Further Investigation of the Impact of Idealized Continents and SST Distributions on the Northern Hemisphere Storm Tracks

Building on previous studies of the basic ingredients of the North Atlantic storm track (examining land sea contrast, orography, and SST), this article investigates the impact of Eurasian topography and Pacific SST anomalies on North Pacific and Atlantic storm tracks through a hierarchy of atmospheric GCM simulations using idealized boundary conditions in the Hadley Centre HadGAM1 atmospheric circulation model. The Himalaya Tibet mountain complex is found to play a crucial role in shaping the North Pacific storm track. The northward deflection of the westerly flow around northern Tibet generates an extensive pool of very cold air in the northeastern tip of the Asian continent, which strengthens the meridional temperature gradient and favors baroclinic growth in the western Pacific. The Kuroshio SST front is also instrumental in strengthening the Pacific storm track through its impact on near-surface baroclinicity, while the warm waters around Indonesia tend to weaken it through the impact on baroclinicity of stationary Rossby waves propagating poleward from the convective heating regions. Three mechanisms by which the Atlantic storm track may be affected by changes in the boundary conditions upstream of the Rockies are discussed. In the model configuration used here, stationary Rossby waves emanating from Tibet appear to weaken the North Atlantic storm track substantially, whereas those generated over the cold waters off Peru appear to strengthen it. Changes in eddy-driven surface winds over the Pacific generally appear to modify the flow over the Rocky Mountains, leading to consistent modifications in the Atlantic storm track. The evidence for each of these mechanisms is, however, ultimately equivocal in these simulations.