Muons have a rest mass of 106 MeV and are created by collisions in the Earth’s atmosphere. Their half-life is 2.2 microseconds, which is 600 metres at the speed of light. From that you can immediately deduce that any muons you detect are travelling fast enough for relativistic time dilation to be very significant. If one is created in the upper atmosphere, at 60km say, the time dilation needs to be a factor of 10. Their relativistic mass increases by the same fraction, so to create a muon in the centre of mass frame requires 1.06GeV. If an anti-muon is also created, as opposed to an anti- muon neutrino, double the energy budget. Now throw in conservation of momentum; the recoiling nucleus will also carry off a chunk of energy.
To the best of my knowledge, very few particles in the solar wind have kinetic energies of well over 1 GeV. I would be astounded if there is any noticeable variation with the solar cycle.
(All figures above rounded.)