4.2
Attributing regional climate variations to tropical SST changes
Prashant Sardeshmukh, NOAA/ESRL/PSD, CDC/CIRES, Boulder, CO
Numerous observational and modeling studies have sought to understand climate anomalies over the continents as remote responses to both tropical and extratropical SST anomalies. In this talk, we present important new evidence that the tropical SST anomalies 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 occur over the Warm Pool, away from the eastern tropical Pacific region of 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 response to prescribed observed global SSTs over the last 50 years (i.e, in "AMIP"-type "GOGA" simulations) is 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 response 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 research 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.
Session 4, Detection and Attribution of Regional Climate Change
Wednesday, 17 January 2007, 1:30 PM-2:30 PM, 214D
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