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Abstract
Clear air echo layers have been studied by weather radars, and already in 1960’s the origin of most of these echoes was found to be insects. However, turbulent variations in refractive index of the air cause the most distinct echo layers related to sharp inversions. The visible echo layers are produced by the combination of insect sizes and their abundance, and therefore also the biological differences of species may have an effect. In Finland most of the insects insects are typically below 1.5 km, but the altitude range depends on air temperature. Large insects migrating near freezing temperatures have regularly been observed at levels up to 3 km above the ground.
We have studied insect layers that are frequently observed by the University of Helsinki C-band Doppler weather radars in Finland. Dual polarization radar measurements were used to separate insect related echoes from other sources. We compare the properties of these layers to profiles of meteorological parameters, and we used the data provided by the various instruments in the Helsinki Testbed campaign. Profiling equipment in the area included radiosondes, ceilometers, Doppler lidar, sodar, wind profiler and RASS. The observations are made near the coastline, which makes it possible to study the situation over the land and sea surface at the same time.