Low-level Jet Water Vapor Transport Observed by Ground-based and Airborne Lidars

Understanding precipitation in the Great Plains (GP) region of the United States is important for agriculture and severe weather prediction, but many challenges exist in accurately forecasting the frequent warm season nocturnal convective systems in the GP. The large multi-agency Plains Elevated Convection at Night (PECAN) field campaign of 2015 was designed to study these precipitation events and related phenomena such as low-level jets (LLJs). GPLLJs are known to carry momentum, warm temperatures, and moisture northward, priming the atmosphere for convection or feeding directly into storms. While this role of the GPLLJ is known and documented on the large-scale, only one previous study in the literature (to the authors’ knowledge) has examined this moisture transport in high resolution. Other past studies have been limited to relatively coarse radiosonde launches or reanalysis data.

This presentation will utilize lidar and other observations from PECAN to examine the detailed structure of LLJ moisture transport in space and time. Specifically, a case study of 11 July 2015 has been chosen, wherein supercells are sustained and grow overnight downwind of a strong LLJ. Spatial and temporal heterogeneities in the LLJ moisture field will be presented with special attention to features affecting the nearby convection. Two fixed ground sites hosted Doppler lidars and water vapor lidars (DIAL and Raman), allowing calculation of horizontal moisture advection in stationary timeseries profiles. Separate PECAN aircraft hosting the NASA Lidar Atmospheric Sensing Experiment (LASE) DIAL and the University of Wyoming compact Raman lidar (CRL) provide a mesoscale spatial perspective on the water vapor field. The CRL also profiles temperature and lidar scattering ratio, aiding analysis of the evolving convective environment. Findings will be compared to convection-allowing WRF ensemble forecasts that were used operationally during PECAN.