Tuesday, 10 July 2012
St. George (Westin Copley Place)
Global climate is changing. Near-surface winds over the oceans, which are a key component of the Earth's climate system, have also been changing. When linking the QuikSCAT (1999-2009) time series with SSM/I (1987 onward) passive wind speed retrievals and COADS (1980 onward) marine surface wind observations, the global wind speed shows a pronounced upward trend as ocean warms up in recent decades. The rate of increase in wind speed is strikingly in phase with the rate of warming in SST: the faster increase in winds before 1998 coincided with a rapid warming and the relatively steady phase after 1998 has been associated with a slow warming tendency. The coherent change between SST and wind substantiates the viewpoint that ocean winds hold important information in deciphering the cause of the observed changes in SST. Wind and SST are closely coupled and their interactions are known to generate rich space-time structures of the basin-scale climate variability (Bjerknes 1964). However, time series of wind speed alone is far from sufficient. We need to understand how the ocean vector wind field changes in the warm climate, because vector wind affects wind-driven ocean circulation, which affects ocean heat transport and modulates SST and in turn modulates the global climate. That ocean vector winds affect virtually every detail of the oceanic role in climate change can never be overstated. Effort to establish and maintain a high-resolution, continuous, and consistent vector wind time series that encompasses the entire satellite period from July 1987 to present has been undertaken by the Objectively Analyzed air-sea fluxes (OAFlux) project through synthesizing microwave passive radiometers and scatterometers. This study takes advantage of the 23-year wind analysis to provide the first global view of low-frequency variations of ocean vector winds over the satellite era and to unveil pattern of coherent changes in the large-scale near-surface atmospheric circulation. The study will discuss the decadal trends in the global near-surface vector wind fields, the pattern of change in the global ocean basins, and the relationship to the large-scale atmospheric modes of variability.
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