New nonlinear mechanisms of midlatitude atmospheric low-frequency variability

The observed attractors exhibit spatial and temporal low-frequency patterns comparing well with those observed in the atmosphere. For h0≤800m the periodic orbits have a period of about 10 days and patterns in the vorticity field propagate eastward. For h0≥800m, the period is longer (30-60 days) and patterns in the vorticity field are non-propagating. The dynamics on the strange attractors are associated with low-frequency variability: the vorticity fields show weakening and strengthening of non-propagating planetary waves on time scales of 10-200 days. The spatio-temporal characteristics are “inherited” (by intermittency) from the two families of periodic orbits and are detected in a relatively large region of the parameter plane. This scenario provides a characterisation of low-frequency variability in terms of intermittency due to bifurcations of waves.