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Science Bits

Massachusetts Institute of Technology, NOAA, NCAR
Auto-nowcaster goes on line in Memphis

An automated thunderstorm forecasting tool developed by NCAR's Research Applications Program is undergoing its first major real-world test this summer. Tests of the auto-nowcaster, which spots incipient storms and predicts their development up to a half-hour in advance, are under way at the Federal Aviation Administration's Integrated Terminal Weather Support Site near Memphis, Tennessee. The FAA is supporting the project. Collaborators on the Memphis test include the Massachusetts Institute of Technology's Lincoln Laboratories and NOAA's National Severe Storms Laboratory.

A cumulus cloud can blossom into a thunderstorm in as little as 10 to 20 minutes. Although operational computer forecast models have proven useful in predicting large-scale weather developments 12 to 48 hours in advance, they do not have the resolution to make accurate forecasts on the thunderstorm scale. With help from new techniques for analyzing Doppler radar data, the auto-nowcaster looks for gust fronts and other lines of converging air on which storms might be induced to form. (These boundaries cannot be simulated directly by larger-scale computer models.) Other parts of the auto-nowcaster examine whether atmospheric conditions are sufficient to support storms once formed and how storm motion might evolve over time.

"It has been a major team effort to get the auto-nowcaster ready for field testing," says project manager James Wilson of NCAR's Atmospheric Technology Division, "and we are very anxious to get feedback from this summer's test. We expect the auto-nowcaster will be issuing thunderstorm advisories on its own in the near future." For more information, contact Wilson (303-497-8818 or jwilson@ucar.edu).

University of Alabama in Huntsville, NASA
Cooling event chills globe

A La Nina cooling event has been chilling global temperatures for at least five months, but proving that it caused any short-term changes in weather patterns is difficult, according to John Christy, an associate professor of atmospheric science in the Earth System Science Lab at the University of Alabama in Huntsville (UAH). He made the observation in a report on global temperatures that the lab issues monthly.

"The La Nina weather patterns are less robust than those from El Nino," he said. "In terms of impact on the United States, the effects of the cool phase are less consistent than the effects of the warm phase."

While atmospheric temperatures in the eastern tropical Pacific Ocean were generally less than 0.5 degree C below seasonal norms, the large area of cool Pacific water chilling the atmosphere helped hold the global composite temperature below seasonal norms for the months between December and April. Data for May and June are not yet available.

A large region of cooler-than-normal air stretched from Central Africa across the eastern Mediterranean, Russia, China, Japan, and across the North Pacific into southern Canada as far east as Quebec. The coolest air was over northern Japan and the North Pacific where temperatures in April averaged as much as 3.5 degrees C below seasonal norms.

As part of an ongoing UAH/NASA joint project, Christy and Roy Spencer, of the Global Hydrology and Climate Center in NASA's Marshall Space Flight Center, use data gathered by microwave sounding units on NOAA's TIROS-N satellites to get accurate temperature readings for most regions of the Earth.

Once the monthly temperature data are collected and processed, they are placed in a public computer file for immediate access by atmospheric scientists in the United States and abroad. Scientists can access the data by anonymous ftp_198.116.60.11. For more information, contact Christy (205-922-5763 or christy@atmos.uah.edu) or Spencer (205-922-5960 or roy.spencer@msfc.nasa.gov).

University of Nebraska-Lincoln, Ohio State University
Discovery of Antarctic moss bed fuels climate controversy

Scientists from the University of Nebraska-Lincoln and Ohio State University have uncovered a bed of moss dating back at least 3 million years. The discovery was made during the last Antarctic field season in January and February.

The unmineralized moss is the latest in a series of finds in recent years that are fueling a controversy over how warm Antarctica's ancient climates were and when the southernmost continent was transformed to its current icy state. David Harwood, assistant professor of geology at UNL, and Peter Webb, professor of geologic sciences and a member of the Byrd Polar Research Center at Ohio State, said team members found the moss bed while searching for fossils in the Oliver Bluffs region of the Dominion Range, about 483 kilometers from the South Pole. The moss was buried under layers of rock and debris at the site.

On previous NSF-funded expeditions, Harwood and Webb found sticks, twigs, and leaves from ancient plants in the same area. These artifacts suggest that the region resembled an arctic tundra environment as recently as 3 million years ago. Harwood said he believes the moss was growing on a wetland area that eventually was covered by silt from a nearby river or stream during a glacial advance into the area.

The moss bed was found in sediments near an ancient peat bog, which probably preserved organic material that thrived in the area before it became ice-covered, according to Harwood. Identifying these organisms can help scientists determine what life was like in the area, including ancient climate patterns.

Scientists disagree over the history of the area's rock beds. One group suggests that the area has not changed for as much as 20 to 30 million years. The other group, including Harwood and Webb, think the area, with its rock deposits, is much younger-perhaps as young as 3 million years old.

The age dispute is significant for a number of reasons. This recent find, as well as those of past years, was high up in the Transantarctic Mountain range. That suggests that the terrain has risen substantially since the moss, sticks, twigs, and leaves were buried. If so, the mountains must have risen in a remarkably short time.

The Transantarctic Mountains form a dam of sorts, blocking the vast East Antarctic Ice Sheet from spilling down into the Ross Sea. If the mountains did rise in what geologists consider a very short time, then it could change many ideas about the recent history of the region, how many times the ice and glaciers had spread and receded, and when the region was locked into its present deep freeze.

For more information, contact Ohio State science writer Earl Holland (614-292-8384 or holland.8@osu.edu) or Harwood at UNL (402-472-2648 or dharwood@unlinfo.unl.edu).

A fine line between storms and sunshine

A temperature difference of only 1 degree C, which falls within the margin of error of most weather observations, can spell the difference between potentially severe storms and no rain at all. Similarly, small discrepancies in moisture can have the same effect. Andrew Crook of NCAR's Mesoscale and Microscale Meteorology Division analyzed these and other aspects of storm development and presented his findings at the American Meteorological Society's 18th Conference on Severe Local Storms in San Francisco in February.

Using computer models of the atmosphere, Crook conducted forward-sensitivity experiments. These bring a set of slightly varying scenarios forward in time to see how a given weather situation might evolve. Wind, temperature, and moisture values were derived from surface, radar, and radiosonde (weather balloon) observations. On average, these data had temperature errors of around 1 degree C and errors in liquid water content of around 1 gram per kilogram (g/kg). The latter is about 7 to 10% of the total atmospheric moisture present on a typical warm, humid day.

Crook found that a temperature decrease of 1 degree C was enough to shut off storm development entirely, while a 1 degree C increase led to a fourfold increase in rainfall. Similarly, rainfall dropped by 80% when liquid water content was lowered by 1 g/kg, while it more than doubled for a 1 g/kg increase. Crook's findings reinforce the difficulty in forecasting where and when thunderstorms might develop on days when conditions are borderline. However, knowing the possible impact of observational error should help forecasters better quantify the uncertainty in a forecast. For more information, contact Crook (303-497-8980 or crook@ucar.edu).

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Edited by Carol Rasmussen, carolr@ucar.edu
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Last revised: Tue Apr 4 09:33:26 MDT 2000