Abstract. From June to August 1998 the ALOMAR Rayleigh/Mie/ Raman lidar, located at 69øN and 16øE in Northem Norway, repeatedly observed noctilucent clouds (NLCs) overhead the lidar. Due to a recent upgrade in detector technology, the lidar was able to obtain 151 hours of NLC observations, simultaneously at 355, 532, and 1064 nm. For the 11 strongest NLC events, we have calculated size distributions for the NLC particles from the b•kscatter ratios measured at the 3 wavelengths and using the assumptions of spherical ice particles with a monomodal lognormal size distribution. For all events evaluated at the layer maxima, we obtain well-defined median radii rmea, width parameters a, and particle number densities N•_c for the NLC particle distributions. Mean values for 10 out of the 11 events are r,,,ea = 51 nm, a = 1.42, and NNLc = 82 crn -3.

[1] We report on observations of noctilucent clouds (NLCs) by a ground-based lidar located in northern Norway at 69°N, 16°E. The ALOMAR Rayleigh/Mie/Raman (RMR) lidar conducted measurements of the Arctic middle atmosphere from 1 June to 15 August during each year from 1997 to 2001. This data set contains 1122 hours of lidar observations whereof 408 hours include NLC signatures. The interannual variation of the NLC occurrence frequency shows a decrease of strong NLCs, while weak NLCs occur more frequent. The seasonal variation of the NLC occurrence shows a well pronounced core period where NLCs appeared during 43% of the time. The basic properties of NLCs are characterized by three parameters: maximum value of the volume backscatter coefficient b max (brightness), centroid altitude z c , and half width dz (thickness). A typical NLC above ALOMAR during the 5-year period reported here owns a brightness of b max = 9.6 Â 10 À10 m À1 sr À1 , an altitude of z c = 83.3 km, and a thickness of dz = 1.2 km. The interannual variation of the parameters shows a decrease of the brightness, an increase of the altitude, and a nearly constant thickness, while seasonal variability is higher than these interannual changes. During the core period, the NLCs are noticeably brighter than at the beginning as well as the end of the season. Altitude and thickness of NLCs decrease during the season.

Abstract. From 1997 were observed by lidar above the ALOMAR observatory in Northern Norway (69 • N) during a total of 1880 measurement hours. This data set contains NLC signatures for 640 h, covering all local times, even during the highest solar background conditions. After data limitation imposing a threshold value of 4×10 −10 m −1 sr −1 for the volume backscatter coefficient of the NLC particles, a measure for the cloud brightness, local time dependencies of the NLC occurrence frequency, altitude, and brightness were determined. On average, over the 7 years NLC occurred during the whole day and preferably in the early morning hours, with a maximum occurrence frequency of ∼40% between 4 and 7 LT. Splitting the data into weak and strong clouds yields almost identical amplitudes of diurnal and semidiurnal variations for the occurrence of weak clouds, whereas the strong clouds are dominated by the diurnal variation. NLC occurrence, altitude, as well as brightness, show a remarkable persistence concerning diurnal and semidiurnal variations from 1997 to 2003, suggesting that NLC above ALOMAR are significantly controlled by atmospheric tides. The observed mean anti-phase behavior between cloud altitude and brightness is attributed to a phase shift between the semidiurnal components by ∼ 6 h. Investigation of data for each individual year regarding the prevailing oscillation periods of the NLC parameters showed different phase relationships, leading to a complex variability in the cloud parameters.

We report on the first observation of persistent inertia gravity wave signatures in the horizontal wind and temperature by Doppler Rayleigh lidar in the middle atmosphere. The observations were performed at the Arctic Lidar Observatory for Middle Atmosphere Research station in northern Norway (69°N,16°E) between 21 and 23 January 2012. The measurements cover the altitude range from 20 km to about 80 km during nighttime and to about 70 km during daytime. We observe amplitudes of 5 to 25 m/s and 1 to 8 K in wind and temperature, respectively. The measured kinetic to potential energy density ratio is about 10, indicating that the majority of variability is due to waves with intrinsic frequencies close to the inertial frequency. The entire wavefield is mainly characterized by the presence of multiple waves; however, quasi‐monochromatic waves could be identified at limited times around 60 km altitude with a mean momentum flux in direction of propagation of 3.8 m2/s2.