The Impact of Soil Moisture on the Oklahoma Dryline During the 2011 Drought

During April and May 2011, evolution of drought over Oklahoma impacted surface conditions such that an atypical pattern of soil moisture developed. Along with this, drylines developed anomalously to the east in conjunction with this anomalous pattern of soil moisture, further strengthening this atypical pattern. To quantify the impact of variable surface conditions on dryline evolution and convective initiation (CI) during this period, simulations were completed using the WRF-ARW for multiple dryline cases. Specifically, soil moisture conditions were altered to “wet” and “dry” across the entire domain by replacing the CONTROL soil moisture values by each soil categories soil porosity (MOIST) or wilting point (DRY) volumetric soil moisture value. As a result, numerous impacts on the dryline boundaries simulated in each simulation were noted when compared to the CONTROL simulation which utilized high resolution land data assimilation system (HRLDAS) surface conditions as truth for the initialization of surface conditions. Overall, the dryline boundary, dryline position, and CI during each case were modified depending on the removal or addition of soil moisture over the domain. Accumulated precipitation was also affected by the modification of soil moisture, with a negative feedback being analyzed for most of the sensitivity simulations. Removal of soil moisture resulted in an eastward shift of the dryline boundary, warmer and drier near-surface conditions along with a drier and deeper (on the order of 0.5 – 1 km deeper) planetary boundary layer, with the addition of soil moisture having the opposite effects. Further, the position of the dryline during May, under weak synoptic forcing or quiescent conditions, was extremely sensitive to surface conditions. This is compared to April dryline simulations in which the differences were not as significant. The simulations demonstrated that modifying surface conditions impacted the nature of the dryline during this period, and showed that soil moisture conditions which developed during the early warm season in 2011 (1) modified the typical dryline pattern and (2) led to the evolution and perpetuation of drought over Oklahoma in 2011.-7-2015-->