Extended Abstract (1.8M)1B.6
Three dimensional structure of easterly wave disturbances over Africa and the tropical North Atlantic
George N. Kiladis, NOAA/AL, Boulder, CO; and C. D. Thorncroft
The statistical structure of easterly waves over Africa and the adjacent tropical Atlantic is studied using a combination of satellite, radiosonde, and various reanalysis products. Easterly waves can be readily isolated using Outgoing Longwave Radiation data filtered to retain only westward propagating fluctuations of zonal wavenumbers greater than 6 with periods less than 6 days. This filtering effectively identifies individual synoptic-scale waves and can be used to characterize the amount of wave activity on intraseasonal or interannual time scales. The index can also be used as a basis for the projection of the dynamical structures of easterly waves at various locations. As was found in previous studies, easterly waves over the Atlantic originate near the coast of Africa, and occasionally over the African continent itself, and within a few days propagate into the genesis region of Atlantic tropical depressions within the ITCZ. As was found during the GATE field experiment, these waves have westward tilts with height in dynamical fields such as meridional wind and temperature, such that these signals reverse sign between the lower and upper troposphere. Over the African continent, the vertical scales of the dynamical signals are similar, but the vertical tilt is in the opposite direction, that is, eastward with height. This relationship is maintained for waves from west Africa all the way across the continent to the waves which form over the Ethiopian Highlands. These incipient disturbances can be traced back to features originating over the tropical Pacific which propagate along the easterly jet through the south Asian monsoon region before initiating convection over east Africa.
Session 1B, CONVECTION, waves, and precipitation I
Monday, 3 May 2004, 8:30 AM-10:15 AM, Napoleon I Room
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