Evidence of the formation of noctilucent clouds due to propagation of an isolated gravity wave caused by a tropospheric occluded front

Abstract

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.

A case study of long gravity wave crests in noctilucent clouds and their origin in the upper tropospheric jet stream

“…In accordance to the error analysis of the NLC height given by Dalin et al . [], the precision of the height determination for this particular case of very low NLC elevation angles is in the range of 0.7–1.1 km, corresponding to the two‐pixel uncertainty. Given the precision of synchronization and the two‐pixel uncertainty of the NLC point identification, the total altitude uncertainty was estimated to be 0.9–1.3 km.…”

“…A full description of the NLC triangulation technique and its error analysis are given by Dalin et al . [].…”

“…Dalin et al . [] have shown that the passage of an occluded tropospheric front can excite an isolated GW due to strong horizontal wind shears at about 5 km altitude, propagating upward to NLC heights. Atmospheric fronts and instabilities in the upper tropospheric jet stream are supposed to be among the tropospheric GW sources [e.g., O'sullivan and Dunkerton , ; Uccellini and Koch , ; Zhang , ].…”

Common volume satellite studies of polar mesospheric clouds with Odin/OSIRIS tomography and AIM/CIPS nadir imaging

“…NLC camera networks can capture the horizontal evolution of a geographically limited region of the PMC layer. Numerous ground-based studies from NLC camera networks systems have led to remarkable insight into the complexity of spatial structures of the clouds, planetary wave influence on NLC occurrence frequency, gravity wave effects on the NLC layer and cloud height measurement (e.g., Dalin et al, 2016Dalin et al, , 2015Kirkwood and Stebel, 2003;Witt, 1962). Ground-based lidar systems on the other hand possess the unique capacity to monitor the vertical structure of the cloud with resolution as fine as 30 sec and 50 m (Baumgarten et al, 2012) and give detailed insight into the vertical structure and microphysical processes of a cloud as well as climatology and Atmos.…”

Results of Russian studies of the middle atmosphere (2015–2018)

“…Особенности в площади мезосферных облаков исследовались с использованием данных аппарата CIPS на спутнике AIM [17]. В работе [44] рассмотрен уникальный случай распространения внутренней гравитационной волны, которая генерировала компактный и тонкий слой серебристых облаков (СО) на высоте 82.7-85.2 км с характеристикой горизонтального масштаба 65-70 км, наблюдавшихся в Московской области ночью 18-19 ию ля 2013 г. Это продолжалось около часа. Модельное исследование показало, что волна имела тропосферный источник, связанный с прохождением окклюдированного фронта.…”