On the assessment of the moisture transport by the Great Plains low-level jet

Abstract

Abstract. Low-level jets (LLJs) can be defined as wind corridors of anomalously high wind speed values located within the first kilometre of the troposphere. These structures are one of the major meteorological systems in the meridional transport of moisture on a global scale. In this work, we focus on the southerly Great Plains low-level jet, which plays an important role in the moisture transport balance over the central United States. The Gulf of Mexico is the main moisture source for the Great Plains low-level jet (GPLLJ), which has been identified as a key factor for rainfall modulation over the eastern and central US. The relationship between moisture transport from the Gulf of Mexico to the Great Plains and precipitation has been well documented in previous studies. Nevertheless, a large uncertainty still remains in the quantification of the moisture amount actually carried by the GPLLJ. The main goal of this work is to address this question. For this purpose, a relatively new tool, the regional atmospheric Weather Research and Forecasting Model with 3-D water vapour tracers (WRF-WVT; Insua-Costa and Miguez-Macho, 2018) is used together with the Lagrangian model FLEXPART to estimate the load of precipitable water advected within the GPLLJ. Both models were fed with data from ERA Interim. From a climatology of jet intensity over a 37-year period, which follows a Gaussian distribution, we select five cases for study, representing the mean and 1 and 2 standard deviations above and below it. Results show that the jet is responsible for roughly 70 %–80 % of the moisture transport occurring in the southern Great Plains when a jet event occurs. Furthermore, moisture transport by the GPLLJ extends to the north-east US, accounting for 50 % of the total in areas near the Great Lakes. Vertical distributions show the maximum of moisture advected by the GPLLJ at surface levels and maximum values of moisture flux about 500 m above, in coincidence with the wind speed profile.

Global atmospheric moisture transport associated with precipitation extremes: Mechanisms and climate change impacts

“…Eiras-Barca, Miguez-Macho, et al, 2019;Dominguez et al, 2018) of water vapor movements, respectively, using reanalysis data or high-resolution model simulations.…”

“…However, other than some limited weather analysis for LLJ impacts on regional precipitation extremes, in‐depth understanding of the mechanisms of LLJ occurrences and associated heavy precipitation from a climatology perspective is typically absent (Liu et al, ). The features of atmospheric moisture transports with LLJs and their contribution to precipitation totals and extremes were identified by the Euler's method (Berg et al, ) and the Lagrangian trajectory analyses (Algarra, Eiras‐Barca, Miguez‐Macho, et al, ; Dominguez et al, ) of water vapor movements, respectively, using reanalysis data or high‐resolution model simulations.…”

Atmospheric moisture transport and river runoff in the mid-latitudes

“…The source contribution from the Gulf of Mexico is similar in MAM as in JJA. During this warm season, the Bermuda High is shifted westward enhancing the Great Plains LLJ which results in large amounts of moisture being transported from the Gulf of Mexico as far as the northeast USA (Algarra et al, 2019).…”

“…So far, moisture source regions are mostly determined for present climate (Algarra et al, 2019;Bosilovich and Chern, 2006;Bosilovich and Schubert, 2001;Brubaker et al, 2001;Dirmeyer and Brubaker, 1999;Knoche and Kunstmann, 2013;Sodemann et al, 2008;Stohl and James, 2005). Consequently, one of the remaining questions in atmospheric moisture transport was stated in the review by Gimeno et al (2012): "How will climate change alter the location and significance of source regions and the transport of moisture from these toward continental areas in the future?"…”

“…A large set of climate models indicates that in the future those wet regions (southeast and Rocky Mountains) get wetter (CMIP3; Seager et al 2010 and CMIP5;. In summer time, moisture transport is related to the Great Plains low level jet, ranging from the Gulf of Mexico inlands (Algarra et al, 2019;Helfand and Schubert, 1995;Higgins et al, 1997). This supply of moisture, together with large surface fluxes results in convective precipitation in summer over the Mississippi basin.…”