  The temperature of the upper atmosphere affects the height of primary cosmic
ray interactions and the production of high-energy cosmic ray muons which can
be detected deep underground. The MINOS far detector at Soudan MN, USA, has
collected over 67 million cosmic ray induced muons. The underground muon rate
measured over a period of five years exhibits a 4% peak-to-peak seasonal
variation which is highly correlated with the temperature in the upper
atmosphere. The coefficient, $\alpha_T$, relating changes in the muon rate to
changes in atmospheric temperature was found to be: $\alpha_T = 0.874 \pm
0.009$ (stat.) $\pm 0.010$ (syst.). Pions and kaons in the primary hadronic
interactions of cosmic rays in the atmosphere contribute differently to
$\alpha_T$ due to the different masses and lifetimes. This allows the measured
value of $\alpha_T$ to be interpreted as a measurement of the K/$\pi$ ratio for
$E_{p}\gtrsim$\unit[7]{TeV} of $0.13 \pm 0.08$, consistent with the expectation
from collider experiments.
