Analysis of air and ground temperatures for detecting climate change.

摘要

Air and ground temperatures measured at the geothermal Emigrant Pass Observatory in Northwest Utah are studied for climate change implications. Eight years of observations are analyzed to understand the influence of common meteorological parameters on transient subsurface temperatures. The temperature difference between the ground surface and the standard air temperature measurement at 2 m, ΔT_g-a, averages 2.55°C (±0.01) over the interval from 1993–2001. The temperature varies from 2.50°C to 2.60°C when averaged over an annual cycle. Incident solar radiation is the primary variable in determining the temperature difference between the ground surface and air temperature (ΔT_g-a = 1.48°C per 100 Wm −2). At annual and longer time scales, ground and air temperature track remarkably well; measured ground temperatures at a depth of 1 m agree with the temperature calculated from the observed air temperature time series to within 0.04°C. The in-situ thermal diffusivity of surface rock and soil at the observatory varies seasonally from 0.42–1.14 × 10−6m2s−1, depending upon water saturation and temperature. Building on these results from Emigrant Pass Observatory we construct a combined air and ground temperature history for Wendover, Utah over the period 1500–2000 A.D. Dendroclimatic data are also linked to the temperature history to include annual variability. The results imply an 18th century temperature that is 0.4°C cooler than the 1971–2000 meteorological mean of 11.2°C.