Cloud‐radar observations of insects in the UK convective boundary layer

Abstract

ABSTRACT:Radar has been applied to the study of insect migration for almost 40 years, but most entomological radars operate at X-band (9.4 GHz, 3.2 cm wavelength) and can only detect individuals of relatively large species, such as migratory grasshoppers and noctuid moths, over all of their flight altitudes. Many insects (including economically important species) are much smaller than this, but development of the requisite higher power and/or higher frequency radar systems to detect these species is often prohibitively expensive. In this paper, attention is focused upon the uses of some recently-deployed meteorological sensing devices to investigate insect migratory flight behaviour, and especially its interactions with boundary layer processes. Records were examined from the vertically-pointing 35 GHz 'Copernicus' and 94 GHz 'Galileo' cloud radars at Chilbolton (Hampshire, England) for 12 cloudless and convective occasions in summer 2003, and one of these occasions (13 July) is presented in detail. Insects were frequently found at heights above aerosol particles, which represent passive tracers, indicating active insect movement. It was found that insect flight above the convective boundary layer occurs most often during the morning. The maximum radar reflectivity (an indicator of aerial insect biomass) was found to be positively correlated with maximum screen temperature.

Predicting Insect Migration Density and Speed in the Daytime Convective Boundary Layer

“…Flight conditions, particularly temperature-insect relationships at altitude, have been described formally since Johnson [12]. More recently Wood et al [23] established that warmer days are associated with more aerial migration and that the minimum threshold was around 13–14°C. Hotter days are associated with more frequent, longer-lasting and deep convective plumes allowing more insects to be spread through the CBL (Fig.…”

“…The novelty of this work is that whilst there are hundreds of studies of insects and spiders migrating within their FBL (i.e. usually ∼0.5–10 m; [9], [26], [33]–[34]) there are few empirical non-invasive surveys of day-flying insects within the convective boundary layer [CBL] above the level of the FBL (Ecological: [13], [19], [23]; Meteorological: [35]–[36]). These latter studies either focus on a time-series of just a few days when either particular meteorological, or insect phenomena, were apparent or are purely meteorological.…”

BASTA: A 95-GHz FMCW Doppler Radar for Cloud and Fog Studies

“…The reflectivity of the radars has been corrected from gaseous attenuation. Note that the echoes observed by the KAZR below 2 km between 1000 and 1400 UTC and not by BASTA are coming from insects (Wood et al 2009); because of their large size and their rather small concentration, the 35-GHz radar is more sensitive to their presence. There is clearly excellent agreement between the pulsed radar and the FMCW radar observations of this ice cloud.…”

Recent Insights from Radar Studies of Insect Flight

“…Flight activity could then be monitored for insects ranging in size from sphingid moths and locusts, through planthoppers (∼1-2 mg; 85), to aphids, small Diptera, and minute parasitic wasps (∼0.05-0.5 mg). Radars operating at 9 and 3 mm have been developed for atmospheric observations and on warm cloudless days detect insects in large numbers (119). The great profusion of small taxa will present a target identification challenge that will be best tackled by sampling, at least occasionally, with a balloon-borne net (20).…”