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Characteristics of Warm Season Precipitation in the Australian Region

T.D. Keenan¹ and R. Carbone²

¹Bureau of Meteorology Research Centre , GPO Box 1289K, Melbourne 3001

²National Center for Atmospheric Research, Boulder, CO, 80307-3000

As part of study to characterize the global character of warm season precipitation the Australian tropics and subtropics are being examined. Australia is different from other regions studies in that it has less significant orography but does have a Great Dividing Range along the eastern coast and elevated areas within the western and central desert regions. The climatology is derived using GMS IR data from 1996-2001 (November-March inclusive) to infer the characteristics of precipitation over the domain 0-40S and 110-160E. Hourly 4 km resolution GMS TBB data are put on to a 0.2 by 0. 2 degree latitude-longitude grid with the frequency of black body temperature (TBB) <,-45,-55K analyzed following the method of Carbone et al., 2002. In the higher latitiude region (30-40S) diurnal forcing is much less evident but can be important. The Great Australian Divide on the east coast is a significant source region for diurnally forced convective activity impacting the downstream Tasman Sea region. There is a tendency for coincidence with troughs suggesting that thermal forcing and topography are not nearly as influential as other regions. Once events occur, they exhibit similar trough, streak/event speeds and propagation to those found in North America. In the sub-tropics (20-30 S), more intra-seasonal variation is evident. During late Spring, the streaks typically are similar to those observed in 30-40S latitude band. In summer there is an increased presence of diurnally-forced events, many of which may be non-propagating, for periods of a few days to two weeks. Convection occurs preferably at fixed meridians that maybe associated either with quasi-stationary synoptic forcing and/or thermal forcing from an elevated heat source. When shifts in the location of convection occur, the activity can lock on to narrow meridional regions that may be tied to topography( e.g. Eastern Divide)

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