Variability and Trends of Global Atmospheric Frontal Activity and Links with Large-Scale Modes of Variability

Presented here is a global analysis of frontal activity variability derived from ERA-Interim data over the 34-yr period of January 1979-March 2013 using a state-of-the-art frontal tracking scheme. In December-February over that epoch, there is a northward shift of frontal activity in the Pacific in the Northern Hemisphere (NH). In the Southern Hemisphere (SH), the largest trends are identified in the austral summer and are manifested by a southward shift of frontal activity over the Southern Ocean. Variability of frontal behavior is found to be closely related to the main modes of atmospheric circulation, such as the North Atlantic Oscillation (NAO) for the Atlantic-European sector in the NH and the southern annular mode (SAM) in the middle and high latitudes of the SH. A signal associated with El Nino and hence emanating from the tropics is also apparent in the behavior of frontal systems over the Pacific by a reduction in the number of fronts in the middle South Pacific and intensification of frontal activity in high and low latitudes throughout the year. It is shown in general that the associations of the large-scale modes with frontal variability are much stronger than with cyclones. This indicates that the quantification of the behavior of fronts is an important component of understanding the climate system. At the very high latitudes, it is also shown here that, in the recent years of rapid sea ice reduction in the Arctic, there have been fewer summer fronts observed over the Canadian Arctic.