Winter time radiation and energy balance components and cloudiness in a mountainous valley

Extreme cold weather associated with snow is one of the important winter-time characteristics of the semi-arid mountain valley. Using the weather data from two stations, we conducted an experiment to study the energy balance components and cloudiness during January, 2000, in Logan (41o 47' N, 111o 51' W, 1460 m above mean sea level), Utah, U.S.A. One of the stations measures (every two seconds) the incoming and outgoing solar (shortwave) radiation, the incoming (atmospheric) and outgoing (terrestrial) longwave radiation, and net radiation continuously throughout the year. All radiation sensors at this station are ventilated continuously to prevent formation of dew or frost on the sensors. Having the 2m air and humidity data and information about the radiation components, information about cloud base (temperature and height) and cloud coverage can be derived. The other station measures (every two seconds) the dew-point and air temperature gradients between one and two meters above the ground, along with precipitation (using a heated rain gage), wind speed and direction, and pressure continuously. The data at both stations are averaged into 20- minute intervals for this study. Data analysis shows that of the 195.6 MJ m-2 incoming solar radiation during January, 2000, about 60.0 MJ m-2 was reflected back to the sky (an average albedo=31 %). The terrestrial and atmospheric radiation amounted to 887.4 MJ m-2 and 803.7 MJ m-2, respectively, during this month, which yields an available radiation (net radiation) of 52.2 MJ m-2 during January 2000. Of the 52.2 MJ m-2 net radiation in this month, about 11.4 MJ m-2 was used for warming the soil (negative surface soil heat flux), 19.7 MJ m-2 for the process of evaporation, and the rest (4.4 MJ m-2) for warming the air. The average cloud coverage was 85 %, the cloud base averaged 162 m (from zero, fog, up to about 1 km). The modules proposed at this study can be applied as nested models to the downscaled general circulation models (GCMs).