Airborne Radar Observations of Eye Configuration Changes, Bright Band Distribution, and Precipitation Tilt During the 1969 Multiple Seeding Experiments in Hurricane Debbie

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  • 1 National Hurricane Research Laboratory, Environmental Research Laboratories, NOAA, Miami, Fla.
  • | 2 Radar Meteorology Laboratory, Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Coral Gables, Fla.
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Abstract

Project Stormfury radar precipitation data gathered before, during, and after the multiple seedings of the eyewall region of hurricane Debbie on Aug. 18 and 20, 1969, are used to study changes in the eye configuration, the characteristics of the radar bright band, and the precipitation tilt. Increases in the echo-free area within the eye followed each of the five seedings on the 18th, but followed only one seeding on the 20th. Changes in major axis orientation followed only one seeding on the 18th, but followed each seeding on the 20th. Similar studies conducted recently on unmodified storms suggest that such changes do not occur naturally. However, the studies do not exclude this possibility. Changes in the radius of maximum winds follow closely the changes in eyewall radius. It is suggested that the different results on the 2 days might be attributable to seeding beyond the radius of maximum winds on the 18th and inside the outer radius of maximum winds on the 20th.

The bright band is found in all quadrants of the storm within 100 n.mi. of the eye, sloping slightly upward near the eyewall. The inferred shears are directed outward and slightly down band with height in both layers studied. The hurricane Debbie bright band and precipitation tilt data compared favorably with those gathered in Betsy of 1965 and Beulah and Heidi of 1967.

Abstract

Project Stormfury radar precipitation data gathered before, during, and after the multiple seedings of the eyewall region of hurricane Debbie on Aug. 18 and 20, 1969, are used to study changes in the eye configuration, the characteristics of the radar bright band, and the precipitation tilt. Increases in the echo-free area within the eye followed each of the five seedings on the 18th, but followed only one seeding on the 20th. Changes in major axis orientation followed only one seeding on the 18th, but followed each seeding on the 20th. Similar studies conducted recently on unmodified storms suggest that such changes do not occur naturally. However, the studies do not exclude this possibility. Changes in the radius of maximum winds follow closely the changes in eyewall radius. It is suggested that the different results on the 2 days might be attributable to seeding beyond the radius of maximum winds on the 18th and inside the outer radius of maximum winds on the 20th.

The bright band is found in all quadrants of the storm within 100 n.mi. of the eye, sloping slightly upward near the eyewall. The inferred shears are directed outward and slightly down band with height in both layers studied. The hurricane Debbie bright band and precipitation tilt data compared favorably with those gathered in Betsy of 1965 and Beulah and Heidi of 1967.

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