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

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 their warm season (April-September) interannual variability peaks in May with 2-6 year 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 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-five, 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(LLJUC) teleconnection 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 U.S. that modulate near-surface geopotential and temperature gradients across the SCP.

Changes in Great Plains Low‐Level Jet Structure and Associated Precipitation Over the 20th Century

“…Coupled jet properties in NGP and CGP and uncoupled jet properties in CGP share a median breakpoint of 1941–1942, which closely corresponds with a December 1943 breakpoint detected in the CERA‐20C‐derived Pacific Decadal Oscillation index (PDO) of Agrawal et al. (2021). PDO was predominantly positive over the two decades preceding 1943 and remained predominantly negative from 1944 until July 1976, when a well‐known shift back to its positive phase took place (e.g., Meehl et al., 2009).…”

“…PDO was predominantly positive over the two decades preceding 1943 and remained predominantly negative from 1944 until July 1976, when a well-known shift back to its positive phase took place (e.g., Meehl et al, 2009). A positive PDO and its associated large-scale circulation (e.g., Newman et al, 2016) have previously been linked to suppressed May coupled jet frequency in the Plains (Agrawal et al, 2021; their Figure 9c). Consistent with that work, July NGP and CGP and August CGP coupled jet frequencies are found here to be significantly inversely correlated with PDO (not shown).…”

“…At interannual time scales, variations in the seasonality and/or frequency of both jet types is likely related to a circumglobal teleconnection outlined by Agrawal et al (2021), NASH (e.g., Zhou et al, 2021), and collective changes in the positioning of the mid-latitude jet stream (e.g., Burrows et al, 2020; their Figure 1). At decadal-to-multidecadal timescales, jet variability has been linked to atmospheric conditions in the North Pacific as indexed by the PDO, especially during May (Agrawal et al, 2021). The analysis was designed to complement Burrows et al (2020) but by adopting its Eulerian perspective inherited certain limitations.…”

“…(2021), NASH (e.g., Zhou et al., 2021), and collective changes in the positioning of the mid‐latitude jet stream (e.g., Burrows et al., 2020; their Figure 1). At decadal‐to‐multidecadal timescales, jet variability has been linked to atmospheric conditions in the North Pacific as indexed by the PDO, especially during May (Agrawal et al., 2021).…”

“…Coupled jet structural changes are more likely to be linked to remote, atmospheric circulation changes, whereas uncoupled jet structural changes are more likely to be linked to local land-atmosphere interactions. At interannual time scales, variations in the seasonality and/or frequency of both jet types is likely related to a circumglobal teleconnection outlined by Agrawal et al (2021), NASH (e.g., Zhou et al, 2021), and collective changes in the positioning of the mid-latitude jet stream (e.g., Burrows et al, 2020; their Figure 1). At decadal-to-multidecadal timescales, jet variability has been linked to atmospheric conditions in the North Pacific as indexed by the PDO, especially during May (Agrawal et al, 2021).…”