Forcing Processes of the Summertime Circumglobal Teleconnection Pattern in a Dry AGCM

Abstract

To better understand the predictability of the wavelike circumglobal teleconnection (CGT) pattern prevailing during boreal summer, two sets of experiments are performed using a nonlinear dry atmospheric model. Each experiment consists of a 10-member ensemble of 26-yr integrations driven by the diabatic heating derived from reanalysis data: one with the monthly climatological mean heating (CLIM) and the other with the monthly heating for 1979?2004 (HIST). Both do well in reproducing the observed summer mean state, as well as the low-frequency variance distribution. The CGT pattern identified in the monthly meridional wind anomalies at 200 hPa shows zonally oriented wave packets over Eurasia. The simulated CGT has a nearly identical phase structure with the observations and indicates little difference between the CLIM and HIST results. While this indicates that the origin of CGT lies in the internal dry dynamics, the ensemble mean of the CGT in HIST is partly controlled by the slow variation in the heating field, as indicated by the high potential predictability of the simulated CGT pattern. Diagnoses using the linearized model demonstrate that the heating anomaly most responsible for the CGT-like steady response is located over the eastern Mediterranean region, where the heating may be coupled with the CGT pattern. In addition to the heating near the CGT, remote heating and cooling anomalies over North America and equatorial Africa are found to be effective at exciting stationary Rossby waves trapped on the Atlantic and Asian jets. It is thus suggested that the mechanisms generating the heating anomalies over these regions are the key to the predictability of the CGT pattern.