Processes controlling rapid temperature variations on rock surfaces

In arid environments, thermal oscillations are an important source of rock weathering. Measurements of temperature have been made on the surface of rocks in a desert environment at a sampling interval of 0.375 s, with simultaneous measurements of wind speed, air temperature, and incoming shortwave radiation. Over timescales of hours, the temperature of the rock surface was determined primarily by shortwave radiation and air temperature, while rapid temperature variations, high dT/dt, at intervals of seconds or less, were determined by wind speed. The maximum values of temperature change and time spent above 2 degrees C min(-1) increased at high measurement rates and were much higher than previously reported. The maximum recorded value of dT/dt was 137 degrees C min(-1) and the average percentage time spent above 2 degrees C min(-1) was similar to 70 +/- 13%. Maximum values of dT/dt did not correlate with the maximum values of time spent above 2 degrees C min(-1). Simultaneous measurements of two thermocouples 5.5 cm apart on a single rock surface had similar temperature and dT/dt values, but were not correlated at sampling intervals of less than 10 s. It is suggested that this is resulting from rapid fluctuations due to small spatial and timescale wind effects that are averaged out when data is taken at longer sampling intervals, similar to 10 s or greater. Published in 2010 by John Wiley & Sons, Ltd.