A multidiagnostic investigation of the mesospheric bore phenomenon

Abstract

[1] 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 1 2 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 À1 km À1 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.

First observation of an undular mesospheric bore in a Doppler duct

“…These observational facts lead us to believe that the front should be a mesospheric bore suggested by Dewan and Picard (2001), which is: the presence of an extended bright front, followed by short wavelength wave trains and the presence of wave ducting condition. Several previous works have used the same criteria (Medeiros et al, 2001Smith et al, 2003Smith et al, , 2005She et al, 2004;Fechine et al, 2005). A similar mesospheric wave front has also been observed by Swenson et al (1998).…”

“…The occurrence of this sort of event would be associated with a temperature inversion layer that Correspondence to: A. F. Medeiros (afragoso@df.ufcg.edu.br) acts as a wave duct. Smith et al (2003) and She et al (2004) first reported simultaneous occurrence of the mesospheric bore and temperature inversion layer. Since then it has been recognized that the inversion layer could play an important role in the formation of the mesospheric bore.…”

Upper atmospheric gravity wave details revealed in nightglow satellite imagery

“…Many DNB-observed nightglow wave features have no obvious ties to lower atmospheric forcing (e.g., produce a readily identifiable signature in nightglow emissions (47). From a surface observer's perspective, the visual appearance of a bore's passage entails a sudden brightening of the night sky (the "bright night" effect; 48), followed by a sharp wave front associated with the hydraulic jump, and finally a series of linearly oriented alternating bright and dark bands (49). This trailing wave pattern, the bore's principle mechanism for energy dissipation, is phase-locked to the hydraulic jump.…”

Imaging science at El Leoncito, Argentina

“…The highly curved nature of the wave fronts indicates that the source region was relatively localized and nearby, but a search of limited meteorological data on that night was not conclusive. Far more dramatic was the passage of the mesospheric bore event on 22 August 2001 (lower panel) that resulted in a strong reduction in the O( 1 S) emission brightness due to an upward displacement in the O( 1 S) layer height (Taylor et al, 1995;Smith et al, 2003). More thorough studies of mesospheric dynamics will be possible with a new detector installed at El Leoncito in early 2006, together with additional diagnostics systems from collaborating scientists.…”