Recent shift in the sub-seasonal teleconnection between tropics and Arctic in boreal summer

Abstract:

Using the self-organizing map (SOM) analysis of the 200-hPa geopotential obtained from ECMWF-Interim data, we have classified teleconnection patterns over the Northern Hemisphere during boreal summer. One of the patterns, which is referred to as SOM5 here, shows a dramatic increase in their frequencies after the late 1990s. The spatial pattern of SOM5 is characterized by zonal wavenumber five with anomalous high-pressure cores over central Asia, Northeast Asia, northeastern Pacific, the eastern US, and the Greenland. While the structure in the mid-latitudes resemble the circumglobal teleconnection pattern (CGT), unlike the typical CGT, the center of the action includes the Greenland.

To investigate the temporal evolution of the atmospheric circulation associated with SOM5, we perform the time-lagged composites relative to those days when the daily 200-hPa geopotential field most closely resembles SOM5. From -10 days to 0 days, there is a wave train that propagates from the central tropical Pacific to the Greenland . This is followed by an establishment of quasi-stationary centers in the midlatitudes and over the Greenland. The high pressure centers coincide with temperature extremes. There are also precipitation extremes associated with this pattern. These findings suggest that this CGT-like teleconnection is associated with extreme summer weather in the midlatitudes, and that changes in the forcing from the tropical central Pacific Ocean may have triggered more frequent extreme weather events since the late 1990s.