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- ItemAtomic oxygen number densities in the mesosphere–lower thermosphere region measured by solid electrolyte sensors onWADIS-2(Katlenburg-Lindau : Copernicus, 2019) Eberhart, Martin; Löhle, Stefan; Strelnikov, Boris; Hedin, Jonas; Khaplanov, Mikhail; Fasoulas, Stefanos; Gumbel, Jörg; Lübken, Franz-Josef; Rapp, MarkusAbsolute profiles of atomic oxygen number densities with high vertical resolution have been determined in the mesosphere-lower thermosphere (MLT) region from in situ measurements by several rocket-borne solid electrolyte sensors. The amperometric sensors were operated in both controlled and uncontrolled modes and with various orientations on the foredeck and aft deck of the payload. Calibration was based on mass spectrometry in a molecular beam containing atomic oxygen produced in a microwave discharge. The sensor signal is proportional to the number flux onto the electrodes, and the mass flow rate in the molecular beam was additionally measured to derive this quantity from the spectrometer reading. Numerical simulations provided aerodynamic correction factors to derive the atmospheric number density of atomic oxygen from the sensor data. The flight results indicate a preferable orientation of the electrode surface perpendicular to the rocket axis. While unstable during the upleg, the density profiles measured by these sensors show an excellent agreement with the atmospheric models and photometer results during the downleg of the trajectory. The high spatial resolution of the measurements allows for the identification of small-scale variations in the atomic oxygen concentration. © Author(s) 2019. This work is distributed under the Creative Commons Attribution 4.0 License.
- ItemPhotocurrent modelling and experimental confirmation for meteoric smoke particle detectors on board atmospheric sounding rockets(Katlenburg-Lindau : Copernicus, 2018-9-20) Giono, Gabriel; Strelnikov, Boris; Asmus, Heiner; Staszak, Tristan; Ivchenko, Nickolay; Lübken, Franz-JosefCharacterising the photoelectron current induced by the Sun's UV radiation is crucial to ensure accurate daylight measurements from particle detectors. This article lays out the methodology used to address this problem in the case of the meteoric smoke particle detectors (MSPDs), developed by the Leibniz Institute of Atmospheric Physics in Kühlungsborn (IAP) and flown on board the PMWEs (Polar Mesosphere Winter Echoes) sounding rockets in April 2018. The methodology focuses on two complementary aspects: modelling and experimental measurements. A detailed model of the MSPD photocurrent was created based on the expected solar UV flux, the atmospheric UV absorption as a function of height by molecular oxygen and ozone, the photoelectric yield of the material coating the MSPD as a function of wavelength, the index of refraction of these materials as a function of wavelength and the angle of incidence of the illumination onto the MSPD. Due to its complex structure, composed of a central electrode shielded by two concentric grids, extensive ray-tracing calculations were conducted to obtain the incidence angles of the illumination on the central electrode, and this was done for various orientations of the MSPD in respect to the Sun. Results of the modelled photocurrent at different heights and for different materials, as well as for different orientations of the detector, are presented. As a pre-flight confirmation, the model was used to reproduce the experimental measurements conducted by Robertson et al. (2014) and agrees within an order of magnitude. An experimental setup for the calibration of the MSPD photocurrent is also presented. The photocurrent induced by the Lyman-alpha line from a deuterium lamp was recorded inside a vacuum chamber using a narrowband filter, while a UV-sensitive photodiode was used to monitor the UV flux. These measurements were compared with the model prediction, and also matched within an order of magnitude. Although precisely modelling the photocurrent is a challenging task, this article quantitatively improved the understanding of the photocurrent on the MSPD and discusses possible strategies to untangle the meteoric smoke particles (MSPs) current from the photocurrent recorded in-flight.
- ItemAdvanced hodograph-based analysis technique to derive gravity-wave parameters from lidar observations(Katlenburg-Lindau : Copernicus, 2020) Strelnikova, Irina; Baumgarten, Gerd; Lübken, Franz-JosefAn advanced hodograph-based analysis technique to derive gravity-wave (GW) parameters from observations of temperature and winds is developed and presented as a step-by-step recipe with justification for every step in such an analysis. As the most adequate background removal technique the 2-D FFT is suggested. For an unbiased analysis of fluctuation whose amplitude grows with height exponentially, we propose applying a scaling function of the form exp (z∕(ςH)), where H is scale height, z is altitude, and the constant ς can be derived by a linear fit to the fluctuation profile and should be in the range 1–10. The most essential part of the proposed analysis technique consists of fitting cosine waves to simultaneously measured profiles of zonal and meridional winds and temperature and subsequent hodograph analysis of these fitted waves. The linear wave theory applied in this analysis is extended by introducing a wave packet envelope term exp(−(z−z0)2/2σ2) that accounts for limited extent of GWs in the observational data set. The novelty of our approach is that its robustness ultimately allows for automation of the hodograph analysis and resolves many more GWs than can be inferred by the manually applied hodograph technique. This technique allows us to unambiguously identify upward- and downward-propagating GWs and their parameters. This technique is applied to unique lidar measurements of temperature and horizontal winds measured in an altitude range of 30 to 70 km.
- ItemIntercomparison of middle-atmospheric wind in observations and models(Katlenburg-Lindau : Copernicus, 2018-4-6) Rüfenacht, Rolf; Baumgarten, Gerd; Hildebrand, Jens; Schranz, Franziska; Matthias, Vivien; Stober, Gunter; Lübken, Franz-Josef; Kämpfer, NiklausWind profile information throughout the entire upper stratosphere and lower mesosphere (USLM) is important for the understanding of atmospheric dynamics but became available only recently, thanks to developments in remote sensing techniques and modelling approaches. However, as wind measurements from these altitudes are rare, such products have generally not yet been validated with (other) observations. This paper presents the first long-term intercomparison of wind observations in the USLM by co-located microwave radiometer and lidar instruments at Andenes, Norway (69.3∘ N, 16.0∘ E). Good correspondence has been found at all altitudes for both horizontal wind components for nighttime as well as daylight conditions. Biases are mostly within the random errors and do not exceed 5–10 m s−1, which is less than 10 % of the typically encountered wind speeds. Moreover, comparisons of the observations with the major reanalyses and models covering this altitude range are shown, in particular with the recently released ERA5, ECMWF's first reanalysis to cover the whole USLM region. The agreement between models and observations is very good in general, but temporally limited occurrences of pronounced discrepancies (up to 40 m s−1) exist. In the article's Appendix the possibility of obtaining nighttime wind information about the mesopause region by means of microwave radiometry is investigated.