Diurnal and Seasonal Ground Temperature Variations at Wairakei

Abstract

Weekly readings of ground temperatures to a depth of 6' I) metres were made at Wairakei, New Zealand, between 195R and 1962. These readings were supplemented by multi-point Brown potentiometer recordings to a depth of 3 m for more than a year. Air temperatures were also available for the five-year period. Results show that the mean annual air temperature was 12°c; the range of the diurnal variation (from max. to min.) was less than 1 deg C at depths greater than 30 cm; the range of the seasonal variation was less than 1 deg c at depths greater than I) m; the mean annual temperature at a depth of 1 m was 3 deg c greater than the mean annual air temperature; the mean annual thermal dilfusivity and conductivity were 3' 5 X 10-3 cm'/sec and 11) X 10-' cal/sec cm deg c respectively; the thermal conductivity of the pumice soil varied with moisture content, being 40 X 10-' cal/sec cm deg c when the water content was 73i% by volume (voids completely filled with water) and 4 X 10-' cal/sec cm deg c when the water content was 5 %; and the mean annual geothermal heat flux at the surface was 40 X 10-6 cal/cm2 sec, which is about 40 times the world average. © 1964 Taylor & Francis Group, LLC. All rights reserved.