We report on the first common volume ground‐based and space measurements of the mesospheric front in noctilucent clouds (NLCs). The detailed ground‐based observations were performed with automated digital cameras located at the Athabasca University Geophysical Observatory (Canada) on the night of 29–30 June 2012, while simultaneous space measurements were conducted onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite using the Sounding of the Atmosphere using Broadband Emission Radiometry instrument. The large temperature difference of 20–25 K between two different air masses at about 85 km altitude was responsible for the front jump separating the area filled with NLCs from the area with no NLCs. The front jump (soliton) had a pronounced elevation of 12 km up to the altitude of 96 km relative to the undisturbed NLC layer located between 84.5 and 86.3 km. Considering present and previous ground‐based measurements of the NLC height, we conclude that altitude of 96–97 km is the upper limit of possible heights of NLCs.

Atmospheric gravity waves with very long crests (of 450–500 km length) and short horizontal wavelengths of about 20 km were observed in noctilucent clouds and were studied in detail for the first time. The gravity waves were slowly moving in opposite direction to the background wind indicating their forced generation outside the mesopause region. A ray‐tracing analysis using meteorological reanalysis and empirical atmospheric model data shows that a source of such peculiar gravity waves observed in noctilucent clouds was located near the tropopause and could be associated with the jet stream at altitudes 8–10 km. Two considered examples of very long wave crests confirm a significant role of the upper tropospheric jet stream as a source of gravity waves and reveal that these waves could propagate without critical levels to the mesopause in summertime.

We consider a unique case of a propagating internal gravity wave that has generated in situ a compact and thin layer of noctilucent clouds (NLC) at 82.7-85.2 km with a characteristic horizontal scale of 65-70 km, as observed in the Moscow region on the night of 18-19 July 2013. This particular transient isolated gravity wave together with the whole NLC layer suddenly appeared in the clear twilight sky and lasted about 1 h traveling eastward, which differs significantly from previously observed cases of gravity waves propagating through preexisting NLC layers. Our model studies demonstrate that the wave had a tropospheric source connected to the passage of an occluded front. The wave was likely generated due to strong horizontal wind shears at about 5 km altitude.

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