S.S. Znatkova

Pressure balance on the magnetopause near the subsolar point according to observational data of the THEMIS project satellites

An analysis of the pressure balance on the magnetopause near the subsolar point has been made for 18 crossings of the magnetopause by the THEMIS project satellites under magneto-quiet conditions. Dynamic and static pressures of plasma are determined, as well as magnetic pressure in the magnetosheath, and magnetic and plasma static pressure inside the magnetosphere. Variations of the total pressure have been studied in the case when one satellite is located inside the magnetosphere and another one stays in the magnetosheath near the magnetopause. It is demonstrated that for 18 investigated events the condition of pressure balance at the subsolar point is valid on average with an accuracy of 7%, within measurement errors and under applicability of the approximation of anisotropic magnetic hydrodynamics to collisionless plasma of the magnetosheath and magnetosphere.

Topology of High-Latitude Magnetospheric Currents

The structure and localization of high latitude transverse and field-aligned currents are analyzed using the data from the Themis satellite mission. A number of evidences resumed in this paper, including daytime compression of magnetic field lines and the existence of magnetic field minima far from the equatorial plane make necessary to reanalyze the traditional points of view about the topology of high-latitude magnetospheric currents. Comparison between the dayside integral transverse currents at the geocentric distances 7–10R E , calculated assuming the validity of the condition of magnetostatic equilibrium and the nighttime transverse currents, showed that ordinary ring current has the high latitude continuation until geocentric distances ∼10–13R E . The problem of the location of Region 1 field-aligned current of Iijima and Potemra is discussed.

Magnetospheric substorms and discrete arcs of the polar aurora

A brief review of the results of the research in physics of the Earth’s magnetosphere leading to a substantial modification of the previously developed approaches is presented. The main emphasis is placed on physics of magnetospheric substorms and the nature of auroral arcs. It is shown that the formation of powerful electron beams that produce multiple arcs can be associated with the penetration of cold electrons of an ionospheric origin into the region of field-aligned acceleration of hot magnetospheric electrons.

Turbulence in the Magnetosheath and the Problem of Plasma Penetration Inside the Magnetosphere

Chapman & Ferraro (1931) introduced the concept of confinement of the Earths magnetic field in a cavity carved in the solar plasma flow. The balance between the Earth’s magnetic field (more accurately between the magnetic pressure at the boundary of the cavity) and the solar wind dynamic pressure was considered as the condition of the formation of the boundary of the cavity. Chapman-Ferraro model is called a closed magnetosphere. Low energy particles can not penetrate through the boundary of the cavity. Dungey (1961) made the most drastic revision of Chapman-Ferraros original theory. Dungey envisaged that the connection process, called reconnection, takes place on the dayside magnetopause and that the connected field lines are then transported in the antisolar direction by the solar wind, resulting in the magnetotail. Subsequently, the field lines are reconnected there and then transported back to the dayside magnetosphere. Such process takes place when interplanetary magnetic field (IMF) has the southward direction. The large scale reconnection takes place at high latitudes when IMF has the northward direction. The scheme shown on Fig. 1 demonstrates Dungey’s concept of reconnection at the dayside magnetopause when IMF has southword (a) and northward (b) directions. The model of Dungey qualitatively accounts for such phenomena as the inward motion of the dayside magnetopause, equatorward motion of the cusp, expansion of the auroral oval, increase in magnetotail magnetic field strength, and expansion of the magnetotail radius which occur when the IMF turns southward. It can also easily explain the penetration of the plasma of solar wind origin inside the magnetosphere. That is why this concept for a long period was the dominant concept in the physics of the magnetosphere and was widely used for the description of different phenomena including the formation of boundary layers (see, for example, the review Lavraud et al. (2011)). However step by step a number of observations ant theoretical arguments have appeared which give the possibility to throw doubts on the applicability of the scheme shown on Fig. 1 for the real situation.

Evolution of spectral index of energetic protons in the magnetopause crossing at the subsolar point

The evolution of the spectral index of the omnidirectional differential flux of protons (within a range of 40 to 600 keV) in the magnetopause crossing near the subsolar point was analyzed. The work is based on the measurement data of the THEMIS international project as of July 18, 2007. A specific feature of the event under study is the possibility of determining the spectral index at energies >40 keV with a time resolution of 3 s. It is shown that the ion distribution functions, both outside and inside the magnetopause, can be approximated by kappa-like distributions with power low high-energy tail in the analyzed crossing. A high level of fluctuations of the spectral index of energetic ions was shown to have been observed near the magnetopause. The fluctuation level substantially reduces inside the magnetosphere. In this case, the spectral index has a value of ~6 on average and remains constant up to inner regions of the magnetosphere.

Determining the thickness of the low-latitude boundary layer in the Earth’s magnetosphere

We describe a method for determining the thickness of the low-latitude boundary layer (LLBL) of the Earth’s magnetosphere at the dayside near the equatorial plane based on the data gathered by a single satellite that traverses the layer and measures the plasma velocity. The method may be applied when the position of the magnetopause and the magnetosheath parameters fluctuate. The necessity of taking the presence of outer and inner LLBL regions into account is analyzed. The developed method is tested using the analysis results of two almost simultaneous close traverses of the magnetopause completed by the THEMIS mission satellites that provided relatively precise data on the LLBL thickness. It is shown that the developed method makes it possible to determine the LLBL thickness with an accuracy of ∼10%.

Thickness of the low latitude boundary layer at different levels of magnetic field fluctuations in the magnetosheath

The role of a high fluctuations level in the Earth’s magnetosheath in plasma penetration into the magnetosphere and in the formation of the low-latitude boundary layer (LLBL) has been considered based on the events that occurred on November 1 and 5, 2007, using the THEMIS-A satellite observations. During the selected LLBL crossings the satellite was measuring behind the quasi-parallel and quasi-perpendicular bow shocks. The angle between the magnetic field direction in the solar wind and the normal to the bow shock (ΘBn) has been taken as a parameter reflecting the level of magnetic field and plasma paremeters fluctuations in the magnetosheath. It has been indicated that a thick LLBL is observed when angle ΘBn is small and the turbulence level in the magnetosheath is high. When angle ΘBn is large, the layer thickness decreases. The possible mechanisms by which a thick LLBL is formed are discussed.