THE WEST DESERT BASIN MICROCLIMATE

We set up two automatic weather stations over a playa (the flat floor of an undrained desert basin that becomes at times a shallow lake), approximately 65 km east-west by 130 km north-south, located in Dugway (40^o 08^' N, 113^o 27^' W, 1124 m above mean sea level) in the West Desert Basin of Utah, U.S.A., in 1999. These stations measured the radiation budget components, namely: incoming (R_si) and outgoing (R_so) solar or shortwave radiation, using two Kipp and Zonen pyranometers (one inverted), the incoming (R_li or atmospheric) and outgoing (R_lo or terrestrial) longwave radiation, using two Kipp and Zonen pyrgeometers (one inverted) during the year 2000. These sensors were ventilated throughout the year to prevent dew and frost formation. Summation of these components yields the net (R_n) radiation.

We also measured the air temperatures and humidity at one and two meters and the soil moisture and temperature (Campbell Sci., Inc., CSI) to evaluate the energy budget components (latent, LE; sensible, H; and the surface soil, G_sur; heat fluxes). The 3-m wind speed (U₃) and direction (R.M. Young wind monitor), precipitation (CSI), and the surface temperature (Radiation and Energy Balance Systems, REBS) were also measured during 2000. The measurements were taken every two seconds, averaged into 20-min, continuously, throughout the years.

The annual comparison of radiation budget components indicates that about 34 % of the annual Rsi ( 6937.7 MJ m^-2 y^-1) was reflected back to the sky as R_so, and R_li and R_lo, amounting to 9943.4 MJ m^-2 y^-1 and 12789.7 MJ m^-2 y^-1, respectively. This yields about 1634.3 MJ m^-2 y^-2 as R_n which is about 24% of the annual R_si. Of the total 1634.3 MJ m^-2 y^-1 available energy, about 25 % was used for the process of evaporation (LE) and 77 % for heating the air (H). The annual heat contribution from the soil to the energy budget amounted to -2 % during the experimental period.

Our studies showed that the total annual measured precipitation amounted to 108.0 mm y^-1 during the year 2000, but the total evaporation was 167.6 mm y^-1, which means some water was extracted from the shallow water table (about 60 cm on the average depth during the year 2000).