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An Expanded Dataset of Hurricane Eyewall Sizes and Slopes

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  • 1 National Center for Atmospheric Research, Boulder, Colorado
  • 2 Lawrence University, Appleton, Wisconsin
  • 3 Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida
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Abstract

Using airborne Doppler radar data from 39 flights into hurricanes from 2004 to 2010, the authors examine the outward slope of the eyewall, revisiting the recent studies of Stern and Nolan. The slope of the radius of maximum winds (RMW) is found to increase nearly linearly with size and is uncorrelated with intensity. The slope of the eyewall absolute angular momentum surface M increases with increasing size (strong correlation) and decreases with increasing intensity (weak to moderate correlation). Two other measures of eyewall slope are also investigated: the 20-dBZ reflectivity isosurface (dBZ20) and the radius of maximum azimuthal-mean updraft (RWMAX). The slopes of both dBZ20 and RWMAX increase with their size. The slope of dBZ20 decreases with intensity, though the correlation is weak, while the slope of RWMAX is uncorrelated with intensity. The absolute angular momentum decreases on average along the RMW by 9% from 2- to 8-km heights. With this larger dataset, the previous results are generally confirmed: the slope of the eyewall is mostly a function of the size of the RMW.

The vertical decay rate of the maximum tangential winds (Vmax) is also reexamined. On average, Vmax decreases by 20% from 2- to 8-km heights, but this varies from 8% to as large as 42%. This percentage decay rate increases with increasing size and decreases with increasing intensity. Three cases are found where Vmax increases with height from 2 to 4 km, which is likely a consequence of unbalanced flow.

Corresponding author address: Daniel P. Stern, National Center for Atmospheric Research, 3450 Mitchell Lane, Boulder, CO 80301. E-mail: dstern@ucar.edu

Abstract

Using airborne Doppler radar data from 39 flights into hurricanes from 2004 to 2010, the authors examine the outward slope of the eyewall, revisiting the recent studies of Stern and Nolan. The slope of the radius of maximum winds (RMW) is found to increase nearly linearly with size and is uncorrelated with intensity. The slope of the eyewall absolute angular momentum surface M increases with increasing size (strong correlation) and decreases with increasing intensity (weak to moderate correlation). Two other measures of eyewall slope are also investigated: the 20-dBZ reflectivity isosurface (dBZ20) and the radius of maximum azimuthal-mean updraft (RWMAX). The slopes of both dBZ20 and RWMAX increase with their size. The slope of dBZ20 decreases with intensity, though the correlation is weak, while the slope of RWMAX is uncorrelated with intensity. The absolute angular momentum decreases on average along the RMW by 9% from 2- to 8-km heights. With this larger dataset, the previous results are generally confirmed: the slope of the eyewall is mostly a function of the size of the RMW.

The vertical decay rate of the maximum tangential winds (Vmax) is also reexamined. On average, Vmax decreases by 20% from 2- to 8-km heights, but this varies from 8% to as large as 42%. This percentage decay rate increases with increasing size and decreases with increasing intensity. Three cases are found where Vmax increases with height from 2 to 4 km, which is likely a consequence of unbalanced flow.

Corresponding author address: Daniel P. Stern, National Center for Atmospheric Research, 3450 Mitchell Lane, Boulder, CO 80301. E-mail: dstern@ucar.edu
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