Global Warming and Storms

The way storms form is easy to understand.  Air rises until it saturates, then water vapor carried by the air condenses.  The reason for the rise can be one of several mechanisms.  One common cause is temperature difference where the warmer air, which is lighter, is pushed up and out of the way of colder, heavier air.  This is a gravity driven mechanism.  The other two involve air moving relative to a barrier.  One is orographic uplift, where air is deflected upwards by a hill or mountain.  The other in a frontal boundary where air on one side of the front is heavier, so the air on the other side is force to rise.

Regardless of the mechanism, the fuel is heat energy, which once introduced enhances the rise of the air.  That heat comes from water vapor condensing.  Water releases an enormous amount of heat when it comes out of vapor, and even more if it freezes. 

Where does global warming enter the picture?  Well, if the air was warmer than it would have been without global warming, before it began rising it would have had the capacity of holding more water vapor.  This extra energy would have been added to the cloud, making it grow bigger than it would have been otherwise.  In some cases it might make the difference in whether the cloud simply became a cloud, or whether it became a storm.

This is important in understanding some of the material that will follow. 

The Earth spins one complete rotation every twenty-four hours.  So, air at the equator must travel quite a distance every day, while air at a latitude closer to one of the poles has a shorter distance to travel each day.  What this does is have air deflect to the right in the northern hemisphere.  Going away from the equator, the air outruns the Earth, while going towards the equator the Earth outruns the air.  This is the same reason water spirals down a drain.

If a thunderstorm gets larger due to more energy in the air from higher temperatures, and more energy being release from water condensing, or even freezing, there is a tendency for that storm to grow larger.  The energy release from condensing water vapor, in particular, makes the air more buoyant, and caused it to rises more rapidly.  If a strong updraft develops the rising air can even hold precipation aloft over the updraft, which is detected on radar.  This is why hook echoes occur, the precipitation that wraps around the updraft appears as a comma shape.

This morphing into a severe thunderstorm may occur due to the added buoyancy that extra condensation releases.

A severe thunderstorm can drop a tornado if the updraft fails.  The partial vacuum is filled with air from around it, which spirals in.  This is due to the Coriolis effect.  The rotation can become a tornado, an enhancement that might not have happened if the storm had not become severe.

The updraft in a severe thunderstorm raises air rapidly from the rear of the storm to the front.  Often air descends to replace some of the air that has moved upwards.  When the descending air hits the ground, it can move out at high speeds, causing line winds.  This might not have been a problem if the storm had not grown.

The updraft can also hold things aloft, like hailstones, until they grow large enough to fall through the rising air. 

There are thunderstorms that morph into severe thunderstorms normally, but with the extra heat from more condensing water vapor it becomes more likely.  Hence, global warming is enhancing the possibility of severe thunderstorms, with the attendant added problem they bring.

The jet stream is a band of air that travels around the Earth, and there are jet streams in both hemispheres.  The area where weather is unsettled and storms form is where the jet stream moves away from the lower latitudes. 

The Jetstream meanders, not unlike a river, only the meanders change more rapidly.  It can dip towards the equator in as few as three, or as many as six, places.  This is a function of how much energy the Earth’s atmosphere has, so anything that affects the energy of the atmosphere impacts the location of storms.  This can mean having storms where they are less frequent, making them more destructive.  A large thunderstorm in an arid region is likely to do more damage than one near a coast where such storms are normal.

The Earth has a circulation pattern, where air is lifted to form strong thunderstorms near the equator, cools and descends away from the equator, and spreads out.  The air that is moving towards the poles meets cold air flowing from the polar region, and there is no place to go but up, forming a band of storms at about forty-five degrees latitude.

As the sun is overhead in each hemisphere, it drags the equatorial storms with it.  This is a convergence known as the Intertropical Convergence Zone.  As the Intertropical Convergence Zone moves far enough from the equator, the easterlies that cross the equator are deflected to flow from the west because of the Coriolis effect, and may buckle the convergence band, like a low forming on a cold front, only there is no colder side.  This is how a large number of tropical systems start.

If this pattern shifts due to energy change the whole global pattern shifts with it.  And if the shift is far enough from the equator a circulation is possible, thus a storm forms.  Within a few degrees, usually about eight to ten degrees, of the equator the Coriolis effect is too small to deflect air and start a rotation.

One thing I have not heard discussed is global warming is greater in the northern hemisphere, and this makes the air in the northern hemisphere warmer and lighter than the air in the southern hemisphere that collides with it.  So, it seems the convergence zone should have an earlier encroachment far enough north to allow tropical systems to form, and remain far enough north longer, thus extending the hurricane season.

In summary, global warming adds energy to the air making it warmer and more buoyant.  The warmer air can hold more water vapor, and the condensation of water from vapor releases heat into the atmosphere.  A storm is a heat engine, and the fuel is the water vapor that condenses. 

On a larger scale, the energy in the atmosphere shifts the jet streams, and on a global scope shifts the circulation pattern of the Earth.  This impacts the location, and even the frequency, of storms. 

So, a warmer Earth is a stormier Earth.  

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