  It is well known that the rate of cosmic ray muons depends on the atmospheric
temperature, and that for events with a single muon the peak of the rate is in
summer, in underground laboratories in the northern hemisphere. In 2015 the
MINOS experiment, in USA, found that, for small distances between the
multiple-muons, the rate of multiple-muons peaks in the winter and that the
amplitude of the modulation is smaller than in the case of a single muon. I
have done a re-analysis of data of the past MACRO experiment. The result is
that under Gran Sasso the rate of multiple-muons at small distances peaks in
the summer. This difference with MINOS could be explained by differences in the
atmospheric temperature due to latitude. This results could be of interest for
dark matter experiments looking to dark matter seasonal modulation due to the
Earth's motion.
