Climatology of Tropical Overshooting Tops in North Atlantic Tropical Cyclones

Abstract

rganized tropical convection, often characterized by overshooting tops, is a distinguishing quality of tropical cyclones (TCs). In this study, the climatology of tropical overshooting tops (TOTs) in North Atlantic Ocean TCs from 2004-2015 is examined. Previous studies have investigated the distribution of convection in TCs based on lightning data. The purpose of this study it to examine the distribution of TC convection from geostationary satellites using an objective TOT detection algorithm based on infrared brightness temperatures and empirically-dependent thresholds. It will be shown that TOTs can provide an additional metric for identifying the characteristics of TC convection.Based on the 12-year (2004-2015) climatology, a distinct semi-diurnal cycle in TOT activity is detected within 500km of the TC center. In agreement with lightning data from previous studies, a pre-dawn maximum (local to the TC) in TOTs is observed within 300 km of the TC center. A second pre-dusk maximum is associated with TOTs between 300-500 km of the TC center. TC intensity and intensity trend along with environmental factors can affect the number and distribution of TOTs. For example, an exponential relationship exists between the number of TOTs and increasing sea surface temperatures. Conversely, increasing vertical wind shear magnitude decreases the density of TOTs, with a higher percentage of TOTs observed downshear of the wind direction. Generally, within 100 km (100-300 km) of the TC center, the preferred quadrant for TOTs is downshear left (downshear right), and increased TOT activity is observed right of TC motion. The findings both corroborate previous lightning study results while providing additional insights into TC convection.