Group seminar on 12. December, 14:15 CET
Warm Pool: Modulating Atmospheric Responses to Equatorial SST Perturbations
Yuan-Bing Zhao
In this talk, I will share initial findings examining the influence of the tropical warm pool (WP) on the atmospheric responses to perturbations in equatorial sea surface temperature (SST). These findings originate from a series of aqua-planet simulations that employ an idealized background SST, closely resembling typical SST patterns, particularly within the tropics, with a focus on the WP. The WP-like background SST induces the Walker circulation within the tropics and gives rise to planetary stationary waves in extra-tropical regions, disrupting the zonal symmetry of the background state. Notably, the mid-latitude jet adjacent to the WP weakens in downstream regions, coinciding with a local peak in temporal variability. These distinctive features play a crucial role in shaping the atmospheric response to perturbations in equatorial SST.
We observe robust atmospheric responses to (positive) SST perturbations around the WP. The most pronounced responses, evident in both zonal-mean circulation and wave circulation, are caused by SST perturbations on either side of the WP center. Across all sensitivity experiments, there is a discernible increase in zonal mean energy, mirroring the responses in zonal-mean circulation. SST perturbations within the WP region enhance wave energy, while those outside diminish it—a contrast to the corresponding circulation responses. This discrepancy is likely attributed to the alignment of wave circulation responses with the background wave field for the former and an opposing phase for the latter.
Regarding temporal variability, SST perturbations at the WP center and its western flank generally lead to reductions, whereas those on the eastern side result in enhancements. Spatially, temporal variability responses consistently intensify in areas with local maximum background variability, regardless of the locations of SST perturbations.