Field Mill

Charging by induction

Initially neutral

Introduce a charge, creating an electric field

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+ + E

Charging by inductionContact charging

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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

Electrical properties of water

• Polarity• Dielectric• Induction

Charging Mechanisms

• Induction– Result is a

polarized hydrometeor

• Ion particle charging

• Particle-particle charging

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Laboratory Experiments

Selective Ion Capture

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E

Gravity plays a role in differential charge separation

Negative charge transfer to larger particles, which then fall to lower levels in the cloud.

Lightning Types

Frequency of occurrence

The Electrification of thunderstorms is related to thermodynamics

Flash Rate and cloud top height

Efforts to find a power law relationship

Flash Rate and Cloud Tops

A deep Florida T-storm

Note max flash rate corresponding to cloud top

Ground and intra-cloud flashes

The IC/CG ratio increases with total

Flash Rate and radar reflectivity

On average the ground flash rate increases rapidly with storm size.

Charge distribution in T-storms

Different geographic areas: different buoyancy and other environmental parameters

Note similarities, but differences

Balance of updraft and terminal velocities

Ice particle collision may be the primary mechanism for charge separation.

Hailstones and cloud top velocity

Lightning and Hail at the ground

Corona or Point Discharge

E

Corona (point discharge)

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

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

Atmospheric E-field conditions

Density dependent dielectric strength of air

Electric Field strength

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)