Feature-Based Jet Variability in the Upper Troposphere

Abstract

Jets in the upper troposphere constitute a cornerstone of both synoptic meteorology and climate dynamics, providing a direct link between weather and midlatitude climate variability. Conventionally, jet variability is often inferred indirectly through the variability of geopotential or sea level pressure. As recent findings pointed to physical discrepancies of this interpretation for the Southern Hemisphere, this study presents a global overview of jet variability based on automated jet detections in the upper troposphere. Consistent with previous studies, most ocean basins are dominated by variability patterns comprising either a latitudinal shift of the jet or a so-called pulsing, a broadening/narrowing of the jet distribution without a change in the mean position. Whereas previous studies generally associate a mode of storm track variability with either shifting or pulsing, jet-based variability patterns frequently represent a transition from shifting to pulsing, or vice versa, across the respective ocean basin. In the Northern Hemisphere, jet variability is consistent with geopotential variability, confirming earlier analyses. In the Southern Hemisphere, however, the variability of geopotential and jets often indicates different modes of variability. Notable exceptions are the consistent dominant modes of jet and geopotential variability in the South Pacific and, to a lesser extent, the south Indian Ocean during winter, as well as the dominant modes in the South Atlantic and south Indian Ocean during summer. Finally, tropical variability is shown to modulate the jet distribution in the Northern Hemisphere, which is in line with previous results. The response in the Southern Hemispheric, however, is shown to be markedly different.