Dual-Doppler analysis of shear features within a convective rainband of Hurricane Frances (2004)

Dual-Doppler analysis of shear features within a convective rainband of Hurricane Frances (2004)

Scott Gunter and John Schroeder

Texas Tech University

Lubbock Severe Weather Conference

February 17, 2010

Research Objectives

A robust dataset was collected as Hurricane Frances made landfall on the eastern coast of Florida on 5 September 2004. This dataset included dual-Doppler coverage of a convective cell in an outer rainband. Using this dataset, the objectives of this research are:

1. To characterize the kinematic structure of the convective cell and compare it to current conceptual models.

2. Examine changes in the kinematic structure of the convective cell as it crosses the coastline.

Conceptual Models/Previous Research

Powell (1990)

Hence and Houze (2008)

Hurricane Frances (2004)

Hurricane Frances SMART-R Deployment

• SR-1 deployed at Merritt Island Regional Airport

• SR-2 deployed at the Space Coast Regional Airport in Titusville.

• Both radars sampled the northern portions of Frances, including the convective outer rainband.

• Several shear features are evident

Shear Features 1 and 2

Shear Feature 3 from the Melbourne, FL, WSR-88D

Shear Feature 3

Data Processing

• Radar data were processed through REORDER and CEDRIC resulting in 35 x 20 x 2.2 km grids of reflectivity, velocity, and horizontal convergence with 100 m spatial resolution.

• Two radar volumes were processed: • When the convective cell was immediately off shore • When the convective cell was immediately on shore

• Roughly 5 minutes elapsed between radar volumes

Preliminary Analysis Summary

Preliminary analysis shows:

• The convective cell compares nicely with conceptual models: convergence on inside of convection and speed max on outside

• The convective cell seems to straddle the shear feature • The shear feature most pronounced at the lowest levels

(especially the speed minimum) • Horizontal convergence decreases substantially with height • Horizontal convergence also decreases as the cell makes

landfall

Next Steps…

• Compute vertical velocity and vorticity for both volumes.

• Construct vertical slices to evaluate dBz structure and kinematic properties

• Compare with WSR-88D

References

Hence, D.A. and R.A> Houze Jr., 2008: Kinematic structure of convective-scale elements in the rainbands of Hurricanes Katrina and Rita (2005). Journal of Geophysical Research, 113, D15108, doi:10.1029/2007JD009429.

Powell, M.D., 1990a: Boundary layer structure and dynamics in outer hurricane rainbands. Part I: Mesoscale rainfall and kinematic structure. Monthly Weather Review , 118, 891-917.