A series of ensemble integrations with the Center for Ocean-Land-Atmosphere Studies (COLA) model are conducted to determine the impact of observed global SST and a proxy observed global soil wetness initial condition on the initiation, maintenance and decay stages of the life cycles of the 1988 U.S. drought and heat wave, which were unusual compared to historical U.S. drought and heat wave life cycles. The results from these experiments are carefully compared to the observed anomalies and to the results of previously published studies, which focused on the time-mean drought and heat wave, rather than on their life cycles.
The prescribed time-varying observed global SST is found to be capable of forcing the initiation of the drought during April, given a SST analysis which accurately describes the strong negative SST anomalies observed in the eastern equatorial Pacific. In agreement with previously published studies, the observed global SST is also found to contribute to the drought maintenance during May and June. The proxy observed initial soil wetness also contributes to the drought maintenance during June. The SST and the initial soil wetness both contribute to the heat wave life cycle from June through July, but fail to force the month to month variability observed. Neither the SST nor the soil wetness anomalies appear to be responsible for the drought decay in early July. An important role for the internal dynamics of the atmosphere in forcing this month to month variability, as well as the drought decay is suggested. Important interactions between the SST and soil moisture forcing are noted, and the need for a soil moisture data set based on observations is emphasized.
last update: 28 October 1994
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