Original Article

International Journal of Biometeorology

, Volume 50, Issue 4, pp 193-204

The influence of the atmospheric boundary layer on nocturnal layers of noctuids and other moths migrating over southern Britain

  • Curtis R WoodAffiliated withDepartment of Meteorology, University of ReadingRothamsted Radar Entomology Unit, Plant and Invertebrate Ecology Division, Rothamsted Research Email author 
  • , Jason W ChapmanAffiliated withRothamsted Radar Entomology Unit, Plant and Invertebrate Ecology Division, Rothamsted Research
  • , Donald R ReynoldsAffiliated withNatural Resources Institute, University of Greenwich
  • , Janet F BarlowAffiliated withDepartment of Meteorology, University of Reading
  • , Alan D SmithAffiliated withRothamsted Radar Entomology Unit, Plant and Invertebrate Ecology Division, Rothamsted Research
  • , Ian P WoiwodAffiliated withRothamsted Radar Entomology Unit, Plant and Invertebrate Ecology Division, Rothamsted Research

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Abstract

Insects migrating at high altitude over southern Britain have been continuously monitored by automatically operating, vertical-looking radars over a period of several years. During some occasions in the summer months, the migrants were observed to form well-defined layer concentrations, typically at heights of 200–400 m, in the stable night-time atmosphere. Under these conditions, insects are likely to have control over their vertical movements and are selecting flight heights that are favourable for long-range migration. We therefore investigated the factors influencing the formation of these insect layers by comparing radar measurements of the vertical distribution of insect density with meteorological profiles generated by the UK Meteorological Office’s (UKMO) Unified Model (UM). Radar-derived measurements of mass and displacement speed, along with data from Rothamsted Insect Survey light traps, provided information on the identity of the migrants. We present here three case studies where noctuid and pyralid moths contributed substantially to the observed layers. The major meteorological factors influencing the layer concentrations appeared to be: (a) the altitude of the warmest air, (b) heights corresponding to temperature preferences or thresholds for sustained migration and, (c) on nights when air temperatures are relatively high, wind-speed maxima associated with the nocturnal jet. Back-trajectories indicated that layer duration may have been determined by the distance to the coast. Overall, the unique combination of meteorological data from the UM and insect data from entomological radar described here show considerable promise for systematic studies of high-altitude insect layering.

Keywords

Insect layering Nocturnal boundary layer Temperature inversion Noctuid moths Entomological radar