Two typical examples of the mirror image relation between the electric field and precipitation charge in winter thunderclouds were analyzed, by making an approximation of the vertical distributions of electric field, precipitation charge density and non-precipitation charge density with sinus curves.
As a result it was theoretically found that a good mirror image relation is obtained immediately after the gravitational charge separation (downward shift of precipitation charge from non-precipitation charge) but the electric field resulting from the separation is very small, and that as the separation proceeds the relation becomes deformed and finally reaches a positive relation, although the magnitude of electric field itself increases.