Tropospheric Thermodynamic Conditions Necessary for Tropical Cyclone Rapid Intensification

Abstract

As a part of the Tropical Cyclone Rapid Intensification (TCRI) project, we investigated thermodynamic conditions necessary for cyclone intensification. While high sea surface temperature and low tropospheric wind shear are well known environmental factors contributing to storm intensification, they are not sufficient to predict intensification and rapid intensification in particular. To explore thermodynamic factors contributing to intensification, we used dropsondes deployed in pre-storm and storm environments interpolated on a regular grid via a 3D variational analysis. We find that in mesoscale convective areas an instability index, which measures the stability of the atmosphere to moist convection, and saturation fraction, which measures the moisture content of the atmosphere, show a narrow range of values favorable for intensification, and rapid intensification in particular.