontal‐mean temperature and humidity...
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| Format: | Article |
| Language: | English |
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American Geophysical Union (AGU)
2019-01-01
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| Series: | Journal of Advances in Modeling Earth Systems |
| Subjects: | |
| Online Access: | https://doi.org/10.1029/2018MS001448 |
| _version_ | 1818314996992442368 |
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| author | Xiaoli Zhou Christopher S. Bretherton |
| author_facet | Xiaoli Zhou Christopher S. Bretherton |
| author_sort | Xiaoli Zhou |
| collection | DOAJ |
| description | Abstract This is the second of two large‐eddy simulation studies on the mechanisms of mesoscale cellular organization in drizzling (open cells) and nondrizzling marine stratocumulus (closed cells). This study uses a hard nudging approach which maintains fixed horizontal‐mean temperature and humidity profiles for a well‐mixed boundary layer with a constant boundary layer depth. For the case studied, closed cells develop and broaden by 32 hr to an aspect ratio of 25. Simulations show that the closed‐cell mesoscale cellular convection is driven by positive feedback from cloud‐induced mesoscale perturbations of longwave radiative cooling. A conceptual model for closed‐cell stratocumulus as a mesoscale wavelength hydrodynamic instability in which mesoscale moist and dry anomalies spontaneously grow is presented. In simulations in which long‐wavelength sinusoidal moisture anomalies are initially imposed, these anomalies evolve into amplifying closed cells. The cell structure is visualized with a compositing approach based on sorting grid columns by their mesoscale‐smoothed total water path. A thermally direct mesoscale circulation pattern develops in the interior of the boundary layer with buoyant mesoscale updrafts, thicker cloud, and a slightly higher capping inversion in the moister columns. There is a mesoscale flow of above‐inversion air down the slightly sloping capping inversion from the moist to the dry regions, reinforced by cloud top radiative cooling. This strengthens the mesoscale anomalies by preferentially cooling and drying the already dry regions. The sloping inversion flow is not driven as efficiently if the radiative cooling is artificially horizontally homogenized, partly disrupting this positive feedback and the resulting closed‐cell development. |
| first_indexed | 2024-12-13T08:58:31Z |
| format | Article |
| id | doaj.art-40c4e9becc94446896b66609eedf167e |
| institution | Directory Open Access Journal |
| issn | 1942-2466 |
| language | English |
| last_indexed | 2024-12-13T08:58:31Z |
| publishDate | 2019-01-01 |
| publisher | American Geophysical Union (AGU) |
| record_format | Article |
| series | Journal of Advances in Modeling Earth Systems |
| spelling | doaj.art-40c4e9becc94446896b66609eedf167e2022-12-21T23:53:12ZengAmerican Geophysical Union (AGU)Journal of Advances in Modeling Earth Systems1942-24662019-01-0111131810.1029/2018MS001448Simulation of Mesoscale Cellular Convection in Marine Stratocumulus: 2. Nondrizzling ConditionsXiaoli Zhou0Christopher S. Bretherton1Department of Atmospheric Sciences University of Washington Seattle WA USADepartment of Atmospheric Sciences University of Washington Seattle WA USAAbstract This is the second of two large‐eddy simulation studies on the mechanisms of mesoscale cellular organization in drizzling (open cells) and nondrizzling marine stratocumulus (closed cells). This study uses a hard nudging approach which maintains fixed horizontal‐mean temperature and humidity profiles for a well‐mixed boundary layer with a constant boundary layer depth. For the case studied, closed cells develop and broaden by 32 hr to an aspect ratio of 25. Simulations show that the closed‐cell mesoscale cellular convection is driven by positive feedback from cloud‐induced mesoscale perturbations of longwave radiative cooling. A conceptual model for closed‐cell stratocumulus as a mesoscale wavelength hydrodynamic instability in which mesoscale moist and dry anomalies spontaneously grow is presented. In simulations in which long‐wavelength sinusoidal moisture anomalies are initially imposed, these anomalies evolve into amplifying closed cells. The cell structure is visualized with a compositing approach based on sorting grid columns by their mesoscale‐smoothed total water path. A thermally direct mesoscale circulation pattern develops in the interior of the boundary layer with buoyant mesoscale updrafts, thicker cloud, and a slightly higher capping inversion in the moister columns. There is a mesoscale flow of above‐inversion air down the slightly sloping capping inversion from the moist to the dry regions, reinforced by cloud top radiative cooling. This strengthens the mesoscale anomalies by preferentially cooling and drying the already dry regions. The sloping inversion flow is not driven as efficiently if the radiative cooling is artificially horizontally homogenized, partly disrupting this positive feedback and the resulting closed‐cell development.https://doi.org/10.1029/2018MS001448mesoscale organizationboundary layer dynamicsstratocumuluslarge‐eddy simulationmesoscale cellular convectioncloud top radiative cooling |
| spellingShingle | Xiaoli Zhou Christopher S. Bretherton Simulation of Mesoscale Cellular Convection in Marine Stratocumulus: 2. Nondrizzling Conditions Journal of Advances in Modeling Earth Systems mesoscale organization boundary layer dynamics stratocumulus large‐eddy simulation mesoscale cellular convection cloud top radiative cooling |
| title | Simulation of Mesoscale Cellular Convection in Marine Stratocumulus: 2. Nondrizzling Conditions |
| title_full | Simulation of Mesoscale Cellular Convection in Marine Stratocumulus: 2. Nondrizzling Conditions |
| title_fullStr | Simulation of Mesoscale Cellular Convection in Marine Stratocumulus: 2. Nondrizzling Conditions |
| title_full_unstemmed | Simulation of Mesoscale Cellular Convection in Marine Stratocumulus: 2. Nondrizzling Conditions |
| title_short | Simulation of Mesoscale Cellular Convection in Marine Stratocumulus: 2. Nondrizzling Conditions |
| title_sort | simulation of mesoscale cellular convection in marine stratocumulus 2 nondrizzling conditions |
| topic | mesoscale organization boundary layer dynamics stratocumulus large‐eddy simulation mesoscale cellular convection cloud top radiative cooling |
| url | https://doi.org/10.1029/2018MS001448 |
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