Submitted to the Journal of Climate for consideration in the US CLIVAR Drought Working Group Special Issue.

• Main Authors: Yochanan Kushnir, Richard Seager, Mingfang Ting, Naomi Naik, Jennifer Nakamura
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2009
• Subjects: North Atlantic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.188.6942; http://www.ldeo.columbia.edu/res/div/ocp/pub/kushnir/Kushnir_etal-Atlantic_Drought.pdf

The dynamical mechanisms associated with year-to-year variability in tropical North Atlantic (TNA) sea surface temperatures (SSTs) during the cold and warm half of the hydrological year (October-September) are examined. Observations indicate that during both seasons warmer than normal TNA SSTs are associated with a reduction of precipitation over the North America, west of about 90°W and that that effect can be up to 30 % of the year-to-year seasonal precipitation RMS variability. This finding confirms earlier studies with observations and models. While not as large as the seasonal effects of ENSO during the cold season, the Atlantic impact, per one standard deviation of TNA SSTs, is larger than that of the former during the warm season. When the observed association between TNA SST anomalies and global and regional (North American) precipitation and sea level pressure variability are compared with the output from an atmospheric general circulation model (AGCM) forced with observed SSTs, we find that the SST variability can be viewed as the cause for circulation and rainfall variability. The mechanism of the upstream influence on the American West is seasonally dependent, as confirmed by a set of experiments with a linear general circulation model forced with the tropical heating field derived from the full AGCM response. In the warm half of the year, the SST-induced increase in TNA