Figure 1.

Examples of hourly profiles of log aphid density on log height for 8 August 1955 (adapted from Johnson 1957). The trapping heights were 3, 6, 15, 76 and 305 m above ground. The density of aphids (numbers per 10⁶ m³ of air) diminishes with height such that the linear regression coefficient, b, of log density on log height provides a single-parameter characterization of the vertical density profile. The dashed lines are least-squares fits to the simulation data above 10 m with linear regression, b. The coefficient b has the following values: (a) b=−0.61 at 08.00 (r²=0.93), (b) b=−0.72 at 10.00, (c) b=−0.74 at 12.00, (d) b=−1.24 at 14.00, (e) b=−1.32 at 16.00, and (f) b=−1.88 at 18.00 (r²=0.98). The atmosphere was unstable up to approximately 15.00, the surface temperate at the monitoring site (Cardington, UK) increasing from 15°C at 09.00 to 20.6°C at 14.00. At approximately 15.00 however, a steady cooling of the atmosphere began (Johnson 1957).