13 Mar 2024
 | 13 Mar 2024
Status: this preprint is open for discussion and under review for Weather and Climate Dynamics (WCD).

Impact of stochastic physics on the representation of atmospheric blocking in EC-Earth3

Michele Filippucci, Simona Bordoni, and Paolo Davini

Abstract. Atmospheric blocking is a synoptic-scale phenomenon that consists in an obstruction of the normal easterly progression of weather patterns in the midlatitudes, leading to persistent atmospheric conditions sometimes associated with extreme weather. State-of-the-art climate models systematically underestimate winter atmospheric blocking frequency, especially over Europe. This is often attributed to a poor representation of small-scale processes that are fundamental for the onset and maintenance of blocking events. Here, we explore how the implementation of two stochastic parameterizations, namely the Stochastically Perturbed Parameterization Tendencies (SPPT) scheme and the Stochastic Kinetic Energy Backscatter (SKEB) scheme, influences the representation of Northern Hemisphere winter blocking in EC-Earth3.

Surprisingly, the activation of the two stochastic schemes has detrimental effects on blocking representation. Such deterioration is attributed to changes in the mean winter atmospheric circulation, primarily manifested in a strengthening of the mid-latitude jet stream and an intensification of the Hadley Cell. Ultimately, these circulation differences arise from a modified condensation process in tropical clouds that impacts the tropical stationary eddy activity, which in turn modifies the zonal momentum balance. Our findings reconnect with earlier literature on similar experiments and suggest that the activation of stochastic parameterizations may require a retuning of the model to correct for significant biases in the mean atmospheric circulation.

Michele Filippucci, Simona Bordoni, and Paolo Davini

Status: open (until 03 May 2024)

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Michele Filippucci, Simona Bordoni, and Paolo Davini
Michele Filippucci, Simona Bordoni, and Paolo Davini


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Short summary
Atmospheric blocking is a recurring phenomenon in midlatitudes, causing winter cold spells and summer heatwaves. Current models underestimate it, hindering understanding of global warming's impact on extremes. In this paper, we investigate whether stochastic parameterizations can improve blocking representation. We find that blocking frequency representation slightly deteriorates, following a change in midlatitude winds. We conclude by suggesting a direction for future model development.