Band 35, Heft 1

The paper deals with the problem of the equatorial ionization anomaly (EIA) modelling and its representation in the global dynamical models of Earth’s ionosphere and thermosphere. A new version of the coupled thermosphere-ionosphere global dynamical model which reproduce the equatorial anomaly considerably well is presented. Key processes responsible for the EIA formation are outlined and their representation in the model is indicated. It was shown that the developed coupled thermosphere-ionosphere model with additional accounting of vertical electromagnetic drift at the equator realistically represents the EIA characteristics.

Algorithms of Monte Carlo method for estimating probabilistic moments of the parameter of time exponential asymptotics of particle flux with multiplication in a random medium are constructed. It was analytically and numerically shown that the asymptotics of the mean number of particles is close to an exponential one with the factor containing a summand proportional to square of time.

In the present work the possibility of turbulence closure applying to improve barotropic jet instability simulation at coarse grid resolutions is considered. This problem is analogous to situations occurring in eddy-permitting ocean models when Rossby radius of deformation is partly resolved on a computational grid. We show that the instability is slowed down at coarse resolutions. As follows from the spectral analysis of linearized equations, the slowdown is caused by the small-scale normal modes damping arising due to numerical approximation errors and nonzero eddy viscosity. In order to accelerate instability growth, stochastic and deterministic kinetic energy backscatter (KEBs) parameterizations and scale-similarity model were applied. Their utilization led to increase of the growth rates of normal modes and thus improve characteristic time and spatial structure of the instability.

Direct numerical simulation data of a stratified turbulent Couette flow contains two types of organized structures: rolls arising at neutral and close to neutral stratifications, and layered structures which manifest themselves as static stability increases. It is shown that both types of structures have spatial scales and forms that coincide with the scales and forms of the optimal disturbances of the simplified linear model of the Couette flow with the same Richardson numbers.