Interannual variations and future change of wintertime extratropical cyclone activity over North America in CCSM3

Abstract

Climatology and interannual variations of wintertime extratropical cyclone frequency in CCSM3 twentieth century simulation are compared with the NCEP/ NCAR reanalysis during 1950-1999. CCSM3 can simulate the storm tracks reasonably well, although the model produces slightly less cyclones at the beginning of the Pacific and Atlantic storm tracks and weaker poleward deflection over the Pacific. As in the reanalysis, frequency of cyclones stronger than 980 hPa shows significant correlation with the Pacific/North America (PNA) teleconnection pattern over the Pacific region and with the North Atlantic Oscillation (NAO) in the Atlantic sector. Composite maps are constructed for opposite phases of El Nino-Southern Oscillation (ENSO) and the NAO and all anomalous patterns coincide with observed. One CCSM3 twenty-first century A1B scenario realization indicates there is significant increase in the extratropical cyclone frequency on the US west coast and decrease in Alaska. Meanwhile, cyclone frequency increases from the Great Lakes region to Quebec and decreases over the US east coast, suggesting a possible northward shift of the Atlantic storm tracks under the warmer climate. The cyclone frequency anomalies are closely linked to changes in seasonal mean states of the upper-troposphere zonal wind and baroclinicity in the lower troposphere. Due to lack of 6-hourly outputs, we cannot apply the cyclone-tracking algorithm to the other eight CCSM3 realizations. Based on the linkage between the mean state change and the cyclone frequency anomalies, it is likely a common feature among the other ensemble members that cyclone activity is reduced on the East Coast and in Alaska as a result of global warming.

Cold surge activity over the Gulf of Mexico in a warmer climate1

“…This El Niño-like anomalous pattern might be responsible of the significant impacts on the West Coast midlatitude wave activity (Teng et al, 2008). The change of the 500 hPa wind field in winter 2080-2089 relative to 1980-1989 (Figure 10) resembles some of the changes observed under El Niño conditions (Magaña et al, 2003).…”

“…Such set of realizations with the Earth Simulator is available at a coarser spatial resolution and it may be worth exploring the robustness of the signal examined in this work. There are several studies that address the issue in mildatitude wave activity under climate change (Meehl et al, 2007;Teng et al, 2008), but only a few examine the potential changes in tropical midlatitude interactions in a warmer climate as a process study. This type of analyses may serve to gain confidence in the elements that may determine the signals of climate change in particular regions.…”

“…Following Walland and Simmonds (1999), the baroclinicity of the atmosphere for present and future conditions, may be examined in terms of the meridional temperature gradient and the static stability of the atmosphere, considering the amplification rate of the most unstable baroclinic wave in the lower troposphere. Teng et al (2008) found in one CCSM3 twenty-first century A1B scenario that there was significant increase in the extratropical cyclone frequency on the US west coast and decrease in Alaska. Lindzen and Farrell (1980), Walland and Simmonds (1999), and Teng et al (2008), suggest that the baroclinicity of the atmosphere for present and future climate conditions can be determined considering the atmospheric static stability and the maximum Eady growth rate at the lower and middle troposphere.…”

“…Teng et al (2008) found in one CCSM3 twenty-first century A1B scenario that there was significant increase in the extratropical cyclone frequency on the US west coast and decrease in Alaska. Lindzen and Farrell (1980), Walland and Simmonds (1999), and Teng et al (2008), suggest that the baroclinicity of the atmosphere for present and future climate conditions can be determined considering the atmospheric static stability and the maximum Eady growth rate at the lower and middle troposphere.…”

“…As a result of climate change, the mean atmospheric meridional temperature gradient, the baroclinicity, the static stability and the mean flow are to be affected (e.g., Teng et al, 2008). These changes may have important consequences in climate at the regional level (IPCC, 2013) for instance, in the tropical Americas (Karmalkar et al, 2011), as they alter cold surge activity.…”