Validation of Atmospheric Infrared Sounder (AIRS) data using GPS dropsondes in tropical cyclone environments

The environment surrounding a tropical cyclone (TC) plays a large role in determining the future intensification or weakening of the cyclone. This study focuses on the effects of the Saharan Air Layer (SAL) on Atlantic TCs. SAL environments are stable in the middle levels, and are not conducive to sustained convection that is required for a TC to survive. Previous studies (e.g. Dunion and Velden 2004, Jones et al. 2007) suggest the SAL has a negative effect on African easterly waves (AEWs) and existing cyclones. The stable SAL can lead to dry convective downdrafts, which can weaken or prevent intensification of AEWs and existing TCs.

One aspect of this study was to compare satellite data from the Atmospheric Infrared Sounder (AIRS) with GPS dropsonde data obtained from NOAA/HRD G-IV flights. Individual AIRS profiles were compared with spatially and temporally close dropsondes. It was noted that in SAL environments, AIRS was able to capture the sharp vertical moisture gradient often present at the base of the SAL, but it generally underestimated the amount of moisture present between the surface and the SAL base. In moist (non-SAL) environments, AIRS also struggled to capture the high mixing ratios in the boundary layer. It is possible that cloud cover prevented AIRS from accurately sampling the conditions in the lowest levels.

Total precipitable water (TPW) maps have been created on daily, monthly, and seasonal time scales across the Atlantic basin. The entire AIRS dataset, from its launch in May 2002 to the present, was considered. This climatology shows inter- and intra-annual differences in moisture distribution across the tropical Atlantic. Future work includes analyzing the performance of AIRS in the different quadrants of a tropical cyclone and at different stages of the TC life cycle.