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The earth's bow shock has been investigated as a magnetohydrodynamic discontinuity using the plasma and magnetic data supplied by the European satellite Heos 1. The jumps of the fluid parameters through the shock have been studied as a function of the Mach number and of the geometry of the shock surface. The solar wind specific heat ratio has been found to be γ1 = 1.75 or 2.25 depending on the presence or absence of upstream waves. Computations of the shock velocity performed for 23 crossings gave an average speed of ∼85 km/sec.

Properties of plasma and magnetic field within the magnetosheath in the period December 1968 to December 1969 are presented as observed by the European satellite Heos 1. Three states of the magnetosheath plasma have been distinguished on the basis of different upstream conditions and are characterized by low magnetosonic Mach number (M1 < 3) and low β, high values of M1 and β and absence of upstream waves, and presence of upstream waves. The distribution function of proton velocities and the magnetic turbulence in the magnetosheath have been studied in connection with these three upstream situations.

In this article the suggestion is made that phenomena happening well away from the ecliptic plane may be important controlling factors in the modulation of cosmic rays received at the Earth.

The heliographic latitude depen- dence of the interplanetary magnetic field was studied by using simultaneous measurements taken with Pioneer l0 at 1.0-4.3 AU and with earth satellites Heos i and 2 at 1.0 AU during Bartels solar rotations (SR) 1896-1913. The results indicate that the greater the difference in heliographic latitude between spacecraft, the greater, on the average, is the observed difference in percentage positive polarity (fields pointing outward from the sun) per SR. In particular, the percentage of positive polarity is greater as the heliographic latitude is more northern. This result is consistent with earlier (1962-1968) evidence of the lati- tude dependence of dominant polarity, provided the phase shift of the dominant polarity sinu- soid, which occurred between 1969 and 1972, is taken into account.