M. Kopp

Diurnal variations of midlatitude NLC parameters observed by daylight-capable lidar and their relation to ambient parameters

rence rate) below 60 i latitude. We present the first study of diurnal variations of midlatitude NLCs based on lidar obser- vations with full diurnal coverage at Kuhlungsborn since 2010 independent from solar elevation. Overall, � 100 h of NLCs with a backscatter coefficient ofmax,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 � 1a nd� 3 � 10 -10 m -1 sr -1 with maxima at 4 and 18 LST. The simultaneously observed temperatures show a system- atic (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. Hoffner, and F.-J. Lubken (2013), Diurnal variations of midlatitude NLC parameters observed by daylight-capable lidar, and their rela- tion to ambient parameters, Geophys. Res. Lett., 40, 6390-6394,

Lidars With Narrow FOV for Daylight Measurements

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.