Abstract:
The components of the interplanetary magnetic field (IMF) at the Earth's orbit are described by the model of Parker [1958]. In it, the solar rotation rate is assumed constant. In the present paper we compare in-situ measurements of the azimuthal IMF component By to the model predictions taking into account the variable solar rotation. A very good and highly significant correlation is found between the calculated and the measured By both on longer time-scales and - in most cases - on day-to-day basis. The difference between the observed and calculated yearly averaged IMF azimuthal component can be both positive and negative, with its sign determined by the solar magnetic polarity. In periods of interplanetary shocks, By doesn't obey Parker's model, and in almost half of the observed cases is instead highly correlated to the solar rotation rate.
