Mesoscale moisture transport by the low-level jet during the IHOP field experiment

Abstract

Previous studies of the Low-Level Jet (LLJ) over the Central Great Plains of the U.S. have been unable to determine the role that mesoscale and smaller circulations play in the transport of moisture. To address this issue, two aircraft missions during the International H2O Project (IHOP) were designed to closely observe a well-developed LLJ over the Great Plains (primarily Oklahoma and Kansas) with multiple observation platforms. In addition to standard operational platforms (most importantly radiosondes and profilers) to provide the large-scale setting, dropsondes released from the aircraft at 55 km intervals and a pair of onboard lidar instruments (HRDL for wind and DIAL for moisture) observed the moisture transport in the LLJ at greater resolution. Using these observations, we describe the multiscalar structure of the LLJ. We then focus attention on the bulk properties and effects of scales of motion by computing moisture fluxes through cross-sections that bracket the LLJ. From these computations, we are also able to compute Reynolds averages within the cross-sections. This allows us to estimate the bulk effect of integrated estimates of the contribution of small-scale (meso- to convective-scale) circulations to the overall transport. Finally, we briefly examine the performance of the Weather Research and Forecasting (WRF) model in forecasting the intensity and evolution of the LLJ for this case.