Figure 1 shows the global distribution of storm activity as it was perceived in the mid-nineteenth century ( Hinman 1888). The synoptic classification of such preferred regions of storm (cyclone) activity, or storm tracks, dates at least to the mid-nineteenth century. Given this fact, it is natural that the geographical organization of these transients, whether in terms of their preferred paths of travel, relative frequency of occurrence, or the “average” magnitude of variability, has been and remains a topic of extreme relevance to the science and practice of weather forecasting. It has long been appreciated that mobile, O(1000 km) scale high and low pressure systems generate much of the day-to-day variability in sensible weather in the midlatitudes. 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. The success as well as remaining problems in idealized storm track modeling, which is based on a linearized dynamical system, are discussed. The final part of the review deals with the ability to model storm tracks. The eddy energy budget is presented to show that all of these processes are important in the maintenance of the storm tracks. 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 roles played by baroclinic processes, linear instability, downstream development, barotropic modulation, and diabatic heating are discussed. Physical processes important to storm track dynamics make up the second part of the review. 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. The climatological storm track structure is described, and the seasonal, interannual, and interdecadal storm track variations are discussed. Observed storm track structures and variations form the first part of the review. This paper reviews the current state of observational, theoretical, and modeling knowledge of the midlatitude storm tracks of the Northern Hemisphere cool season.
0 Comments
Leave a Reply. |