Nocturnal means of OH(3-1) airglow rotational temperatures from the mesopause region above Europe obtained during the minimum between solar cycles 24 and 25

The temperatures are derived from the rotational vibrational transition of the OH molecule originating from a thin layer in approximately 86-87 km centroid height. The respective spectra have been obtained with the Ground-based Infrared P-branch Spectrometers (GRIPS) at eight different sites located across Europe. The contributing observation sites are located at Oberpfaffenhofen (OPN; 48.09°N, 11.28°E), Germany, at Otlica Observatory (OTL; 45.94°N, 13.91°E), Slovenia, at Sonnblick Observatory (SBO; 47.05°N, 12.96°E), Austria, at the Environmental Research Station Schneefernerhaus (UFS; 47.42°N, 10.98°E), Germany, at the Evgeni Kharadze Georgian National Astrophysical Observatory in Abastumani (ABA; 42.82°N, 41.75°E), Georgia, at Catania (CAT; 37.51°N, 15.04°E), Italy, at the Observatoire de Haute-Provence (OHP; 43.93°N, 5.71°E), France and at Wuppertal (WUP; 51.25°N, 7.15°E), Germany. The data set covers the time period from the night of 31st July 2019 to 1st October 2019 (62 nights). All instruments are part of the international Network for the Detection of Mesospheric Change (NDMC). The data are analyzed in detail by Mackovjak et al. (2025) submitted Earth and Space Science. The wavelength range covered by the instruments allows the observation of the OH(3-1) Q- and P-branches as well as of the OH(4-2) R- and Q-branches. Rotational temperatures are calculated using OH(3-1) P-branch emissions between 1520 nm and 1550 nm. Details concerning the derivation of rotational temperatures from the airglow are presented in Schmidt et al. (2013): A ground-based spectrometer equipped with an InGaAs array for routine observations of OH(3-1) rotational temperatures in the mesopause region. Journal of Atmospheric and Solar-Terrestrial Physics (JASTP) 102 (2013) 125–139. https://dx.doi.org/10.1016/j.jastp.2013.05.001. All GRIPS are equipped with a Czerny-Turner spectrograph and a thermoelectrically cooled InGaAs array. Only the P1(2), P1(3) and P1(4) rotational lines of the (3-1) vibrational transition are used for the derivation of temperatures. Intensities are only read out at the line centers of the smoothed spectra due to residual overlapping of the lines at their wings. Important physical constants applied during the processing are taken from Mies (1974) (Einstein coefficients) and Krassovsky et al. (1962) (rotational term values). For the estimation of a nocturnal mean (individual time series) value all samples of the nightly temperature time series are weighted according to their individual precision. Thus, mean temperatures are between 1 and 2 K lower compared to the unweighted arithmetic mean (cloud covered periods are excluded from analysis; insufficient removal however will result in low precision values with a warm bias due to spectral characteristics of water / ice droplets). Data of a given night from a specific site are regarded only if its effective observation amounts to at least 2 h. The following table describes the content of the ASCII-file containing the data (separator between two columns is “,” aka a comma). Column parameter unit Format description 1 date ISO8601 A 20-character string 2 temperature Kelvin F5.1 refers to site in column #4 3 temperature Kelvin F6.2 mean of all sites for date in column #1 4 NDMC site code n.a. A 3-character string 5 Longitude Degree F5.2 refers to site in column #4 6 Latitude Degree F5.2 refers to site in column #4