Microphysics Modeling Team

Team Leader:	Robert Rogers (NOAA/HRD)

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

Collaborators: 	Shuyi Chen (UM/RSMAS)
			Manuel Lonfat (RMS)

Team Objective:

There are many factors that determine a tropical cyclone's intensity and rainfall, such as the magnitude and direction of vertical shear affecting the storm core, upper oceanic temperature structure, and low- and mid-level environmental relative humidity.  Ultimately, though, intensity and rainfall are dependent on the magnitude and distribution of the release of latent heat within the core of the storm.  High-resolution (grid length ( 1 km) numerical models have been used as a tool to investigate the processes important in determining tropical cyclone intensity and rainfall.  Such high resolution obviates the need for the parameterization of deep convection, a traditional source of uncertainty in determining latent heating profiles.  While convective parameterization is avoided using high resolution, the parameterization of microphysical processes such as hydrometeor production, conversion, and fallout, is still necessary at this resolution.  The dependence of these microphysical processes on the rainwater, ice and graupel distributions thus assumes great importance in determining latent heating distributions and, ultimately, tropical cyclone intensity and rainfall.  Despite this importance, very little work has been done in performing detailed, rigorous comparisons between models and these observational datasets.  
The efforts of this team are directed toward developing techniques for comparing high-resolution tropical cyclone simulations with observations of microphysics fields from a variety of storms in order to evaluate the ability of the models to reproduce the statistics of the distributions of vertical motion, reflectivity, and hydrometeor mixing ratio seen in the data.  The observations used in the intercomparisons are airborne Doppler radar measurements of reflectivity and vertical motion, airborne microphysical probe measurements of hydrometeor mixing ratio, and spaceborne (NASA TRMM satellite) measurements of reflectivity from numerous storms over several years.  Since convective processes occur on very small temporal and spatial scales, it is quite difficult to have model output and observations at precisely the same location, and at the same time, in the life cycle of any such small-scale feature.  The technique of comparing the statistical properties (e.g., means, standard deviations, probability distribution functions, and correlations) of the distribution of relevant parameters in both the models and the observations obviates the need for a precise temporal and spatial match, and it allows for a more comprehensive and robust evaluation of the microphysical parameterization scheme to be performed. The work of this team provides a comprehensive comparison between high-resolution simulations of tropical cyclones and observations from a variety of storms, in order to provide a more robust measure of the performance of the microphysical scheme in the model and identify possible areas for improvement.


Accomplishments:

* Compiled statistics and performed comparisons from high-resolution simulations and observational databases;
* Identified differences between the two databases (e.g., differences in profiles of mean vertical motion and reflectivity, distributions of vertical motions and reflectivity, and correlations between vertical motion and hydrometeor mixing ratio/reflectivity);
* Suggested areas of microphysical parameterization scheme to target to improve reproduction of variables in simulations;
* Performed some sensitivity simulations testing impact of different microphysics parameters (e.g., graupel intercept parameter, graupel fall speed) and different microphysical parameterization schemes.


Milestones:

* Continue sensitivity simulations testing impacts of planetary boundary layer parameterization and horizontal and vertical resolution on the simulated fields of vertical motion, reflectivity, and hydrometeor mixing ratio and compare results using same evaluation framework;
* Stratify simulations and airborne Doppler radar fields into eyewall and stratiform regions using reflectivity only (in a manner similar to what was done using TRMM data);
* Revise manuscript describing comparisons between simulations and airborne data, resubmit to Journal of the Atmospheric Sciences.