The equilibrium anisotropy in the flux of 10‐MeV solar flare particles and their convection in the solar wind

The portion of an anisotropy, in the flux of cosmic rays in the interplanetary medium, that arises from the motion of the solar wind plasma is in the same direction as the flow of the solar wind and is not perpendicular to the interplanetary magnetic field. The amplitude of this convective component of anisotropy is given by the Compton‐Getting formula (2 + αγ) V/υ. The convective component was calculated for seven events during which the equilibrium anisotropy was observed in the flux of 7.5‐ to 45‐Mev solar flare particles and it accounted for all (in four cases) or most of the anisotropy. From this we conclude that, when the equilibrium anisotropy is observed, low‐energy solar flare particles are being transported mainly by convection in the solar wind. The ∼14‐hour decay time for the particle density, calculated by assuming only convective transport and adiabatic deceleration in a spherically expanding solar wind, is in reasonable agreement with observed values. The diffusive component of anisotropy is toward the sun in one event, thus implying a positive particle density gradient. Convective transport can produce a positive particle density gradient late in a flare event, but diffusive transport alone cannot. The diffusive transport velocity appears to be so small in some cases that the Alfvén velocities of the magnetic irregularities that scatter particles may affect the scattering theory.