A Comparison of Temperatures from Mountaintops and the Free Atmosphere—Their Diurnal Variation and Mean Difference

Abstract

The diurnal temperature variation at the 850, 700 and 500 mb levels is evaluated using radiosonde data gathered at short time intervals in the Alpine region and is found to be very close to sinusoidal. The amplitude is of the order of 1°C and decreases with height. Using this information, operationally collected upper-air temperature values were interpolated in time and compared to temperatures obtained from neighboring mountaintop stations. The differences show a strong diurnal variation; they decrease with increasing cloud cover and/or increasing wind at the mountaintop. Finally, mean temperature differences (averaged over 24 hours) between mountaintops and the free atmosphere are found to be less than 1°C; they are clearly influenced by the wind at the mountaintop.