Factors Affecting the Evolution of Hurricane Erin (2001) and the Distributions of Hydrometeors: Role of Microphysical Processes Ϩ GREG M
JANUARY 2006 M CFARQUHAR ET AL. 127 Factors Affecting the Evolution of Hurricane Erin (2001) and the Distributions of Hydrometeors: Role of Microphysical Processes ϩ GREG M. MCFARQUHAR,* HENIAN ZHANG,* GERALD HEYMSFIELD, ROBBIE HOOD,# JIMY DUDHIA,@ ϩ JEFFREY B. HALVERSON, AND FRANK MARKS JR.& *Department of Atmospheric Sciences, University of Illinois at Urbana–Champaign, Urbana, Illinois ϩNASA Goddard Space Flight Center, Greenbelt, Maryland #NASA Marshall Space Flight Center, Huntsville, Alabama @National Center for Atmospheric Research, Boulder, Colorado &NOAA/Hurricane Research Division, Miami, Florida (Manuscript received 11 November 2003, in final form 8 March 2005) ABSTRACT Fine-resolution simulations of Hurricane Erin are conducted using the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) to investigate roles of thermodynamic, boundary layer, and microphysical processes on Erin’s structure and evolution. Choice of boundary layer scheme has the biggest impact on simulations, with the minimum surface pressure (Pmin) averaged over the last 18 h (when Erin is relatively mature) varying by over 20 hPa. Over the same period, coefficients used to describe graupel fall speeds (Vg) affect Pmin by up to 7 hPa, almost equivalent to the maximum 9-hPa difference between microphysical parameterization schemes; faster Vg and schemes with more hydrometeor categories generally give lower Pmin. Compared to radar reflectivity factor (Z) observed by the NOAA P-3 lower fuselage radar and the NASA ER-2 Doppler radar (EDOP) in Erin, all simulations overpredict the nor- malized frequency of occurrence of Z larger than 40 dBZ and underpredict that between 20 and 40 dBZ near the surface; simulations overpredict Z larger than 25 to 30 dBZ and underpredict that between 15 and 25 or 30 dBZ near the melting layer, the upper limit depending on altitude.
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