Extended Abstract (500K)14D.6
Low-level Kinematic, Thermodynamic, and Reflectivity Fields of Hurricane Bonnie (1998) near Landfall
Rebecca Schneider, University of Hawaii at Manoa, Honolulu, HI; and G. Barnes and P. Dodge
Eighty-five dropwindsondes were deployed from two NOAA WP-3d aircraft over nearly twelve hours on August 26th, 1998, prior to Hurricane Bonnie’s (965 hPa) landfall. The dropwindsondes are used to establish storm-relative composites of tangential and radial winds as well as temperature, humidity and equivalent potential temperature at various horizontal levels from 10 m to 2 km. We believe that this is the first time that such fields have been produced without having to resort to the reduction of aircraft data from higher altitudes. The dropwindsondes extend to a radius of 250 km from the storm center. Aircraft radar as well as the WSR-88Ds at Morehead City and Wilmington, North Carolina provide reflectivity fields.
The low-level kinematic, thermodynamic, and reflectivity fields are examined to determine if the hurricane is affected by the proximity of land. Bonnie’s low-level radial flow is asymmetric, with outflow to the northeast of storm center and strong inflow to the southwest. Temperature is not isothermal in the inflow, verifying the earlier statistical approaches that used buoy and ODW data. Instead, there is a cool annulus collocated with convective bands and the eyewall, and a cool wake to the right rear of the hurricane. The specific humidity field at low levels is asymmetric with drier air to the southwest; highest values are in the eye of the hurricane. Equivalent potential temperature varies considerably near the radius of maximum winds with values nearly 8 K lower on the south side of the hurricane. Preliminary results indicate asymmetries exist in both thermodynamics and kinematics but are limited to the lower levels and fade by 2 km. Reflectivity fields change little in the onshore flow, yet a suppression of high reflectivity is evident at greater radii from storm center in the offshore flow.
Many different causes may be responsible for producing asymmetries in a hurricane. We will use the kinematic, thermodynamic, and reflectivity fields to infer that Bonnie’s asymmetries are heavily influenced by the proximity of land.
Session 14D, Tropical cyclones at landfall III
Thursday, 6 May 2004, 1:30 PM-3:00 PM, Napoleon III Room
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