The Circumglobal Teleconnection’s Role in Modulating the Interannual Variability of May Great Plains Low-Level Jets

Abstract:

A spectral analysis of Great Plains 850-hPa meridional winds (V850) from ECMWF’s coupled climate reanalysis of 1901-2010 (CERA-20C) reveals that the greatest warm season interannual variability in low level jet (LLJ) frequency occurs in May and the V850 2-6 year variability mode contributes 42% of the total variance. The prominence of LLJ’s 2-6 year variability mode points to a large-scale teleconnection component to May LLJ variability. By using an objective, dynamical jet classification framework based on 500-hPa wave activity, we pursue a large-scale teleconnection hypothesis separately for Great Plains LLJs that are uncoupled (LLJUC) and coupled (LLJC) to the upper-level jet stream. Separate analyses of teleconnection influences on LLJC and LLJUC lead to identifying for the first time, a very clear signature of the Circumglobal Teleconnection (CGT) influence on LLJ frequency and dynamical class in May; positive and negative phases of CGT support LLJC and LLJUC event frequencies, respectively. Over the 1901-2010 period, CGT explains almost 38% of variability in May LLJC frequency and 23% of variability in May LLJUC frequency. Of the total variance explained by the CGT, nearly 50% is contributed by the western U.S. CGT center-of-action and the remaining 50% by remote CGT centers-of-action in the Pacific Ocean and Asia. Further analyses expose decadal scale changes in the CGT-LLJC(UC) teleconnection attributable to decadal variability of the PDO. In brief, a positive CGT in conjunction with a negative PDO phase increases LLJC frequencies whereas a negative CGT in conjunction with a positive PDO phase increases LLJUC frequencies. The impetus to better understand and predict May LLJs is related to their association with nearly 40% of May precipitation received in the Great Plains, which dictates growing season initial soil moisture and regional drought susceptibility.