A multidiagnostic investigation of the mesospheric bore phenomenon

Abstract

Imaging measurements of a bright wave event in the nighttime mesosphere were made on 14 November 1999 at two sites separated by over 500 km in the southwestern United States. The event was characterized by a sharp onset of a series of extensive wavefronts that propagated across the entire sky. The waves were easily visible to the naked eye, and the entire event was observed for at least 5 hours. The event was observed using three wide‐angle imaging systems located at the Boston University field station at McDonald Observatory (MDO), Fort Davis, Texas, and the Starfire Optical Range (SOR), Albuquerque, New Mexico. The spaced imaging measurements provided a unique opportunity to estimate the physical extent and time history of the disturbance. Simultaneous radar neutral wind measurements in the 82 to 98 km altitude region were also made at the SOR which indicated that a strong vertical wind shear of 19.5 ms−1km−1 occurred between 80 and 95 km just prior to the appearance of the disturbance. Simultaneous lidar temperature and density measurements made at Fort Collins, Colorado, ∼1100 km north of MDO, show the presence of a large (∼50 K) temperature inversion layer at the time of the wave event. The observations indicated that the event was most probably due to an undular mesospheric bore, a relatively uncommon disturbance which has only recently been reported [Taylor et al., 1995a]. Evidence is also shown to suggest that a large east‐west tropospheric frontal system lying over the northern United States was the origin of the disturbance.