Analyzing Gaps in Hurricane Rain Coverage to Inform Future Satellite Proposals

Justin P Stow,Heather M Holbach,Mark A Bourassa

doi:10.3390/rs12172673

Abstract

This study assesses where tropical cyclone (TC) surface winds can be measured as a function of footprint sizes and wavelengths (Ka- Ku- and C-band). During TCs, most high-resolution surface observations are impeded by considerable ‘rain contamination.’ Under these conditions, high-resolution surface observations typically come from operational aircraft. Other techniques that provide high-resolution surface observations through rain are also hindered somewhat by rain contamination and are very sparse in space and time. The impacts of rain are functions of the remotely sensed wavelength and rain–drop size. Therefore, relative long wavelengths have been used to observe the surface, but at the cost of a larger footprint. We examine how smaller footprint sizes could be used to observe through gaps between moderate to heavy rainbands that circulate around the main low-pressure center of a TC. Aircraft data from the National Oceanic and Atmospheric Administration’s (NOAA’s) WP-3D turboprop aircraft will be used to create realistic maps of rain. Our results provide information on the satellite instrument characteristics needed to see the surface through these gaps. This information is expected to aid in developing hurricane-related applications of new higher-resolution satellites.

Highlights

Wavelengths from active aircraft instrumentation and satellites are attenuated much more in heavy rainbands than lighter ones, making observations of the surface difficult during heavy rain events [1]
There were fewer rainband gaps with these low vertical wind sheared storms as the regions of stratiform precipitation were too strong to meet any of the rain rate thresholds
The Lower Fuselage (LF) reflectivities of Hurricanes Jose (Figure 3c) and Nate (Figure 3e) demonstrated evidence of strong vertical wind shear as their southwest and northwest quadrants, respectively, were devoid of reflectivities greater than 20–25 dBz. These storms appeared to possess larger rainband gaps and presented more opportunity to see the surface between precipitation structures

Summary

Introduction

Wavelengths from active aircraft instrumentation and satellites are attenuated much more in heavy rainbands than lighter ones, making observations of the surface difficult during heavy rain events [1]. There is considerable rain contamination during heavy rain events that make it difficult to see through these bands [2], and this rain can contaminate observations that have their nominal footprint outside the heavy rain, but radar sidelobes within the rain. This problem can be mitigated by observing with wavelengths much longer than the size of the rain–drops. The distribution of gaps in the moderate to heavy rainbands that circulate around the main low-pressure center of a TC with respect to current satellite technology has not been studied in copious detail. Kepert [11] utilized a diagnostic TC boundary layer model to conclude that this atmospheric phenomenon is dependent on a number of factors, namely geographical location, temperature gradients, frictional convergence, boundary layer mean flow, and amplitude

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Conclusion