Model description of LIMA-ICE
A 3-d Lagrangian ice transport model called LIMA-ICE is superimposed on LIMA which allows to study the formation and life cycle of ice particles in the polar mesopause region. LIMA-ICE includes modules for a simplified mesospheric chemistry and transport of water vapor, and a Lagrangian transport and microphysical scheme of ice particles (Berger and von Zahn, 2002; von Zahn and Berger). The ice transport model itself requires a nearly continuous initialization (once per hour) of atmospheric 3-d background winds, temperatures, air pressure and densities which are provided by either our former COMMA/IAP model (Berger and von Zahn, 2002; von Zahn and Berger, 2003; Berger and von Zahn, 2007) or by LIMA (Berger and Lübken, 2006; Lübken and Berger, 2007). Furthermore, water vapor data must be provided at the spatial boundaries of the ice model domain (78 to 94 km in altitude, 37.5°N/S to 90°N/S in latitude) to specify boundary conditions of the water vapor transport scheme inside the ice model domain.
The combination of the Lagrangian ice transport model with LIMA background conditions is called LIMA-ICE. In order to calculate ice cloud formation during a full length of a summer season LIMA-ICE starts at May 15th for a northern summer season, and November 15th for a southern summer season. LIMA-ICE initializes the mesopause region with an ensemble of 20 million condensation nuclei (CN). We assume that at the time of model initialization these CN exist in number densities and size distribution similar to the results from Hunten et al. (1980). This distribution is characterized by comprising only particles with radii between 1.5 and 3.5 nm with a large majority of all particles with radii of 1.5-2.0 nm. After initialization we investigate the time-dependent transport of CN in 3-d during a full summer season until August 25th (NH) and February 25th (SH), respectively. LIMA-ICE follows the trajectories of each of the 20 million particles with high temporal resolution (every 45 sec) while they are transported by LIMA background winds, particle eddy diffusion, and sedimentation.
Ice layer simulations are shown as animations.