Stratospheric observations of noctilucent clouds: a new approach in studying middle- and large-scale mesospheric dynamics

Abstract

The Stratospheric Observations of Noctilucent Clouds (SONC) experimental campaign was conducted on the night of 5–6 July 2018 with the aim of photographing noctilucent clouds (NLCs) and studying their large-scale spatial dynamics at scales of 100–1450 km. An automated high-resolution camera (equipped with a wide-angle lens) was lifted by a stratospheric sounding balloon to 20.4 km altitude above the Moscow region in Russia (∼56∘ N, 41∘ E), taking several hundreds of NLC images during the flight that lasted 1.7 h. The combination of a high-resolution camera and large geographic coverage (∼1500 km) has provided a unique technique of NLC observations from the stratosphere, which is impossible to currently achieve from either the ground or space. We have estimated that a horizontal extension of the NLC field as seen from the balloon was about 1450×750 km, whereas it was about 800×550 km as seen from the ground. The NLC field was located in a cold area of the mesopause (136–146 K), which was confirmed by satellite measurements. The southernmost edge of the NLC field was modulated by partial ice voids of 150–250 km in diameter. A medium-scale gravity wave had a wavelength of 49.4±2.2 km and an amplitude of 1.9±0.1 km. The final state of the NLC evolution was represented by thin parallel gravity wave stripes. Balloon-borne observations provide new horizons in studies of NLCs at various scales from metres to thousands of kilometres. Here we present a review paper on our experiment describing the initial results. Detailed studies on the time evolution of the cloud movements will be done in the future.