Collisionless Bow Shock Research Articles

THE PHYSICS OF THE EARTH'S COLLISIONLESS SHOCK WAVE

A fast mode collisionless bow shock is a permanent feature of the solar wind interaction with the earth. The shock is approximately stationary in earth coordinates, its structure, however, changes in space due to different [MATH] values, and in time, due to different solar wind conditions (Mach number M and β, Te/T1...). The earth's bow shock has revealed itself as an impressive tool for studying collisionless shock waves. After the large theoretical efforts in studying collisionless shock waves, in the past, it is possible, today, to verify experimentally that different dissipation mechanisms are at work in different plasma regimes. The extensive examination of bow shock morphology allow us, today, to correlate distinctions in bow shock structure, revealed by a variety of diagnostics, with M, β and Bn in the solar wind. For quasi parallel geometries and apparently for any M and β, the shock layer broadens and breacks up, showing limited level of plasma wave noise and marked precursor effects. For quasi perpendicular shock waves, on the contrary, electromagnetic turbulence increases with β, almost independent of M ; while electrostatic noise level increase with M, almost independent of β. Comparison with the different theories valid in the different plasma regimes is the present task.

Studies of a Plasma Wind Tunnel for Simulating the Collisionless Bow Shock of the Earth

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Studies of a Plasma Wind Tunnel for Simulating the Collisionless Bow Shock of the Earth

Formulas are given for the plasma density and velocity required to simulate the flow of the solar wind over the magnetosphere of the earth. A description of a plasma source (coaxial arc-jet) intended to produce appropriate plasma flows is given. The operation of the device is described. Preliminary measurements of the density and velocity, made with a bolometer and a ballistic pendulum, indicate that plasma densities of 1013/cm3 and velocities of 107 cm/sec have been achieved in a jet of 1 m diameter. These parameters have been verified by microwave and Langmuir probe measurements and are appropriate for the desired simulation. In addition, it has been shown for the first time that this plasma has the required percentage ionization for solar wind simulation.

The Earth's magnetic tail

Extensive measurements of the magnetic field of the earth at distances greater than approximately 7Re (earth radii) have been performed by the Imp 1 satellite. These magnetic field measurements began on November 27, 1963, and ended on May 30, 1964. During this six-month interval the apogee-earth-sun angle in solar ecliptic coordinates decreased from 336° to 156°. The apogee of the satellite was 31.7Re, and the range of the magnetometers was between 0.25 and 300γ. This paper is concerned principally with the topology of the magnetic field within the magnetosphere and the position of both its boundary and the detached collisionless bow shock wave. The geomagnetic field is observed to trail out far behind the earth in the antisolar direction, thus forming a magnetic tail. Magnetic field strengths of approximately 10 to 30 γ are observed out to satellite apogee. The diameter of the magnetosphere at a distance of 30Re behind the earth is found to be approximately 40Re. The direction of the field is parallel to the earth-sun line and in the antisolar direction below the solar magnetospheric equatorial plane and in the solar direction above this plane. A neutral surface separating antisolar directed fields in the southern hemisphere from solar directed fields in the northern hemisphere has been detected over a large area. This experimental result suggests the development of quantitative theories explaining the aurora, gegenschein, day-night asymmetry, and formation of the radiation belts. On the basis of a preliminary review of the data, it appears that the geomagnetic field trails out far behind the earth following the flow field of the solar plasma to a distance far beyond the orbit of the moon. No termination of the magnetic tail is detected or suggested by the data. Thus the earth can be compared to the nucleus of a comet, the radiation belts and co-rotating magnetosphere being the coma and the magnetic tail being the cometary tail.

THE EARTH'S MAGNETIC TAIL*

Extensive measurements of the magnetic field of the earth at distances greater than approximately 7Re (earth radii) have been performed by the Imp 1 satellite. These magnetic field measurements began on November 27, 1963, and ended on May 30, 1964. During this six-month interval the apogee-earth-sun angle in solar ecliptic coordinates decreased from 336° to 156°. The apogee of the satellite was 31.7Re, and the range of the magnetometers was between 0.25 and 300γ. This paper is concerned principally with the topology of the magnetic field within the magnetosphere and the position of both its boundary and the detached collisionless bow shock wave. The geomagnetic field is observed to trail out far behind the earth in the antisolar direction, thus forming a magnetic tail. Magnetic field strengths of approximately 10 to 30 γ are observed out to satellite apogee. The diameter of the magnetosphere at a distance of 30Re behind the earth is found to be approximately 40Re. The direction of the field is parallel to the earth-sun line and in the antisolar direction below the solar magnetospheric equatorial plane and in the solar direction above this plane. A neutral surface separating antisolar directed fields in the southern hemisphere from solar directed fields in the northern hemisphere has been detected over a large area. This experimental result suggests the development of quantitative theories explaining the aurora, gegenschein, day-night asymmetry, and formation of the radiation belts. On the basis of a preliminary review of the data, it appears that the geomagnetic field trails out far behind the earth following the flow field of the solar plasma to a distance far beyond the orbit of the moon. No termination of the magnetic tail is detected or suggested by the data. Thus the earth can be compared to the nucleus of a comet, the radiation belts and co-rotating magnetosphere being the coma and the magnetic tail being the cometary tail.