On the influence of the meridional circulation and surface pressure change on the Arctic Oscillation

Abstract

Eddy‐forced meridional circulation and the corresponding surface pressure change associated with the month‐to‐month variability of the Arctic Oscillation (AO) are examined in the framework of Eulerian mean dynamics and are compared with the AO‐like variability associated with stratospheric vacillation known as the Polar‐night Jet Oscillation (PJO). Surface signals associated with both the AO and the AO‐like variability associated with the PJO are produced through the eddy‐forced meridional circulation. In the case of the AO, however, a surface pressure change is found to be produced by meridional circulation driven mainly by the mechanical forcing of zonal wave number 2 or 3 and high‐frequency transient eddies in the troposphere. This largely contrasts with the AO‐like variability associated with the PJO, which is mainly produced by the eddy forcings of zonal wave number 1 in the troposphere and stratosphere. A close relationship among the eddy forcing, meridional velocity, surface pressure change, and AO index was found to exist not only for the month‐to‐month variability but also on a decadal timescale. The separation of the AO index into tropospheric and stratospheric components in the decadal timescale revealed that the recent increasing trend mainly comes from the stratosphere whereas the decadal variation comes from the troposphere.