65th IHC Booklet/Program (pdf - 4.9MB) - Office of the Federal ...

Improving SHIPS Rapid Intensification (RI) Index Using 37 GHz Microwave Ring Pattern
around the Center of Tropical Cyclones
Haiyan Jiang 1 , Margie Kieper 2 , Tie Yuan 1 , Edward J. Zipser 3 , and John Kaplan 4
(haiyan.jiang@fiu.edu)
1 Department of Earth & Environment, Florida International University
2 Private Consultant; 3 Department of Atmospheric Sciences, University of Utah
4 NOAA/HRD
The physical processes associated with rapid intensification (RI) of tropical cyclones (TCs)
remain unsolved. Predicting these events is one of the most challenging aspects for TC
forecasters. Recently, a robust ring pattern in the inner core area of TCs has been found in the 37
GHz microwave images to be associated with RI. Margie Kieper initiated a subjective forecast
method using the 37 GHz color product developed by the Naval Research Laboratory (NRL) to
predict the onset of RI. She reviewed numerous microwave TC images, and found that a cyan
color ring around the eye could be an early indicator of RI when environmental conditions are
favorable. She tested this method in real time for the 2008 hurricane season in the Atlantic
(ATL) and 2009-2010 hurricane seasons for both ATL and East Pacific (EPA) basins in
conjunction with the SHIPS RI index. The result was very encouraging. So it will be optimal to
translate this subjective forecast method into an objective one for wider forecast applications.
However, the NRL 37color product is constructed by using 37 GHz vertically polarized
(V37) and horizontally polarized (H37) brightness temperatures, and polarization correction
temperature (PCT37). V37 and H37 are sensitive to sea surface (cold) and low-level clouds/rain
(warm), while PCT37 is sensitive to convection (cold). The product implements a red/green/blue
color composite from PCT37, H37 and V37 so that the sea surface in the color product appears
green, deep convection appears pink, and low-level water clouds and rain appear cyan. Although
this product provides unique qualitative information, quantitative information is sacrificed. It has
been a mystery for the TC community what the cyan color truly represents. This hinders us from
translating Margie Kieper’s eye-based subjective method into an objective and automatic
prediction method.
In this study, we discovered the mystery by determining quantitative values for the cyan
color region in the NRL 37 GHz color product using a 12-yr Tropical Rainfall Measurement
Mission (TRMM) tropical cyclone precipitation feature database. Based on these findings, an
objective 37 GHz ring pattern RI index is developed by strictly following Margie Kieper’s ring
pattern identification and forecasting methodology. Evaluation of the index has been done by
using the TRMM Microwave Imager (TMI) observations of TCs in the ATL and EPA basins
from 2002 to 2009. It is found that the 37 GHz ring pattern RI index is an independent predictor
relative to the SHIPS RI index. By adding this ring pattern index to the SHIPS RI index, the skill
score of the new combined indices can be as high as 55% for the ATL basin and 75% for the
EPA basin for RI threshold at 25-kt intensity increase during 24 hours.
Session 11 – Page 5