Spring is here and for the
eastern half of the country it has been some winter. Very cold into the deep south and plenty of
snow up north. The sun is now advancing
slowly northward and hot weather will be upon us. Hello to another weather
phenomenon, the thunderstorm. We are all
familiar with thunderstorms, heavy rain, gusty winds, lightning, thunder and
even sometimes hail. Let’s take a closer
look at a thunderstorm and see what causes it.
Basically you need heat,
cold and moisture. Specifically, very
warm or hot air at the surface, plenty of moisture available and a very
important ingredient cold air in the upper atmosphere. When it is hot at the surface and cold aloft,
we say the atmosphere is unstable. So,
here We go…on a hot summer afternoon, surface temperature readings in the 90’s,
the surface air is very moist, the air begins to rise. As long as this Parcel of air is warmer than
the air surrounding it, the air will continue to rise. As this air rises higher in the sky, the
upper air surrounding the parcel continues to be colder and colder. This causes the air to continue to rise.
The air will rise until the air surrounding
this parcel is the same temperature as the parcel. If, however, the upper atmosphere is cold all
the way up to 60,000-70,000 ft. The parcel will rise that high. Also, remember the surface air contained a
great deal of moisture. Well, air is
like a sponge, warm air can hold a large amount of moisture, however, as the
air gets colder, it is like squeezing the Sponge. Water is released, if you squeeze the sponge quickly, a great
deal of water is released at once….a Heavy downpour. So, in general, rising air causes clouds and
precipitation because rising air expands and cools and can not hold as much moisture as warm air
can. That explains the rainfall during a thunderstorm…what about the lightning
and thunder? Let’s forget mathematics
etc and explain these features in a very down to earth fashion. In a thunderhead cloud, also called a
cumulonimbus cloud, there is plenty of water vapor. Water, as you know, is h20
Two hydrogen atoms and one oxygen atom. Hydrogen has an electrical charge of plus
one. Since there are two hydrogen atoms,
it has a plus two Charge. However,
oxygen has a negative charge, a minus 2 charge.
So, when you combine two hydrogen (+2) with one oxygen (-2), you get
water.
With a zero charge.
In a thunderhead cloud there are tremendous up and down drafts of
air. Planes flying through a thunderhead
would be damaged severely if not destroyed completely. Anyway, these up and down drafts of air rip
the water molecules apart. The h’s are
ripped from the (oh’s). These particles are
now charged. The (oh) has a negative
charge while the “h” has a positive charge.
The positive charges accumulate at the top of the cloud while the
negative charges are found at the base of the cloud. Beneath the cloud, positive charges
prevail. Since opposites attract, the
positive and negatives try to interact.
As the storm system moves along, the positive charges on the ground
follow along. Finally, when A high
object appears in the storm’s path,
the positive charges climb up the high object, be it a tree, a hill, a tall
building. The negative charge and the
positive charge are now closer together and there is less resistance between
them.
A huge spark occurs when the charges comes together. We call this lightning. Lightning can go from cloud to ground, we
call this cloud to ground lightning.
Sometimes lightning goes from one cloud to another cloud and does not
strike the ground. We call this cloud to
cloud lightning. Next week i will talk
more about lightning , a few safety measures and then discuss thunder and hail.