In measurements of the electric field associated with the current of a sprite 450 km from ground-based field sensors, it was observed that the sign of the electric field was positive when positive charge was lowered from the ionosphere. A recent model for the electric field associated with the sprite current also predicts positive field changes at 450 km from the sprite. A well-known analysis of a vertical dipole in a thundercloud shows that the electric field on the ground reverses its sign at an easily computed distance from the dipole. A similar simplified electrostatic analysis of a sprite predicts a field reversal distance around 130 km. A more accurate electrodynamic analysis based on Maxwell's equations indicates that the field reversal distance should be between 70 and 80 km.
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