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Field Mill. Charging by induction Initially neutral Introduce a charge, creating an electric field +...
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Transcript of Field Mill. Charging by induction Initially neutral Introduce a charge, creating an electric field +...
Field Mill
Charging by induction
Initially neutral
Introduce a charge, creating an electric field
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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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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
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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)