The following description is from the webpage of Niels Bohr Institue's Former Centre for Ice and Climate
The Earth reacts to the solar wind by increasing the strength of the shielding magnetic field. Therefore, higher solar activity results in stringer shielding and thus lower production of cosmogenic isotopes.
The first intuition is the solar wind will cancel Earth's magnetic field but it seems in reality it will make Earth's magnetic field stronger. How should we explain this phenomenon?