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The Jet Streams are caused by temperature variations both with change in altitude and change in latitude. In other words, air moves between areas of high temperature and low temperature both from the land surface upwards and from the equator northwards. As the air lifts northwards and upwards, the earth, in rotation, drags the circulation with it to the east.
The earth rotates at a speed of approximately 1000 mph at the equator; the speed of rotation decreasing with latitude. The Jet Streams range in speed from approximately 40 to 90 mph, being normally weakest near the equator.
We have only about 70 years of data of actual measurements of the Jet Streams starting in circa 1948. This is about the same as what we have for measurements of ozone (Click Here) and less than our understanding of ocean circulation.
One study has used measured data during the last 30 years or so to indicate that the Jet Streams rose in altitude and moved closer to the poles with time. The jet stream in the Northern Hemisphere weakened while the Southern Hemisphere subtropical jet stream weakened and the polar jet stream strengthened. Despite every apparent intention to do so, the authors could not confidently attribute these changes to man-made climate change.
Another study looked at data for the past 8000 years, using oxygen isotopes in caves and lake sediments. The result of the study was that a decrease in the Sun’s energy approximately 4000 years ago resulted in cooler temperatures and an increase in the jet stream “curviness.” According to this study, the jet streams should be reverting back to “straighter” flow, but that the curviness is being exacerbated by climate change.
Apparently, the two studies are contradictory. The short term study using actual mapped and measured data surmised that flattening of the jet streams, along with wreaking and movement, may be associated with climate change, while the long term prehistoric data postulated wilder amplitude swings in the jet streams due to climate change. Actually, the long term study predicted, without the influence of global warming, what the short term study shows.
Does this mean that the results of either study are wrong? Not necessarily. But it is also inappropriate to associate any changes in the position, curviness, or strength of the jet streams with climate change, less than it may be appropriate to associate climate change with changes in the jet streams. The cause of the jet streams is the planet’s rotation on its axis and the degrees of solar radiation, it stands to reason that changes in the rotation, tilt, and wobble of the earth, along with solar cycles are the cause of variability.
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