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Field Mill

Field Mill. +. + . + . + . Charging by induction. Introduce a charge, creating an electric field. -. -. +. -. +. -. -. E. Initially neutral. Charging by induction. Contact charging. -. +. E. Storm Electrification . Is NOT well understood There is more than one parameter

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Field Mill

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  1. Field Mill

  2. + + + + Charging by induction Introduce a charge, creating an electric field - - + - + - - E Initially neutral

  3. Charging by induction Contact charging - + E

  4. Storm Electrification • Is NOT well understood • There is more than one parameter • Buoyancy • Hydrometeor type • Conductivity • Even within the same storm • Role of charge separation

  5. Electrical properties of water • Polarity • Dielectric • Induction

  6. Charging Mechanisms E • Induction • Result is a polarized hydrometeor • Ion particle charging • Particle-particle charging + - + + - - + - - +

  7. Laboratory Experiments

  8. - + Selective Ion Capture - - - - - E - - - - - + + + + + + + + + +

  9. Gravity plays a role in differential charge separation Negative charge transfer to larger particles, which then fall to lower levels in the cloud.

  10. Lightning Types Frequency of occurrence

  11. The Electrification of thunderstorms is related to thermodynamics

  12. Flash Rate and cloud top height Efforts to find a power law relationship

  13. Flash Rate and Cloud Tops A deep Florida T-storm Note max flash rate corresponding to cloud top

  14. Ground and intra-cloud flashes The IC/CG ratio increases with total

  15. Flash Rate and radar reflectivity On average the ground flash rate increases rapidly with storm size.

  16. Charge distribution in T-storms Note similarities, but differences Different geographic areas: different buoyancy and other environmental parameters

  17. Balance of updraft and terminal velocities Ice particle collision may be the primary mechanism for charge separation.

  18. Hailstones and cloud top velocity

  19. Lightning and Hail at the ground

  20. Corona or Point Discharge E

  21. Corona (point discharge) • The presence of some sort of conductive point • Disruption of the Electric Field • Electron Avalanche (non-ohmic)

  22. Sprites and Elves Associated with MCS • Active convective regions associated with ground flashes negative polarity • Stratiform regions associated with less frequent, but more energetic, ground flashes with positive polarity

  23. Atmospheric E-field conditions Density dependent dielectric strength of air Electric Field strength

  24. The Atmosphere and the Lab Positive anode: red light The red sprite light is due to nitrogen first positive emission (neutral nitrogen excited by colliding free electrons)

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