Not-Hebdomadal

10 Day Quasi-Periodic Weather

The weather during the 110 days from the first day of February 1953 to the 21st day of May 1953 exhibited a strong quasi-periodic “cycle”. At issue in this case is cyclogenesis aka storm development.

Source material for this blog is Jerome Namias (1954). Quasi-periodic Cyclogenesis in Relation to the General Circulation. Tellus VI:1- 13.

Atmospheric pressure declines with altitude. Altitude may be recorded in feet or meters or in millibars (mb). The pressure at the surface is about 1000 mb. As you go up pressure falls to 900 mb then 800 mb, then 700 mb, then 600 milliards, then at 500 mb. At 500 MB we are about half way up to the top of the atmosphere. Namias chose to study pressure at the 700 mb level. He recorded that level in terms of its height above the ground in feet. At the lowest point the 700 MB surface is about 9,400 feet above the surface. At its highest elevation it was at 10,400 feet. His measurements were taken at 40N and 110W, an area known as the four corners. Cyclogenesis is common in the four corners area. Newly minted cyclones (storms) then move across Oklahoma toward the Midwest and then New England.

A graph of Namias’ history of pressure above the four corners area follows.

Each of the storms that evolved is marked sequentially with a letter of the alphabet. Everywhere along the graph the pressure is the same (700 mb). Weather balloons record and send back to weather data twice daily.

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