In reading of the extreme cold in the eastern U.S., Tuesday, I noted the reference to the so-called, “polar vortex," a term that has been popularized in recent years in describing these cold arctic outbreaks. This refers to a system of counter-clockwise upper atmospheric winds that commonly keep cold polar air confined to the arctic regions. The polar vortex strengthens and expands during the winter and weakens in summer.

When these upper winds strengthen(the so-called Arctic Oscillation is in positive phase) fewer polar outbreaks will come down into the lower 48 states. In the negative phase, when winds are weaker, cold air invasions are generally more common, such as is occurring at this time. Furthermore, when the jet stream is in the right trajectory, it will guide polar air down into the northern U.S, at times reaching all the way to the Gulf of Mexico.

One further fact should be mentioned. The coldest part of the northern hemisphere is not the Arctic Ocean but over the vast expanses of Siberia and northern Canada, where extensive, relatively thin snow cover and extremely dry air accumulate in the winter months, particularly in lower basins. The Arctic does have a brief, intense summer, a time to be out and explore the renewal of life in relative comfort in the long hours of that soft angular light.

The sense of time is altered, and the eternal muted rhythms of the planet are more clearly sensed in the pristine silence.

Evan Tibbott


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