M. I. Pudovkin

Low frequency 1/f-like fluctuations of the AE-index as a possible manifestation of self-organized criticality in the magnetosphere

Low frequency stochastic variations of the geomagnetic AE-index characterized by 1/fb-like power spectrum (where f is a frequency) are studied. Based on the analysis of experimental data we show that the Bz-component of IMF, velocity of solar wind plasma, and the coupling function of Akasofu are insufficient factors to explain these behaviors of the AE-index together with the 1/fb fluctuations of geomagnetic intensity. The effect of self-organized criticality (SOC) is proposed as an internal mechanism to generate 1/fb fluctuations in the magnetosphere. It is suggested that localized spatially current instabilities, developing in the magnetospheric tail at the initial substorm phase can be considered as SOC avalanches or dynamic clusters, superposition of which leads to the 1/fb fluctuations of macroscopic characteristics in the system. Using the sandpile model of SOC, we undertake numerical modeling of space-localized and global disturbances of magnetospheric current layer. Qualitative conformity between the disturbed dynamics of self-organized critical state of the model and the main phases of real magnetospheric substorm development is demonstrated. It is also shown that power spectrum of sandpile model fluctuations controlled by real solar wind parameters reproduces all distinctive spectral features of the AE fluctuations.

Magnetic field reconnection theory and the solar wind magnetosphere interaction: a review

This review considers the theory of the magnetic field line reconnection and its application to the problem of the interaction between the solar wind and the Earths magnetosphere. In particular, we discuss the reconnection models by Sonnerup and by Petschek (for both incompressible and compressible plasmas, for the asymmetric and nonsteady-state cases), the magnetic field annihilation model by Parker; Syrovatskys model of the current sheet; and Birns and Schindlers solution for the plasma sheet structure. A review of laboratory and numerical modelling experiments is given.Results concerning the field line reconnection, combined with the peculiarities of the MHD flow, were used in investigating the solar wind flow around the magnetosphere. We found that in the presence of a frozen-in magnetic field, the flow differs significantly from that in a pure gas dynamic case; in particular, at the subsolar. part of the magnetopause a ‘stagnation’ line appears (i.e., a line along which the stream lines are branching) instead of a stagnation point. The length and location of the stagnation line determine the character of the interaction of the solar wind with the Earths magnetosphere. We have developed the theory of that interaction for a steady-state case, and compare the results of the calculations with the experimental data.In the last section of the review, we propose a qualitative model of the solar wind — the Earths magnetosphere interaction in the nonsteady-state case on the basis of the solution of the problem of the spontaneous magnetic field line reconnection.

Magnetic storms in October 2003

Preliminary results of an analysis of satellite and ground-based measurements during extremely strong magnetic storms at the end of October 2003 are presented, including some numerical modeling. The geosynchronous satellites Ekspress-A2and Ekspress-A3, and the low-altitude polar satellites Coronas-F and Meteor-3M carried out measurements of charged particles (electrons, protons, and ions) of solar and magnetospheric origin in a wide energy range. Disturbances of the geomagnetic field caused by extremely high activity on the Sun were studied at more than twenty magnetic stations from Lovozero (Murmansk region) to Tixie (Sakha-Yakutia). Unique data on the dynamics of the ionosphere, riometric absorption, geomagnetic pulsations, and aurora observations at mid-latitudes are obtained.

Variations of the cosmic rays as one of the possible links between the solar activity and the lower atmosphere

Abstract Effects of the solar and galactic cosmic ray variations on the large-scale circulation of the lower atmosphere have been investigated. The results obtained show that these effects do really exist both on the time scale of a few days and in the 11-year solar cycle. Thus, the variations of the cosmic rays, both solar and galactic, may be responsible for the changes in the large-scale atmospheric circulation associated with solar activity phenomena, the energy of cosmic particles being ∼0.1–1 GeV. A possible mechanism of the cosmic ray effects on the lower atmosphere involves changes in the atmospheric transparency and cloud cover due to the changes in the stratospheric ionization produced by the considered cosmic particles. Experimental evidence of the cosmic ray influence on the high-level cloud formation is provided.

Influence of solar flares and disturbances of the interplanetary medium on the atmospheric circulation

Abstract The atmospheric circulation response to solar flares and geomagnetic disturbances is studied. It is shown that solar flares cause an increase of the zonal circulation intensity in the latitudinal belt ϑ = 45–65°, while geomagnetic disturbances are associated with a decrease of the circulation intensity. The energy necessary to produce the observed atmospheric circulation changes is estimated. The variation of the atmospheric transparency is suggested to be a possible source of that energy.

Anisotropic MHD model of the dayside magnetosheath downstream of the oblique bow shock

Large-scale flow in the dayside magnetosheath is calculated by using a three-dimensional anisotropic MHD model for the case when the angle between the interplanetary magnetic field and the solar wind velocity is 45°. The behavior of plasma and magnetic field parameters downstream of the quasi-perpendicular and quasi-parallel bow shocks is compared in the results from a single calculation. The model includes a limit on the proton temperature anisotropy based upon thresholds for onset of the ion cyclotron and mirror instabilities. Results are presented for three different values of the isotropization rate. The model shows the existence of the plasma depletion layer, corresponding to an increase of the magnetic field intensity and a decrease of the plasma density near the magnetopause, for all angles of the bow shock normal relative to the interplanetary magnetic field. There is a thin layer downstream of the quasi-parallel shock where T‖p > T⊥p. The magnetosheath regions are shown where the threshold conditions for ion cyclotron and mirror instabilities are satisfied.

Application of the bounded anisotropy model for the dayside magnetosheath

Experimental data show existence of the proton temperature anisotropy in the dayside magnetosheath (T⊥p > T‖p where ⊥ and ‖ denote directions perpendicular and parallel, respectively, to the background magnetic field). The adiabatic MHD model for an anisotropic plasma is known as CGL equations. However, an application of the CGL equations for magnetosheath modeling overestimates the temperature anisotropy T⊥p/T‖p. To improve this situation, the CGL model was modified into the bounded anisotropy model [Denton et al., 1994; Gary et al., 1994]. This new class of model takes into account proton pitch angle scattering resulting from a growth of plasma anisotropy instabilities. The present paper contains the calculations of three-dimensional MHD flow around a spherical body with the use of the bounded anisotropy model as well as a comparison between the obtained results and satellite observations of the dayside magnetosheath. The calculated proton temperature anisotropy obtained by the bounded anisotropy model corresponds reasonably to the observed data. The results of the isotropic and anisotropic MHD models are compared. The calculated magnetosheath width is showrn to be greater for the anisotropic double adiabatic model.

Meteorological characteristic changes in the high-latitudinal atmosphere associated with Forbush decreases of the galactic cosmic rays

Abstract Variations of the pressure level heights, temperature profiles and wind characteristics in the troposphere and lower stratosphere have been studied during Forbush-decreases of the galactic cosmic rays, the data of aerological soundings from Sodankyla (Finland, ϕ ≈ 67°) being used. It has been found that the Forbush-decreases are accompanied by the pressure increase in the whole troposphere, the maximum of the effect taking place on the 3–4th day after the event onset. Simultaneously the temperature decrease is observed in the troposphere during the first few days of the Forbush-decreases. The pressure increase might be related to the changes of wind characteristics in the middle and upper troposphere. A possible mechanism of the observed effects seems to involve radiation budget changes in the atmosphere due to the cloudiness variations associated with Forbush-decreases of the galactic cosmic rays.

Effects of the galactic cosmic ray variations on the solar radiation input in the lower atmosphere

Abstract The influence of galactic cosmic rays on the solar radiation input to the lower atmosphere was investigated in the different latitudinal belts. Increases of the total radiation fluxes associated with Forbush-decreases in the galactic cosmic rays were found at the stations with high frequencies of cirrus clouds situated at latitudes ϕ≈60°–68°. It is shown that the total radiation input in the winter months at stations in subauroral zone anticorrelates with the galactic cosmic ray intensity in the 11 yr solar cycle. In the auroral zone the solar radiation input seems to be affected by auroral phenomena. The variations of the total radiation fluxes associated with different cosmophysical phenomena seem to be of great importance for the radiation budget of the lower atmosphere.

Geomagnetic substorms as perturbed self-organized critical dynamics of the magnetosphere

The e0ect of self-organized criticality (SOC), known from the theory of complex nonlinear systems, is considered as an internal mechanism of geomagnetic 4uctuations accompanying the development of magnetospheric substorms. It is suggested that spatially localized current sheet instabilities, followed by magnetic reconnection in the magnetotail, can be considered as SOC avalanches, the superposition of which leads naturally to the 1=fpower spectra (f — frequency, � — numerical parameter) of geomagnetic activity. A running 2D avalanche model with controlled dissipation rate is proposed for numerical investigation of the multi-scale plasma sheet behavior in stationary and nonstationary states of the magnetosphere. Two basic types of perturbations have been studied, the 9rst induced by an increase in the solar wind energy input rate and the second induced by a decrease in critical current density in the magnetotail. The intensity of large-scale perturbations in the model depends on accumulated energy level and internal dissipation in a manner similar to the dependence characteristic of real magnetospheric substorms. A spectral structure of model dynamics exposed to variations of solar wind parameters reveals distinctive features similar to natural geomagnetic 4uctuations, including a spectral break at 5h separating frequency bands with di0erent spectral slopes. c � 2001 Elsevier Science Ltd. All rights reserved.