Observations over a 5-year period at a site at Ottawa showed that the ground temperature had significant Fourier components with period graphicand 2 years. The average annual ground temperature and amplitudes of the Fourier components of period 1 year and graphic year underwent non-periodic fluctuations of almost 1 C degree at a depth of 10 cm. The amplitude of this fluctuation decreased with depth, and its maximum occurred later in time. There was evidence of a gradual increase in average annual ground temperature amounting to about 0.2 C degree over the 5-year period at the 610-cm depth. The significance of such small temperature changes in areas where the ground temperature is close to 0 °C is pointed out.

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