Abstract
This study investigates the asymmetric distribution of hurricane boundary layer height scales in a storm-motion-relative framework using global positioning system (GPS) dropsonde observations. Data from a total of 1916 dropsondes collected within four times the radius of maximum wind speed of 37 named hurricanes over the Atlantic basin from 1998 to 2015 are analyzed in the composite framework. Motion-relative quadrant mean composite analyses show that both the kinematic and thermodynamic boundary layer height scales tend to increase with increasing radius in all four motion-relative quadrants. It is also found that the thermodynamic mixed layer depth and height of maximum tangential wind speed are within the inflow layer in all motion-relative quadrants. The inflow layer depth and height of the maximum tangential wind are both found to be deeper in the two front quadrants, and they are largest in the right-front quadrant. The difference in the thermodynamic mixed layer depth between the front and back quadrants is smaller than that in the kinematic boundary layer height. The thermodynamic mixed layer is shallowest in the right-rear quadrant, which may be due to the cold wake phenomena. The boundary layer height derived using the critical Richardson number ( R i c ) method shows a similar front-back asymmetry as the kinematic boundary layer height.
Highlights
The atmospheric boundary layer (ABL) is the turbulent layer close to the Earth’s surface that is influenced by surface friction
The ABL plays an important role in the energy transport processes related to hurricane intensification and maximum intensity [32,55,56,57,58,59,60] and it is essential to understand the ABL structure
The results show a clear departure between thermodynamic and kinematic boundary layer heights with the thermodynamic boundary layer height much shallower than the kinematic boundary layer height
Summary
The atmospheric boundary layer (ABL) is the turbulent layer close to the Earth’s surface that is influenced by surface friction. The top of the ABL (i.e., the boundary layer height) is a key parameter that determines the vertical distribution of turbulent mixing in numerical models that require a boundary layer parameterization. In numerical models where turbulent fluxes are parameterized using a first-order K-profile method, the boundary layer height is usually defined as the height at which the bulk Richardson number (Ric ) reaches a threshold (typically 0.25), where Ric is defined as the ratio of buoyancy to shear forcing [1,2,3]. Richardson number method was previously used in observational studies to determine the boundary layer height in non-hurricane conditions [4,5,6,7,8].
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