The Great Plaines Irrigation Experiment (GRAINEX): Observations and LES studies

In the spring and summer of 2018, two intensive observation periods were conducted in Southeastern Nebraska by the National Center for Atmospheric Research Earth Observing Laboratory (EOL) and the Center for Sever Weather Research (CSWR), NASA's Hydrological Sciences Laboratory and a group of research universities. The objective of the experiment was to obtain an expansive observational data set to investigate the impact of irrigation on land-atmosphere coupling, particularly the diurnal planetary boundary layer evolution, outflow boundary development and evolution, low-level jet modification, and cloud and precipitation development on both local and regional scales. Southeastern Nebraska was chosen for its sharp gradient in applied irrigation across the Big Blue River region. The domain is one of the most heavily irrigated regions of the world thanks to the Ogallala Aquifer. Large Eddy Simulation nests are embedded in a mesoscale mother domain to examine the turbulent structure across a homogenous land cover (cropland) but with a soil moisture gradient that opposes the climatological gradient. Particular attention will be given to the contrasts of the following three periods: Morning transition through mid-morning when boundary layer growth and entrainment are maximized. Mid-morning though mid-afternoon in which surface and entrainment fluxes are well mixed in the boundary layer through sensible heating. Mid-afternoon through the afternoon-evening transition when turbulence collapses and a dewpoint maximum is achieved through moisture flux convergence in a stabilizing surface layer. Furthermore, the significance of accurate soil moisture initialization will be touched upon.