The Moon
plane of the ecliptic, geomagnetic activity reaches a
minimum during the 2nd lunar quarter and a maximum
during the 3rd lunar quarter. Lunar modulation near the
ecliptic suggests that the Moon is influencing the solar
corpuscular flux which, guided by the solar magnetic
field, generally approaches the earth from close to the
plane of the ecliptic. Some of these particles become
trapped in the magnetosphere.
There is a thin, neutral-sheet region close to the ecliptic
plane, in the tail of the earth's magnetosphere that the
Moon may be modulating when it is traveling near the
plane of the ecliptic. The high density of field lines near
the ecliptic would make this region particularly sensitive
to a magnetic perturbation, which could modulate the
flux of particles reaching our atmosphere. In short, there
is evidence that the moon has a magnetohydrodynamic
wake with an enhanced magnetic field, which, when in
the magnetospheric tail, causes magnetic disturbances
on the earth.