The influence of climate change on low‐level jet characteristics over the South‐Central Plains as simulated by CMIP5 models

Abstract

Previous studies have projected the Central Plains low‐level jet (LLJ) to form more frequently over the South‐Central Plains region in the future, with limited projected changes in its speed and height. This work's objective was to assess future LLJ characteristics with wind speed outputs obtained from the Phase 5 of the Coupled Model Intercomparison Project (CMIP5) suite of models. Improvements in model resolution and simulation of climate dynamics relevant to LLJs were made in CMIP5, and a multi‐model study that focuses specifically on the LLJ's future state using these models is yet to be done. Occurrences of LLJs were identified by applying an LLJ definition based on wind shear to six‐hourly vertical wind profiles derived from the model outputs. Changes in future LLJ speed, frequency, and height versus a historical control were subsequently calculated on seasonal and diurnal temporal scales. As seen in previous work, the largest expected changes in LLJ characteristics are those of its frequency, especially in summer, autumn, and at night. Evidence was also found for large increases in frequency in the northern half of the study region, consistent with previous expectations. CMIP5 models with finer horizontal and vertical resolutions tended to project greater increases in LLJ frequency than those with coarse resolutions. Projected changes in LLJ speed and height were by contrast largely insignificant, also consistent with previous findings. However, these characteristics, along with frequency, exhibited notable diurnal variability in historical and future simulations, especially in winter. An increase in cold‐season LLJ variability could have implications for the consistency of synoptically driven LLJs. This finding, along with the projected warm‐season poleward shift in the LLJ's frequency maximum over the study region, elucidates the LLJ's future state as projected by a selection of CMIP5 models, and the consequences for processes that depend upon the LLJ's consistency.

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

“…Improving mechanistic understanding, modeling, and forecasting of the GPLLJ has been a research priority for over half a century (e.g., Blackadar, 1957; Bonner, 1968; Du & Rotunno, 2014; Holton, 1967; Parish, 2017; Shapiro et al., 2016; Smith et al., 2019), spurred by the GPLLJ’s relevance to regional wind and water resources (e.g., Barandiaran et al., 2013; Wilczak et al., 2015), severe weather (e.g., Weaver et al., 2012), heatwaves (e.g., Thomas et al., 2020), aviation (e.g., Gultepe et al., 2019), and pollutant transport (e.g., Corsmeier et al., 1997). More recently, efforts to simulate future GPLLJ strength, northward extent, and seasonality (e.g., Tang et al., 2017; Wimhurst & Greene, 2020), including the effects of an ever‐increasing U.S. irrigation‐equipped area on the GPLLJ (e.g., Arcand et al., 2019; Yang et al., 2020), are trending.…”