Using airborne Doppler radar to examine eyewall momentum and vorticity budgets

Mesoscale budget analyses of angular momentum and relative vorticity in the hurricane inner core are presented using airborne dual-Doppler wind data from multiple storms. It is well known that phenomena with time frequency greater than the sampling frequency of the wind field may adversely impact quantitative agreement between observed and budget-estimated vortex changes. Dry idealized numerical experiments initialized with the basic structural characteristics of observed hurricanes are used to explore the extent to which a budget analysis based on a single "snapshot" of the wind field reflects the longer-term changes in the hurricane core. Additionally, in the case where consecutive snapshots are available, the impact of temporal resolution of the output on the quantitative agreement between observed and budget-estimated changes is made. The accuracy of the Doppler-derived wind field also impacts the budget analysis. Through an examination of multiple cases, aspects of the data processing and Doppler synthesis procedure that most directly impact the budgets are identified (e.g., fall speed removal, boundary layer resolution, and sampling strategy). In Hurricanes Olivia (1994) and Guillermo (1997) multiple consecutive passes were made through the storm, allowing observed and budget-estimated changes to be directly assessed. In each case a comparison of the primary contributions to the angular momentum and vorticity budgets is made with published budget studies using full-physics models.