Regional climate model simulations of North Atlantic cyclones: frequency and intensity changes

Abstract

Frequency and intensity of cyclones over the North Atlantic are investigated using 2 data sets from simulations with the Rossby Centre regional climate model RCA3. The model domain comprises large parts of the North Atlantic and the adjacent continents. RCA3 is driven by ECHAM5-OM1 general circulation model data for May to December from 1985 to 2000 and May to December from 2085 to 2100 assuming the SRES-A2 emission scenario. We apply an objective algorithm to identify and track tropical and extratropical cyclones, as well as extratropical transition. The simulation indicates increase in the count of strong hurricanes and extratropical cyclones. Contrasting, and generally weaker, changes are seen for the less extreme events. Decreases of 18% in the count of extratropical cyclones and 13% in the count of tropical cyclones with wind speeds of ≥18 m s -1 can be found. Furthermore, there is a pronounced shift in the tracks of hurricanes and their extratropical transition in November and December-more hurricanes are seen over the Gulf of Mexico, the Caribbean Sea and the western Sargasso Sea and less over the southern North Atlantic.

Review on the Projections of Future Storminess over the North Atlantic European Region

“…Results of the study of [50], which scored ES = 9, showed an increase in cyclone activity in a large number of projections made in their study. Only one study did not identify a change in wind intensity [47].…”

“…The reported tendency (T) in the long-term evolution of the reported variables was assessed and quantified using the categorical interpretation key (i) T = -1 for a decreasing tendency; (ii) T = 0 for no tendency; and (iii) T = +1 for an increasing tendency. Interestingly enough, in total, only four [45][46][47][48] out of the 58 evaluated studies reported no tendency in any one of the assessed categories of future storminess.…”

“…The spectral grid resolutions of the GCMs used in these studies varied at least between T21 and T213, which equal horizontal grid resolutions of 500 km to 49 km in the study area. With one exception [47], the evaluated studies have a focus on the European cold season including the months September to April. Typical terms and acronyms found in the reviewed studies referring to the cold season were "winter" without specifying individual months and "DJF" (December, January, and February).…”

“…Compared to the North Atlantic region north of 60˝N, a different picture emerges in the North Atlantic region south of 60˝N (Table 2, [2,9,13,31,45,47,50,52,54,[56][57][58][59][60][61][62]). Results from 16 evaluated studies demonstrate that it is indisputable that storminess is projected to generally increase.…”

Scenario changes in the climatology of winter midlatitude cyclone activity over eastern North America and the Northwest Atlantic

“…Studies with the Canadian Regional Climate model (CRCM) show that it has skill in downscaling large‐scale information to regional scales and in successfully reproducing the means and variations of a number of fields, such as SLP and precipitation [ Denis et al , 2002]. In addition, RCMs have been successfully implemented to investigate possible changes in the future cyclone climatology [ Muskulus and Jacob , 2005; Lionello and Giorgi , 2007; Semmler et al , 2008]. Simulations with the Rossby Center regional climate model RCA2 suggest an 18% decrease in the extratropical cyclone count for the North Atlantic under the SRES‐A2 scenario [ Semmler et al , 2008].…”