  We report measurements of annual and diurnal modulations of the cosmic-ray
muon rate in the Yangyang underground laboratory (Y2L) using 952 days of
COSINE-100 data acquired between September 2016 and July 2019. A correlation of
the muon rate with the atmospheric temperature is observed and its amplitude on
the muon rate is determined. The effective atmospheric temperature and muon
rate variations are positively correlated with a measured effective temperature
coefficient of $\alpha_{T}$ = 0.80 $\pm$ 0.11. This result is consistent with a
model of meson production in the atmosphere. We also searched for a diurnal
modulation in the underground muon rate by comparing one-hour intervals. No
significant diurnal modulation of the muon rate was observed.
