Updated Long‐Term Trends in Mesopause Temperature, Airglow Emissions, and Noctilucent Clouds

Abstract

We have updated long‐term trends in mesopause temperature, airglow emission intensities, and noctilucent clouds (NLCs) based on ground‐based observations conducted in the Moscow region (Russia). Trends in mesopause temperature and airglow emissions have been derived for the period 2000–2018 (19 years), and long‐term trends in NLC characteristics have been obtained for 1968–2018 (51 years). Trends in airglow emissions have been estimated separately for winter and summer seasons. There are statistically significant negative trends in molecular oxygen O2 A(0‐1) and hydroxyl OH(6‐2) emission intensities in both winter and summer. Responses of the airglow intensities to solar activity have been found to be significantly positive, with winter ones being 1.5–2 times greater than summer ones. There is a rather strong and statistically significant cooling of the summer mesopause at a rate of −2.4±2.3 K/decade, whereas the winter mesopause demonstrates a small and statistically insignificant cooling of −0.4±2.2 K/decade. The response of the mesopause temperature to solar activity is positive and about 2 times greater in winter than in summer. We consider long‐term trends in the summer mesopause temperature and NLC for the same time period and same geographical region. Secular trends in NLC parameters have been found to be small and statistically insignificant as observed from midlatitudes. NLCs demonstrate statistically significant negative response to solar activity. Ozone forcing produces minor effects on both airglow and NLC characteristics. The observed small secular NLC trends contradict large modeled NLC trends recently obtained by Lübken et al. (2018, https://doi.org/10.1029/2018GL077719).

Capability of Airline Jets as an Observation Platform for Noctilucent Clouds at Middle Latitudes

“…One can clearly see that there are signi cant spatial voids of 17-18 degrees between adjacent orbits of the AIM spacecraft at middle latitudes due to the spacecraft orbiting the Earth. These voids in the spatial midlatitude coverage produce gaps in PMCs observations by the CIPS instrument at middle latitudes as was mentioned in Dalin et al (2020a). On the other hand, expected sampling points based on the test observation by NH105 ight shows much denser distribution in longitude between 145° E and 215° E. We also see several NLC observations as seen from jets (red marks in Fig.…”

Capability of airline jets as an observation platform for noctilucent clouds at middle latitudes

“…One can clearly see that there are significant spatial voids of 17–18 degrees between adjacent orbits of the AIM spacecraft at middle latitudes due to the spacecraft orbiting the Earth. These voids in the spatial midlatitude coverage produce gaps in PMCs observations by the CIPS instrument at middle latitudes as was mentioned in Dalin et al ( 2020a ). This fact is one of the causes that makes difficult to observe NLCs in the middle latitude region by a satellite in a near-polar orbit.…”

Trends in the Airglow Temperatures in the MLT Region—Part 3: Ground-Based and SABER Measurements

“…Both datasets showed weak correlations with Ap index, with the SABER temperatures displaying a positive trend of 0.1 K/nT and the HPB OH temperatures a negative trend of 0.2 K/nT. While [28,29] suggested that a long-term trend study should be done separately for different seasons, and that "there is no physical sense to discuss a trend based on annual average temperatures" [28], we would argue otherwise. In order to minimize dynamical contribution from waves, seasonal variation, etc., the common procedure is to perform an average of the data on a timescale longer than the timescale of the variations.…”