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Tuesday, June 12, 2007
10:30 AM - 11:30 AM
CNLS Conference Room (TA-3, Bldg 1690)

Colloquium

Sensitivity of Regional Climates to Remote Tropical Ocean Changes

Prashant Sardeshmukh
Cooperative Institute for Research in Environmental Science

Numerous studies have sought to understand climate changes over the continents as responses to remote sea surface temperature (SST) changes. In this talk, we present important new evidence that the tropical SST changes are predominant in this regard; that their influence is approximately and (for attribution purposes) usefully linear; and that this influence occurs in a relatively low-dimensional space of forcing/response pattern pairs. Furthermore, the most sensitive regions of tropical forcing for generating large global responses are found to be over the Warm Pool, away from the eastern tropical Pacific region of the largest observed ENSO-related SST variability. These conclusions have been reached through a comprehensive sensitivity analysis of the global atmospheric responses to an array of localized SST anomaly patches prescribed throughout the tropics in the NCAR atmospheric GCM. The GCM's global responses to prescribed observed global SST changes over the last 50 years are shown to be very well approximated by linear combinations of the responses to our tropical SST patches. Further analysis establishes the low-dimensionality of the linear operator G linking the global responses to the tropical SSTs. In other words, the sensitivity of the global climate to tropical SSTs can be understood in terms of a relatively small set of forcing/response singular vector pairs of G. Our study clearly demonstrates the dominance, linearity, and low-dimensionality of tropical influences upon the global climate. Another notable result of practical importance is the opposite sensitivity of many aspects of the global response to SSTs in the Indian and western Pacific halves of the Warm Pool. This dipole sensitivity makes it critical for coupled climate models used in global change studies to accurately predict the details of the projected ocean warming in the Warm Pool to generate reliable projections of regional climate changes around the globe.

Host: Balu Nagida