Explainer: 10 wonders in a winter wonderland
Thoughts of winter often drift to the perennial question: Is it really true that no two snowflakes are alike? The answer depends on how alike "alike" is, and the definition of a snowflake, according to Kenneth Libbrect, a physicist at the California Institute of Technology who studies ice crystals. At the molecular scale, there are so many ways molecules of water can combine to form a typical snow crystal that the chance of two being the same is close to zero, he says. At the optical microscope level, it's quite possible that two simple hexagonal crystals will appear identical. But at the level of larger, complex snowflakes — many, many crystals stuck together — the possibility of finding two that are alike is once again about nil, Libbrecht says.
Click the "Next" arrow above for nine more looks at the winter wonderland of science.
— By John Roach, msnbc.com contributor
The stars come out on cold, dark nights
Looking for the way to an astronomer's soul? Skip the hot summer night and head straight for the dark, icy glare of winter. That's because cold air is thin on moisture, giving the sky a crystal clarity that's untenable in summer's steamy atmosphere. Bundle up and step outside to be treated to prominent displays of the winter constellations such as Orion the Hunter, which includes three bright stars that form an unmistakable line known as Orion's Belt. Or head to Northern Canada, get cozy, and catch the northern lights, shown here.
Time indoors + kids = the flu
Got a fever, aches, pains, a sore throat and a dry cough? It must be flu season. Incidence of the sickness peaks from December to March because people spend more time indoors, which eases transmission of the virus from person to person. The virus is most commonly spread in droplets that are sent airborne by the coughs and sneezes of infected people. Recent research indicates that kids, such as the one pictured here, are key flu spreaders. That may be because they spend hours each day huddled together in crowded classrooms — and, as parents know, don't always cover their mouths when they sneeze or cough. In an effort to combat the virus, scientists now recommend that all kids, from 6 months to 18 years of age, get a flu shot.
Frigid air spawns mother-of-pearl clouds
Some of the most frigid temperatures on the planet spawn some of nature's coolest, and rarest, clouds. The nacreous clouds, sometimes called mother-of-pearl clouds for their iridescent appearance similar to the interior of mollusk shells, occur only at high polar latitudes and temperatures of less than minus 176 degrees Fahrenheit. Also known as polar stratospheric clouds, they form in the lower stratosphere — between six and nine miles high. Their iridescence stems from predawn or post-sunset light that passes through water ice crystals. This picture of nacreous clouds was taken from Australia's meteorological base in Antarctica. The clouds are also occasionally spotted in high-latitude Scandinavian countries, Northern Canada and Alaska.
Mount Washington: Worst weather in the world
The weather observatory atop Mount Washington in New Hampshire bills itself as the "Home of the World's Worst Weather." The 6,288-foot-tall, wind-scraped peak sits at the confluence of three major storm tracks. Wet, gusty, icy, foggy and generally miserable conditions are the norm. In fact, it holds a record for the highest recorded gust: 231 miles per hour, set in 1934. A team of meteorologists thrive on the nastiness, monitoring the conditions around the clock all year long. They also conduct scientific research such as monitoring cosmic radiation and ozone and studying air pollutants and climate variability.
Nor'easter: The science of the East's winter storms
Between October and April each year, the East Coast is all but guaranteed at least one bout of torrential rain, coastal flooding or a blizzard that results from a meteorological phenomenon called a nor'easter. It occurs when a northward-creeping low-pressure system in the Gulf Stream collides near the North Carolina coast with a high-pressure system of frigid, dry arctic air carried south by the jet stream. The systems' winds combine and form a potent front that travels along a northeastern track, dropping rain and snow on the mid-Atlantic states and New England. In this picture, a person walks along the New York waterfront in the midst of a powerful nor'easter.
El Nino and La Nina influence winter weather
Ever wonder why some winters are exceptionally brutal and others are awkwardly delightful? Over the past decade or so, scientists have made great strides toward answering the question with detailed studies of a phenomenon known as the El Nino/Southern Oscillation cycle. The term refers to periodic warming (El Nino) and cooling (La Nina) of the tropical Pacific Ocean, which affects weather patterns around the world. In the U.S., for example, El Nino winters feature a strong jet stream and storm track across the southern portion of the country, whereas the jet stream in La Nina years is wavelike, bringing stormier than normal conditions to the northern states. This sea surface temperature map, based on data from a NASA satellite, shows a bulge of warm water off the west coast of South America during 1997's El Nino.
Groundhogs, weather prediction and hibernation
Every year on Feb. 2, thousands of people descend on Punxsutawney, Pa., to find out if a groundhog named Phil sees his shadow. If he does, bundle up for six more weeks of cold winter weather. If he doesn't, spring is around the corner. At least that's what Groundhog Day lore dictates. Scientists put little faith in the groundhog's prognostication skill — a Canadian study shows he's right about 37 percent of the time, just above chance levels. But hibernating groundhog cousins called marmots do sometimes emerge early from their burrows. A Colorado State University professor says this has more to do with an overload of fatty acids than with shadows in February, however.
Wet winters bring life to Death Valley
About once every 100 years, powerful winter storms pound Southern California and drench the usually arid region known as Death Valley, one of the hottest and driest places on Earth. When it happens, as it did in 2005, thick or waxy coated seeds sprout, carpeting the desert with wildflowers. The flowers, in turn, attract caterpillars, which act as a lure for birds and small rodents. Snakes and foxes follow suit. The thriving food chain lasts for a few months and then shrivels under the summer heat. Dropped seeds lie in wait for the next wet winter.
Ice shelf, glaciers erode in winter
Between May and July 2008, which is winter in the Southern Hemisphere, the Wilkins Ice Shelf in Antarctica all but disintegrated. Scientists thought the deep freeze of winter would temporarily halt the ice shelf's demise. In July, an enormous ice tunnel that periodically forms on the famous Perito Moreno glacier in Argentina collapsed in front of a few off-season tourists. Scientists said both events fit into a picture of a warming world, attributed to a buildup of greenhouse gases in Earth's atmosphere.
Nelson Mandela, the revered South African anti-apartheid icon who spent 27 years in prison, led his country to democracy and became its first black president, died Thursday at home. He was 95.
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