[Eoas-seminar] EOAS Colloquium this Friday 3:30 CAR 101

eoas-seminar at lists.fsu.edu eoas-seminar at lists.fsu.edu
Sun Sep 30 19:22:54 EDT 2018

This week seminar will be back to its usual 3:30 time slot in CAR 101.

Speaker: Prof. Jie He, Department of Earth and Atmospheric Sciences, Georgia Institute of Technology.

Title: Precipitation Sensitivity to Sea Surface Temperature Variability in the Tropics

Abstract: The great dependence of human society and natural ecosystems on rainfall makes precipitation variability an essential aspect of the earth’s climate. Precipitation variability is particularly important in the tropics, as it not only affects local water supply but also regulates global weather and climate patterns. It is well accepted that variations in tropical sea surface temperatures (SSTs) play an important role, as warm SST anomalies tend to increase local precipitation. Observations from the 1980s showed that the relationship between SST and precipitation anomalies has a non-monotonic dependence on the background SSTs. In scatter plots made from monthly mean data with SST on the x-axis and precipitation on the y-axis, a curve fit to the data steepens with a large positive slope as the background SST reaches approximately 27.5oC but flattens and turns over with a negative slope at very high SSTs. It was later argued that the decrease in precipitation and the associated lack of cloud shading is what creates the very high SSTs. This indicates that the interaction between SST and precipitation is inherently a two-way coupling. While SST anomalies affect precipitation, precipitation variability can also be internally driven by atmospheric intrinsic dynamics and in turn influences the SST. Because the atmospheric intrinsic variability is essentially chaotic, it cannot be extracted from a fully coupled system. The inability to separate the SST-induced and atmospheric intrinsic variability has hindered the quantitative understanding their underlying dynamics and thus created a fundamental challenge in interpreting coupled SST-precipitation relationships.
In this presentation, I will introduce a linear framework derived from uncoupled atmosphere-only simulations. This framework allows for a clean separation and quantification of the SST-induced and atmospheric intrinsic precipitation variability. Through a focus on local SST-precipitation relationships, I will show that the precipitation sensitivity to local SST variability is predominantly controlled by the local background SST. In addition, the strength of the precipitation response increases monotonically with the background SST, with a very sharp growth at high SSTs. I will interpret these findings by using basic principles of moist static stability.

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