Atmosphere Ocean Science Colloquium

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Recent progress in the energetics framework linking extratropical forcing and tropical rainfall distribution

Speaker: Sarah Kang, UNIST, South Korea

Location: Warren Weaver Hall 1302

Date: Wednesday, February 13, 2019, 3:30 p.m.

Synopsis:

I briefly revisit the energetics framework that connects extratropical energy perturbations to the ITCZ shifts. Then, some limitations of the energetics framework will be discussed. First of all, despite ample modeling evidence of the extratropical influence on the ITCZ, we currently lack observed evidence of extratropics-to-tropics teleconnection. To address this issue, we design idealized experiments in which the extratropics are perturbed by a cyclic thermal forcing with a varying frequency. It is shown that extratropical forcing only on multidecadal timescales is able to shift the ITCZ. Secondly, the application of energetics framework is complicated by ocean dynamical adjustment. Recent fully coupled model studies suggest that the ITCZ is much less sensitive to extratropical forcing than previously thought. Although a series of theoretical studies have attributed the damped ITCZ response in the fully coupled system to the Ekman transport, we argue that the Ekman damping effect is limited due to its small gross stability. Instead, we identify the importance of the Atlantic Meridonal Overturning Circulation and the circumpolar upwelling over the Southern Ocean for damping the effect of extratropical forcing.