A Satellite Analysis of Mid-Tropospheric Humidity and its Importance in Tropical Cyclogenesis

In an attempt to improve our understanding of tropical cyclogenesis, satellite observations of mid-tropospheric relative humidity from AMSU-B are analyzed to identify its importance in the development and intensification of African Easterly Waves (AEW). To demonstrate its proficiency in remotely-sensing mid-level relative humidity, we first compare brightness temperature measurements from channel 19 (183 +/- 3 GHz) of the AMSU-B microwave satellite with dropsonde measurements from the NOAA G-IV aircraft. A radiative transfer model is used to simulate the corresponding brightness temperatures based upon the dropsonde profiles of temperature and humidity. Then both the satellite-observed and dropsonde-simulated brightness temperatures are converted into column-averaged relative humidity between 400-700mb using a simplified theoretical relationship. Initial comparisons show the satellite and dropsonde measurements to agree to within 10%. The satellite measurements are then used to create a storm-centered composite of the mid-tropospheric relative humidity environment for both developing and non-developing AEWs in the Atlantic Basin from 2001-2009. Higher water vapor concentrations in the mid-troposphere in the storm's environment are hypothesized to be conducive for genesis.