Quantifying the Frequency of Hot Towers: A Comprehensive Satellite-Based Analysis

Atmospheric deep convective updrafts aid in vertically transporting energy and mass within the tropics, thus influencing both local and large-scale circulations. As the climate is changing, it is necessary to capture properties, such as the frequency, spatial distribution, intensity, and size of updraft regions in the present-day climate system. In 1979 with limited access to observations, Herbert Riehl and Joanne Simpson (Malkus) estimated that 1600-2400 undilute convective cores vertically transport energy to the tropopause at any given time within a region where upper-tropospheric energy is only exported from the tropics. The focus of this study is to provide an updated hot tower estimate using a novel approach that combines multiple satellite observing perspectives of hot towers within the tropical trough zone (between 13°S and 19°N). Cloud vertical profiles from CloudSat and CALIPSO measurements supply convective core diameters and proxies for intensity and convective activity, and these proxies are augmented with brightness temperature data from geostationary satellite observations, precipitation information from IMERG, and cloud radiative properties from CERES. It is found that less than 35% of all deep cores are classified as hot towers. We estimate that 800-1700 hot towers occur at any given time over the course of a day, with the mean maximum core and hot tower frequency occurring at the time of year when peak convective intensity and precipitation occur. Convective objects that contain hot towers frequently contain multiple cores, and the largest systems with five or more distinct cores most frequently occur in regions where organized mesoscale convective systems and the highest climatological mean rain rates are known to occur. Analysis of co-located radar and infrared brightness temperatures reveals that passive observations alone are not sufficient to unambiguously identify and distinguish hot towers using simple TB thresholds.