On the horizon

New insight on a seasonal shift

Sometimes spring seems to come with the flip of a switch. One week, it's frigid; the next, robins are scouring the yard for worms. Now, scientists think they've found the reason for the sudden change: Blame it on a windy dance between the lowest layer of the atmosphere, called the troposphere, and the layer just above it - the stratosphere.

As winter ends, a high-speed stream of westerly winds in the stratosphere weakens, then reverses direction, they found. When that happens, a similar "jet stream" it couples to in the troposphere slows dramatically. Once that transition takes place, the shift in seasons can take about a week. The stratosphere's "final warming" can come as early as mid-March or as late as mid-May, say researchers from the University of Illinois at Urbana-Champaign and Georgia Tech in Atlanta. The earlier the change, the less time it takes for seasonal weather patterns to shift.

The work, to be unveiled Thursday at an American Meteorological Society conference in Cambridge, Mass., could lead to more accurate forecasts for the onset of spring weather, which profoundly influences regional rainfall, the growing season, and the overall productivity of local ecosystems.

Expired star sends new signals

As if taking a page from Monty Python, a star that quenched its fires in an enormous explosion some 325 years ago has signaled to astronomers: "I'm not dead yet."

Its message has left astronomers wondering if they have found an extremely rare, mysterious object called a magnetar - a dense stellar remnant whose surface shudders and cracks, releasing intense bursts of gamma radiation.

The star, Cassiopeia A, exploded as a supernova in the late 1600s. But "accidental" observations with the Spitzer Space Telescope show that the star, roughly 10,000 light years away, appears to have sent out a weaker burst of energy as recently as 53 years ago. The evidence is found in "light echoes" that trace the radiation's movement through the cloud of dust the star blasted away when it first exploded. As the gamma rays travel outward at the speed of light, they in effect illuminate different sections of the dust cloud. University of Arizona researchers involved in the work reported their results in the current issue of the journal Science.

The world's 'oldest' plant

Biologists in Israel have coaxed a 2,000-year-old date seed into sprouting, making it the "oldest" plant germinated from an ancient seed. They've dubbed the 12-inch-tall sapling Methuselah. The previous record-holder was a lotus grown from a 1,200-year-old seed in China.

The seeds came from Masada, a mountaintop fort in the Dead Sea Valley, where archaeologists have been piecing together the story of the Roman siege in AD 73. Back then, the plant, a long-extinct Judean date palm, was highly valued for medicinal purposes, archaeologists say. So scientists hope Methuselah will grow to maturity to see if its fruit contains compounds potentially useful as medicine. Date palms generally don't bear fruit until they're about 30 years old; that is, if the plants are female. And if the plant turns out to be a boy? "The genetics of the plant will turn out to be interesting, whatever sex it is," says Sarah Sallon, who heads the research team at the Louis Borick Natural Medicine Research Center in Jerusalem, where the work is being conducted.

Mixing Atlantic and Pacific

Before Teddy Roosevelt and the Panama Canal, there was the Panamanian Gateway - an open passage between the Atlantic and Pacific Oceans some 64 million years ago. Its closure some 3 million to 16 million years ago goes a long way toward explaining why a dip in the North Pacific can turn lips blue, according to a study out of Japan.

Researchers at the Meteorological Research Institute used sophisticated ocean-circulation models to see what the North Pacific might have been like with the gap open between what is now North and South America. With the gateway open, warm salty water would have flowed into the Pacific only to sink. This would have driven an ocean "conveyor belt" that would have brought warmer water and air farther north than today's conditions do. Once the gap closed, the mixing stopped, generating ocean conditions more like today's. The results appear in the current issue of Geophysical Research Letters.

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