Azimuthal Variation of L-Band Tilting Roughness Inside Tropical Cyclones

With a wind wave spectrum model and input of surface wind speed and dominant wave period, the L-band lowpass mean square slope (LPMSS) can be calculated. Wind and wave data simultaneously measured in four different hurricane hunter missions are analyzed to study the spatial pattern of LPMSS inside tropical cyclones (TCs). There is a clear azimuthal variation in the LPMSS dependence on wind speed. Dividing the TC coverage area into quarters or halves with reference to the TC heading for the same wind speed, the LPMSS in the back quarter (half) is about 12% higher than that in the front quarter (half) for wind speeds up to about 50 m/s. The LPMSSs of the left and right quarters are between those of the front and back quarters and with much smaller differences. There is indication that the LPMSS wind speed dependence steepens in winds greater than 50 m/s, which occurs more frequently in the right half of the TC coverage area. Including all data available with a maximum wind speed up to 67 m/s, the front/back LPMSS difference is about 20%.