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

Objective Diagnosis of the Eyewall Replacement Cycle in Mature Tropical Cyclones
Elizabeth R. Sanabia and Nicholas P. Celone
(sanabia@usna.edu)
United States Naval Academy
Typhoon Sinlaku underwent an eyewall replacement cycle shortly before making landfall
over Taiwan in September 2008 during the Tropical Cyclone Structure – 2008 (TCS-08) field
program. Eyewall replacement cycles in tropical cyclones are often associated with intensity
fluctuations and increased predictability challenges (Willoughby et al. 1982). Currently,
microwave satellite imagery is an accepted and often effective means by which to detect various
stages in the eyewall replacement cycle; however, the near 12-h temporal resolution and hit-ormiss
spatial sampling of microwave sensors are insufficient to capture the detailed evolution of
the eyewall replacement cycle process, which frequently lasts less than 24 h (Kossin and
Sitkowski 2009).
Here, the eyewall replacement cycle during TY Sinlaku is examined using differences in
water vapor and infrared satellite brightness temperatures from geostationary sensors to detect
deep convection that penetrates the tropopause (Fritz and Laszlo 1993; Olander and Velden
2009). The geostationary data are transformed into a cylindrical grid about the storm center, and
the water vapor – infrared differences are examined over varying radial bands. A new diagnostic
technique is then used to map this deep convection over time. In the case of Typhoon Sinlaku,
the deep convection is mapped during a 72-h period that includes the eyewall replacement cycle
and provides clear evidence of inner eyewall decay as well as outer eyewall development and
subsequent contraction. These results are compared with other satellite data and TCS-08 aircraft
observations, and links between the evolution of deep convection and changes in intensity are
assessed.
The eyewall mapping technique is then extended to other cases to examine the potential
for improving intensity forecast accuracy during eyewall replacement cycles. While diagnostic
in nature, this eyewall mapping technique may be applied on a real-time basis and provide the
forecaster with unique, objective insight regarding the evolution of a tropical cyclone throughout
its lifecycle and be of particular use in the diagnosis of eyewall replacement cycles. The
technique may also provide new insights into the behavior of deep convection and possible
correlation to periods of rapid intensification and rapid decay.
_____________
Fritz, S., and I. Laszlo, 1993: Detection of water vapor in the stratosphere over very high
clouds in the tropics. J. Geophys. Res., 98 (D12), 22,959-22,967.
Kossin, J. P., and M. Sitkowski, 2009: An objective model for identifying secondary
eyewall formation in hurricanes. Mon. Wea. Rev, 137, 876-892.
Olander, T. L. and C. S. Velden, 2009: Tropical cyclone convection and intensity
analysis using differenced infrared and water vapor imagery. Wea. Forecasting,
24, 1558-1572.
Willoughby, H. E., J. A. Clos, and M. G. Shoreibah, 1982: Concentric eye walls, secondary wind
maxima, and the evolution of the hurricane vortex. J. Atmos. Sci., 39, 395–411.
Poster Session – Page 25