Guojun Gu - 613 Seminar Series

Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD

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During the post-1979 period in which the satellite-based precipitation measurements with global coverage are available, in addition to anthropogenic related global surface warming, several internal climate modes including the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO) might have also played critical role in affecting the strength and spatial distribution of global temperature variability/change. In particular, the evolutions of both PDO and AMO specifically their respective, recent phase shifts might have partially contributed to the rapid global temperature increase during 1980s-1990s and may also account for the temperature “hiatus” during the recent past of about 10-15 years (post-1998/1999). It is further noted that the PDO phase shift might have dominated the Pacific basin by showing decadal-scale La Niña-type cooling in the tropical central-eastern Pacific during the recent past decade, while the AMO might have contributed to a seemingly hemispheric warming in the Northern Hemisphere following its shift around the mid-1990s. Long-term precipitation changes during the post-1979 period may therefore have been modulated by all these three major factors: anthropogenic related global surface warming (GW), PDO, and AMO. The spatial patterns of precipitation changes in the Pacific tend to manifest the PDO’s phase shift around 1998/1999. The AMO effect on precipitation changes can be identified in the pan-Atlantic basin and is also discernible beyond of it, extending to both the Pacific and Indian Ocean basins. The impact of global warming on precipitation during the post-1979 period is hence greatly smeared by the influences from these two internal modes. However, the anthropogenic related global warming signal in precipitation could still be discerned especially in the zonal-mean context after the effects of the PDO and AMO are removed.