Estimating Tropical Cyclone Intensity Using the SSMIS and ATMS Sounders

This poster will present results of a new algorithm to estimate Tropical Cyclone (TC) Minimum Sea Level Pressure (MSLP) and Maximum Sustained Winds (MSW) using the Special Sensor Microwave Imager/Sounder (SSMIS) and the Advanced Technology Microwave Sounder (ATMS). These algorithms are tailored after the CIMSS Advanced Microwave Sounding Unit (AMSU) algorithm.

Microwave sounders operating in the 53-55 Ghz frequency range are transparent to cloud cover and allow the mapping of the TC warm core in the 350-100 mb layer. A robust relationship exists between the brightness temperature (Tb) anomalies measured by the satellite in this layer and aircraft-measured MSLP anomalies. AMSU-based algorithms developed by both CIMSS and CIRA have been used by warning agencies around the world since 2006 as part of a suite of current intensity estimates.

The SSMIS sounder has a resolution of 37.5 km in channels 3-5. This is a significant improvement over AMSU which as a resolution of 48 km at nadir increasing to greater than 70 km near the limb for the same frequencies. In addition the conical scanning strategy employed by SSMIS results in a resolution that does not change across the scan swath the way AMSU's cross-track scanning method does. Good coverage is currently provided by three SSMIS satellites (F-16, F17 and F18). Initial testing of the SSMIS intensity algorithm using dependent data from 2006-2010 (N=190) suggests the intensity method is as skillful as the CIMSS AMSU and ADT methods. Results from this initial analysis along with comparisons to existing sounder-based methods will be presented.

NPP represents the next generation of polar orbiting satellites and was launched in October of 2011. ATMS flown on NPP is the latest microwave temperature/moisture sounder. Like SSMIS this instrument represents an improvement over the previous generation AMSU sounder. Higher resolution and a larger scan swath will result in more accurate estimates of TC intensity as well as more frequent over-passes of TC's. At nadir the resolution is 32 km increasing to 60 x 137 km at the limb (like AMSU ATMS is a cross-track scanning radiometer). AMSU scanning/TC geometry for data from 1998-2010 can be used to estimate ATMS TC warm core observations. This approach will allow for the development of an ATMS TC intensity algorithm that can be used as soon as ATMS data becomes available instead of having to wait for a critical number of TC/ATMS matches to develop an algorithm. Results of this initial work will also be presented.