A Comparison of Radiative and Actual Nocturnal Cooling Rates over Grass and Snow

Measured divergence of net nocturnal longwave flux between 1 and 3 m over a snow-covered field under clear skies and weak regional winds show that the rate of radiative cooling is higher than similar cooling rates over a short grass cover by a 2:1 ratio. On the average, the radiative cooling rate was about 2.5 times the actual rate over the two surfaces but the variation in the hourly rate was higher over grass than over snow. This is held to be indicative of the stronger role played by forced turbulence over grass than snow.