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The Competition between Cloud Radiative Heating and Latent Heating for Zonal Wind Variability and Forced Response

Presentation Date
Monday, December 13, 2021 at 2:00pm
Convention Center - Poster Hall, D-F



Annular modes – the primary mode of sub-seasonal variability in the location of the tropospheric, zonal-mean eddy-driven jets – have much deeper significance than just circulation variability. Rather, to the extent that the fluctuation-dissipation theorem is relevant for global climate, annular modes act as a window into the spatial patterns of change driven by external forcings. Recent work has even identified an annular-mode-like response as a “least-damped” mode of response to weak thermal forcings, prompting further questions about the significance of annular modes.

Despite this significance of annular modes, understanding their persistence beyond synoptic timescales remains a theoretical challenge. Compounding this, current models produce annular modes which are too persistent, likely due to a deficit in simulating the relevant eddy-jet feedbacks. Specifically, diabatic heating represents a crucial energy source driving this persistence. Cloud radiative heating is strongly correlated with the Northern Annular Mode (NAM), although latent heating may have a larger impact on NAM persistence. From a forced response perspective, cloud-circulation feedbacks seem to induce the bulk of jet shifts in global warming simulations, highlighting the key role of diabatic heating.

In order to investigate the role of latent heating and cloud radiative heating for annular mode variability and forced response, we analyze a novel suite of cloud-locking, global-warming simulations using an eddy-mean flow interaction framework which can quantify the impacts of different diabatic heating sources. As a baseline, we carry out this same analysis for 15 years of MERRA2 reanalysis data. Early results suggest that much of the eddy generation due to all sky radiative heating is specifically a result of cloud radiative effects, but that much of this generation is offset by destruction resulting from latent heating. Thus, total diabatic effects on the mean flow are a residual between these competing effects, and shifts in the balance between radiative and convective processes are likely responsible for the net response.

Funding Program Area(s)