[PAOCQ] Aaron Donohoe (U of Washington)

“Poleward Heat Transport in the Climate System; Model Biases, Invariance Under External Forcing and Relationship to Heatwaves”

Poleward energy transport in the climate system plays a crucial role in moderating spatial gradients in temperature both in the mean climate state and in response to external forcing. This presentation analyzes coupled climate model biases in poleward energy transport, its partitioning between the atmosphere and the ocean and model changes in energy transport in response to external forcing. Coupled climate models transport too much energy in the atmosphere and not enough in the ocean relative to observational estimates. These biases are linked to excessive evaporation in the models, which adds energy to the atmosphere, thereby driving atmospheric energy transport at the expense of oceanic heat transport. In response to external forcing ranging from the last glacial maximum to a quadrupling of carbon dioxide, simulated total poleward heat is nearly unchanged. This invariance result from: i) compensating changes in absorbed solar radiation and outgoing longwave radiation and ii) compensating changes in the atmosphere and ocean partitioning of heat transport.

High-frequency variability in atmospheric temperature, such as that associated with heatwaves and cold snaps, is primarily driven by atmospheric heat transport (convergence). Turbulent energy fluxes from the surface and radiative processes exhibit an order of magnitude less temporal variability on daily timescales compared to atmospheric heat transport. This suggests that the intensity of heatwaves is largely determined by atmospheric circulation and is constrained by the heat capacity of the atmosphere. This framework provides a useful energetic perspective for understanding model biases and predicting future changes in heatwave intensity. We discuss the implications and limitations of this energetic framework for forecasting future heatwave trends.

PAOC Colloquium —

Interdisciplinary seminar series that brings together the whole PAOC (Program in Atmospheres, Oceans, and Climate) community. Seminar topics include all research concerning the physics, chemistry, and biology of the atmospheres, oceans and climate, as well as talks about societal impacts of climatic processes.

Contact: paoc-colloquium-comm@mit.edu