HR: 1400h
AN: A43C-03    [Abstracts]
TI: The Role of the tropical Atlantic in the Dynamics of Persistent US Droughts
AU: * Kushnir, Y
EM: kushnir@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia Univerisity, 61 Route 9W, Palisades, NY 10964, United States
AU: Ting, M
EM: ting@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia Univerisity, 61 Route 9W, Palisades, NY 10964, United States
AU: Seager, R
EM: rich@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia Univerisity, 61 Route 9W, Palisades, NY 10964, United States
AU: Velez, J
EM: jennie@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia Univerisity, 61 Route 9W, Palisades, NY 10964, United States
AB: The role of the Atlantic in US hydroclimate variability has often been discussed in the literature. In most past studies the focus has been on East Coast precipitation. Recently however, there has been increased interest in the effect of long-term variability in Atlantic SST on the dynamics of droughts in the Great Plains (GP) and the US West (USW). Most of these areas are semi-arid and prone to sever droughts. As recent modeling studies show, the major external forcing of these droughts are low-frequency fluctuations of tropical Pacific SST. Here however, we study the dynamics of an apparent causal association between tropical Atlantic SST variability and the frequency of occurrences and intensity of these droughts. In particular, we are interested in finding out how an anomalously warm tropical Atlantic Ocean induces, as it seems, dry conditions in the GP and USW. We use an atmospheric GCM (NCAR CCM3) forced with observed SST and find that such warm SST conditions are associated with a local response within the basin that entails a weakening of the subtropical high, with non-local, upstream high-pressure anomaly in the Pacific. The low-pressure response in the Atlantic occurs year-round but the Pacific response is a wintertime phenomenon. To understand the dynamics of these influences we utilize a series of controlled experiments with a linear, primitive equation model where the diabatic heating field from the full GCM is used. The linear model mimics the overall winter and summer effects of tropical Atlantic heating on the Azores high and the upstream Pacific response. These results confirm that weak but persistent forcing from the tropical Atlantic can modulate the influence of tropical Pacific SST on western US precipitation variability.
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 3319 General circulation (1223)
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4513 Decadal ocean variability (1616, 1635, 3305, 4215)
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly