P2.4 REMOTE SENSING OF MICROPHYSICAL PARTICLES IN HURRICANES FROM AIRCRAFT OBSERVATIONS Cerese M. Albers and Dr. Gail Skofronick-Jackson Florida State University, Tallahassee, FL and NASA Goddard Space Flight Center Code 970 Remote Sensing Branch, Greenbelt, MD I. Abstract This observed data will be helpful in In an effort to better understand the understanding whether the model slice is number concentration characteristics and particle appropriate and if the accompanying size distributions of frozen hydrometeors in parameterization is useful for these types of hurricanes, brightness temperatures were hydrometeors. There is a correlation between high compared with observations of Hurricane Erin frequencies (>= 85 GHz) and the accurate (2001) from CAMEX-4 radiometers on the ER-2 detection of frozen particles’ radiative signatures in aircraft. Frozen hydrometeors and hurricane storms. Higher frequencies are particularly sensitive particle microphysics play a large role in the to the frozen hydrometeors, and finding a multi- development and strength of tropical cyclones frequency retrieval algorithm for ice particle through the convective processes in the rain bands characteristics is the goal. present. Previous studies have proven that it is difficult to select proper ice particle parameterizations and that in situ measurements and additional studies are key to defining appropriate parameterizations. II. Introduction The observations from the Fourth Scientists often seek to refine their Convection and Moisture Experiment (CAMEX-4) observations to obtain more precise measurements and ER-2 Doppler reflectivities were co-located with of their desired distributions. In a time when the brightness temperatures from the High Altitude remote sensing of microphysical particles from MIMC Sounding Radiometer (HAMSR) and the aircraft and satellite has become increasingly Advanced Precipitation Microwave Radiometer (see important this is certainly a priority. The applications figure 2). In order to obtain atmospheric profile of this important and relatively new field include information for radiative transfer calculations along better prediction of storm development and the flight line of interest, supporting temperature, severity. By studying in situ satellite and aircraft relative humidity, and wind speeds were obtained measurements, analyzing them, and comparing from a Mesoscale Model-5 (MM5) simulation of them at different frequencies to known radar data, Hurricane Erin. Of 250 slices of simulated data in we seek to find the optimal operational frequencies each direction, one ideal slice needed to be at which the best data of different hydrometeors selected for use with the observed flight line. The can be obtained. While much is known about observations had a definitive eye, several rainfall distributions and optimum frequencies for convective rain bands, and anvil ice clouds. The detection in hurricanes and tropical convective slice of data that proved to be ideal was number storms, much remains to be discovered about the 123 in the i-direction, and is taken at the latitudes frozen particle distributions in them. between 32.0 to 33.2 degrees north, and the A recent attempt to discover the best longitude of -64.7879 degrees. The maximum manner in which to proceed with observing the ice altitude of the data slice was 15 km, and the particles was conducted as part of the Fourth simulated temperature, relative humidity, density of Convection and Moisture Experiment (CAMEX-4 cloud ice, density of graupel, density of cloud water, experiment). density of rain water, and density of snow profiles The objectives proposed by the CAMEX-4 were extracted. experiment were to investigate a combined analysis Bilinear interpolation was used to convert of both active radar and wideband passive the model data in 250 points with a resolution of microwave brightness temperature measurements 2km to 200 points with a resolution of 2.5km in (from 10 to 183 GHz) measured from heavily order to match the observed data for purposes of precipitating storm clouds around hurricanes comparison. acquired from the ER-2 (see the flight path in figure *Corresponding author address: Cerese M. Albers, 1). Other CAMEX-4 sensors provided a rich set of 1242 Minerva Ave. West Islip, NY 11795 collaborating data with concurrent DC-8, in situ (631) 398-4112; email: [email protected] particle probe measurements, and ground based observations. This study and analysis enhanced the understanding of cloud dynamics, electrification, layers (see figures 18 and 19). The amount of and microphysics, providing insight for cloud scattered radiation for a given layer (if the incident resolving models, and improving rain rate radiation intensity is known) is a function of the rain estimations. The specific objectives of the research and ice particles within that layer. These particles were: (1) To estimate the vertical distribution of scatter, absorb, and emit radiation, and multiple microphysical cloud parameters (e.g., content, size scattering can also occur. Please refer to figure 17 distribution, shape and phase of the cloud particles for an illustration of this process and how the and hydrometeors) in precipitating clouds by Eddington approximation lends itself to this minimizing the difference between forward active detection. and passive calculations based on the estimated profile observations from primarily the CoSMIR, IV. Case Study: Hurricane Erin AMPR, NAST-MTS, and EDOP instruments on the One particular event that was studied in ER-2 aircraft. (2) To investigate active and high this summer’s research was Hurricane Erin, which frequency (greater than 90 GHz) passive began as a tropical depression on 7 September microwave observations in order to better define 2001 and rapidly intensified into a well-developed the high altitude ice microphysics and its hurricane by 8 September 2001, maintaining its relationship to cloud electrification. (3) To determine intensity off the east coast of the United States on the impact of low versus high frequency microwave 10 September 2001. When Erin’s intensification measurements on retrievals, Skofronick-Jackson finally waned, it was 0000 UTC 15 September (2000). 2001, and it transitioned from a tropical storm into an extratropical system. The case study of this Observations from the ER-2 Doppler storm provides us with a unique opportunity to (EDOP) reflectivities co-located with brightness study the well-organized structure and distribution temperatures from the High Altitude MIMC of the hydrometeors present in the storm and to Sounding Radiometer (HAMSR) and the Advanced experiment with figuring out which parameters and Precipitation Microwave Radiometer (AMPR) were frequencies serve to give us the best view of our used to create horizontal plots of relative humidity desired particles. along the flight path at 6 different altitudes as Taking data from the flights made through derived from a combination of 3 CAMEX-4 ER-2 the hurricane by the ER-2 plane, we can make dropsondes and MM5 model results from a slices that give us information about the Hurricane Andrew case study. It was found that the precipitation profile. This was accomplished utilizing previous form of the Eddington Forward Radiative IDL, the Interactive Data Language program. By transfer (FRT) model succeeded relatively well in creating routines that cut the data into slices, modeling liquid hydrometeors, but it did not do as exploration of 250 slices in both the i and j well modeling the ice phase microphysics (high directions was possible. Then the parameters for frequencies, i.e. the 183+/- 10 GHz channel). As a which type of hydrometeor was to be examined result, we persist in our quest to discover which were included. The output data was then assigned frequencies and equipment give us the best and a location from which these thousands of slices most accurate interpretation of the location, size could be viewed and compared. The optimal slices distribution and type of frozen hydrometeors that consisted of those which included a clear view of exist in hurricanes, blizzards and tropical the precipitation in Hurricane Erin’s eye, strong convective storms. This particular research makes regions of convection and anvil ice. The plots were use of a specific radiative transfer model named the accomplished using a scale of reflectivity which Eddington Radiative Transfer Model, which we will plotted the longitude or latitude on the abscissa use our computed model data will validate. versus the altitude of the precipitation detected in the slice on the ordinate in kilometers. The set III. The Eddington Radiative Transfer Model height of the slices was predetermined to be up to The Eddington Radiative Transfer Model is about 16 kilometers. Once an optimal slice for the a method of modeling radiative intensity in the desired parameters was achieved (see Fig. 1) the atmosphere as would be observed by a radiometer. data was analyzed. This can be found at the The radiometer measures brightness temperatures location “C:\Documents and Settings\Student\My and is attached to an aircraft, an ER-2 in this case. Documents\Cerese 2004\Final Presentation Brightness temperatures are a measure of the Stuff\New Final Presentation Output.” Overhead electromagnetic radiation intensity. Radiation precipitation plots were utilized to find the best path intensity is converted to a brightness temperature through which a slice should be taken based on a using Planck's function. Sources of radiation