DOI: 10.26042/wdcrsat.xzb5tzqg
title: Nocturnal means of OH(3-1) airglow rotational temperatures (version 1.0) from the mesopause region obtained at the Environmental Research Station “Schneefernerhaus” between 2009 and 2020, Germany

description: 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 5, GRIPS 7 and GRIPS 8) located at the Environmental Research Station “Schneefernerhaus” (UFS: 47.42°N, 10.98°E) - a measurement station of the international Network for the Detection of Mesospheric Change (NDMC). The instruments are operated by the German Remote Sensing Data Center (DFD) of the German Aerospace Center (DLR). The covered wavelength range 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. 660 km2 in 87 km height, as the instruments point southwards with a zenith angle of 45°. GRIPS 7 usually acquires one spectrum every 10s due to its outstanding performance. Both GRIPS 5 and GRIPS 7 were also operated with different field of views in the context of various sensitivity studies. Systematic differences due these changes were identified and accounted for in the calculation of the site mean temperature. The data set covers the time period from 1 July 2009 until 30 June 2020, i.e. 4018 nights / 11 years and thus it allows for a thorough investigation of the decade 2010-2019.
description: 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). All data are corrected for systematic differences caused by either calibration offsets or changes to the instruments (via linear relationships). The temperatures derived from GRIPS 8 serve as a reference in this context, because this instrument was not changed between 2010 and 2019, when it had to be repaired. If data from two instruments are available, a mean is only calculated if observation times differ less than 1.75 h (absolutely) and less than 17.5% (relatively) and observation times are longer than 3 h. Otherwise only data from the instrument with longer observation time is regarded if its observation amounts to at least 2 h. If observation time of both instruments is less than 2 h, data are flagged with “NaN”, i.e. missing value. In addition, two parameters contain the time series, in which the remaining gaps have been filled by either the 2010-2019 mean temperature for the respective date or by applying a combination of Harmonic Analysis (removing seasonal variation) and Maximum-Entropy Method (MEM) in its capacity as a linear prediction filter. Further 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. Concerning the MEM for gap interpolation refer to Bittner, M., Offermann, D. and H.H. Graf (2000): Mesopause temperature variability above a midlatitude station in Europe. Journal of Geophysical Research: Atmospheres 105(2), 2045-2058, https://doi.org/10.1029/1999JD900307.