NOAA-NESDIS
Regional And Mesoscale Meteorology Team
Daily Satellite Discussion
Monday June 8, 1998
Today's discussion demonstrates the utility of the 85 GHz channel aboard the SSMI spacecraft in observing tropical cyclones. The focus of the discussion is tropical cyclone 3A, which is located in the Arabian Sea. TC-03A was located at 19.7 N, 67.7 E and is forecast to maintain its intensity close to 95 knots as it moves north toward the India-Pakastan border (see Fig 1).
Fig. 1 (Forecast Track provided by Joint Typhoon Warning Center, Guam)

click picture to enlarge

Last Friday (June 5th) the tropical cyclone was located at approximately 12 N and 70 E as shown by the Meteosat 6 satellite at 21 UTC in Fig. 2. The image is unfortunately at the limb and shows reduced spatial resolution as a result. Luckily, NOAA-14 also made a pass at approximately 10Z with 1km resolution in the IR (see Fig 3). This image has been remapped to the same Mercator projection as Fig. 2 producing a wonderfully detailed image (4kmX4km for comparison).

Figure 2
Fig. 2 (Meteosat 6 IR June 5, 1998 21 UTC)
(click to enlarge)
Figure 3
Fig. 3 (NOAA-14 AVHRR LAC IR image, June 5, 1998 10 UTC, 1 km resolution)
(click to enlarge)

As can be seen by these images the storm appears sheared from the east-northeast, resulting in a difficult center fix. Images from the Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave Imager (SSMI) 85 GHz channel, however, can help place the center by seeing through the cirrus in the deep Central Dense Overcast (CDO) area revealing the characteristic spiral banded structure of a mature tropical cyclone. A 4-km remapped SSMI image that roughly matches Figures 2 and 3, is shown in Fig. 4. Note the clear spiral banding and the easily identifiable center.
Fig. 4 (DMSP SSMI 85 GHz channel, June 5, 1998 20 UTC)

click picture to enlarge


Figures 5 and 6, 3 days later, also show the same east-northeast shear and very deep convection obscuring the center of TC-03A, yet again the 85GHz channel shows the center located to the east edge of the CDO. It is clear that the SSMI instrument is very useful in identifying the center of tropical cyclones, which have their centers, obscured by deep convection.

John Knaff
Figure 6
Fig. 5 (Meteosat 6 IR June 8, 1998 12 UTC)
(click to enlarge)
Figure 5
Fig. 6 (DMSP SSMI 85 GHz channel, June 8, 1998 16 UTC)
(click to enlarge)

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