Model simulation of the global circulation in the middle atmosphere for January conditions

International audienceA mathematical model of the global neutral wind system of the Earth's atmosphere, developed earlier in the Polar Geophysical Institute (PGI), is utilized to simulate the large-scale global circulation of the middle atmosphere for January conditions. The utilized model enables to calculate not only the horizontal components but also the vertical component of the neutral wind velocity by means of a numerical solution of a generalized Navier-Stokes equation for compressible gas, so the hydrostatic equation is not applied. Global distributions of the horizontal and vertical wind, calculated for January conditions, are compared with simulation results, obtained earlier for conditions corresponding to summer in the northern hemisphere. It was found that the global distributions of the neutral wind, calculated both for winter and for summer periods in the northern hemisphere, in particular, the large-scale circumpolar vortices, are consistent with the planetary circulation of the atmosphere, obtained from observations

A Simulation Study of the Effect of Powerful High-Frequency Radio Waves on the Behavior of Super-Small-Scale Irregularities in the F-layer Ionospheric

Magnetic field aligned super-small-scale irregularities in the concentration of charged particles are often observed in the Earthrsquos ionosphere and magnetosphere. Earlier, the time evolution of such irregularities was studied with the help of the mathematical model, developed in the Polar Geophysical Institute. This model is based on a numerical solution of the Vlasov-Poisson system of equations. This mathematical model is used in the present paper. The purpose of the present paper is to examine numerically how high-power high-frequency radio waves, utilized for artificial heating experiments and pumped into the ionosphere by ground-based ionospheric heaters, influence on the time evolution of the super-small-scale irregularities present naturally in the F-layer ionospheric plasma. The results of simulation indicate that a presence of high-power high-frequency radio wave ought to influence essentially on the behavior of physically significant parameters of the plasma inside and in the vicinity of the irregularity.nbs

Simulation study of the large-scale modification of the mid-latitude F-layer by HF radio waves with different powers

A mathematical model of the ionosphere, developed earlier, is applied to investigate the large-scale mid-latitude F-layer modification by HF radio waves with different powers. Simulations are performed for the point with geographic coordinates of the "Sura" heating facility (Nizhny Novgorod, Russia) for autumn conditions. The calculations are made for distinct cases, in which the effective absorbed power has different values belonging to the 5–100 MW range, both for nocturnal and daytime conditions. The frequency of powerful HF waves is chosen to be close to the most effective frequency for the large-scale F2-layer modification. The results of modeling indicate that the effective absorbed power can influence considerably the F-layer response to high-power radio waves in the mid-latitude ionosphere

Numerical Simulation of the Time Evolution of Small-Scale Irregularities in the F-Layer Ionospheric Plasma

Dynamics of magnetic field-aligned small-scale irregularities in the electron concentration, existing in the F-layer ionospheric plasma, is investigated with the help of a mathematical model. The plasma is assumed to be a rarefied compound consisting of electrons and positive ions and being in a strong, external magnetic field. In the applied model, kinetic processes in the plasma are simulated by using the Vlasov-Poisson system of equations. The system of equations is numerically solved applying a macroparticle method. The time evolution of a plasma irregularity, having initial cross-section dimension commensurable with a Debye length, is simulated during the period sufficient for the irregularity to decay completely. The results of simulation indicate that the small-scale irregularity, created initially in the F-region ionosphere, decays accomplishing periodic damped vibrations, with the process being collisionless

First simulation results of Titan's atmosphere dynamics with a global 3-D non-hydrostatic circulation model

We present the first results of a 3-D General Circulation Model of Titan's atmosphere which differs from traditional models in that the hydrostatic equation is not used and all three components of the neutral gas velocity are obtained from the numerical solution of the Navier-Stokes equation. The current version of our GCM is, however, a simplified version, as it uses a predescribed temperature field in the model region thereby avoiding the complex simulation of radiative transfer based on the energy equation. We present the first simulation results and compare them to the results of existing GCMs and direct wind observations. The wind speeds obtained from our GCM correspond well with data obtained during the Huygens probe descent through Titan's atmosphere. We interpret the most unexpected feature of these data which consist of the presence of a non-monotonicity of the altitude profile of the zonal wind speed between 60 and 75 km

Inverse cascade in the structure of substorm aurora and non-linear dynamics of field-aligned current filaments

We investigate time evolution of scaling index αA that characterizes auroral luminosity fluctuations at the beginning of substorm expansion. With the use of UVI images from the Polar satellite, it is shown that αA typically varies from values less than unity to ~1.5, increasing with breakup progress. Similar scaling features were previously reported for fluctuations at smaller scales from all-sky TV observations. If this signature is interpreted in terms of non-linear interactions between scales, it means that the power of small-scale fluctuations is transferred with time to larger scales, a kind of the inverse cascade. Scaling behavior in the aurora during substorm activity is compared with that in the field-aligned currents simulated numerically in the model of non-linear interactions of Alfvénic coherent structures, according to the Chang et al. (2004) scenario. This scenario also suggests an inverse cascade, manifesting in clustering of small-scale field-aligned current filaments of the same polarity and formation of "coarse-grained" structures of field-aligned currents