Precipitation Characteristics in the Community Atmosphere Model and Their Dependence on Model Resolution

Tuesday, December 11, 2018 - 13:40
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Precipitation amount (A), frequency (F), intensity (I) and duration (D) are equally necessary to fully characterize precipitation, estimations of these characteristics are sensitive to resolution of input data. This study analyzed F, I and D reproduced by Community Atmospheric Model (CAM) version 4 (CAM4) and version 5 (CAM5), and the influence of horizontal resolutions (including 0.23º×0.31º, 0.47º×0.63º, 0.9º×1.25ºand 1.9º×2.5º) on these simulated characteristics. Results show both CAM4 and CAM5 reproduce comparable A with observation, but systematically overestimate F and D and underestimate I. Convective precipitation in CAM5 is both (0-10%) more frequent and intense, particularly over the tropics. Non-convective precipitation is more frequent in CAM4. D is unrealistically long in both versions but overall shorter in CAM5. All four characteristics (except total precipitation A) depend on model horizontal resolution. Convective (non-convective) precipitation A and F increases (decreases) with grid size. Intensity decreases and duration increases remarkably with grid size. Results also suggest resolution dependence in CAM is a combination of grid aggregation effects and physical processes adjustments as resolution changes. In addition, CAM5 exhibits less resolution-dependence. We believe that different microphysics schemes in CAM4 (single-moment) and CAM5 (double-moment) are mainly responsible for difference in simulated precipitation characteristics between CAM4 and CAM5. CAM5 microphysics also contributes to less resolution dependence of CAM5 precipitation.

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