Friday, March 23 at 11:00am
Jie He, Princeton University
Title: Quantifying air-sea interaction in the tropics
Abstract: Air-sea interaction plays an important role in climate variability. A well-known example in the tropical region is the El Niño–Southern Oscillation, during which the anomalous sea surface temperature (SST) in the equatorial Pacific drives substantial changes in local precipitation. This is reflected in the large co-variability between SST and precipitation that has been observed in the equatorial Pacific region. Because it is commonly assumed that variations in tropical SST have a dominant effect on local precipitation variability, the observed SST-precipitation relationships are often used to infer the strength of SST forcing of precipitation. Such practice has yielded some interesting but not necessarily intuitive results. For example, early research based on the observed SST-precipitation relationships suggested that precipitation starts to respond strongly to SST variability when the background SST reaches approximately 27.5oC but further increases in SST somehow appear to have little impact on precipitation variability. In this talk, I will show that using observed air-sea relationships to infer the oceanic forcing of the atmosphere is problematic due to the two-way interaction between the atmosphere and ocean, which is very difficult to disentangle in a fully coupled atmosphere-ocean system. This issue can be circumvented by using simulations of uncoupled atmosphere-only models. Based on these uncoupled simulations, I will introduce a fundamental framework for interpreting the observed air-sea relationships.