Subsurface temperature profiles in the Nobi Plain, central Japan

摘要

Vertical temperature profiles in the Nobi Plain areable to be classified into there types, recharge type, discharge typeand intermediate type, according to the temperature gradient.Moreover, there are many temperature inventions in the verticaltemperature profiles which are classified as the recharge type.These temperature inventions are manifested as the minimumtemperature in the vertical temperature profile below theisothermal layer. All of the type of profiles that show the inversionare located in recharge area outside the discharge area. Annualmean surface temperature has increased about 2 deg C during thelast 100 years in the Nobi Plain, and it is assumed that this surfacewarming causes subsurface temperature inversions. A numericalanalysis including the effect of surface warming shows thatsubsurface temperatures in shallow layers are affected by changesin surface temperature. In the discharge area, however, temperatureinversions cannot be recognized because the depth of inversion hasbeen shifted to within 20 m of the surface by upward groundwaterflow, where seasonal fluctuation of subsurface temperatureconceals the inversion.