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How Wind Shear Affects Trade-wind Cumulus Convection.
K C Helfer1, L Nuijens1, S R de Roode1
1Department of Geoscience and Remote Sensing Delft University of Technology Delft Netherlands.
Journal of Advances in Modeling Earth Systems
|December 31, 2020
Summary
Vertical wind shear significantly impacts marine low cloud cover. Backward shear limits cloud growth, creating shallower, moister clouds, while forward shear can organize clouds but still limits vertical development.
Area of Science:
- Atmospheric Science
- Cloud Physics
- Meteorology
Background:
- Observed relationship between marine low cloud cover and surface wind speed.
- Trade-wind cumulus convection is crucial for Earth's energy budget.
- Vertical wind shear is a key atmospheric dynamic parameter.
Purpose of the Study:
- Investigate the effect of vertical wind shear on trade-wind cumulus convection.
- Analyze how different shear profiles influence cloud development and structure.
- Understand the mechanisms driving shear-induced changes in marine clouds.
Main Methods:
- Large-eddy simulations of idealized trade-wind convection.
- Implementation of varying vertical shear profiles in zonal wind.
- Analysis of cloud properties, including depth, moisture, and cloud cover.
Main Results:
- Backward shear limits vertical cloud development, resulting in shallower, moister, and cloudier conditions.
- Forward shear also limits cloud top height but can enhance moisture aggregation and cloud clustering on larger domains.
- Shear across the cloud layer reduces updraft speeds by increasing downward pressure perturbation forces.
Conclusions:
- Vertical wind shear is a critical factor in regulating trade-wind cumulus convection.
- Backward shear, common in winter trades, plays a key role in establishing the typical trade-wind layer structure.
- Understanding shear effects is vital for accurate climate modeling of marine low clouds.
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