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Speaker: Xiyue (Sally) Zhang, Johns Hopkins University

Title: Global impacts of observed Southern Ocean surface temperature variability

Abstract: Despite global warming, the Southern Ocean (SO) surface cooled from 1979 to recent years. This SO cooling phase was preceded by a warming phase from 1950 to 1978 that is stronger than the global mean surface temperature trend. The global impact of the SO cooling has been investigated recently by a series of GCM simulations where the SO surface temperature anomalies are nudged to observed evolution. The most significant response to observed SO cooling is found in the tropical South Atlantic, where increased clouds and strengthened trade winds cool the sea surface, partially offsetting the radiatively forced warming trend. When we boost the signal by simulating the earlier SO warming phase, a significant response in the tropical eastern Pacific emerges. While the response in the tropical Pacific is weaker than expected, the efficiency of this teleconnection is dependent on the strength of the subtropical low cloud feedback. When we repeat the same experiment with a model with stronger low cloud feedback, we find a more robust global response, including Southeast Pacific cooling, equatorial Pacific drying, Aleutian Low weakening, North Pacific warming, and Antarctic sea-ice expansion. Our results suggest that SO surface temperature variability can contribute to observed tropical Pacific variability, which offers new insights into the model-observation discrepancy in the recent climate trends.

Bio: Xiyue (Sally) Zhang is an Assistant Research Scientist at the Department of Earth and Planetary Sciences, Johns Hopkins University. Her research focuses on polar cloud dynamics, extratropical teleconnection, and tropospheric transport. Prior to her appointment at Johns Hopkins, Sally was an Advanced Study Program Postdoctoral Fellow at the National Center for Atmospheric Research. Sally received her B.S. in Earth and Space Sciences from the University of Washington, and obtained her Ph.D. in Environmental Science and Engineering at Caltech.