DIFFERENTIAL NOCTURNAL COOLING IN THE LANDSCAPE DETECTED BY MOBILE MEASUREMENTS

In June 1986 mobile air temperature measurements were performed in the Kivik area in Sweden. The measuring trips were repeated each hour dur ing a night with calm and clear weather conditions. Along a loop, 8650 m long and traversing a hilly landscape, the air temperature was meas ured at four levels (0.2, 1.0, 2.0 and 3.0 m a g). In this study the r esults are focused on the measurements at the standard level, 2.0 m a g, in order to make it easier to compare this study with earlier mobil e studies. Sudden rises in air temperature at 2.0 m occurred at a numb er of elevated locations along the loop, at a max. rate of 3.5 degrees C/hour, indicative of the influence of dynamic turbulence. Lower part s of the loop did show a drop in air temperature at the same time, wit h a max. of 3.8 degrees C/hour, indicative of cold air influence. In m ost earlier studies the mobile measurements were compensated for the n octurnal cooling in order to make it possible to directly compare the different measurement points. This study highlights the problems due t o turbulence as mentioned above. It also stresses the fact that more r eference measurements at more than one point along a loop are needed i n hilly terrain.