 |
 |
Regional And Mesoscale Meteorology Team Daily Satellite Discussion Thursday October 9,1997 |
|
|
In today's discussion, the Dvorak digital IR technique is used to
assign T-numbers for intensity estimations. This technique which
follows the approach of Dvorak (1984) has been applied to the digital
IR data from Hurricane Pauline. The algorithm developed by Dvorak
extracts two temperatures from the IR data and relates them to current
intensity. A 55 km circle centered on the eye is used to find the
surrounding temperature. The "surrounding temperature" is defined as
the warmest pixel located on the circle. Intensity increases as the
surrounding temperature decreases. The warmest IR pixel in the eye is
the other temperature, and intensity increases as eye temperature
increases. Dvorak expresses intensity in terms of an index or T-no.
corresponding to typical daily intensity changes. T-no. can be
converted to maximum sustained wind speed and minimum sea-level
pressure (MSLP). Dvorak,V.F. 1984: Tropical Cyclone Intensity Analysis Using Satellite Data. NOAA Tech. Rep. NESDIS 11, 47 pp. | |
 |
|
|
The above graph shows a 6 hour running mean of intensity (T nos.)
using the Dvorak technique. The red line is the T number, considering
a 55 km. radius, and the light blue line is the maximum T number
using multi-radius computations. These values can be converted to
Maximum Surface Wind Speed and Minimum Sea-Level Pressure. For
example, a T-No. of 6.0 corresponds to a 115 kt. hurricane. Notice
the two intensity maxima. Two possible factors which would cause a
fluctuation in intensity are eye wall cycle influences and a slight
increase in vertical wind shear, which would explain weakening. The
accompanying satellite image shows the storm on Oct. 8 when it was at
its maximum T no. (using this technique). For satellite imagery of the latest tropical activtiy, take a look at: RAMM Tropical | |
 |
Carol Vaughn We welcome your comments and discussion at
ramsdis@comet.ucar.edu |
| Information Contact: Jack Dostalek | |
| CIRA/RAMM WebMaster: Roger Phillips | |
| Author: Carol Vaughn | |
| Last Updated: October 9, 1997 |