Abstract

Charging of upper and lower horizontal boundaries of extensive layer‐clouds results from current flow in the global electric circuit. Layer‐cloud charge accumulation has previously been considered a solely electrostatic phenomenon, but it does not occur in isolation from meteorological processes, which can transport charge. Thin layer‐clouds provide special circumstances for investigating this dynamical charge transport, as disruption at the cloud‐top may reach the cloud base, observable from the surface. Here, a thin (∼300 m) persistent layer‐cloud with base at 300 m and strong wind shear at cloud‐top was observed to generate strongly correlated fluctuations in cloud base height, optical thickness and surface electric Potential Gradient (PG) beneath. PG changes are identified to precede the cloud base fluctuations by 2 min, consistent with shear‐induced cloud‐top electrical changes followed by cloud base changes. These observations demonstrate, for the first time, dynamically driven modification of charge within a layer‐cloud. Even in weakly charged layer‐clouds, redistribution of charge will modify local electric fields within the cloud and the collisional behaviour of interacting charged cloud droplets. Local field intensification may also explain previously observed electrostatic discharges in warm clouds.
Original languageEnglish
Pages (from-to)3667-3679
Number of pages13
JournalQuarterly Journal of the Royal Meteorological Society
Volume145
Issue number725
Early online date26 Aug 2019
DOIs
Publication statusPublished - 1 Oct 2019

Keywords

  • Kelvin–Helmholtz billows
  • atmospheric electricity
  • cloud microphysics
  • stratiform cloud

ASJC Scopus subject areas

  • Atmospheric Science

Cite this

Shear-induced electrical changes in the base of thin layer-cloud. / Harrison, R Giles; Marlton, Graeme; Aplin, Karen L.; Nicoll, Kerianne.

In: Quarterly Journal of the Royal Meteorological Society, Vol. 145, No. 725, 01.10.2019, p. 3667-3679.

Research output: Contribution to journalArticle

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N2 - Charging of upper and lower horizontal boundaries of extensive layer‐clouds results from current flow in the global electric circuit. Layer‐cloud charge accumulation has previously been considered a solely electrostatic phenomenon, but it does not occur in isolation from meteorological processes, which can transport charge. Thin layer‐clouds provide special circumstances for investigating this dynamical charge transport, as disruption at the cloud‐top may reach the cloud base, observable from the surface. Here, a thin (∼300 m) persistent layer‐cloud with base at 300 m and strong wind shear at cloud‐top was observed to generate strongly correlated fluctuations in cloud base height, optical thickness and surface electric Potential Gradient (PG) beneath. PG changes are identified to precede the cloud base fluctuations by 2 min, consistent with shear‐induced cloud‐top electrical changes followed by cloud base changes. These observations demonstrate, for the first time, dynamically driven modification of charge within a layer‐cloud. Even in weakly charged layer‐clouds, redistribution of charge will modify local electric fields within the cloud and the collisional behaviour of interacting charged cloud droplets. Local field intensification may also explain previously observed electrostatic discharges in warm clouds.

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