Diagram and graphs from the paper.
(a) The four locations considered in the sensitivity experiments to changes in SST are shown in the ellipses. In the background, the values of a proxy for convective instability (h0 – h*500) in the control simulation is shown. Regions where this parameter is high tend to have deep convection, while negative regions typically have subsidence. (b) Changes in SST ( -4K to +4K) and the corresponding changes in the global mean radiation at the top of atmosphere (RTOA) in the four regions shown in panel (a) for each of the sensitivity experiments. (c) Similar to (b) but showing changes in the mean free-tropospheric saturation moist static energy (h*500), which is typically considered a threshold for convection in the tropics. Credit: Williams et al. [2023], Figure 2
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: Geophysical Research Letters

In order to understand how climate responds to changes in sea surface temperature (SST), it is common to use linear approximations, i.e. the response is assumed to vary linearly with the sign and magnitude of the SST changes. Williams et al. [2023] use model simulations and theory to show that the response of the climate to changes in SST in the tropics can be quite non-linear. For instance, the response in the climate if the SST warms or cools is asymmetric.

Similarly, there is a magnitude dependence on the response that is not linearly related to the magnitude of the change. These differences in the climate response are related to the convective regime in the regions in which the SST changes occur, i.e. if the region typically has strong deep convection or not. These results have important implications as they show the typical assumption that the response is linear is not applicable in parts of the tropics and that the existing frameworks must be modified to take that into account.

Citation: Williams, A. I. L., Jeevanjee, N., & Bloch-Johnson, J. (2023). Circus tents, convective thresholds, and the non-linear climate response to tropical SSTs. Geophysical Research Letters, 50, e2022GL101499. https://doi.org/10.1029/2022GL101499

—Suzana Camargo, Editor, Geophysical Research Letters

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