Investigation of the phenomenon "mesospheric bore" based on observations of all-sky cameras and satellites

Understanding the mechanisms of air mass movement is very important and remains a pressing issue in the era of global climate change. Occasionally, among the usual wave disturbances in the mesosphere, one can observe the manifestation of a clearly distinguishable wave front that separates a part of the space already involved in the wave process from the area in which oscillations have not yet occurred. This wave phenomenon was given the name – mesospheric bore. Mesospheric bore, which is an amplification of atmospheric gravity waves, can affect the flows of momentum and energy, and thereby affect the thermal regime and composition at all levels of the atmosphere. In this study, two mesospheric bore events recorded over the Maimaga test site (63.0° N, 129.5° E) located in the central part of Yakutia are considered. The registration of this phenomenon was carried out in the airglow of the night sky of the all-sky cameras (emission of hydroxyl OH and atomic oxygen [OI] radiation). The first event was observed on November 19, 2017, the second event – ​​on January 30, 2022. The phase velocity of the bore propagation, its direction of motion, the length of successive internal gravity waves, the wave period, the time and duration of the event were calculated. Knowing the propagation velocity of the bore and the time required for its formation, the approximate radius of the bore formation region was calculated. The passage of the mesospheric bore is accompanied by a sudden jump in temperature in the structure of the mesospheric inversion layers (MIL). In this regard, in the supposed region of bore formation, the data on the upper atmosphere temperatures of the Aura Microwave Limb Sounder (MLS) satellite observations and the instantaneous temperature of the MLT region (mesosphere and lower thermosphere) of the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on board the TIMED satellite were analyzed. Based on temperature data, vertical profiles of the square of the Brent-Väisälä frequency were constructed to check the static stability of MIL, which is a favorable condition for the mesospheric bore. The bore, in the all-sky camera airglow emission, can be dark or light, depending on the altitude of its passage. Having summarized all the data obtained from images and satellites, an approximate calculation of the mesospheric bore propagation altitude was made. After that, to find possible sources of mesospheric bore generation, synoptic maps of the Arctic and Antarctic Research Institute (AARI) and global maps of winds and weather conditions according to NCEP (National Centers for Environmental Prediction) were studied. Airflow movements at different geopotential altitudes (700 hPa, 500 hPa, 250 hPa, 70 hPa) were considered. During both events, the hydrometeorology and environmental monitoring department issued storm warnings for severe cyclones in the proposed area of the bore formation.