Why Does the Ion Density in a Plasma Sheet Depend on the Density of the Solar Wind?

Measurements of heavy (M/q > 3) ions on the Phobos-2 satellite revealed that the density of these ions in the central plasma sheet of the areomagnetic tail is proportional to the proton density of the solar wind flowing around the planet. ISEE-2 ion measurements in the near-Earth plasma sheet close to the neutral line were also compared to solar wind data obtained on the ISEE-3 satellite. It was found that the density of protons in the near-Earth plasma sheet is proportional to the density of solar wind protons as well. Analysis of the magnetic and plasma pressure balance in the solar wind and inside the magnetotails of the Earth and Mars showed that the previously found correlations are the result of the necessary equality of pressures at the magnetosphere boundary and inside the magnetic tails of the planets.