The dynamical impacts on the northern hemispheric winter storm tracks by the diabatic heating (radiative forcing, surface heat flux and self-regulated condensational heating) in conjunction with orographic forcing are studied with a nonlinear primitive equation model. The relative importance of these forcings is assessed from an intercomparison of the results of four numerical simulations using different combinations of the processes. Orographic forcing is found to be necessary but not sufficient for adequate simulation of separate Pacific and Atlantic storm tracks. Incorporating a surface sensible heat flux in the model improves the localization and reduces the maximum intensity of both storm tracks. When condensational heating is also included, not only is the position and localization further improved for each storm track region, but the Atlantic storm track becomes more intense than the Pacific one as observed. Additional properties of the storm tracks in the most successful simulation are delineated in terms of a local energetic diagnosis as well as analyses of the wavepackets and wave-mean flow interaction. The asymmteric response of the storm track intensity occurs primarily due to organized disturbances which originate in the Pacific sector, propagate into the Atlantic jet and reintensify. We suggest that the two storm tracks are best viewed as embedded in a global storm track complex in which low-level disturbances are initially generated upstream of the Pacific storm track via local instability and upper-level disturbances are strongly attenuated downstream in the Asiatic sector. Furthermore, the condensational heating induces the time-mean jets to shift poleward and raises the time-mean temperature in both the Pacific and Atlantic sectors. The time-mean surface temperature field and low-level stratification are strongly modified by the inclusion of surface sensible heat flux.
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12th Conference on Atmospheric and Oceanic Fluid Dynamics