Abstract Author: Jae-Kyung E. Schemm, K. C. Mo and S.-H. Yoo
Abstract Title: Perpetual Sea Surface Temperature Forcing and Drought over the United States: CLIVAR Drought experiments
Abstract: The CLIVAR drought experiments together with composites based on observed sea surface temperature anomalies (SSTAs) and precipitation (P) data were used to examine the impact of perpetual ENSO and the Atlantic multi decadal oscillation (AMO) on droughts over the United States. The experiments were designed to force an AGCM with prescribed SSTAs for ENSO or the AMO superimposed on the monthly mean SST climatology. The length of runs varies between 35-51 years. There are total four models examined for this study: NCEP/GFS, GFDL, NSIPP and CCM3. P was extracted from the model archive and the 6-month standardized precipitation index (SPI 6) was computed from the P time series. Month under drought was identified when SPI6 is less than -0.8.
The ensemble mean of four models and composites based on observations both show that a cold ENSO is associated with drought over the Southwest, the Colorado basin and the Great Plains. While a cold ENSO winter is conducive to rain over the east coast and the Southeast, a cold ENSO summer has the opposite impact. A perpetual cold ENSO does not create favorable conditions for drought to persist over these areas. From observations, the composites based on the AMO have very weak anomalies because the decadal signals explains very small percentage of variance in comparison to interannual variations. However, the model results indicate that a perpetual warm phase of the AMO does create a favorable condition for drought over the Southwest, the north central United States and wet conditions over Florida.