Improved Tropical Cyclone Boundary Layer Wind Retrievals from Airborne Doppler Radar

Recent studies have highlighted the importance of boundary layer dynamics in tropical cyclone (TC) intensification and structure change. Numerical models suggest that a supergradient jet at the top of the boundary layer (Kepert and Wang 2001) associated with boundary layer convergence and forcing of deep convection may play a critical role in the formation of secondary eyewalls (Huang et al. 2012). Additional TC boundary layer (TCBL) phenomena such as turbulent kinetic energy, horizontal rolls, and momentum fluxes are also important for TC evolution. However, kinematic fields with adequate spatial resolution to resolve TCBL features are difficult to obtain due to limitations in our observation capabilities.

Airborne Doppler radar can provide some of the highest resolution wind measurements near the top of the TCBL, but the data quality is degraded near the sea surface. Dropsondes and Stepped Frequency Microwave Radiometers (SFMR) can provide near surface wind information in the TCBL, but have their own limitations. An improved methodology to retrieve high-resolution low-level TC winds from multiple data sources will be presented based on the radar technique from Lorsolo et al. (2010). A new spline-based, 3-D variational analysis technique called SAMURAI can supplement Doppler radar data with SFMR, flight level, and dropsonde observations. New airborne Doppler quality control procedures, combined with an improved analysis methodology are used to obtain reliable wind fields as close to the surface as possible. An error analysis using analytic data and some preliminary results from the RAINEX and PREDICT/GRIP/IFEX field campaigns will also be presented.