Boundary Layer Evolution during Bore Events as Observed by a Mobile Profiling System during PECAN

Atmospheric bores are a type of gravity wave that form when a density current interacts with a stable boundary layer. Bores are thought to aid in nocturnal convective initiation by changing boundary layer stability via turbulent mixing and by mechanically lifting air parcels from the stable boundary layer up to a level of free convection. Because of their importance to nocturnal convective initiation, it is important to understand the thermodynamic and dynamic effects that bore passages may have on the stable boundary layer.

Given the spatial and temporal resolution of the North American radiosonde network, observations of thermodynamic variables and wind profiles of bore passages are rare to non-existent outside of specially focused field campaigns. The Plains Elevation Convection At Night (PECAN) field project aimed to overcome this by utilizing a network of fixed profiling sites and deploying a network of mobile vehicles, including eight mobile radars and four mobile profiling systems. The fixed sites provided continuous sampling of the boundary layer every day during the campaign, while mobile profiling systems were used to profile the boundary layer for time periods of several hours in particular locations of interest. The University of Wisconsin Space Science and Engineering Center (SSEC) Portable Atmospheric Research Center (SPARC) was one such mobile sounding system and was equipped with a Doppler Lidar and an Atmospheric Emitted Radiance Interferometer (AERI). The Doppler Lidar uses a laser at 1.5 microns to measure horizontal wind speed and direction and vertical velocities in the lower 2500 meters of the atmosphere. AERI measures downwelling infrared radiation from 520 to 3000 cm^-1, at a spectral resolution of about 1 cm^-1, from which temperature and moisture profiles can be retrieved. Combined, these two instruments offer high-temporal resolution kinematic and thermodynamic observations of the stable boundary layer, ideal for observing boundary layer waves. In addition to remotely sensing boundary layer winds, temperature, and moisture, radiosondes were also launched to validate the instruments and offer in situ observations of the boundary layer.

Data from SPARC is used to identify the evolution of the boundary layer during the five SPARC-observed bores during the PECAN campaign. Temperature, moisture, and wind retrievals from AERI and the Doppler lidar will be analyzed to determine characteristic changes of boundary-layer stability in the pre- and post-bore environment. These observations will be validated by comparing to the collocated radiosonde launches. This analysis paves the way to integrating the other fixed and mobile profiling datasets, that use the same instrumentation, helping to characterize the ducting layer of bores and providing insight into the role of bores in the convective initiation process.