Stationary Wave Interference, and Its Relation to Tropical Convection and Arctic Warming

The interference between transient eddies and climatological stationary eddies in the Northern Hemisphere is investigated. The amplitude and sign of the interference is represented by the Stationary Wave Index (SWI), which is calculated by projecting the daily 300-hPa stream function anomaly field onto the 300-hPa climatological stationary wave. ERA-Interim reanalysis data for the years 1979 to 2013 is used. The amplitude of the interference peaks during boreal winter. The evolution of outgoing long wave radiation, Arctic temperature, 300-hPa stream function, 10-hPa zonal wind, Arctic sea-ice concentration, and the Arctic Oscillation (AO) index are examined for days of large SWI values during the winter.

Constructive interference during winter tends to occur about one week after enhanced warm pool convection, and is followed by an increase in Arctic surface air temperature, along with a reduction of sea ice in the Barents and Kara Seas. The warming of the Arctic does occur without prior warm pool convection, but it is enhanced and prolonged when constructive interference occurs in concert with enhanced warm pool convection. Furthermore, reduced sea ice in the Barents and Kara Seas is associated with constructive interference with the zonal wave number-1 component of the climatological stationary wave. This is followed two weeks later by a weakening of the stratospheric polar vortex, and a decline of the AO. All of these associations are reversed in the case of destructive interference. Potential climate change implications are briefly discussed.