[1] Noctilucent Clouds (NLCs) are an important phenomenon of the summer mesopause region. While relatively common in high latitudes, NLCs are sparse (Ä 10% occurrence rate) below 60 ı latitude. We present the first study of diurnal variations of midlatitude NLCs based on lidar observations with full diurnal coverage at Kühlungsborn since 2010 independent from solar elevation. Overall, 100 h of NLCs with a backscatter coefficient ofˇm ax,532nm > 0.5 10 -10 m -1 sr -1 are observed within 1800 h. Occurrence rates decrease regularly from 12% at 5 local solar time (LST) to 2% at 19 LST. The mean NLC brightness varies between 1 and 3 10 -10 m -1 sr -1 with maxima at 4 and 18 LST. The simultaneously observed temperatures show a systematic (tidal) variation, but we do not find a direct relation to NLC rates. Comparing NLCs and ambient winds, we find strong indications for the meridional wind (advection) being the main driver for NLC occurrence above our site. Citation: Gerding, M., M. Kopp, P. Hoffmann, J. Höffner, and F.-J. Lübken (2013), Diurnal variations of midlatitude NLC parameters observed by daylight-capable lidar, and their relation to ambient parameters, Geophys. Res. Lett., 40,[6390][6391][6392][6393][6394]

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[1] Noctilucent clouds (NLC) are an important tracer of temperature and dynamics of the summer mesopause region. Our site at Kühlungsborn (Germany, 54 N) is at the equatorward edge of the NLC region and therefore of special interest for the understanding of these clouds. 41 nights (63 h) of NLC are observed since 1997. They form the largest lidar data set from mid-latitudes. NLC are typically weak, with nearly 70% having a backscatter coefficient b max,532nm < 2 Á 10 À10 m À1 sr À1 . The seasonal variation of NLC shows maximum occurrence around the temperature minimum (saturation maximum) but lower temperatures (higher saturation) at the beginning compared to the end of the season. Mean centroid altitude is 82.7 AE 0.03 km, with strong NLC being typically lower and vertically thinner compared to weak clouds.

Abstract. Temperature measurements by lidar are an important tool for the understanding of the mean state of the atmosphere as well as the propagation of gravity waves and thermal tides. Though, mesospheric lidar soundings are often limited to nighttime conditions (e.g., solar zenith angle > 96 • ) due to the low signal-to-noise ratio during the day. By this, examination of long-period gravity waves and tides is inhibited, as well as soundings in summer at polar latitudes. We developed a new daylight-capable RayleighMie-Raman (RMR) lidar at our site in Kühlungsborn, Germany (54 • N, 12 • E), that is in routine operation since 2010 for temperature soundings up to 90 km or ∼ 75 km (night or day) and soundings of noctilucent clouds. Here we describe the setup of the system with special emphasis on the daylight suppression methods like spatial and spectral filtering. The small bandwidth of the Fabry-Pérot etalons for spectral filtering of the received signal induces an altitude-dependent transmission of the detector. As a result, the signal is no longer proportional to the air density and the hydrostatic integration of the profile results in systematic temperature errors of up to 4 K. We demonstrate a correction method and the validity of correction by comparison with data obtained by our co-located, nighttime-only RMR lidar where no etalon is installed. As a further example a time series of temperature profiles between 20 and 80 km is presented for day and night of 9-10 March 2014. Together with the other data of March 2014 these profiles are used to calculate tidal amplitudes. It is found that tidal amplitudes vary between ∼ 1 and 5 K depending on altitude.

Daytime lidar operation in the middle atmosphere requires a narrow field of view (FOV) of the receiving telescope for effective background reduction and a high-transmission narrow-band detection. The laser beam position in the atmosphere relative to the optical axis of the receiving telescope is subject to high-frequency disturbances such as turbulence, vibration, and wind as well as comparable slow drift (thermal effects of the laser, stability of the building, etc.). We developed a beam stabilization system (BSS) that ensured a pulse-to-pulse stabilization of the laser beam with ∼ 3 μrad remaining jitter, allowing ∼ 60 μrad FOV. With BSS and single-pulse data acquisition system, the optimal alignment of the laser and telescope can be controlled, and information on the FOV and laser divergence in the far field can be derived. The capability of the BSS is to stabilize the laser against all internal and external disturbances below the repetition rate of the laser.Index Terms-Daylight Rayleigh lidar, laser beam stabilization system (BSS), middle atmosphere.