Connecting Turbulent Eddies in Mature Hurricanes Through Wavelet Analysis on SAR and IWRAP Data

Abstract:

Satellite Synthetic Aperture Radar (SAR) measurements have been providing unique, wide swath views of mesoscale and microscale features in hurricanes at the ocean-atmosphere interface for many years. Studies have documented the structure of rain bands, the eye/eyewall interface including mesovortices, and boundary layer rolls.

The main goal of this work is to understand and interpret SAR imagery of the ocean/atmosphere interface in hurricanes. The horizontal winds in a hurricane put significant stress on the ocean surface. The peak winds in a hurricane are at the lower levels, due to the warm-core nature of the system, which interact strongly with the ocean surface producing significant vertical wind shear. This vertical wind shear produces turbulent eddies, which leave an imprint on the ocean surface that the SAR can detect. It is difficult to understand the wind structure of these SAR features, but new IWRAP data can provide the resolution and coverage of these features to understand them better. It is difficult to get an exact match up in time between a SAR overpass (instrument on polar orbiting satellite) and an IWRAP flight. Ideally we would like an exact matchup in time to study the features. To circumvent the time issue, we adopt a statistical methodology here. The premise is to gather statistics of the eddy features in both SAR and IWRAP data and then compare the parameters of these distributions (mean, variance, etc.). Statistics such as eddy wavelength, horizontal and vertical wind speed perturbations, momentum flux, etc. can be analyzed using the statistical analysis. The advantage of the SAR data is the high resolution over a very large domain. Once we identify similar statistical properties of the turbulent eddies, we can use the large coverage area of the SAR to make some estimates of the impact of the eddies on the mean flow. For example, the small-scale striations in the SAR data extend over large azimuthal distances and have repeating patterns in radius. If the eddies seen in the IWRAP data are similar to those in the SAR, then these eddies will project very strongly onto the mean fields and associated mean dynamics. It could be concluded that the eddies play an integral role in the intensity change of the hurricane.