Occurrence of Mesospheric Frontal Structures Over the High Latitude Station, Tromsø, Norway

Observational data sets for the high latitude middle atmosphere are key to understand the dynamics over those latitudes and the coupling between the lower and middle atmosphere. Utilizing long‐term data sets from an all‐sky imager at Tromsø, Norway (69.6°N, 19.2°E), the characteristics of 18 mesospheric frontal events in the Arctic winter mesosphere from 2011 to 2015 were studied. These frontal events exhibit horizontal extensions exceeding 500 km and were characterized by a sharp leading front, sometimes followed by a quasi‐monochromatic wave train or a turbulent region. A subset of these frontal gravity wave events has been identified in the past as “bores.” While there have been numerous previous reports from low‐ and mid‐latitude sites, and also from southern high latitudes, there have been a few from northern high latitudes. This study focuses on the frontal events in the northern high latitudes and provides new insights into the characteristics of these events. Their horizontal wavelengths primarily ranged from 20 to 40 km, and they exhibited phase speeds in the range 30–80 m/s. Most events were observed before local midnight. No clear link between these events and auroral activity was found. The majority of fronts were found propagating in the north‐west direction, which might be due to the wind filtering effects. Plain Language Summary To better understand the dynamics of the high latitude middle atmosphere, we used long‐term data from various instruments in Tromsø, Norway. Our focus was on examining mesospheric frontal events that occurred in the Arctic winter mesosphere between 2011 and 2015. These events were notable for their large horizontal extent, often exceeding 500 km, and their distinctive characteristics, such as a sharp leading front, followed at times by a wave train or a region of turbulence. Some of these events were previously referred to as “bores.” While similar events have been reported for lower and mid‐latitudes, there has been limited research focusing on northern high latitudes. Our study fills this gap, providing new insights into this phenomenon. We found that such events are less frequent in the northern high latitudes compared to the southern high latitudes. These frontal structures mostly traveled in directions ranging from northwest to north, and also to the southeast. While there was no clear link between these events and auroral activity, the majority of fronts were found to be propagating in the northwest direction,