Ionic Charge Emission Into Fog From a Remotely Piloted Aircraft

Abstract

Water droplets in air occur commonly in clouds and fogs. The droplets act to remove the molecular cluster-ions generated by radioactivity and cosmic rays. Through this attachment process, droplets acquire a net charge (Gunn, 1954). This can influence their behavior, for example, through modifying collisions and evaporation (Harrison & Ambaum, 2008;Khain et al., 2004). Introducing charge artificially may therefore provide a method of influencing natural droplet systems, with potential applications to fog dispersal, rainfall enhancement or modifying cloud reflectivity (Harrison et al., 2015). In situ investigation through direct experimentation on a natural fog is described here, using an aircraft for charge release.Clouds and fogs are sensitive systems where droplet growth rates and size distributions are important properties. Small changes, for example, in droplet sizes can lead to cloud brightening (Hobbs et al., 2000). Electrical influences on droplet behavior have long been recognized (Strutt, 1879), with recent modeling showing that charge-enhanced collection hastens droplet growth to raindrop sizes (Ambaum et al., 2022;Guo & Xue, 2021). Charging a droplet until the electrical force generated exceeds the droplet's surface tension, will lead to physical disruption and fragmentation (Duft et al., 2003;Rayleigh, 1882). Modifying charges in clouds has been attempted by releasing corona ions upwards from the surface, for investigation of cloud electrification (Vonnegut et al., 1962) and weather modification (Wilderer et al., 2011). Charge release can now be achieved into clouds

Charge in non-thunderstorm clouds and fogs

“…Figure 6 summarises the aircraft trajectories used and presents data obtained from a photodiode sensor carried on the aircraft measuring the reflected sunlight from the fog beneath. Full details are given in [6]…”

“…It has been suggested that the droplet charging influences the properties of the clouds, such as the stability of small droplets, the growth times from cloud droplets to raindrops by coalescence [3] and their reflection of sunlight [4], but this has hardly been investigated in natural water drop systems. To investigate the general possibilities around introducing artificially generated charge into natural droplet systems, real world experiments have been undertaken using corona ion emission into fogs, releasing from within [5] and above [6]. In this paper, the theory underlying the charging of the fog droplets is described (section 2), followed by the effect of charge on droplet evaporation (section 3).…”

“…(Right panel) Reflected solar radiation from fog, measured from aircraft (thin lines individual circles, thick line mean), for (a) positive ioniser on, (b) negative ioniser on and (c) both ionisers on. Adapted from[6]…”

A charge emitter for use in evaluating aircraft rainfall enhancement

“…The UAV is instrumented with one positive and one negative ioniser, mounted beneath the wings, with ionisers switched on and off under manual control from the UAV pilot. UAV flights over an electric field mill have demonstrated a clear change in electric field during ion emission from the aircraft [5]. Subsequent UAV flights in fog demonstrated a change in the radiative properties of the fog during ion emission periods, as measured by downward-looking radiation sensors onboard the aircraft [5].…”

“…UAV flights over an electric field mill have demonstrated a clear change in electric field during ion emission from the aircraft [5]. Subsequent UAV flights in fog demonstrated a change in the radiative properties of the fog during ion emission periods, as measured by downward-looking radiation sensors onboard the aircraft [5].…”