Originally published: Dec 22 2014 - 11:45am, Inside Science News Service
By: Katharine Gammon, Contributor
(Inside Science) -- Residents of the Northern Hemisphere, don’t worry about the winter solstice – it’s not the middle of winter, and in some places, it’s not even the start of wintry weather.
So why exactly is the shortest day of the year so distant from the coldest temperatures? It’s usually another month before the bone-aching freezes of winter hit their worst.
That gap is what’s known as the seasonal lag, said Anthony Arguez, a physical scientist with the National Oceanic and Atmospheric Administration's National Climatic Data Center in Ashville, North Carolina. The lag occurs primarily because the earth’s land and oceans absorb some of the sun’s energy and release it slowly over time.
“There’s not a good answer for why people say that December 21 is the beginning of winter,” he said. “There’s nothing magical that says that winter has to happen after the solstice.” While the temperature of soil more than 30 feet below the surface remains basically constant, the soil higher up holds in heat, even while the air temperatures drop off. Arguez pointed out that summertime temperatures have a similar lag – the hottest day of the year in the Northern Hemisphere is typically in July or August.
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