Session 6C.6 Conditions Influencing Hurricane Emily's (2005) Precipitation Patterns, Convection and Upper Tropospheric Outflow

Tuesday, 29 April 2008: 11:30 AM
Palms H (Wyndham Orlando Resort)
Kevin R. Quinlan, University of Alabama, Huntsville, AL; and D. Cecil and J. R. Mecikalski

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Hurricane Emily (2005) was examined to better understand interactions between the upper-tropospheric outflow, precipitation patterns, and intensity of a major hurricane. Data for this study was collected during the Tropical Cloud Systems and Processes (TCSP) experiment. The radial mass flux of the outflow layer was computed using the GOES-11 derived wind algorithm from CIMSS at the University of Wisconsin in Madison. These winds were then processed through a Barnes analysis scheme and were separated into eight separate theta-e levels. These plots were produced for nearly every hour during the duration of the storm. Analysis of this data depicts an outward mass flux in the northern quadrants of the storm and weak outflow in most of the southern regions. NCEP re-analysis data at 200 hPa shows consistent southerly flow between July 13 and July 20, which is consistent with the trends in the radial mass flux data.

Time series of rain rates and 200-850 hPa vertical wind shear are analyzed for Hurricane Emily. Sources of rainfall information come from multiple satellite-borne sensors, such as TRMM, SSMI, and AMSR-E. In instances of southerly shear, it can be shown that the strongest precipitation occurred in the two northern quadrants. Rainfall patterns continued to be concentrated in the northeast and northwest quadrants until the storm approached the Yucatan Peninsula on July 18. This distribution is supported because the shear is predominantly from the south and southwest. This pattern continues until July 19 when the storm moved into the Bay of Campeche. At this time the shear became northwesterly, but the rainfall distribution became much more symmetric. This however, could be due to other factors such as landfall in mainland Mexico.

On July 17, intense convection in the eyewall was observed by the ER-2 aircraft. Analysis of this convection is being conducted using AMPR, EDOP, and the GOES-11 infrared imagery. EDOP data shows convection reaching over 17 km, with GOES cloud top temperatures cooling down to near -83 degrees Celsius at 0753 UTC. This convection featured updraft speeds of up to 35 m/s (~78 mph). Although cold cloud tops were persistent and extensive in Hurricane Emily at this time, the ER-2 overflew a new cell while it was explosively developing on the inner edge of the northwestern eyewall. Emily's central pressure had risen from 929 hPa (2340 UTC) to 943 hPa (0534 UTC) during the recon mission prior to this ER-2 flight, and was 946 hPa (1201 UTC) when the next recon arrived a few hours after the ER-2 flight. Although we cannot know if there were short-term intensity fluctuations associated with the intense convection, it is noteworthy that this convection was encountered after substantial filling had occurred.

Beyond this work, we plan on determining if a correlation exists between upper tropospheric outflow patterns and intensity, rainfall coverage and intensity, and inertial stability patterns in the upper troposphere (isentropic levels above ~335 K). We will also be looking closely at the IR data to determine if these convective bursts were common in the eyewall of this system, or if this convection was uncharacteristic in this event. This will involve processing all divergence, inertial stability, and storm-integrated rainfall in a manner that highlights relationships across Emily over time as the cyclone evolved and propagated poleward.

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