We analysed more than 30 years (1988–2021) of OH*(3,1) rotational temperatures observed from Wuppertal, Germany, with respect to periodic fluctuations (2 to 60 d) using the Lomb-Scargle periodogram. The main type of fluctuation observed in the last decades shows a period of about 28 d. Other periods which are frequently found in the observations lie in the period ranges around 2, 5 to 6, 8 to 12 d, and around 15 d and can likely be assigned to the quasi-2-day, the quasi-5-day, the quasi-10-day, and the quasi-16-day wave, respectively. The occurrence frequency of the waves is typically higher in winter time than in summer time because of the different wave filtering in summer and winter. This winter to summer difference holds for waves with longer periods, but it breaks off in the case of shorter periods below about 20 d. The occurrence frequency of these waves with periods below 20 d exhibit two smaller maxima around the equinoxes. A further division of these observations shows that waves with periods below 10 d account for the majority of observations in the month April to September. Waves with periods between 10 and 20 d are more equally observed throughout the year except for summer. The long-term behaviour of the wave activity indicates a quasi-bidecadal, which is likely driven by the amplitude of the waves.

We analysed the time series of OH*(3,1) rotational temperatures observed from Wuppertal in the time interval 1988 - 2022. The longterm evolution of the time series is characterised by two components. Firstly, we derived a significant correlation of the temperatures and the F10.7 cm solar radio flux. The sensitivity to the 11 -year cycle of solar activity is 4.8 +/- 0.7 K (100 SFU)-1. Then we show that the second major component in addition to this solar influence is a significant long-period oscillation. The oscillation has a period of P = 22.2 +/- 1.5 years with an amplitude of A = 1.8 +/- 0.4 K. A significant linear trend cannot be derived for the time series of OH*(3,1) rotational temperatures. Due to the long-period oscillation the derivation of linear trends heavily depends on the analysed time interval. This explains the different linear trends that have been derived in past studies for this time series. All of the previous results for this quantity are in good agreement with the long-period oscillation determined here, because different parts of the time series and, therefore, different parts of the oscillation (e.g mainly downswing or a complete cycle) have been analysed which led to largely different linear trends. (c) 2023 COSPAR. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Doppler asymmetric spatial heterodyne (DASH) interferometry is a novel concept for observing atmospheric winds. This paper discusses a numerical model for the simulation of fringe patterns and a methodology to correct fringe images for extracting Doppler information from ground-based DASH measurements. Based on the propagation of optical waves, the fringe pattern was modeled considering different angular deviations and optical aberrations. A dislocation between two gratings can introduce an additional spatial modulation associated with the diffraction order, which was seen in laboratory measurements. A phase correction is proposed to remove phase differences between different row interferograms, which is the premise for calculating the average interferogram to improve the signal-to-noise ratio. Laboratory tests, simulation results, and Doppler velocity measurements indicate that a matrix determined in the laboratory can be applied to correct interferograms obtained from ground-based DASH measurements.

Abstract The NDMC (Network for the Detection of Mesospheric Change) is a global network of measurement sites dedicated to the surveillance of the mesopause region. One main objective of the network is the early identification of climate signals. A key parameter is the mesopause temperature which can be derived from the emission spectrum of a layer of vibrationally excited hydroxyl (OH) at an altitude of approximately 87 km87\hspace{0.1667em}\text{km}. Foremost, emission lines in the SWIR regime between 1520 nm1520\hspace{0.1667em}\text{nm} and 1550 nm1550\hspace{0.1667em}\text{nm} are of interest for remote temperature sensing. This report deals with the development of a new generation of GRIPS instruments, which are commonly employed for the observation of mesopause temperatures. The new prototype demonstrates how the application of so called Spatial Heterodyne Interferometers (SHI) can overcome the limitations of currently used grating spectrometers, in terms of spectral resolution and optical throughput. The presented prototype proposes improvements in optical throughput and spectral resolution of about one order of magnitude, significantly reducing the uncertainties of the measured mesopause temperatures. Furthermore, an SHI can be built in monolithic configurations which are aligned and characterized once during assembly without the need of realignment at the measurement site. This makes SHI based instruments ideal for mobile applications.

We report on a thermally stable monolithic Doppler asymmetric spatial heterodyne (DASH) interferometer with field-widening prisms for thermospheric wind measurements by observing the Doppler shift of the airglow emission. Analytical deduction and numerical simulation are applied to determine the central optical path difference, the thermal compensation condition and the field-widening design. A monolithic interferometer with optimized configuration was built and tested in the laboratory. Laboratory tests show that the best visibility of 0.94 was realized with the 9 ° field-of-view illumination, while the thermal responses of the spatial frequency and the optical phase offset are 0.0154 cm−1/°C and 0.469 rad/°C, respectively.

The NDMC (Network for the Detection of Mesopause Change) is a global network of ground based observatories with the objective of monitoring key parameters of the mesopause region. For temperature monitoring GRound-based Infrared P-branch Spectrometers (GRIPS) are widely deployed. These spectrometers allow for the retrieval of the mesopause temperature from the OH* P-band emission lines around 1530 nm. A common technology for GRIPS instruments are spectrometers based on diffraction gratings. To overcome the limitations of conventional grating spectrometers, a new type of spectrometer is being developed within the project Metrology for Earth Observation and Climate - 3 (MetEOC-3) which is coordinated by the European Metrology Project for Innovation and Research (EMPIR). The new spectrometer shall improve the quality and traceability of the atmospheric data obtained by the NDMC. It is intended to serve as a reference instrument with significantly smaller measurement uncertainties. It is also designed to identify temperature trends of 1K/decade. A Spatial Heterodyne Interferometer (SHI) was chosen as the most promising technology, offering several advantages. Compared to conventional grating spectrometers, the throughput and resolution of the interferometer is one order of magnitude larger. The use of a two-dimensional detector array in combination with an imaging optics enables the detection of spatial temperature distributions in the mesopause region, as caused by dynamical processes like gravity waves. The talk gives an introduction to the technology of spatial heterodyne interferometry, and the new instrument design and calibration results are presented.

We present an approach to analyse time series with unequal spacing. The approach enables the identification of significant periodic fluctuations and the derivation of time-resolved periods and amplitudes of these fluctuations. It is based on the classical Lomb–Scargle periodogram (LSP), a method that can handle unequally spaced time series. Here, we additionally use the idea of a moving window. The significance of the results is analysed with the typically used false alarm probability (FAP). We derived the dependencies of the FAP levels on different parameters that either can be changed manually (length of the analysed time interval, frequency range) or that change naturally (number of data gaps). By means of these dependencies, we found a fast and easy way to calculate FAP levels for different configurations of these parameters without the need for a large number of simulations. The general performance of the approach is tested with different artificially generated time series and the results are very promising. Finally, we present results for nightly mean OH* temperatures that have been observed from Wuppertal (51∘ N, 7∘ E; Germany).

This article presents the characterization and analysis of a commercial off-the-shelf ( COTS) CMOS detector utilized in a miniaturized satellite payload for atmospheric temperature measurements. To evaluate the performance of the selected CMOS detector, a series of tests were performed. The temperature dependent dark current, the readout noise and the system gain are determined, which are provided for the subsequent system performance evaluation and data processing. A case study is established to simulate the space radiation effect to determine the needed shielding thickness on the instrument. The effect of radiation damage on the CMOS image sensors is investigated using a Co-60 Gamma radiation source.

We analyzed plasma scale height observations (about 80 km altitude) over the Eifel region (50 degrees N, 6 degrees E) observed from Kuhlungsborn (54 degrees N, 12 degrees E) in the time interval 1959-2016 and OH* temperatures (center altitude 87 km) observed from Wuppertal (51 degrees N, 7 degrees E) in the time interval 1988-2016. In summer months both time series show a dominant oscillation with a period of about two decades (20-26 years) with amplitudes of about 180 m and 3 K, respectively. These two oscillations are anticorrelated, because their observation altitudes are located above and below the temperature minimum in the mesopause region in summer, i.e. in a region of a positive and negative temperature gradient, respectively. We assume that a periodic vertical displacement of the mean temperature profile (upward and downward shifts following each other) in long-term variability leads to such an anticorrelated temperature evolution at the different observation altitudes. This mechanism is confirmed by SABER observation on board the TIMED satellite.

A highly miniaturized limb sounder for the observation of the O-2 A-band to derive temperatures in the mesosphere and lower thermosphere is presented. The instrument consists of a monolithic spatial heterodyne spectrometer (SHS), which is able to resolve the rotational structure of the R-branch of that band. The relative intensities of the emission lines follow a Boltzmann distribution and the ratio of the lines can be used to derive the kinetic temperature. The SHS operates at a Littrow wavelength of 761.8 nm and heterodynes a wavelength regime between 761.9 and 765.3 nm with a resolving power of about 8000 considering apodization effects. The size of the SHS is 38 x 38 x 27 mm(3) and its acceptance angle is +/- 5 degrees. It has an etendue of 0.01 cm(2) sr. Complemented by front optics with an acceptance angle of +/- 0.65 degrees and detector optics, the entire optical system fits into a volume of about 1.5 L. This allows us to fly this instrument on a 3- or 6-unit CubeSat. The vertical field of view of the instrument is about 60 km at the Earth's limb when operated in a typical low Earth orbit. Integration times to obtain an entire altitude profile of nighttime temperatures are on the order of 1 min for a vertical resolution of 1.5 km and a random noise level of about 1.5 K. Daytime integration times are 1 order of magnitude shorter. This work presents the design parameters of the optics and a radiometric assessment of the instrument. Furthermore, it gives an overview of the required characterization and calibration steps. This includes the characterization of image distortions in the different parts of the optics, visibility, and phase determination as well as flat fielding.

We present the analysis of annual average OH* temperatures in the mesopause region derived from measurements of the Ground-based Infrared P-branch Spectrometer (GRIPS) at Wuppertal (51° N, 7° E) in the time interval 1988 to 2015. The new study uses a temperature time series which is 7 years longer than that used for the latest analysis regarding the long-term dynamics. This additional observation time leads to a change in characterisation of the observed long-term dynamics. We perform a multiple linear regression using the solar radio flux F10.7 cm (11-year cycle of solar activity) and time to describe the temperature evolution. The analysis leads to a linear trend of (−0.089 ± 0.055) K year−1 and a sensitivity to the solar activity of (4.2 ± 0.9) K (100 SFU)−1 (r2 of fit 0.6). However, one linear trend in combination with the 11-year solar cycle is not sufficient to explain all observed long-term dynamics. In fact, we find a clear trend break in the temperature time series in the middle of 2008. Before this break point there is an explicit negative linear trend of (−0.24 ± 0.07) K year−1, and after 2008 the linear trend turns positive with a value of (0.64 ± 0.33) K year−1. This apparent trend break can also be described using a long periodic oscillation. One possibility is to use the 22-year solar cycle that describes the reversal of the solar magnetic field (Hale cycle). A multiple linear regression using the solar radio flux and the solar polar magnetic field as parameters leads to the regression coefficients Csolar = (5.0 ± 0.7) K (100 SFU)−1 and Chale = (1.8 ± 0.5) K (100 µT)−1 (r2 = 0.71). The second way of describing the OH* temperature time series is to use the solar radio flux and an oscillation. A least-square fit leads to a sensitivity to the solar activity of (4.1 ± 0.8) K (100 SFU)−1, a period P = (24.8 ± 3.3) years, and an amplitude Csin = (1.95 ± 0.44) K of the oscillation (r2 = 0.78). The most important finding here is that using this description an additional linear trend is no longer needed. Moreover, with the knowledge of this 25-year oscillation the linear trends derived in this and in a former study of the Wuppertal data series can be reproduced by just fitting a line to the corresponding part (time interval) of the oscillation. This actually means that, depending on the analysed time interval, completely different linear trends with respect to magnitude and sign can be observed. This fact is of essential importance for any comparison between different observations and model simulations.

The paper seeks to explore an alternative explanation for the change in slope of the OH temperature time series previously reported in earlier publications using a shorter time series. While the results are promising, I believe there is an overall shortcoming in the analysis technique. While this may not substantially change the overall results, it does put into question their statistical significance. When fitting data using an orthogonal basis set, one can fit the functions simultaneously or sequentially, where the first function is subtracted from the data and the next fit to the residuals. However, in this paper there is a combination orthogonal functions (sinusoids in the case of the periodogram) and non-orthogonal functions (solar cycles and trends) fitted to the data sequentially. For example in Section 4.1, the solar 10.7 cm flux and a trend first are correctly fitted simultaneously as they are non-orthogonal. However, on page 7, lines 1-13, a periodogram, which fits a set of orthogonal sinu-C1

The global distribution of traveling planetary wave (PW) activity in the mesopause region is estimated for the first time from ground-based airglow measurements. Monthly and total mean climatologies of PW power are determined from rotational temperatures measured at 19 sites from 78° N to 76° S which contribute to the Network for the Detection of Mesospheric Change (NDMC). Wave power is expressed as the standard deviation of nocturnal mean temperature around the seasonal temperature variation. The results from 20° N confirm the SABER traveling PW proxy by Offermann et al. (2009, J. Geophys. Res. 114, D06110) at two altitudes. Most sites between 69° S and 69° N show total mean traveling PW activity of about 6K, and only some high latitude sites have considerably higher activity levels. At the two tropical sites, there is practically no seasonal variation of PW activity. At 70% of the midlatitude sites, the seasonal variation is moderate for most of the year, but it is quite appreciable at all high latitude sites. Results about traveling PW activity at 87km and 95km available from several sites signal similar behavior at both altitudes. The total mean climatological results here obtained have further been used to separate the traveling PW contribution from the superposition of wave types contained in OH rotational temperature fluctuations measured by the SCIAMACHY instrument on Envisat. A narrow equatorial wave activity maximum is probably caused by gravity waves, while a tendency towards greater activity at higher northern latitudes may be due to stationary planetary waves.

This paper presents a set of observations and analyses of trace gas cross sections in the extratropical upper troposphere/lower stratosphere (UTLS). The spatially highly resolved (≈0.5 km vertically and 12.5 km horizontally) cross sections of ozone (O3), nitric acid (HNO3), and peroxyacetyl nitrate (PAN), retrieved from the measurements of the CRISTA-NF infrared limb sounder flown on the Russian M55-Geophysica, revealed intricate layer structures in the region of the subtropical tropopause break. The chemical structure in this region shows an intertwined stratosphere and troposphere. The observed filaments in all discussed trace gases are of a spatial scale of less than 0.8 km vertically and about 200 km horizontally across the jet stream. Backward trajectory calculations confirm that the observed filaments are the result of a breaking Rossby wave in the preceding days. An analysis of the trace gas relationships between PAN and O3 identifies four distinct groups of air mass: polluted subtropical tropospheric air, clean tropical upper-tropospheric air, the lowermost stratospheric air, and air from the deep stratosphere. The tracer relationships further allow the identification of tropospheric, stratospheric, and the transitional air mass made of a mixture of UT and LS air. Mapping of these air mass types onto the geo-spatial location in the cross sections reveals a highly structured extratropical transition layer (ExTL). Finally, the ratio between the measured reactive nitrogen species (HNO3 + PAN + ClONO2) and O3 is analysed to estimate the influence of tropospheric pollution on the extratropical UTLS. In combination, these diagnostics provide the first example of a multi-species two-dimensional picture of the inhomogeneous distribution of chemical species within the UTLS region. Since Rossby wave breaking occurs frequently in the region of the tropopause break, these observed fine-scale filaments are likely ubiquitous in the region. The implications of the layered structure for chemistry and radiation need to be examined, and the representation of this structure in chemistry-climate models is discussed.

The CRISTA-NF (Cryogenic Infrared Spectrometers and Telescope for the Atmosphere - New Frontiers) instrument is an airborne infrared limb sounder operated aboard the Russian research aircraft M55-Geophysica. The instrument successfully participated in a large Arctic aircraft campaign within the RECONCILE (Reconciliation of essential process parameters for an enhanced predictability of Arctic stratospheric ozone loss and its climate interactions) project in Kiruna (Sweden) from January to March 2010. This paper concentrates on the measurements taken during one flight of the campaign, which took place on 2 March in the vicinity of the polar vortex. We present two-dimensional cross-sections of derived volume mixing ratios for the trace gases CFC-11, O-3, and ClONO2 with an unprecedented vertical resolution of about 500 to 600 m for a large part of the observed altitude range (a parts per thousand 6-19 km) and a dense horizontal sampling along flight direction of a parts per thousand 15 km. The trace gas distributions show several structures, for example a part of the polar vortex and a vortex filament, which can be identified by means of O-3-CFC-11 tracer-tracer correlations. The observations made during this flight are interpreted using the chemistry and transport model CLaMS (Chemical Lagrangian Model of the Stratosphere). Comparisons of the observations with the model results are used to assess the performance of the model with respect to advection, mixing, and the chemistry in the polar vortex. These comparisons confirm the capability of CLaMS to reproduce even very small-scale structures in the atmosphere, which partly have a vertical extent of only 1 km. Based on the good agreement between simulation and observation, we use artificial (passive) tracers, which represent different air mass origins (e.g. vortex, tropics), to further analyse the CRISTA-NF observations in terms of the composition of air mass origins. These passive tracers clearly illustrate the observation of filamentary structures that include tropical air masses. A characteristic of the Arctic winter 2009/10 was a sudden stratospheric warming in December that led to a split of the polar vortex. The vortex re-established at the end of December. Our passive tracer simulations suggest that large parts of the re-established vortex consisted to about 45% of high- and mid-latitude air.

Abstract. The CRISTA-NF (Cryogenic Infrared Spectrometers and Telescope for the Atmosphere – New Frontiers) instrument is an airborne infrared limb sounder operated aboard the Russian research aircraft M55-Geophysica. The instrument successfully participated in a large Arctic aircraft campaign within the RECONCILE (Reconciliation of essential process parameters for an enhanced predictability of Arctic stratospheric ozone loss and its climate interactions) project from January to March 2010 in Kiruna, Sweden. This paper concentrates on the measurements during one flight of the campaign, which took place on 2 March in the vicinity of the polar vortex. We present two-dimensional cross-sections of volume mixing ratios for the trace gases CFC-11, O3, and ClONO2 with an unprecedented vertical resolution of about 500 to 600 m for a large part of the observed altitude range and a dense horizontal sampling along flight direction of ≈ 15 km. The trace gas distributions show several structures like the polar vortex and filaments composed of air masses of different origin. The situation during the analysed flight is simulated by the chemistry and transport model CLaMS (Chemical Lagrangian Model of the Stratosphere) and compared with the measurements to assess the performance of the model with respect to advection, mixing, and the chemistry in the polar vortex. These comparisons confirm the capability of CLaMS to reproduce even very small-scale structures in the atmosphere. Based on the good agreement between simulation and observation, we use a model concept utilising artificial tracers to further analyse the CRISTA-NF observations in terms of air mass origin. A characteristic of the Arctic winter 2009/10 was a sudden stratospheric warming in early December that led to a split of the polar vortex. The vortex re-established at the end of December. Our passive tracer simulations suggest that large parts of the re-established vortex consisted to about 45% of high- and mid-latitude air.

The Cryogenic Infrared Spectrometers and Telescope for the Atmosphere – New Frontiers (CRISTA-NF), an airborne infrared limb-sounder, was operated aboard the high-flying Russian research aircraft M55-Geophysica during the Arctic RECONCILE campaign from January to March 2010. This paper describes the calibration process of the instrument and the retrieval algorithm employed and then proceeds to present retrieved trace gas volume mixing ratio cross-sections for one specific flight in this campaign. We are able to resolve the uppermost troposphere/lower stratosphere for several trace gas species for several kilometres below the flight altitude (16 to 19 km) with an unprecedented vertical resolution of 400 to 500 m for the limb-sounding technique. The instrument points sideways with respect to the flight direction. Therefore, the observations are also characterised by a rather high horizontal sampling along the flight track, which provides a full vertical profile every ≈15 km. Assembling the vertical trace gas profiles derived from CRISTA-NF measurements to cross-sections shows filaments of vortex and extra-vortex air masses in the vicinity of the polar vortex.During this campaign, the M55-Geophysica carried further instruments enabling trace gas volume mixing ratios derived from CRISTA-NF to be validated by comparing them with measurements by the in situ instruments HAGAR and FOZAN and observations by MIPAS-STR. This validation suggests that the retrieved trace gas volume mixing ratios are both qualitatively and quantitatively reliable.