Regional variation of morphology of organized convection in the tropics and subtropics

Abstract

Properties of organized convection with large horizontal area (> 1000 km2) and with different horizontal structures in the tropics and subtropics are investigated by using 14 years of Tropical Rainfall Measuring Mission observations. First, the convective features (CFs) are defined as contiguous areas of convective precipitation detected by the Tropical Rainfall Measuring Mission precipitation radar. Using the minor and major axes of fitted ellipses, the morphology of the CFs are described as closer to a circular or a line shape. Regional variations and the properties of organized convection are examined with CFs with area>1000 km2 after categorizing them by their shapes. Organized convection tends to have larger extent and a higher fraction of near‐circular shapes over land than over ocean. Shallow organized convection with maximum radar echo top height below 4.5 km is found mainly over ocean and some coastal regions. Of all tropical oceans, most shallow organized convection is found over the east Pacific. The fraction of line shaped organized convection is higher over the ocean than over land, and is higher in the subtropics than in the tropics. More convective lines are found in winter than in summer over oceans, but more in summer over land. Organized convective lines are slightly less convectively intense indicated by lower 30 dBZ echo top heights and warmer 37 GHz brightness temperatures than those with near‐circular shapes. Orientations of organized convective lines are often aligned with fronts, dry lines, warm ocean currents, coastlines, and mountain slopes. Over the subtropics, organized convective lines are tilted more east‐west over land, and more north‐south over oceans. The largest and the most intense convective lines are found over central Africa, Argentina, and southeast U.S. over land, and over several warm currents in subtropical oceans.