The NASA A-Train Takes a Second Look at Hurricane Bill

Due to a convenient alignment between the A-Train orbital trajectory and the path of Hurricane Bill along the eastern coastline of North America, the CloudSat radar and AMSR-E radiometer was able to take a second look at the structure of the cyclone and passed very near to, or perhaps directly across, the cyclone center.  This overpass occurred around 18 UTC on August 22, 2009 when Hurricane Bill was classified as a Category 1 storm, with tropical storm warnings issued for Nova Scotia and Bermuda by their respective meteorological agencies.

Passive microwave brightness temperatures depict the convective towers associated with the eye wall, as well as the cyclonic shape of the symmetric rain bands located to the north and south of the storm.  The most intense activity appears to be in the southeast quadrant, while northwest of the storm, activity may have been deterred as the cyclone was impacted by wind shear associated with an upper level shortwave departing the northeastern United States.

The AMSR-E 89 GHz passive microwave radiometer depicts the brightness temperatures associated with Hurricane Bill at 18 UTC, 22 August 2009 as it departs the eastern coast of the United States.

The CloudSat radar follows a similar track to the Aqua satellite, the platform supporting the AMSR-E instrument.  Therefore, once again their observations are nearly coincident in time.  It is unclear whether CloudSat directly sampled across the eye, however, with the center located near the 36th parallel, it is likely that CloudSat is depicting the structure of convection to the north and south of the storm.  The relative lack of convection near 36 degrees may be associated with the eye of the storm, with some shallow convection present.  The outermost rain bands, approaching the coastlines of New Jersey, New York and Massachussetts, are present in the cross section near the 40th parallel.   Numerous, isolated convective towers are evident in the CloudSat cross section, which is again attenuated severely just below the melting level due to the large amount of liquid precipitation.

Assuming that CloudSat sampled the eye, it is interesting to note that it depicts a layer of relatively thick, high altitude cloud which may have obscured the location of the center in visible or infrared satellite imagery.  CloudSat indicates that some shallower convection may be occurring near the eye center, while AMSR-E is able to use passive microwave brightness temperatures to see through these nonprecipitating ice clouds for a clearer shot at the cyclone center.

CloudSat observes the precipitation and cloud structures of Hurricane Bill, then a category 1 storm, as it travels along the eastern coast of the United States.

Finally, the CALIPSO instrument provides imagery of high altitude ice clouds associated with the tropical cyclone.  The highest cloud tops are located near the cyclone center at 36 degrees, and maintain a cloud top altitude of 15 km as in the previous sampling.  Meanwhile, the outer band approaching the United States appears weaker with tops ranging from 8 to 12 km.

The CALIPSO satellite indicates significant lidar backscatter obtained from the high altitude ice clouds associated with Hurricane Bill as it passes along the east coast of the United States.

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