EBV model: a quantitative model of the seasonal variations of the interplanetary magnetic field southward component

ABSTRACT The interplanetary magnetic field (IMF) that pervades the Solar system interacts with the planetary magnetospheres via the process of magnetic reconnection. Reconnection that causes the dominant energy transfer into Earth’s magnetosphere is most efficient when the IMF is directed southward. The only existing, simplified model of the seasonal variations of the southward component of IMF ($B_{\mathrm{s}}$) was constructed in 1973. Since then, as far as we know, the realistic model of $B_{\mathrm{s}}$ has not been developed although for more than 60 yr the IMF observations have been available that could be used to construct and test the new model. Here, we demonstrate the mathematical formalism to model seasonal variations of $B_{\mathrm{s}}$ and $B_{\mathrm{s}}$ ordered according to the IMF polarity considering the real situation in which the IMF fluctuates about the Parker spiral direction and changes through the solar cycles. The derived quantitative model of the seasonal variations of $B_{\mathrm{s}}$ (EBV model) can completely reproduce all the main features of the measured $B_{\mathrm{s}}$, its absolute value and solar cycle variation. It opens a way to quantify, for the first time, the relation between the seasonal variations of magnetospheric quantities and $B_{\mathrm{s}}$. By clarifying the origin and characteristics of $B_{\mathrm{s}}$, we may be better able to understand the importance of the magnetic reconnection process for structuring the magnetosphere of the Earth and other planets and the role it has in modulating magnetospheric activities.