Icy particles in the summer mesopause region: Three‐dimensional modeling of their environment and two‐dimensional modeling of their transport

Abstract

[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,

Modelling the impact of noctilucent cloud formation on atomic oxygen and other minor constituents of the summer mesosphere

“…The detailed microphysical model of Berger and von Zahn (2002) clearly demonstrates that the H 2 O mixing ratio is dramatically altered by the formation and transport of water ice particles (Fig. 8) mesopause (88-90 km) where they may grow and sediment through the upper mesosphere dehydrating the region as they descend, so that the mixing ratio can fall to less than 0.3 ppm above 85 km -about 10% of the mixing ratio if no ice particles were present.…”

“…The profile of the cloud surface area shown in Fig. 6 is calculated assuming a normal size distribution where the width of the distribution is equal to 0.23 r mean (r mean =mean particle radius) (Berger and von Zahn, 2002). The first-order rate coefficient for uptake of O on the ice surface is then given by:…”

“…Two Z H 2 O profiles were used for this modelling, the first was the profile shown in Fig. 8 that is taken from the model of Berger and von Zahn (2002), where the peak Z H 2 O was about two (solid line in Fig. 8); the second was the same profile, but where all values of Z H 2 O >1 were multiplied by two to bring the H 2 O enhancement in line with the measurements of Summers et al (2001) (dashed line in Fig.…”

Local Time Dependence of Polar Mesospheric Clouds: A model study

“…We note that ice nucleation in MIMAS is described by the concept of critical radius (Turco et al, 1982;Berger and von Zahn, 2002;Berger and Lübken, 2015).…”

Comparison of NLC particle sizes derived from SCIAMACHY/Envisat observations with ground-based LIDAR measurements at ALOMAR (69° N)

“…on the AIM (Aeronomy of Ice in the Mesosphere) satellite ) show a remarkable fine structure in the NLC brightness field on spatial scales as low as several kilometers, and temporal scales of minutes. While the time required to form a 60 nm NLC particle is typically on the order of tens of hours (e.g., Berger and von Zahn, 2002), it only takes several tens of minutes to sublimate the large particles, if the temperature is perturbed (e.g., Rapp et al, 2002). Therefore, we must expect that the strong small scale variations in NLC brightness are also associated with small scale variations in the local NLC particle size distribution, and the mean radius in particular.…”