Tuesday, 29 April 2008
Palms ABCD (Wyndham Orlando Resort)
African easterly waves (AEW) occur throughout the year but are especially important during the summer months. These waves are capable of producing strong Mesoscale Convective Systems (MCSs) that move off the coast and have the ability to form into Tropical Cyclones. The objective of this study is to obtain a better understanding of the formation of Tropical Cyclones (TC) using polarimetric Doppler radar observations of West African MCSs. In addition to radar data, a suite of data collected during the NASA African Monsoon Multidisciplinary Analysis (NAMMA), which includes that from a rain gauge network and atmospheric soundings, is used. Observations from the rain gauge network (38 gauges) and the NASA 10 cm polarimetric Doppler ground-based radar (NPOL) are used to characterize the structure of West African MCSs. Characteristics observed from NPOL data include echo top heights, maximum radar reflectivity, height of maximum radar reflectivity, Doppler velocity, spectrum width, and aerial coverage of radar reflectivity signatures. The observations from the rain gauge network are used with the NPOL observations to measure rainfall amount and rainfall rate. Atmospheric soundings from Dakar, Senegal and the Cape Verde Islands are used to investigate environmental stability characteristics that the MCSs encounter while over land and ocean, respectively. With these soundings, convective available potential energy (CAPE) and environmental wind shear are determined. The structural and environmental characteristics are investigated to determine if differences exist between TC producing and non-TC producing MCS events. Because West African MCSs tend to occur in conjunction with AEW, the strength of these waves will also be taken into account to improve the analysis of MCS characteristics. Eight MCS events from the field project were chosen for study, four of which later produced a TC.
Preliminary results show that MCS echo top heights and maximum reflectivity heights are higher for TC producing events while the maximum reflectivity is greater for non-TC producing events. It is expected that the relationship between the aerial coverage, environmental characteristics, and strength of the AEWs will correlate better for the TC producing events than for non-TC events. A summary of observed characteristics for TC producing and non-TC producing events will be provided during the presentation.
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