The dynamical processes associated with the growth and decay of the circumglobal teleconnetion pattern

The dynamical mechanisms associated with the growth and decay of the circumglobal teleconnection pattern (CTP) are investigated with a multi-level primitive equation model that has a zonally-uniform lower boundary. By varying the radiation equilibrium state, it is found that circumglobal wave packets form most readily in the presence of a strong subtropical jet and weak midlatitude baroclinicity. As in the atmosphere, the model CTP corresponds to a circumglobal wave packet that is dominated by zonal wavenumber 5, with an eastward group speed and a phase speed that is close to zero.

The CTP was found to undergo a cycle of growth and decay over a period of about 40 days. To examine the dynamical processes associated with this growth and decay, the wave field was separated into two orthogonal components, one corresponding to the CTP and the other to the remainder of the wave field. It was found that the growth of the CTP coincides with an enhanced meridional heat flux and the decay to a weakened heat flux, with the CTP contribution to the heat flux being dominant. Throughout the growth and decay, the CTP amplitude was observed to undergo fluctuations with a period of 7 days. This oscillation was shown to be attributed to the constructive and destructive interference between the quasi-stationary CTP and an eastward propagating non-CTP wave field in midlatitudes. An Eliassen-Palm flux analysis showed that this wave interference generates an oscillation in the eddy momentum flux which drives a 7-day strengthening and weakening of the negative phase of the annular mode. The coincidence between a large amplitude negative annular mode and maxima in these heat fluxes suggest that the baroclinic growth of the CTP is due to the wave-wave interaction which generates a zonal mean background flow with a spatial structure that is favorable for rapid baroclinic growth. The decay of the CTP is found to exhibit features consistent with an important influence from the barotropic governor mechanism. The extent to which these processes are observed in the atmosphere is also investigated.