13.2 High-Temporal Resolution Ground-Based Observations of an Eastern Kansas Bore during the PECAN Field Campaign

Thursday, 14 January 2016: 3:45 PM
Room 350/351 ( New Orleans Ernest N. Morial Convention Center)
David M. Loveless, University of Wisconsin-Madison, Madison, WI; and N. Smith, C. M. Rozoff, T. J. Wagner, D. D. Turner, W. F. Feltz, and S. Ackerman
Manuscript (3.7 MB)

The Plains Elevated Convection at Night (PECAN) field campaign took place from 1 June to 15 July 2015 in the Central Plains of the United States. This campaign was designed to provide intensive observation periods of nocturnal convection in the Plains. Missions focused on nocturnal convection in the presence of a stable boundary layer, nocturnal low-level jet, and elevated instability. Two of the primary goals of PECAN were 1) to determine what observations are needed to improve forecasts of formation and evolution of nocturnal convection and 2) to advance the knowledge of wave-like features caused by nocturnal convection. A major question associated with mesoscale boundary layer waves is their role in convective initiation. A prevailing hypothesis is that these wave-like features can be a source of convective initiation by lifting air parcels from the stable boundary layer up to a level of free convection.

Given the spatial and temporal resolution of the North American radiosonde network, in situ observations of thermodynamic variables and wind profiles during boundary layer wave events are rare. PECAN aimed to overcome this by deploying a network of mobile vehicles, including eight mobile radars and four mobile profiling systems. Two of the mobile profiling units used during PECAN were 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 observations of the stable boundary layer, ideal for observing boundary layer waves caused by nocturnal convection.

On 26 June 2015, convection in northeast Kansas resulted in a bore that moved southeast across the network of mobile units, the result being a rich set of observations on the space-time evolution of a mesoscale bore. Initial results show that vertical velocities of parcels in the stable boundary layer exceeded 1 m s-1 at onset, which will be further analyzed in the work proposed. Additionally, we attempt to provide insight into if/why this bore was a trigger for convective initiation in eastern Kansas and as such, contribute to current theories on wave-driven nocturnal convective initiation. This will provide a new set of observations with which to enhance our understanding of bores and nocturnal convective initiation. A better understanding of nocturnal convection could benefit society by increasing the lead time and accuracy of severe weather forecasts, which is critical for saving lives.

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