2A.3
Surface gravity wave measurements in Hurricanes Fabian (2003) and Humberto (2001)
Edward J. Walsh, NASA/GSFC, Wallops Island, VA; and C. W. Wright, D. C. Vandemark, S. E. Feuer, P. Black, and F. D. Marks
The NASA Scanning Radar Altimeter (SRA) carried aboard a NOAA WP-3D hurricane research aircraft measured the surface gravity wave field on consecutive days in Hurricane Fabian during the Coupled Boundary Layer Air Sea Transfer (CBLAST) experiment and Hurricane Humberto during the Coordinated Observations of Vortex Evolution and Structure (COVES) experiment. The basic survey flight pattern is flown at 1500 m altitude and consists of two passes through the eye at right angles to each other, connected by a downwind leg that causes the three legs to resemble the figure 4. A second figure 4 is generally executed, shifted by 45o so the radials through the eye have 45o azimuthal separation.
Some specialized flight patterns are also predetermined each year before the start of the field program. The COVES pattern for the Hurricane Humberto flights on 23 and 24 September 2001 was drawn up to get three coordinated passes through the eye by the two NOAA WP-3D hurricane research aircraft with legs separated by 60o azimuthal intervals. The geographic orientation of the patterns was the same on both days. The initial pass through the eye for the aircraft carrying the SRA was toward the north, the second pass was toward 120o, and third pass was toward 240o. The plan view of the three eye passes and the connecting legs resembles a butterfly. The other WP-3D aircraft also flew a butterfly pattern, but with the geographic orientation of the legs shifted azimuthally by 30o and at a different altitude. The coverage appears excellent, but the track of Humberto changed 30o between the flights. Two SRA flight legs straddled the maximum wave height region on the first flight while one of them passed through it on the second. This made an assessment of the directional wave spectrum changes caused by wind field changes between the flights more difficult.
The Hurricane Fabian flights on 3 and 4 September 2003 were more localized and focused on stepped descent flight patterns between rain bands to get flux measurements and spray droplet size distributions at six heights that could then be extrapolated to the surface at two different wind speeds and three quadrants. The SRA provided detailed wave information along the flight tracks but the patterns limited its ability to describe the general wave field distribution in the vicinity of the storm. These data suggest the great benefit of using a numerical wave model in conjunction with observations. Even the relatively sparse observations in Hurricane Fabian were sufficient to verify the output of a numerical wave model that could then provide information on the wave field everywhere.
.Session 2A, CBLAST II
Monday, 3 May 2004, 10:45 AM-12:00 PM, Le Jardin Room
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