Tropical convective responses to microphysical and radiative processes: a sensitivity study with a 2-D cloud resolving model |
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| Authors: | X Li C-H Sui K-M Lau W-K Tao |
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| Institution: | (1) Joint Center for Satellite Data Assimilation and NOAA/NESDIS/ORA, Camp Springs, Maryland, USA;(2) Institute of Hydrological Sciences, National Central University Chung-Li, Taiwan;(3) NASA/GSFC/Laboratory for Atmospheres Greenbelt, Maryland, USA |
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| Abstract: | Summary Prognostic cloud schemes are increasingly used in weather and climate models in order to better treat cloud-radiation processes.
Simplifications are often made in such schemes for computational efficiency, like the scheme being used in the National Centers
for Environment Prediction models that excludes some microphysical processes and precipitation-radiation interaction. In this
study, sensitivity tests with a 2-D cloud resolving model are carried out to examine effects of the excluded microphysical
processes and precipitation-radiation interaction on tropical thermodynamics and cloud properties. The model is integrated
for 10 days with the imposed vertical velocity derived from the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere
Response Experiment. The experiment excluding the depositional growth of snow from cloud ice shows anomalous growth of cloud
ice and more than 20% increase of fractional cloud cover, indicating that the lack of the depositional snow growth causes
unrealistically large mixing ratio of cloud ice. The experiment excluding the precipitation-radiation interaction displays
a significant cooling and drying bias. The analysis of heat and moisture budgets shows that the simulation without the interaction
produces more stable upper troposphere and more unstable mid and lower troposphere than does the simulation with the interaction.
Thus, the suppressed growth of ice clouds in upper troposphere and stronger radiative cooling in mid and lower troposphere
are responsible for the cooling bias, and less evaporation of rain associated with the large-scale subsidence induces the
drying in mid and lower troposphere. |
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