Global Warming Induces Seasonally Dependent Great Plains Low-Level Jet Changes
The Great Plains low-level jet (GPLLJ), a fast-moving ribbon of air that blows across the Great Plains, accounts for one-third of the moisture transported into the Central United States and affects the region’s climate and weather. Scientists investigated how a warmer future climate changes the GPLLJ and interrogated the drivers of the changes. They found that the GPLLJ will intensify and extend further northward during spring and autumn but exhibits little change in summer. These seasonally dependent GPLLJ changes are induced by distinct changes in the sea-level pressure pattern that arise from the competing effects of the westerly jet stream poleward shift and the enhanced land–sea temperature contrast with warming.
Previous studies noted an enhancement of the GPLLJ under warming, attributing the change to a westward extension or local strengthening of the subtropical high. This study presents a deeper analysis that highlights the seasonally dependent response of the GPLLJ to global warming and clarifies that the poleward expansion of the subtropical high drives the GPLLJ enhancement. The dynamic link can help constrain model projections of the future GPLLJ changes, which have significant impacts on the Central United States hydroclimate and extreme weather, such as mesoscale convective systems.
This study uses a large ensemble of 46 models from Phases 5 and 6 of the Coupled Model Intercomparison Project archives to investigate future seasonal changes of the GPLLJ and reveals their large-scale drivers. The results highlight that the seasonally dependent pattern changes in the North Atlantic subtropical high govern future GPLLJ changes. These seasonally dependent pattern changes arise in turn from the competing effects of the poleward shift in the North America westerly jet and the enhanced land-sea temperature contrast in different seasons. In spring and autumn, the substantial poleward shift in the westerly jet induces a positive sea-level pressure anomaly poleward of the North Atlantic subtropical high, leading to the intensification and more-northward extension of the GPLLJ. In summer, the poleward shift in the westerly jet is weaker and located more northward, separating it from the subtropics. The enhanced land-sea temperature contrast dominates changes to the subtropical high, which mainly feature a westward extension. The sea-level pressure anomaly west of the North Atlantic subtropical high increases the southerly winds over the Gulf of Mexico but has marginal effects on the GPLLJ over the Central United States.