Storm Track Dynamics

Abstract

This paper reviews the current state of observational, theoretical, and modeling knowledge of the midlatitude storm tracks of the Northern Hemisphere cool season.Observed storm track structures and variations form the first part of the review. The climatological storm track structure is described, and the seasonal, interannual, and interdecadal storm track variations are discussed. In particular, the observation that the Pacific storm track exhibits a marked minimum during midwinter when the background baroclinicity is strongest, and a new finding that storm tracks exhibit notable variations in their intensity on decadal timescales, are highlighted as challenges that any comprehensive storm track theory or model has to be able to address.Physical processes important to storm track dynamics make up the second part of the review. The roles played by baroclinic processes, linear instability, downstream development, barotropic modulation, and diabatic heating are discussed. Understanding of these processes forms the core of our current theoretical knowledge of storm track dynamics, and provides a context within which both observational and modeling results can be interpreted. The eddy energy budget is presented to show that all of these processes are important in the maintenance of the storm tracks.The final part of the review deals with the ability to model storm tracks. The success as well as remaining problems in idealized storm track modeling, which is based on a linearized dynamical system, are discussed. Perhaps on a more pragmatic side, it is pointed out that while the current generation of atmospheric general circulation models faithfully reproduce the climatological storm track structure, and to a certain extent, the seasonal and ENSO-related interannual variations of storm tracks, in-depth comparisons between observed and modeled storm track variations are still lacking.

Understanding the varied response of the extratropical storm tracks to climate change

“…Indeed, the increased difference between MAPE and nonconvective MAPE in the warmer climate implies greater available energy for smaller-scale convective storms, particularly in summer in the northern hemisphere. The detailed regional changes in the storm tracks have not been considered here, and would likely be difficult to account for in any simple way because of the complex dynamical processes involved (27). The MAPE scaling should also be useful to reason about changes in storm-track intensity in past climates.…”

Adjustment of the atmospheric circulation to tropical Pacific SST anomalies: Variability of transient eddy propagation in the Pacific–North America sector

“…To check the relative importance of refraction and eddy regeneration we computed the baroclinic energy conversion as given by ᾱ/θ ∂θ/∂p −1 v θ · ∇θ (Chang et al, 2002), whereᾱ is the inverse of the mean density, θ is potential temperature, primes denote high-pass-filtered values and bars denote the specified mean-state fields. The energy conversion for NCEP climatology, El Niño minus La Niña NCEP winters and the El Niño minus La Niña difference from the nonlinear storm-track model, all integrated from 850-300 mb, are shown in Figure 13.…”

Interannual variations and future change of wintertime extratropical cyclone activity over North America in CCSM3

“…However, further down the storm tracks, energy fluxes from upstream becomes more important for eddy development (Chang et al 2002). Change in the mean flow can have direct impacts on the downstream eddies.…”