Teleconnections Governing the Interannual Variability of Great Plains Low-Level Jets in May

A spectral analysis of Great Plains 850-hPa meridional winds (V850) from ECMWF's coupled climate reanalysis of 1901-2010 (CERA-20C) reveals that their warm season (April-September) interannual variability peaks in May with 2-6-yr periodicity, suggestive of an underlying teleconnection influence on low-level jets (LLJs). Using an objective, dynamical jet classification framework based on 500-hPa wave activity, we pursue a large-scale teleconnection hypothesis separately for LLJs that are uncoupled (LLJUC) and coupled (LLJC) to the upper-level jet stream. Differentiating between jet types enables isolation of their respective sources of variability. In the U.S. south-central plains (SCP), May LLJCs account for nearly 1.6 times more precipitation and 1.5 times greater V850 compared to LLJUCs. Composite analyses of May 250-hPa geopotential height (Z250) conditioned on LLJC and LLJUC frequencies highlight a distinct planetary-scale Rossby wave pattern with wavenumber 5, indicative of an underlying circumglobal teleconnection (CGT). An index of May CGT is found to be significantly correlated with both LLJC (r = 0.62) and LLJUC (r = -0.48) frequencies. Additionally, a significant correlation is found between May LLJUC frequency and NAO (r = 0.33). Further analyses expose decadal-scale variations in the CGT-LLJC and CGT-LLJUC teleconnections that are linked to the PDO. Dynamically, these large-scale teleconnections impact LLJ class frequency and intensity via upper-level geopotential anomalies over the western United States that modulate near-surface geopotential and temperature gradients across the SCP.

Automated summary

A spectral analysis and objective dynamical jet classification framework were used to investigate the interannual variability of Great Plains 850-hPa winds during the warm season, with a peak in May potentially influenced by teleconnections. Differentiating between jet types revealed significant differences in precipitation and wind intensity in the U.S. south-central plains, with distinct planetary-scale Rossby wave patterns indicating underlying teleconnections. These large-scale teleconnections impact LLJ class frequency and intensity through upper-level geopotential anomalies, modulating near-surface geopotential and temperature gradients.