Summary
A conceptually simple model based on cloud geometry is proposed to explain direct adjustment of moisture by convective clouds. The model is tested using deep convective cloud geometry and changes in upper tropospheric humidity in the Tropical Western Pacific (TWP) during TOGACOARE. The model and the data emphasize the importance of clouds larger than a General Circulation Model (GCM) grid box in drying the upper topospheric environment and in sub grid scale clouds in moistening the upper topospheric environment. The convective cloud sizes and changes in moisture are shown to be linked to precipitation rates. The change from clouds that moisten to clouds that dry the environment occurs when the average cloud size in 6.8×104 km2 or rain rate of 2.1 mm hr−1. In a study of moisture change in the sub cloud layer due to convection, Barnes and Garstang (1982) demonstrated that precipitation rates greater than 2 mm hr−1 resulted in drying. The critical rain rates above which environmental drying occurs is similar for both upper tropospheric regions and the sub cloud. The similarity of the rain rates indicates that the model concepts maybe used to explain direct adjustment of moisture under a variety of conditions.
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Barr-Kumarakulasinghe, S.A., Lwiza, K.M.M. Deep convective cloud scales and direct adjustment of upper troposphere moisture in TWP environment. Meteorl. Atmos. Phys. 66, 35–50 (1998). https://doi.org/10.1007/BF01030447
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DOI: https://doi.org/10.1007/BF01030447