Abstract
It is well known in the meteorological community that millimetre-wavelength cloud radars contain considerable contamination from aerial biota, and much of this comprises small weakly flying insects. Several methods have been explored for removing insect contamination from cloud radar data yet using this data to study the behaviour of insects remains a relatively unexplored area. Here, the authors describe the use of a collocated Ka-band cloud radar and Doppler LIDAR to study the vertical motion of small insects and investigate how this varies depending on the surrounding vertical air motion. We find that in the convective boundary layer, insects are largely concentrated in updrafts. During the daytime, small insects in downdrafts are found to descend at an average rate of 0.25 m s−1, yet insects caught in updrafts showed a descent response that was dependent upon the strength of the updraft in which they were embedded. Although the downward motion of the insects increased with increasing updraft strength, it was insufficient to overcome the rising motion in the updraft, i.e. in updrafts the insects ascend but at a slower speed than the surrounding air. We also report an ongoing efforts to extend this research to the nocturnal stable boundary layer.
Highlights
The flight behaviour of small insects in the atmospheric boundary layer has long been a topic of investigation for entomologists [1], with the first studies using aerial netting to study the relative density of various taxa at different heights and try to relate this to atmospheric conditions [2]
The study of insect behaviour with respect to the air motion in which they are embedded is of interest both to entomologists concerned with how the insects sense the atmospheric conditions around them [8], and to meteorologists who need a robust method for removing insect clutter from the cloud radar returns and for removing biases introduced into radarderived vertical velocities [9, 10]
By comparing the two figures, we can identify plumes of increased reflectivity occurring at the same time as positive vertical motion, which indicates that the insects are strongly concentrated in convective updrafts
Summary
The flight behaviour of small insects in the atmospheric boundary layer has long been a topic of investigation for entomologists [1], with the first studies using aerial netting to study the relative density of various taxa at different heights and try to relate this to atmospheric conditions [2]. The study of insect behaviour with respect to the air motion in which they are embedded is of interest both to entomologists concerned with how the insects sense the atmospheric conditions around them [8], and to meteorologists who need a robust method for removing insect clutter from the cloud radar returns and for removing biases introduced into radarderived vertical velocities [9, 10]. This study, conducted on summertime fair-weather days in Kansas in the USA Great Plains, found that insects resist ascent when in updrafts. The strength of their resistance to the updraft was found to increase in proportion to the updraft strength. This suggested that the insects are somehow able to sense the vertical motion of the surrounding air, since their response is seen to be dependent on the updraft strength
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