Science: Coldest Cold

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The U.S.S.R., which like California delights in its own superlatives, is the proud possessor of "the coldest spot on earth." Last week Moscow radio announced that at a place in Siberia (Lat. 63 north, Long. 143 east) near the Sea of Okhotsk the thermometer recently dived to —70.2° Centigrade ( — 94.36° F.).

U.S. weathermen admitted that they could not compete. Cold record for the U.S.: -66° F. at Yellowstone Park on Feb. 6, 1933. North America's coldest place is in Canada's lower Mackenzie Valley, where the thermometer at Fort Good Hope has fallen to —79° F.

The world's coldest regions are areas near the poles where there is little or no sun in winter to warm the air, little wind to bring in warm air, and few clouds to screen the ground from outer space. Under these conditions, the air near the surface loses heat by radiation, often getting considerably colder than the atmosphere far above it.

There are three such "source regions" of cold air: Siberia, northern Canada and Antarctica. The first two are fairly well known to meteorologists; but the interior of Antarctica is still something to guess about.

On his last expedition (1935) Rear Admiral Richard Byrd recorded a temperature of —90° F., almost equaling Siberia's record. He believes that the air above the polar plateau may be found to fall below —100°F.

Except when affected by local conditions (such as low level radiation), the air gets steadily colder with increased altitude. The decline continues up to the top of the troposphere (the atmosphere's lowest layer). Above this lies the stratosphere, where the temperature remains almost constant.

Over the poles, the troposphere goes up 14 to 15 kilometers (9 miles) above sea level. Over the equator it goes higher: 17 kilometers (10½ miles). The higher the troposphere rises the colder it gets. So the coldest air temperatures (about —132° F.) are above the hot equator. High above the North Pole, it probably gets no colder than -45° F.