OH airglow temperatures above the Environmental Research Station Schneefernerhaus (UFS) at one minute resolution

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 spectra have been obtained with the Ground-based Infrared P-branch Spectrometers (GRIPS) located at the Environmental Research Station “Schneefernerhaus” (UFS: 47.42°N, 10.98°E, GRIPS 7 and GRIPS 8) and additionally at the German Aerospace Center at Oberpfaffenhofen (OPN: 48.09°N, 11.28°E), Germany. The instruments are operated by the German Remote Sensing Data Center (DFD) of the German Aerospace Center (DLR) and are part of the international Network for the Detection of Mesospheric Change (NDMC). The data set comprises 32 nights with parallel observations of the UFS Rayleigh lidar operated at 355 nm, which were obtained between 2018 and 2024. The data are used in the study of Trickl et al. : "Temperature profiles combined from lidar and airglow measurements", under discussion at AMT: https://doi.org/10.5194/egusphere-2025-1952). 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. During routine operation one spectrum is obtained every 15s, originating from a field of view of approximately 15° x 15°, which corresponds to ca. 560 km² in 87 km height (applying to GRIPS 6 at OPN, which performs observations in zenith direction). The instruments GRIPS 7 and GRIPS 8 operated at UFS point in southward direction with a zenith angle of 45° leading to a slightly larger field of view (FoV). 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). Retrievals of data versions “v1.0” and “v1.4” are identical with the only difference being that “v1.4” indicates a recalibration of the instrument. Details concerning the derivation of rotational temperatures from the airglow are presented in Schmidt, C., Höppner, K. and Bittner, M. (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. Details of the UFS instruments (including conversion factors if more recent physical constants are used in the retrieval) are discussed in Schmidt, C., Küchelbacher, L., Wüst, S. and Bittner, M. (2023): OH airglow observations with two identical spectrometers: benefits of increased data homogeneity in the identification of variations induced by the 11-year solar cycle, the QBO, and other factors. Atmospheric Measurement Techniques (AMT), Vol. 16, 19, 4331-4356. https://doi.org/10.5194/amt-16-4331-2023. At UFS GRIPS 7 and GRIPS 8 perform parallel observations and serve as each other’s backup. Since GRIPS 7 is operated at a higher temporal resolution of 10s the signal-to-noise ratio (SNR) of GRIPS 8 is usually slightly higher. Therefore, the observations of GRIPS 8 are favored in the comparison to the UFS lidar, if GRIPS 8 observations are available. Systematic differences between the instruments are discussed in the above-mentioned study by Schmidt et al. (2023). Temperatures of GRIPS 7 (TG7) are systematically lower than those obtained with GRIPS 8 (TG8), with the best estimates being TG7=0.989*TG8+0.110 K before August 2019 and TG7=0.994*TG8-0.608 K since October 2019. Note: the latter value is more reliable due to a substantially larger data base contributing to the evaluation (1912 nights versus 544 nights, latest assessment: March 2025). The systematic differences may therefore be identical throughout the entire period. The one minute mean values contain one line of parameters for each minute (averages of the high resolution data). Averages are calculated for the exact minute and contain high resolution data acquired ±30s around this time stamp. Therefore, the entries are equidistant and in case of missing or low quality values the entries are given as NaN (IEEE floating values for not a number). The name structure of the data file is GRIPS_X_YYYYMM_D1D2_UTC_1MIN_MEAN_v1.X.dat, with the “GRIPS_X_” part never changing for the given instrument, the “YYYYMM_D1D2_” part noting the given night of observation (e.g., 201912_3101 for December 31st 2019 to January 1st 2020) and “v1.X” describing the processing version. One-minute mean values are always given in UTC. CAUTION: Due to the averaging to exact UTC minutes the first and the last entry of the file may not contain any observations. However, integer values cannot be set to NaN, therefore an 8-digit asterisk entry may appear instead (i.e. “********”). The following table describes the content of the ASCII-file containing the data (separator between two columns is “two blanks” aka “ ” aka ”2X”). Column parameter unit Format description 1 time stamp UTC I24 ISO8601 2 temperature Kelvin F7.2 - 3 Temperature uncertainty Kelvin F6.1 - 4 P1(2)-intensity a.u. F7.1 refers to line center only (“one pixel”) 5 P1(3)-intensity a.u. F7.1 refers to line center only (“one pixel”) 6 P1(4)-intensity a.u. F7.1 refers to line center only (“one pixel”) 7 P(3-1)-intensity (branch) a.u. F8.1 Integrated (1520.5-1546.5nm) 8 Q(3-1)-intensity (branch) a.u. F8.1 Integrated (1496-1514nm) 9 Q(4-2)-intensity (branch) a.u. F8.1 Integrated (1579-1596nm) 10 uncertainty of line intensities a.u. F6.1 refers to line intensities (columns 4,5,6), “one pixel” 11 residual background intensity a.u. F6.1 minimum intensity between 1543nm and 1551nm (“one pixel”) 12 total intensity a.u. F9.1 sum of all 512 pixels (comparable to branch intensities) 13 number of contributing raw spectra n.a. I2 maximum = 4 (for 15s high resolution data; = 6 in case of GRIPS 7), minimum = 2 14 time stamp UTC F16.8 Julian date