A measurement programme was developed to examine the spatial variability of incoming longwave radiation in the city of Goteborg and surrounding areas during cloudless nights.Measurements were taken during the summer of 1996 and 1997. Two Swissteco net radiometers, modified with a blackbody cavity attachment, were used for concurrent measurements of longwave radiation in a both a rural and an urban site. Additional radiation measurements were taken inside urban canyons and parks covering a wide range of sky view factors over a period of several nights. A third set of measurements, consisting in vertical temperature profiles and longwave incoming radiation, were taken during one cloudless night at selected stations following an urban/rural transect.
At the regional scale, the sky emissivity show a decrease with distance from the city centre, a result which is likely to reflect increasing incidence of surface inversions at the rural sites. These results support the main conclusions of Oke and Fuggle (1972) and are further supported by the vertical profile measurements taken on the night of June 6, 1997. At the microscale, the pattern of radiation follows sky view factors, but systematic differences appear between vegetated and urban areas.