Talk by Ivana Cvijanovic, PhD – Niels Bohr Institute - University of Copenhagen

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Talk by Ivana Cvijanovic, PhD

Global energy budget changes to high latitude North Atlantic cooling and the tropical ITCZ response

This study investigates the nature of global energy flux changes in response to North Atlantic high latitude cooling applied in an atmospheric general circulation model coupled to a slab ocean. We focus on key local and remote feedbacks that collectively act to alter the energy budget and atmospheric energy transport. We also investigate the relative roles of tropical SST and energy flux changes in the ITCZ response to North Atlantic cooling.

Using a radiative kernel technique, we quantify the effects of key feedbacks - temperature, cloud and water vapor, to the top-of-the-atmosphere radiative flux changes. The results show partial local energy flux compensation to the initial perturbation in the high latitudes from the negative temperature feedback. However, shortwave albedo and longwave water vapor act as strong positive feedbacks, and as a consequence drive a significant increase in the atmospheric energy transport to the Northern extratropics. The additional energy flux providing this increase comes from the southern tropics, where the majority of feedbacks are negative and act to warm the area, with the energy gain originating from the cloud radiative
feedbacks, temperature and longwave water vapor feedbacks.

It has been previously argued that the role of tropical SST changes was secondary to the role played by the atmospheric energy flux requirements in determining the southward ITCZ shift to Northern Hemisphere cooling. However, we find using idealized simulations with the fixed tropical SSTs that the ITCZ shifts are not possible without the tropical SST changes. The ITCZ shift is influenced mainly by the local (tropical) SST forcing, apparently independent of the actual high latitude energy demand.