Lidar Observations of Water Vapor Transport via Low-level Jets in PECAN

Understanding precipitation in the Great Plains (GP) region of the United States is crucial for local agriculture and severe weather prediction, but many challenges still exist in accurately forecasting the frequent warm season nocturnal rainfall in the GP. The large cooperative Plains Elevated Convection at Night (PECAN) field campaign of 2015 was designed to study these GP summertime nocturnal precipitation events and related phenomena such as low-level jets (LLJs). A LLJ is most simply defined as a strong wind speed maximum in the lower troposphere with a significant decrease in wind speed at higher altitudes. GPLLJs are known to carry moisture northward from the Gulf of Mexico into the GP, priming the atmosphere for condensation or feeding directly into storms. According to the paper by Higgins et al. (1997) on this topic, the GPLLJ increases the nocturnal moisture budget by more than 45% on average over summer nocturnal mean values. While this crucial role of the GPLLJ for moisture is known and documented on the large-scale, only one previous study in the literature (to the author’s knowledge) has examined this moisture transport in high resolution. Other past studies have been limited to relatively coarse twice daily radiosonde launches or reanalysis data.

This presentation will utilize lidar data from PECAN to examine the finer structure behavior of LLJ moisture transport in space and time. Three fixed ground sites hosted Doppler lidars and water vapor lidars (using either DIAL or Raman methods), allowing calculation of horizontal moisture flux in stationary timeseries profiles. Separate PECAN aircraft hosted the NASA LASE DIAL system and the University of Wyoming compact Raman lidar, providing a spatial overview of the LLJ water vapor. Differences in moisture flux in and around the LLJ as well as linkages to GP rainfall events will be examined and presented in a case-study format.