Puzzles of the interplanetary magnetic field in the inner heliosphere

Abstract

Deviations of the interplanetary magnetic field (IMF) from Parker's model are frequently observed in the heliosphere at different distances r from the Sun. Usually, it is supposed that the IMF behavior corresponds to Parker's model overall, but there is some turbulent component that impacts and disrupts the full picture of the IMF spatial and temporal distribution. However, the analysis of multi-spacecraft in-ecliptic IMF measurements from 0.29 AU to 5 AU shows that the IMF radial evolution is rather far from expected. The radial IMF component decreases with the adiabatic power index (|Br| \sim r^-5/3), the tangential component |Bt| \sim r^-1.1 and, the IMF strength B \sim r^-1.4. This means that the IMF is not completely frozen in the solar wind. Possibly, turbulent processes in the inner heliosphere significantly influence the IMF expansion. This means that the IMF is not completely frozen in the solar wind. It is possible that turbulent processes in the inner heliosphere significantly influence the IMF expansion. This is confirmed by the analysis of the Br distribution's radial evolution. We consider a quasi-continuous magnetic reconnection, occurring both at the heliospheric current sheet and at local current sheets inside the IMF sectors, to be a key process responsible for the solar wind turbulization with heliocentric distance as well as for the breakdown of the frozen-in IMF law.