  The Daya Bay Experiment consists of eight identically designed detectors
located in three underground experimental halls named as EH1, EH2, EH3, with
250, 265 and 860 meters of water equivalent vertical overburden, respectively.
Cosmic muon events have been recorded over a two-year period. The underground
muon rate is observed to be positively correlated with the effective
atmospheric temperature and to follow a seasonal modulation pattern. The
correlation coefficient $\alpha$, describing how a variation in the muon rate
relates to a variation in the effective atmospheric temperature, is found to be
$\alpha_{\text{EH1}} = 0.362\pm0.031$, $\alpha_{\text{EH2}} = 0.433\pm0.038$
and $\alpha_{\text{EH3}} = 0.641\pm0.057$ for each experimental hall.
