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Chang, E. K. M. (2018). CMIP5 Projected Change in Northern Hemisphere Winter Cyclones with Associated Extreme Winds. Journal of Climate, (2018).

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Chang, E. K. M. (2018). CMIP5 Projected Change in Northern Hemisphere Winter Cyclones with Associated Extreme Winds. Journal of Climate, (2018).

Projected Significant Decrease in the Number of Extratropical Cyclones with Extreme Winds in the Northern Hemisphere Winter (Chang, 2018)

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Extratropical cyclones are responsible for much of the high impact weather in the mid-latitudes, including heavy precipitation, high winds, and coastal storm surges. Thus how these cyclones may change in the future is of much general interest. Previous studies have suggested a poleward shift in the location of these cyclones, but how their intensity may change remains uncertain, especially in terms of maximum wind speed. This study shows that under global warming, state-of-the-art climate models systematically project a significant decrease in the frequency of extreme extratropical cyclones in the Northern Hemisphere (NH) winter (December-January-February, DJF).

In this study, 19 simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5) have been analyzed to examine how winter cyclones producing extreme near-surface winds are projected to change. Extreme wind thresholds correspond to a top 5 or top 1 cyclone per winter month in the entire NH. The results show that CMIP5 models project a significant decrease in the number of such cyclones, with a 19-model mean decrease of about 17% for the entire NH toward the end of the twenty-first century, under the high-emission RCP8.5 scenario. The projected decrease is larger in the Atlantic (about 21%). Over the Pacific, apart from an overall decrease (about 13%), there is a northeastward shift in the extreme cyclone activity. Less decrease is found in the frequency of cyclones producing extreme winds at 850 hPa (about 5% hemisphere-wide), with models mainly projecting a northeastward shift in the Pacific. These results suggest that 850-hPa wind changes may not be a good proxy for near-surface wind changes. These results contrast with those for the Southern Hemisphere, in which the frequency of cyclones with extreme winds are projected to significantly increase in all four seasons (see Chang, 2017). These results have been published in the Journal of Climate, 31, 6527-6542.

Left: Climatology (DJF 1980-1999) and Right: projected change (DJF 2081-2100, RCP8.5) in the frequency of cyclones with extreme near surface winds in Northern Hemisphere winter, based on 19 CMIP5 models. Contours show frequency of cyclone occurrences (in % of time, contour interval 0.1%). Shades in panel (b) indicate model agreement, with blue shades indicating number of the CMIP5 models projecting a decrease in the frequency of extreme cyclones over that grid box, and pink indicating number of models projecting an increase.

Left: Climatology (DJF 1980-1999) and Right: projected change (DJF 2081-2100, RCP8.5) in the frequency of cyclones with extreme near surface winds in Northern Hemisphere winter, based on 19 CMIP5 models. Contours show frequency of cyclone occurrences (in % of time, contour interval 0.1%). Shades in panel (b) indicate model agreement, with blue shades indicating number of the CMIP5 models projecting a decrease in the frequency of extreme cyclones over that grid box, and pink indicating number of models projecting an increase.

 

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July 18, 2018

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