Passive Measurements of Rain Rate in Hurricanes Ruba A.Amarin CFRSL December 10, 2005

Presentation Outline Objectives Approach RTM-Rain Rate Model Hurricane Katrina Rain Model Comparisons 2D Plots / Hurricane Floyd Summary

Objectives Develop radiative transfer modeling (RTM) and retrieval capability for Rain Rate measurements in hurricanes for upgrading RadTb for aircraft platforms and space.

Approach Uses the new operational (AOC) Stepped Frequency Microwave Radiometer (SFMR) measurements in hurricanes Katrina & Rita to develop and validate RTM Conduct HIRad simulations using hurricane Floyd surface wind and rain rate maps after including the wide swath wind speed model into the RTM

SFMR Algorithm Attenuation Due To Rain Rain Rate Model Absorption Coefficient, where R is Rain Rate and,

Transmissivity At High Rain Rates Relationship between Transmissivity & Absorption Coefficient at Nadir Transmissivity for 5.5 km altitudeTransmissivity at 4 GHz

Typical SFMR Wind Speed and Rain Rate Measurements in Hurricane Georges Uhlhorn and Black, 2003

Multi-frequency SFMR Tb Measurements in Hurricane Georges Uhlhorn & Black 2003

The composite hurricane atmosphere in W. Frank (1977) at 0.7 degrees from the eye shows a freezing height of approximately 5 km, which was used to define the upper altitude for rain absorption and the height of the cloud tops. Hurricane Atmosphere

Figure represents the atmospheric temperature profile for the W. Frank hurricane with a lapse rate of – 4.8 and a surface temperature of approximately 26 deg C. Hurricane Atmosphere

Exponential approximation to water vapor density profile for surface value of 23 gm/m^3 and scale height of 3.5 km

The columnar density of cloud liquid water is also required as an input to RadTb. Using the Remote Sensing Systems website, the value to use, for particular hurricane can be found. For Katrina, the columnar cloud liquid water was approximately 1.7 – 2.0 mm. (which converts to a range of 0.17 gm/cm^2 (ie. 1.7 / 10) to 0.2 gm/cm^2 for use as input to RadTb. The cloud depth assumed for now is 300 m to 6 km) Hurricane Atmosphere

Hurricane Katrina / 2 nd Pass Time vs Tbs

Hurricane Katrina Flight Path 2 nd Pass

Retrievals from Hurricane Katrina August 28, nd Pass

Hurricane Floyd Wind Speed Zoomed High Spatial Resolution Noise Added

Hurricane Floyd WS 2D Histograms High ResolutionWith Noise

Hurricane Floyd WS FFT Without NoiseWith Noise

Hurricane Floyd Rain Rate Zoomed High Spatial Resolution Noise Added

Hurricane Floyd WS 2D Histogram Plots With NoiseHigh Resolution

Future Work Complete retrievals for Fabian, Frances, Rita and Katrina. Study rain retrieval sensitivity to the rain model coefficient term. Include off-nadir, wide swath wind speed algorithm into RTM and complete parametric studies and the 2D, HI-Rad simulations.

Summary Developed MATLAB RTM program that includes SFMR rain absorption model. Observed low transmissivity at higher altitudes and larger incidence angles in parametric studies. Comparisons with SFMR WS & RR retrievals showed excellent results. Began HIRad simulations using Hurricane Floyd (Sep. 13 th,1999) with max winds of 135 knots.