A Comparative Analysis of the Impact of Low-Level Jets and Atmospheric Rivers in the Central U.S.

Abstract

We present a comparative analysis of atmospheric rivers (ARs) and Great Plains low-level jets (GPLLJs) in the central U.S. during April–September 1901–2010 using ECMWF’s CERA-20C. The analysis is motivated by a perceived need to highlight overlap and synergistic opportunities between traditionally disconnected AR and GPLLJ research. First, using the Guan–Walliser integrated vapor transport (IVT)-based AR classification and Bonner–Whiteman-based GPLLJ classification, we identify days with either an AR and/or GPLLJ spanning 15% of the central U.S. These days are grouped into five event samples: 1) all GPLLJ, 2) AR GPLLJ, 3) non-AR GPLLJ, 4) AR non-GPLLJ, and 5) all AR. Then, we quantify differences in the frequency, seasonality, synoptic environment, and extreme weather impacts corresponding to each event sample. Over the 20th century, April–September AR frequency remained constant whereas GPLLJ frequency significantly decreased. Of GPLLJ days, 36% are associated with a coincident AR. Relative to ARs that are equally probable from April–September, GPLLJs exhibit distinct seasonality, with peak occurrence in July. A 500 hPa geopotential height comparison shows a persistent ridge over the central U.S for non-AR GPLLJ days, whereas on AR GPLLJ days, a trough and ridge pattern is present over western to eastern CONUS. AR GPLLJ days have 34% greater 850 hPa windspeeds, 53% greater IVT, and 72% greater 24-hour precipitation accumulation than non-AR GPLLJ days. In terms of 95th percentile 850 hPa windspeed, IVT, and 24-hour precipitation, that of AR GPLLJs is 25%, 45%, and 23% greater than non-AR GPLLJs, respectively.