The interaction between two storm tracks is analysed by using of idealized experiments with a simplified global circulation model. A zonal distance of 180 degree between the storm tracks drives a retrograde traveling zonal wavenumber two wave with an amplitude modulation of about 50 days. The streamfunction tendency equation demonstrates that the amplitude modulation is excited in the storm track regions by the high frequency (periods between 2 and 8 days) eddy forcing; `spatial resonance' of a retrograde propagating zonal wavenumber two Rossby wave and high frequency eddy forcing are proposed as the amplifying mechanism, while friction and self interaction between the low frequency eddies ensure damping.

Low frequency variability and teleconnection patterns induced by two storm tracks depend on their zonal distance. A separation of about 150 degree, which resembles the Northern Hemisphere storm track distribution, reveals teleconnection patterns which are similar to the PNA and NAO. The NAO-like structure is associated with retrograde travelling Rossby waves; barotropic streamfunction tendencies show that the interaction of the stationary eddies with the low frequency flow and the high frequency eddies contribute to the amplification of the pattern. Its decay is due to their interaction with the zonal mean flow, and the low frequency contribution to the divergence term. The PNA-like pattern has a longer memory and is linked to a quasi-stationary wave. The stationary wave activity flux shows the dominating influence of baroclinic processes and the other storm track further upstream.

Idealized experiments show that with increasing zonal asymmetry of the forcing, representing the land/sea temperature contrast, the structure of the variability becomes zonally asymmetric. It is shown that the zonal index (ZI), measured by the first principal component of the zonally and vertically integrated relative angular momentum, is not appropriate for characterizing certain longitudes of a flow with zonally asymmetric forcing. This means, that with increasing zonal asymmetry of the forcing the variability is better described by regional modes, like the North Atlantic Oscillation (NAO), than by an annular mode, like the Arctic Oscillation (AO). The regional mode can be interpreted as a dynamical mode.