NASA A-Train Observes Hurricane Ida in the Gulf of Mexico

Hurricane Ida (now a tropical storm) was located in the eastern Gulf of Mexico at 0745 UTC on November 11, 2009.  A descending orbit of the NASA A-Train observed the tropical cyclone.  Here, rain rates estimated from the passive microwave data of AMSR-E are shown (inset), with widespread heavy rains located throughout the northern half of the circulation center.  Further north, estimated precipitation rates decreased with distance from the strongest convection.  Passive microwave brightness temperatures and retrieved rain rates provide additional detail over the traditional infrared appearance, where the structure of the cyclone rain bands is masked by dense cirrus overhead.

In addition to the AMSR-E aboard Aqua, the CloudSat radar passed just to the west of the circulation center.  Radar reflectivity indicates a steady decrease in (detectable) cloud top height moving from 25 to 28N latitude, or decrease in cloud top altitude with distance from the circulation center.  Neither the AMSR-E or infrared data are able to depict the 5 km variability in cloud top height.  The radar also provides value by highlighting the presence of individual convective cores, where reflectivity is likely enhanced by the presence of graupel.  Near the 4-5 km level, the thin band of enhanced reflectivity suggests the presence of the melting level.  This feature does not seem to appear underneath the higher cloud tops at 25 N, however, the disappearance is likely a result of attenuation of the radar signal through the deeper convective cores.  The CloudSat signal is best suited for small particles and ice, and attenuates rapidly in heavy liquid precipitation.  Therefore, returns are limited below the melting level, given the high rain rates suggested by AMSR-E data.

The multiple, yet nearly simultaneous perspectives provided by the A-Train allow for a more complete depiction of precipitation structures, especially for storms that are offshore and out of the range of ground based radars.

Composite of satellite imagery related to Hurricane Ida: rain rates provided by AMSR-E passive microwave retrieval (inset), and CloudSat 94 GHz radar reflectivity cross section (below), with geostationary infrared imagery provided as a background. Infrared image and CloudSat cross section provided by the Naval Research Laboratory.

2 thoughts on “NASA A-Train Observes Hurricane Ida in the Gulf of Mexico

  1. Selected coastal WFOs are currently using the AMSR-E precipitation rates to monitor off-shore weather systems (out of the range of NEXRAD radar coverage). This post demonstrates the value of the AMSR-E data for this purpose. Have you given any thought about bringing the CloudSt data into AWIPS to portray this type of information to the forecasters?

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