Daily temperature variations at the subsurface combined with water level records in Ajameti, Georgia

Abstract

High resolution temperatures at the subsurface down to 250 m and water level measurements were carried out in a borehole at Ajameti, Georgia. In both cases daily variations were analyzed for time periods of February/March 2018 and April 2018. Their frequency spectra demonstrate that the diurnal and semi-diurnal variations are generated by earth tides. The enhanced amplitude of the diurnal period at depth of 100 m coincides with the growth phase of vegetation. Frequent rainfall did not affect the temperature at 100 m or deeper but raises the water level. Daily surface temperature variations relate to the temperature variation at the subsurface during the growth phase of vegetation in April and down to 175 m. No relation is detected in records obtained during February/March and at 250 m in both cases. Vertical shift of the water column results from the prevailing temperature gradient and the temperature fluctuation. The estimated water flow yields an amplitude of 0.1 m at 250 m but increases continuously to 0.16 m at 100 m. However, the water level variation reaches only 0.03 m at the surface. It is likely that the free surface of the water level has an additional degree of freedom which causes the lower magnitude of fluctuation.