Tropical cyclone precipitation and microphysics

Team Leader 
Robert Rogers (NOAA/HRD)<br>

Team Members 
Michael Black (NOAA/HRD)<br>
Robert Black (NOAA/HRD)<br>
Frank Marks (NOAA/HRD)<br>
Krystal Valde (UM/CIMAS)<br>
Paul Willis (UM/CIMAS)<br>

Collaborators
Shuyi Chen (UM/RSMAS)<br>
Andy Heymsfield (NCAR)<br>
Gerry Heymsfield (NASA/GSFC)<br>
Manuel Lonfat (RMS, Inc.)<br>
Tim Marchok (NOAA/GFDL)<br>

Objective<br>
	Work on this topic is multi-faceted.  The overarching focus is to 
improve the understanding of precipitation and microphysical processes in 
tropical cyclones, including their spatial and temporal variation and 
evolution as a function of storm structure and intensity.  An important goal 
arising from these efforts is the improvement of the representation of these 
processes in high-resolution numerical models.  A variety of datasets are 
being used to address these objectives, specifically airborne radar 
measurements of reflectivity and winds, in situ cloud probe measurements, 
spaceborne measurements of reflectivity from the TRMM Precipitation Radar 
(PR), and high-resolution numerical model simulations.  Specific projects and 
accomplishments are listed below.
<p>
Accomplishments
<ul>
<li> A study is progressing that focuses on the evolution of the structure of 
precipitation in observations and a high-resolution (1.67 km) MM5 simulation 
of Hurricane Dennis (2005).  The evolution of the statistics of the 
precipitation and microphysics fields, including vertical motion, reflectivity,
and hydrometeor concentrations, and the vortex dynamical and thermodynamical 
fields, including vorticity, divergence, and equivalent potential temperature, 
are being compared in the convective and stratiform areas of the storm.  The 
evolution of these variables as the storm progresses through its lifecycle may 
provide some insight on the factors important in tropical cyclone structure 
and intensity change. 
<p>
<li> A multi-year, multi-basin database of TRMM PR measurements is being used 
to study the variation of reflectivity profiles as a function of storm 
lifecycle stage.  This database is being stratified into different stages of a 
storm's lifecycle: pre-depression, depression, tropical storm, and hurricane.  
<p>
<li> The TRMM PR data is also being used to determine if there are any 
systematic differences in the reflectivity profiles in the convective and 
stratiform regions of convective bursts in Atlantic tropical cyclones that 
undergo rapid intensification (RI) and those that experience a convective 
burst but do not undergo RI.  Preliminary comparisons do show some minor 
differences in the reflectivity profiles in high altitudes (8-12 km) for 
RI vs. non-RI cases, though those differences are not as large as differences 
in vertical shear and the proximity of the burst to the storm center.  
<p>
<li> Work has recently been completed that compares the statistics of 
microphysics fields from observations (airborne Doppler radar and cloud physics
probe measurements) and simulations (1.67-km MM5 simulations) of mature 
hurricanes.  Several notable biases were documented in the simulations, such 
as a distinct high bias in reflectivity, a low bias in vertical motion, and an
anomalously high correlation between vertical motion and reflectivity in the 
simulations.  These biases may point to deficiencies in the microphysical or 
planetary boundary layer parameterizations, or insufficient horizontal or 
vertical resolution.  
<p>
<li> Work has also been completed that evaluates operational numerical model 
forecasts of tropical cyclone rainfall as compared with gage-corrected radar 
observations over the United States.  New validation algorithms were developed 
that account for the unique aspects of tropical cyclone rainfall, e.g., closely
tied to track, wide range in rainfall amounts.  Several biases in the 
operational models were documented which will be of use for the forecasting 
community.  
<p>
<li> A parametric model for predicting hurricane rainfall has been developed 
that accounts for vertical shear and topography.  This model is significantly 
improved over the baseline statistical model.  
</ul>
<p>
Milestones
<ul>
<li> Comparisons between the simulated and observed microphysics fields in 
Hurricane Dennis will be continued.
<p>
<li> Statistics of the reflectivity profiles from TRMM PR will be calculated 
at different storm lifecycle stages, partitioned into convective and stratiform
regions.  They will be evaluated to see if there are any systematic differences
in the microphysical structures of the tropical cyclones at these different 
stages.
<p>
<li> Continue work on the RI vs. non-RI databases with TRMM PR data.  Consider 
new ways of stratifying dataset, expanding dataset to other basins and looking 
at other parameters like SST and low-level relative humidity.
<p>
<li> Run tests using varying horizontal and vertical resolutions and changes 
to the microphysical and PBL parameterization schemes of MM5 to determine the 
sensitivity of the statistics of the microphysics fields of mature storm 
simulations to these variations.  Continue this work with HWRF.
<p>
<li> Continue development of parametric rainfall model by adding the impact of 
extratropical transition and developing ensemble-based techniques for 
generating tropical cyclone rainfall guidance.
</ul>
Publications
<p>

Rogers, R.F., M.L. Black, S.S. Chen, and R.A. Black, 2007: An Evaluation of 
Microphysics Fields from Mesoscale Model Simulations of Tropical Cyclones.   
Part I: Comparisons with Observations.  <i>Journal of the Atmospheric Sciences
</i>, <b>64</b>, 1811-1834.
<p>
Lonfat, M., R. Rogers, F. Marks, Jr., and T. Marchok, 2007: The Effect of 
Shear and Topography on Rainfall Forecasting with R-CLIPER.  <i>Monthly 
Weather Review</i>, In press.
<p>
Marchok, T., R. Rogers, and R. Tuleya, 2007: Validation Schemes for Tropical 
Cyclone Quantitative Precipitation Forecasts: Evaluation of Operational Models 
for U.S. Landfalling Cases. <i>Weather and Forecasting</i>, <b>22</b>, 726-746.
<p>