Answer #9:

The positive cloud-to-ground flash is less common than the negative. Coming from higher altitudes in the

cloud, positive flashes make up about 10% of all lightning flashes. They are usually composed of asingle

stroke, and have longer, continuing currents. From the forestry perspective, positive flashes are of more

concern as the longer currents are more likely to start fires.

Several studies have concentrated on the characteristics of the positive flash but results are inconclusive

due to the number of observations. The percentage of positive flash appears to increase with latitude and

with the height of local terrain. Also, positive flashes are more common in winter storms. The apparent

cause for this is that the lower freezing level places the positive charge centre closer to the ground thus

increasing the likelihood of a flash.

Positive flashes are more common in stratiform clouds while negative flashes tend to occur in areas of

strong convection. Also, thunderstorms that predominantly consist of negative flashes in their early

stages, often end with positive discharges as the storm matures and the anvil spreads out. A popular

theory is that horizontal wind shears force a tilting of the dipole axis providing a route for the positive

flash but this has yet to be shown conclusively.