Effects of Irrigation on Planetary Boundary Layer Turbulence

As part of the Great Plains Irrigation Experiment (GRAINEX), two atmospheric profiling sites with 915 MHz wind profilers and lidar ceilometers were deployed as part of an extensive observation network. These observations are combined with results from idealized numerical modeling to determine the influence of irrigation on planetary boundary layer turbulence, with a particular focus on Horizontal Convective Rolls (HCRs). Previously, HCRs have been found to occur in PBLs with specific heat flux and wind shear regimes, which could potentially be modified by changes to soil moisture brought on by irrigation. To analyze this effect, eight case days were simulated using the Regional Atmospheric Modeling System (RAMS). Each case was initialized using atmospheric and soil moisture observations from GRAINEX for both irrigated and non-irrigated conditions. Preliminary results suggest that higher soil moisture contents associated with irrigation do act to decrease turbulent kinetic energy and HCR updraft/downdraft velocities. TKE is decreased by 5% on average across all cases and peak updraft velocity is reduced by 0.5 m s-1 compared to non-irrigated scenarios. Notably, these effects are detected in the morning PBL, when the atmosphere has not yet integrated the cumulative effect of soil moisture on daytime boundary layer heating. These results will be contrasted with observational analysis from the irrigated and non-irrigated profiling sites to verify the conclusions.