Nocturnal air temperature variations between forest and open areas

In this study a variety of instruments were set up to examine the influence of net radiation, cold-air advection, and sheltering on the air temperature pattern in a coniferous forest during clear nights. The air temperature pattern in the forest was compared with both a neighboring large open area (>10 km(2)) and small open areas (<1 km(2)) within the forest. Vertical and horizontal air temperature profiles, mobile measurements of air temperature, and field stations measuring wind and air temperature at several levels were used to describe the air temperature development and air temperature pattern in the forest. The study showed that the correlations among sky view factor (SVF), net radiation, and air temperature were large for points within the forest. Increasing SVF gave a more negative net radiation and lower air temperature. In comparison with the extensive open areas, however, the forest had lower air temperatures even though SVF was lower. The results suggested that the lower air temperatures measured at 2 m in the forest, about 3 degrees C lower than in the open areas, were due to a sheltering effect that increased the possibility for cooling in the forested area because of lower turbulent heating.