Corridors of enhanced transport and dispersion: Global distribution and characteristics

This paper documents the global distribution and characteristics of corridors of enhanced transport and dispersion (T&D), particularly their diurnal and vertical structure. These corridors, generically termed low-level jets (LLJs), are ubiquitous features within the world's land covered areas, and regularly occur during the warm season. To accomplish this goal, a new 21-year global reanalysis was performed with an MM5-based global climate downscaling system using a grid spacing of 40 km. A unique characteristic of the reanalysis is the availability of hourly three-dimensional output, which permits the full diurnal cycle to be analyzed. The first available objectively constructed global maps of recurring NLLJs are created, where the various NLLJs can be simultaneously viewed at or near their peak time. These maps not only highlight all the locations where NLLJs are known to recur, but also reveal a number of new jets. The authors examine the basic mechanisms that give rise to the NLLJs identified in two disparate locations, each having a profound influence on the regional T&D, and illustrate the variety of physiographic and thermal forcing mechanisms that can produce NLLJs. The shallowness of the jets, their dependence on turbulence, their ubiquity and intensity underscore a fundamental challenge to global weather and T&D modeling of the distribution of atmospheric constituents originating from the Earth's surface and human activity.