Lidar measurements of noctilucent clouds at Rio Grande, Tierra del Fuego, Argentina

Kurzfassung

Noctilucent clouds (NLC) are sensitive tracers of upper mesospheric temperature, water vapor and dynamics and thus open windows to study our atmosphere from very large to very small scales, including topics of climate, circulation, waves and turbulence. At northern hemisphere mid-latitudes, the occurrence of NLC seems to increase with time. NLC are weaker in the southern hemisphere, but no vertical soundings at southern hemisphere mid-latitudes had been available until now. We determine the properties of NLC above a southern-hemisphere mid-latitude site at 53.8° S in southern Argentina. The Compact Rayleigh Autonomous Lidar provides high-resolution vertical lidar soundings since 2017. Noctilucent clouds are detected every summer, with the earliest (latest) detection on 29 November (29 January), in total 19 events of 33.8 h length, at an average height of 83.3 km, with a maximum brightness of 24 × 10-10/m/sr, an occurrence rate of 6 % and a maximum in the morning hours (5–7 UT, i.e. 2–4 LT). The latter coincides with a positive amplitude of the semi-diurnal tide of the meridional wind as measured by the Southern Argentina Agile Meteor Radar. The ambient temperature above the site is on average too high to support local ice formation. We find no correlation with the solar flux; indeed, the latest season of 2023/2024 shows the most NLC detections. This leaves transport from more southerly, colder regions and potentially increasing upper mesospheric water vapor levels as a result of increasing space traffic as possible explanations for the occurrence and unexpectedly large brightness of NLC above Rio Grande.