Estimating apparent thermal diffusivity using temperature time series: A comparison of temperature data measured in KMA boreholes and NGMN wells

摘要

Two different time series data sets, shallow ground temperatures of 58 synoptic stations of the Korea Meteorological Administration (KMA) and groundwater temperatures of 67 wells of the National Groundwater Monitoring Network (NGMN), were analyzed to estimate the apparent thermal diffusivity by using the analytical solution of the one-dimensional heat conduction equation. The KMA temperature data measured at 1–5 m depths illustrated values of the phase delay and the amplitude decay coincident with their theoretical relationship, indicating that the conductive heat transport should prevail over the nonconductive processes. On the contrary, some of the estimates from temperatures at a depth of 0.5 m were away from the theoretical values. It is most likely that the deviation would be caused by the effects of latent heat associated with freezing and thawing of the near ground surface. In contrast to KMA data, results obtained from the NGMN data highly deviated from the theoretical ones, and thereafter yielded unacceptably high values of thermal diffusivities as compared to the representative values of soils and rocks. Implication of the discrepancy between two data sets was discussed in conjunction with perturbation of the conductive heat transport by free convection of water and air occurring in large diameter wells as well as the convective heat transport by groundwater flow.