| HOME | CLOUD/PRECIP FCST MOVIE | TEMPERATURE FCST MOVIE | 2007 HURRICANES |
| NATIONAL RADAR | WATCHES & WARNINGS | STORM REPORTS | 2008 HURRICANES |
What causes the jet stream?
But how does the temperature difference between two air masses cause the jet stream? To answer this question, it is first helpful to understand what causes pressure variations (and thus wind) at the Earth's surface. The difference in pressure that cause winds at the surface of the Earth is ultimately due to the horizontal difference in air temperature summed up (integrated) over the entire depth of the atmosphere. Because warm air is less dense (it weighs less), and cold air is more dense (it weighs more), high and low pressure areas represent, in a vertical average sense, cooler and warmer air, respectively.
Jet streams, then, occur at altitudes where the vertically integrated horizontal temperature difference between two air masses is at a maximum. This causes a maximum in the pressure 'gradient' (horizontal difference in air pressure) at that altitude. In the absense of surface friction, the turning of the earth causes the wind (which wants to flow from high pressure to low pressure) to turn to the right (in the Northern Hemisphere), so the wind flows around high and low pressure areas, rather than from high to low pressure.
Interesting facts:
AIRPLANES FLYING BACKWARDS?Just how strong the winds can be in jet streams was discovered during Word War II, when American bombers tried flying from the U.S. to Japan and found they couldn't make any progress flying against the strong winds. Today, aircraft routinely adjust their altitude to either fly with the wind in the jet stream, or move to a different altitude to avoid flying against it.
GLOBAL WARMING AND AIR PRESSURE Since the above discussion about the jet stream mentions that warm air is less dense, you might wonder whether the surface pressure will change if the whole global atmosphere warms up? The answer is no. In that case the air can only expand upward, not horizontally, and this dows not change the surface air pressure (there is still the same amount of air above the surface). So we see that for surface air pressure to change at a point, horizontal expansion (and compression elsewhere) must occur.
Dr. Roy W. Spencer:
GLOBAL WARMING: Manmade or Natural?
Now IN-STOCK at Amazon.com:
CLIMATE CONFUSION:
How Global Warming Hysteria Leads to Bad Science,
Pandering Politicians, and Misguided Policies that Hurt the Poor
without the annoying popups,
from
