Distinct Impacts of the Two Types of El Niño on the Strength of Great Plains Low-Level Jet

Abstract:

The Great Plains low-level jet (GPLLJ) is influential to the hydroclimate in the Great Plains of the U.S. in late spring and early summer. In this study, we stratify the El Niño influences on the summer GPLLJ according to the El Niño type and find the influences are dramatically different between the Eastern Pacific (EP) and Central Pacific (CP) types. Associated with the CP El Niño, negative sea level pressure anomalies are established over the Gulf of Mexico that induce northerly wind anomalies to weaken the GPLLJ. In contrast, the EP El Niño intensifies the GPLLJ via inducing anomalous surface air temperature gradient between northeastern and southwestern U.S. This finding indicates that the El Niño impact on the GPLLJ may have changed after early 1990s, since when the El Niño changed from the conventional EP type to the newly-emerged CP type. A weakened GPLLJ and less transport of heat and moisture fluxes from the Gulf of Mexico into the Great Plains can lead to a drier environment in the central United States.The Great Plains low-level jet (GPLLJ) is influential to the hydroclimate in the Great Plains of the U.S. in late spring and early summer. In this study, we stratify the El Niño influences on the summer GPLLJ according to the El Niño type and find the influences are dramatically different between the Eastern Pacific (EP) and Central Pacific (CP) types. Associated with the CP El Niño, negative sea level pressure anomalies are established over the Gulf of Mexico that induce northerly wind anomalies to weaken the GPLLJ. In contrast, the EP El Niño intensifies the GPLLJ via inducing anomalous surface air temperature gradient between northeastern and southwestern U.S. This finding indicates that the El Niño impact on the GPLLJ may have changed after early 1990s, since when the El Niño changed from the conventional EP type to the newly-emerged CP type. A weakened GPLLJ and less transport of heat and moisture fluxes from the Gulf of Mexico into the Great Plains can lead to a drier environment in the central United States.