# Long-Term Trend of Noctilucent Cloud Altitude Detected: A Comparison of Positional Data with Historical Measurements

“Long-Term Trend of Noctilucent Cloud Altitude Detected: A Comparison of Positional Data with Historical Measurements” (2026), by Oleg S. Ugolnikov et al. Earth and Planetary Sciences research paper. Original abstract below, unchanged. A free PDF is available.

- Authors: Oleg S. Ugolnikov, Ilya S. Yankovsky, М. В. Клименко, Egor O. Ugolnikov, Andrey M. Tatarnikov, Желтоухов Сергей Геннадьевич
- Published: October 30, 2026
- Field: Earth and Planetary Sciences
- DOI: https://doi.org/10.48550/arxiv.2610.41750
- Free PDF: https://arxiv.org/pdf/2610.41750

## Abstract

A large number of photometric and photographic position data of noctilucent clouds (NLC) obtained at 54-61 deg N, 29-50 deg E in 2020-2026 is used, comprising about 20,000 individual measurements of the altitude of NLC fragments recorded by a number of cameras. Comparison with published long-base triangulation measurements starting from 1890 reveals a descending trend in NLC altitude with a 99.5% confidence level. The current descent rate is -1.2 km per century, or half of the model prediction based on the current increase of CO2 in the atmosphere. Other factors that can influence NLC altitude are considered: solar longitude (season), local solar time, lunar tides, latitude, and solar activity. Two independent methods of NLC altitude determination based on the same photometric data are considered and compared.

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