Re: During a lightning storm, why does the ground become positively charged?

The ground was not negatively charged to begin with.
The ground was neutral.  The atoms of the ground are made of a positively
charged nucleus and negatively charged electrons that orbit the nucleus.  
When the base of the cloud becomes negatively charged, some of the 
electrons in the upper part of the ground move deeper.  The nucleus of each 
atom and most of the electrons stay where they are.  The more electrons at 
the base of the cloud, the more electrons are pushed deeper into the 
ground.  Eventually, the positive charge of the ground and the negative 
charge of the cloud become great enough that the electrons jump the gap,
thereby producing lightening.  This leaves the ground with extra electrons,
which may lead to another, more powerful form of lightening, called 
positive flash lightening.  This occurs when the positively charged upper 
part of the cloud produces a bolt of lightening that extends all the way to
the ground.  Since the distance is so much further, a much greater charge 
difference must occur before it happens.  Therefore, when it happens, a 
much greater amount of energy is released.  ZAP!

Matthew Barchok,
        Mad Scientist