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Fall 1998

Science Bits

Texas MesoNet to provide future relief

Texas, which has suffered through a prolonged drought this year, may be better prepared to handle future droughts due to a weather tracking system Texas Technological University researchers are developing. The system, known as the West Texas MesoNet, will be a network of 28 weather stations about 50 km (32 miles) apart, covering every county across Texas' South Plains region (the area around Lubbock). The stations will measure such standard meteorological parameters as wind speed and direction, temperature, and air pressure. In addition, the network will include three atmospheric profilers. Depending on funding, the network could be operational as soon as next spring.

The stations will also provide information on increased soil temperature and moisture that will help farmers plan when to plant, irrigate, and harvest crops. "We can help farmers better use available water in both good times and bad," said system developer Tim Doggett (Texas Tech). "If we can conserve water during the good times, that will lessen the effects during drought periods."

The MesoNet system will also help weather forecasters predict severe thunderstorms. "With the MesoNet data we'll be able to predict where thunderstorms are apt to develop, which thunderstorms are apt to become severe. That will save both lives and money for the general public," said Doggett. The project, which is being developed as part of the Texas Tech Wind Science and Engineering Program, will also assist with ongoing research studying the effects of severe thunderstorm winds on buildings.

During floods, measurements from MesoNet could assist hydrologists in forecasting runoff. Transportation companies will be able to know how wind and weather will affect driving conditions. MesoNet will also help utility companies determine power consumption needs of a region by pinpointing hotter or colder areas. The result could be lower utility costs for residents.

The system follows such networks as the Oklahoma Mesonet, which includes more than 100 stations. Doggett hopes the West Texas MesoNet will be the first step to a statewide Texas network.

Texas Technological University

Southern Ocean may absorb less carbon dioxide than we think

Jorge Sarmiento and colleagues from Princeton University and the NOAA Geophysical Fluid Dynamics Laboratory (GFDLA) have found that changes in Southern Ocean circulation induced by global warming may be reducing its ability to absorb excess atmospheric carbon. If other computer simulations support their results, the researchers suggest, an international effort to collect data on how the Southern Ocean responds to climate change should be undertaken immediately.

In the oceans, atmospheric CO2 dissolves in the surface waters, which eventually circulate into the deep ocean. Previous estimates of how steeply we must decrease CO2 emissions in order to stabilize CO2 concentrations in the atmosphere have assumed that ocean circulation patterns and ocean biota remain constant over time. Sarmiento and colleagues Tertia Hughes, Ronald Stouffer, and Syukuro Manabe coupled an ocean carbon model to the GFDL coupled ocean-atmosphere model and used CO2 estimates from the years 1765 to 1990 and projections from 1990 to 2065.

The results suggest that the oceans will not remain unchanged, but may respond to global warming with changes in salinity, vertical circulation patterns, and biotic activity. According to this model, global warming triggers increased rainfall over vast stretches of the great Southern Ocean. This causes freshening of the water, which in turn creates increased stratification, so that the fresher surface water stays on top. This floating layer of water interferes with the usual ocean cycle, in which deep water wells up and surface water sinks, and slows down the ocean's CO2 uptake.

If the biota remain constant or increase despite this stratification, they may continue to absorb CO2 and counteract the reduction that results from this freshwater "lid." However, the authors say, we don't know enough about ocean biology to predict whether this will happen. Therefore, if other simulations, which also use coupled models but vary the simulation parameters, indicate these circulation changes are likely, we ought to start collecting real data--salinity and temperature, as well as nutrients, oxygen, and other signals of biological life--in the Southern Ocean as soon as possible.

"Our simulations are particularly relevant to international efforts to control future atmospheric carbon dioxide," says Sarmiento. "If the ocean's ability to absorb CO2 is, in fact, being compromised, then the future growth of atmospheric CO2 may be higher than the projections that were used to craft agreements such as the Kyoto Protocols."

The research was reported in the 21 May issue of Nature.

Princeton University

Irrigation is cooling Colorado's Front Range

Human activities such as agriculture and landscaping along Colorado's northern Front Range are changing temperatures, river runoff, and tree-distribution patterns in Rocky Mountain National Park and the surrounding region, and these changes could mean more extreme weather, according to a Colorado State University (CSU) study.

Ecologist Thomas Stohlgren (U.S. Geological Survey at CSU) studied an area of mountains and plains125 miles square centered on Fort Collins, Colorado. About 40% of the study area, including 55% of its native grasslands, is now used for agriculture.

Normal rainfall on the eastern plains is less than 20 inches a year. However, the rougher surfaces of plowed fields enhance moisture loss. Increased evaporation cools the area, and upslope winds carry cooler, moister air into the mountains. In the summer months, this human-made cooling could match or exceed predicted global warming, according to Stohlgren. His colleagues in the study were Jill S. Baron, Thomas Chase, and Roger A. Pielke Sr. of CSU and Timothy Kittel of NCAR and CSU. Their work was published in the June issue of Global Change Biology.

The researchers ran simulations with the Regional Atmospheric Modeling System developed by Pielke and others at CSU. The model suggested average July temperatures for the Fort Collins area might decrease by 0.5 degrees C (1 degrees F) as a result of increased cooling. An examination of temperature records for July for the last 65 years confirmed long-term regional cooling, with significant trends in the last 30-40 years, as land-use changes took off.

The researchers also looked at the locations of seedlings of six kinds of conifers in Rocky Mountain National Park, most of which grow at specific elevation ranges (and hence in defined temperatures) and require certain amounts of moisture. They found that all but one species had moved downslope to locations that historically had been drier.

A third confirmation of cooler, moister air in the mountains came from June-August water flow records dating back 30--40 years for four rivers draining the Front Range section of the study area. Increased discharges for all four drainages suggest decreasing loss of moisture by trees and other vegetation through transpiration. Researchers attributed trees' reduced moisture loss to lower summer air temperatures. In addition, they noted, cooler spring and early summer temperatures may be delaying snowmelt into the midsummer measuring period.

Stohlgren said that Fort Collins, which has grown to more than 100,000 residents over the past few decades, is not large enough to create a weather-influencing "heat island" like large cities do. "Our thought was that it could have, but that reaction apparently is being overwhelmed by the combination of relatively small houses and big yards," he explained. "The town has a very small footprint compared to the millions of surrounding acres devoted to agriculture. It's an issue of scale.

"The effects of this cooling will mean more variability in weather," Stohlgren said. "We face a higher chance of going from droughts to severe rainstorms, for example, and we may well see more days exceeding record temperatures."

Colorado State University, U.S. Geological Survey, NCAR

Sampled forests yield clues to carbon cycle on warming planet

A team led by Steven Wofsy (Harvard University) has been studying the "respiration" of Harvard Forest, 3,000 acres (???? hectares) of mixed oak and maple hardwood stand with scattered white pine and some red-pine plantations in central Massachusetts, since 1990. At the Harvard Forest Environmental Measurement Site (EMS), automated instruments mounted at several heights on a 30-meter (100-foot) tower take continuous measurements at half-hour intervals of a variety of chemical species entering or leaving the forest canopy. Among the species measured are carbon dioxide, ozone, nitrogen oxides, carbon monoxide, and several different hydrocarbons. The Harvard Forest EMS is funded by NSF.

The forest is picking up quite a bit of carbon. The annual net uptake varied from 1.4 to 2.8 metric tons of carbon per hectare between 1991 and 1995. "People were surprised that it was taking up that much," says Wofsy. The forest appears to be responding to longer growing seasons, the resutl of warmer temperatures over the last 30 years, by taking up more CO2.

A second site, BOREAS (Boreal Ecosystem Atmospheric Study), is located in a forest of old black spruce trees in Thompson, Manitoba, Canada. The site is at the northern edge of the boreal forest, where low temperatures and permafrost constrain growth. So the expectation was that warming temperatures would result in more carbon uptake along with more growth. But the forest appears to be releasing CO2 from stored reserves of peat. Lots of peat. "You have 40 tons of carbon per hectare on the surface--trees and moss--and then you have 300 or 400 tons per hectare in frozen peat," Wofsy explains. Peat needs cold, wet conditions to remain stable. As the site has warmed over the last 30 to 50 years, the peat has begun to ablate, releasing carbon as it erodes and thins.

An international venture, BOREAS is sponsored by NASA and several Canadian federal agencies, including the Atmospheric Environment Service, the Canadian Forest Service, the Canada Centre for Remote Sensing, and Parks Canada. Detailed site descriptions are available.

An infrared tunable diode laser spectrometer designed to take readings once per second at low concentrations (less than 100 parts per trillion) will soon be measuring nitric acid (HNO3) and nitrogen dioxide (NO2) at the Harvard Forest site. The Harvard Forest Nitric Acid project will collect data on increases and decreases in reactive nitrogen in the boundary layer and the resulting effect on ozone production. The project is a collaboration between Mark Zahniser, David Nelson, and J. Barry McManus at the Center for Chemical and Environmental Physics at Aerodyne Research, Inc., and Wofsy's group, including J. William Munger and Cassandra Volpe Horii. A prototype that measured only HNO3 was field tested in October and November of 1996 in an intercomparison against a chemical ionization mass spectrometer at the NOAA Aeronomy Lab. The dual HNO3-NO2 instrument will be deployed in the forest this fall or next spring.

Harvard University

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