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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] In summertime, layers of icy particles form in the high-latitude mesopause region, causing the phenomena of noctilucent clouds and polar mesosphere summer echoes. We study the formation of these layers by means of a 3-D general circulation model of the middle atmosphere (COMMA/IAP) including new modules for the mesospheric chemistry and for the microphysics of icy particles. We initialize the mesopause region with an ensemble of two million particles and investigate their time-dependent transport in a 2-D Lagrangian way. We use the model to study in considerable detail ice particle formation by heterogeneous nucleation on smoke particles, freeze-drying of the mesopause region by formation of ice particles, and the influences of tidal waves and particle eddy diffusion on ice particle and noctilucent cloud (NLC) layer behavior. We present model results on the requirements for adequate size of smoke particles to act as condensation nuclei in the mesopause region (directly after initialization > 0.7 nm radius; after 8 hours > 2 nm), the types of ice particle trajectories, the timescale for growth of particles (6 to 8 hours to radii > 20 nm) and sublimation of ice particles (duration of sublimation phase typically 6 hours), the typical altitude range of maximum NLC brightness (82.5-83.0 km), the size distributions of ice particles (closer to Gaussian than lognormal in shape), the importance of the vertical component of the tidal winds on NLC layer behavior, and the dominance of semidiurnal over diurnal tidal effects. Furthermore, the model allows us to make predictions on a number of NLC features that are either currently under study or may become observable in the near future, such as properties of NLC at high arctic latitudes, and the development of layers with strongly enhanced water vapor mixing ratios near the lower border of the NLCs. (3334); 3332 Meteorology and Atmospheric Dynamics: Mesospheric dynamics; KEYWORDS: Lagrangian transport, diffusion, ice particle, mesopause, NLC, mesospheric tides Citation: Berger, U., and U. von Zahn, Icy particles in the summer mesopause region: Three-dimensional modeling of their environment and two-dimensional modeling of their transport,

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