Geophysical Institute of the ASCR

Fig. 3. The borehole climate change station near
Slovenian Kostanjevica established in 2003 monitors
the air, soil and bedrock temperatures down to the
depth of 40 m with a sampling interval of 30 minutes.
Another method of checking the air-ground
temperature coupling is based on a repeated
temperature logging of boreholes. The present rate
of the surface warming is large enough for
a reliable detection of the subsurface temperature
time changes in the temperature- depth profiles
obtained by the repeated logging during several
years. The difference between the logs can be
compared with the difference of the synthetic
temperature - depth profiles based on the surface
air temperature series observed at nearby
meteorological stations. The results of the
repeated logging with a time span of 7 – 17 years
in several boreholes in the three countries clearly
document a transient character of the subsurface
temperature field. The observed time changes of
the subsurface temperature agree reasonably well
with the time changes simulated by using the
surface air temperature series as a ground surface
forcing function.
Beside the problem of the long-term stability of
the mean annual difference between air and soil
temperatures, which is being studied at the three
stations mentioned above, the influence of the
vegetation cover on the soil temperatures is
studied systematically at the fourth observatory
located also on the campus of the Geophysical
Institute at Spořilov. The monitoring system launched in 2002 provides data on the soil temperatures
to the depth of 0.5 m under different surface conditions, namely under grass, barren soil, sand and
asphalt. The soil temperatures at depths of 2, 5, 10, 20 and 50 cm below and the air temperatures at
5 cm above each of the 4 different surfaces are recorded every 5 minutes together with air temperature
of the site at 200 cm height. The soil moisture is measured in the sand at the depth of 20 cm. The
monitoring allows for a detailed study of a mean annual difference between air and soil temperatures,
its long-term stability and dependence on the vegetation cover and provides useful data for an array of
other disciplines like agronomy, forestry, ecological studies or alternative energy sources.
References
Smerdon J.E., Pollack H.N., Čermák V., Enz J.W., Krešl M., Šafanda J. and Wehmiller J.F., 2004. Air-ground temperature
coupling and subsurface propagation of annual temperature signals. J.Geophys.Res., 109, D21107, doi:
10.1029/2004JD005056.
Borehole climate change
The annual seasonal changes are accompanied by the corresponding changes of the air temperature.
The varying surface temperature conditions then propagate downwards and affect the shallow
subsurface temperature field. The amplitude decreases with depth and at the depth below approx.
30 – 40 meters the response to the surface changes is negligible being smaller than 0.001 K (as
example see soil temperatures recorded in the Sporilov hole in 2003, Fig. 4). The response to the longterm
climate changes, however, may penetrate much deeper and changing climate may leave behind
tiny transient temperature perturbations of the steady-state temperature field. By precise temperature
logging these perturbations can be measured and the “climate recollections” interpreted in terms of
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