Role of Convection in Modeling the Diurnal Cycle of Precipitation in Climate Models

Johns, Devon
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The Diurnal Cycle of Precipitation plays an important role in the world’s climate, as it is a representation of the timing of maximum precipitation around the world. Climate models, however, tend to have issues in simulating the Diurnal cycle of precipitation (DCP), primarily accurately representing the time of maximum precipitation. Two models were used in this study, Community Atmospheric Model 5 (CAM5) and the Iowa State University Global Climate Model (ISUGCM), were evaluated. CAM5, the control model, used a CAPE (Convective Available Potential Energy) parameter with a threshold at which convection is triggered once CAPE values exceed this threshold, compared to the ISUGCM which focused more on the change of CAPE by the large-scale advection of temperature and moisture. The output from these two models for the summer months (JJA in the Northern hemisphere and DJF in the southern hemisphere) for tenyear (1980-1989) simulations. In areas that are largely affected by large-scale advection such as the central plains of the United States, eastern China, and central South America saw the largest deviance between the timing of maximum amplitude of the DCP where CAM5 had maximum amplitude occur in the late afternoon when maximum CAPE typically occurs. ISUGCM had a maximum amplitude occur in the late nighttime hours at these locations, which ran consistently with satellite data of maximum precipitation occurring in the late overnight. The ISUGCM also had more accurate output precipitation on a global scale closer to satellite data but also introduced more variation in the output. The use of CAPE changed by large-scale advection in depicting convection is important for better simulating the DCP. With a better representation of the DCP in these areas, better climate simulations will be possible for better describing the DCP.