Dynamics and impacts of the North Pacific eddy-driven jet response to sudden stratospheric warmings

In this study, observations and simulations are used to investigate the mechanisms behind the different surface responses over the North Pacific and North Atlantic basins in response to sudden stratospheric warmings associated with a polar-night jet oscillation event (PJO SSWs). In reanalysis and a...

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Bibliographic Details
Published in:Journal of Climate
Other Authors: Dai, Ying (author), Hitchcock, Peter (author), Simpson, Isla R. (author)
Format: Article in Journal/Newspaper
Language:English
Published: 2023
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Online Access:https://doi.org/10.1175/JCLI-D-22-0300.1
Description
Summary:In this study, observations and simulations are used to investigate the mechanisms behind the different surface responses over the North Pacific and North Atlantic basins in response to sudden stratospheric warmings associated with a polar-night jet oscillation event (PJO SSWs). In reanalysis and a free-running preindustrial simulation, on average, a negative North Atlantic Oscillation (NAO) response is seen, corresponding to an equatorward shift of the eddy-driven jet. This is considered as the canonical tropospheric response to PJO SSWs. In contrast, the response over the North Pacific is muted. This basin-asymmetric response is shaped by the North Pacific air-sea interactions spun up by the tropospheric precursor to PJO SSWs, which prevent the Pacific eddy-driven jet from responding to the downward influence from the stratosphere. To isolate the downward influence from the sudden warming itself from any preconditioning of the troposphere that may have occurred prior to the warming, a nudging technique is used by which a reference PJO SSW is artificially imposed in a 195-member ensemble spun off from a control simulation. The nudged ensembles show a more basin-symmetric negative Northern Annular Mode (NAM) response, in which the eddy-driven jet shifts equatorward in both the Pacific and Atlantic sectors. Monitoring the atmospheric and oceanic conditions in the North Pacific before and at the onset of PJO SSWs may be useful for forecasting whether a basin-asymmetric negative NAO or basin-symmetric negative NAM response is more likely to emerge. This can be further used to improve subseasonal-to-seasonal predictions of weather and climate. Significance StatementStratospheric sudden warming events (SSWs) occur when the eastward winds usually found above the Arctic in the winter spontaneously and rapidly reverse. Following their occurrence, the Northern Hemisphere surface westerlies move southward, sometimes over both the North Atlantic and North Pacific and other times over the North Atlantic only. We therefore ...