Cloud microphysical and precipitation responses to a large-scale forcing in the tropical deep convective regime |
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| Authors: | X Li |
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| Institution: | (1) Joint Center for Satellite Data Assimilation and NOAA/NESDIS/Office of Research and Applications, Camp Springs, Maryland, USA |
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| Abstract: | Summary Cloud microphysical and precipitation responses to a large-scale forcing in the tropical deep convective regime are investigated
based on hourly zonally-averaged, vertically-integrated simulation data from a two-dimensional coupled ocean-cloud resolving
atmosphere model. The model is forced by the large-scale vertical velocity and zonal wind observed and derived from TOGA COARE
for a 50-day period. The accretion of cloud water by graupel induces growth of graupel that enhances raindrops through its
melting during a weak-forcing period, whereas the large deposition rate of vapor associated with a large upper-tropospheric
upward motion causes growth of snow from the conversion of cloud ice and enhancement of graupel from the accretion of snow
during a strong-forcing period. The local changes of raindrops and graupel switch from the negative to positive values as
the forcing strengthens in the weak-forcing case, whereas the variations of cloud hydrometeors are not sensitive to the strength
of the forcing in the strong-forcing case. Phase analysis indicates that cloud water leads the surface rain rate by 1 hour.
The surface rain rate can be calculated based on the conservation of vapor and cloud hydrometeors and the budget of raindrops.
The vapor source and local changes of cloud hydrometeors could have impacts in the calculation of the surface rain rate. The
vapor source determines the surface rain rate in the strong-forcing case whereas the cloud variations could become important
in the weak-forcing case. In the budget of raindrops, the sum of the collection of cloud water by raindrops, the melting of
graupel, and the evaporation of raindrops determines the surface rain rate in the strong-forcing case whereas the other rain-related
microphysical processes become important in the weak-forcing case. |
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