Abstract
Abstract. Large-scale spatial structures of mesospheric bores were observed by the Visible and near-Infrared Spectral Imager (VISI) of the ISS-IMAP mission (Ionosphere, Mesosphere, upper Atmosphere and Plasmasphere mapping mission from the International Space Station) in the mesospheric O2 airglow at 762 nm wavelength. Two mesospheric bore events in southern midlatitudes are reported in this paper: one event at 48–54∘ S, 10–20∘ E on 9 July 2015 and the other event at 35–43∘ S, 24∘ W–1∘ E on 7 May 2013. For the first event, the temporal evolution of the mesospheric bore was investigated from the difference of two observations in consecutive passes. The estimated eastward speed of the bore is 100 m s−1. The number of trailing waves increased with a rate of 3.5 waves h−1. Anticlockwise rotation with a speed of 20∘ h−1 was also recognized. These parameters are similar to those reported by previous studies based on ground-based measurements, and the similarity supports the validity of VISI observation for mesospheric bores. For the second event, VISI captured a mesospheric bore with a large-scale and undulating wave front. The horizontal extent of the wave front was 2200 km. The long wave front undulated with a wavelength of 1000 km. The undulating wave front is a new feature of mesospheric bores revealed by the wide field of view of VISI. We suggest that nonuniform bore propagating speed due to inhomogeneous background ducting structure might be a cause of the undulation of the wave front. Temperature measurements from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) onboard the Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) satellite indicated that bores of both events were ducted in a temperature inversion layer.
Highlights
A mesospheric bore is characterized by a propagating and sharp front in the upper mesosphere
The front was captured in two consecutive passes so that the temporal evolution of the structure can be investigated from the observations
The O2 airglow brightness on the western side of the front is 2500–3000 R, which is 250 %–300 % brighter than that on the eastern side. Another enhancement of airglow brightness can be seen at 15–18◦ E, but the boundary of this enhancement is not sharp, and we will not focus on this enhancement in this study
Summary
A mesospheric bore is characterized by a propagating and sharp front in the upper mesosphere. The mesospheric bore model in a thermal duct has been examined and validated using simultaneous lidar and airglow imager observations (Smith et al, 2003, 2005; She et al, 2004). It has been demonstrated with simultaneous radar observations that wind has an important role in the background condition of mesospheric bores (Fechine et al, 2009; Giongo et al, 2018). Space-borne airglow imaging is a strong tool to study mesospheric bores with global observational coverage and a wider FOV, and can overcome the limitations of ground-based observations. This paper is the first report of an undulating bore front
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