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A cooling troposphere and global warming
can co-exist
Researchers at the Lab say they may have found a way to dispel
a major objection to global-warming theory.
"We want the global-warming community to know that we've
identified a possible explanation for why satellite atmospheric
temperature and surface temperature trends can disagree,"
said Charles "Chick" Keller, director of the Lab's Institute
for Geophysics and Planetary Physics (IGPP). "The truth is
that the temperature trends probably do agree when you consider
the effect that massive ozone depletion caused by large volcanic
eruptions has on the stratosphere and upper troposphere."
Keller and his colleagues -- Manvendra Dubey and Howard Hanson
of Atmospheric and Climate Sciences (EES-8), and Tracy Light of
Space and Atmospheric Sciences (NIS-1) -- are scheduled to present
their findings today at the American Geophysical Union's fall
meeting in San Francisco.
The researchers set out to explain why scientists have seen
less warming in the troposphere, the lowest layer of the atmosphere,
than at the surface. If global warming were actually occurring,
some scientists have said, observers should be able to document
warming trends in the atmosphere as well as on the surface. This
doesn't always happen, however, and critics of global-warming
theory use the trend disparity to discount the idea that Earth
is slowly heating due to a buildup of greenhouse gases such as
carbon dioxide and other environmental factors.
Keller and his colleagues on the Lab team looked at existing
temperature data gathered by high-altitude balloons and satellites
for clues about atmospheric warming trends.
"When you look at the first 13 years of satellite temperature
records, you see pretty good agreement with the surface records.
But from 1992 to 1997 there is disagreement. During that time,
the stratosphere -- the atmospheric layer above the troposphere
that contains the ozone layer -- cooled dramatically," Keller
said. "We wondered if we could see some factor that would
cause this, and that's when we started looking at the June 15,
1991, eruption of Mount Pinatubo in the Philippines."
The massive eruption spewed huge quantities of ash and aerosols
into the stratosphere. Through a complicated mechanism, volcanic
dust enhances destruction of ozone by chlorofluorocarbons already
present. Consequently, the eruption led to a wholesale depletion
of Earth's protective ozone layer in the stratosphere, which has
been observed. Because ozone absorbs the sun's ultraviolet rays,
the layer normally heats the stratosphere; but with depletion
of ozone from the volcanic blast, the stratosphere cooled.
"We surmise that this very cold stratosphere might have
had a cooling effect on the troposphere, the lower atmospheric
layer where the weather is," Keller said.
Keller and his colleagues noticed that after the Pinatubo eruption
and subsequent stratospheric cooling, surface temperatures and
atmospheric temperatures first cooled, then began to rise at comparable
rates, but they maintained a temperature differential greater
than what had been seen before the volcano.
The observation also led Keller and his colleagues to look
at how El Niño and La Niña phenomena affected the
atmosphere during the entire satellite record period from 1979
to present. As a general rule, during El Niño years, the
upper and lower troposphere see greater warming than the surface,
and tropospheric layers see greater cooling than the surface during
La Niña years. However, this was not the case after Mount
Pinatubo erupted. Keller and his team looked at temperatures during
the 1992 El Niño season. The upper troposphere was cooler
than expected during that year, indicating that a cold stratosphere
nestled directly above may have affected the troposphere.
Moreover, Keller and colleagues noticed that researchers at
the Max Planck Institute for Meteorology had used a computer simulation
with a crude approximation of ozone depletion to look at atmospheric
temperatures, and found that the upper troposphere did cool during
the aftermath of Pinatubo. The Lab researchers see this as another
indication that their tropospheric-cooling hypothesis has merit.
Keller said he and his team next will use Lab computer models
of oceans and sea ice coupled with computer models of the atmosphere
and land surface developed by the National Center for Atmospheric
Research to tackle the problem. His research team will plug in
20 years of correct ozone concentrations to see whether the models
will arrive at the level of atmospheric cooling measured during
the 1992-1997 time frame.
"Critics of global warming hold the hypothesis that global
warming doesn't exist because it isn't seen in the atmosphere
by satellites," Keller said. "This observation by our
team potentially eliminates one of the prime objections to global-warming
theory. I think further study could show that ozone depletion
keeps the whole system from warming up, which is what you see
in the satellite temperature data."
--James Rickman
Los Alamos micro-quakes cause widespread
reported effects
Several small, shallow earthquakes near Los Alamos during the
past seven years have produced effects normally associated with
quakes of much greater magnitude, say geologists and seismologists
at the Laboratory.
In a paper scheduled to be presented at the American Geophysical
Union meeting in San Francisco today, Jamie N. Gardner and Leigh
S. House of the Seismic Research Center (EES-1) reported that
the effects of the three "micro-quakes" of less than
magnitude two were particularly intense in residential areas built
on fill or old sedimentary material.
In certain neighborhoods, jolts and loud noise were reported
by many households. A pendulum clock stopped, items were knocked
off shelves, trees and bushes shook and some homes suffered light
plaster damage. The first two events were measured at magnitude
two and the third at one and three quarters.
"It's unusual for these magnitude quakes to even be perceived
by humans," Gardner said.
The quakes, two of which occurred in February 1991 and the
third the day after Thanksgiving 1998, were measured by a small
network of seismographs monitoring the near-constant seismic activity
along the Northern Rio Grande Rift in New Mexico. The network
was established in 1973 as part of the Laboratory's nuclear testing
treaty verification capability but is now used by its engineers
and earth scientists in a seismic hazards program.
All three earthquakes were extremely shallow, a controversial
finding in the seismological world where near-surface rocks are
presumed to have too little strength to store sufficient energy
to generate an earthquake.
"People think about earthquakes happening at the surface
where the effects are observed, but actually they happen at some
depth," Gardner said. "These three microquakes were
unusually shallow, and consequently closer." Proximity to
the epicenter of a quake is one predictor of its felt effects.
Earthquakes are measured on a variety of scales that attempt
to describe their magnitude and intensity. Most people are familiar
with a scale on which a magnitude seven quake is catastrophic
in populated areas and a magnitude two is so minor that it is
undetected by most people. Magnitude is a measure of energy released,
as detected by seismographs.
The Modified Mercalli Intensity scale was developed to evaluate
quake effects on humans and human-made structures. The MMI numbers
for the three Los Alamos micro-quakes were from IV to VI, indicating
significant felt effects.
"It's a measurement of what happens to people and their
stuff. For evaluating potential seismic hazards, it can be more
useful because it synthesizes a host of factors," Gardner
said. "How big was the quake? How far away? What are the
ground conditions and the geology between the person and the quake?"
With the aid of old aerial photographs and maps, Gardner concluded
that areas where many residents reported effects of the quake
were built on a thick package of old, alluvial material deposited
atop the Bandelier tuff, the volcanic rock ejected a million years
ago from the Valles Caldera. Residences built directly on a bedrock
of tuff were far less likely to feel the small quakes.
Other areas reporting effects had been homestead fields worked
before1943. Farmers had used thick topsoils on the tuff to grow
crops.
One reason for studying earthquakes and their effects is to
use historical data to predict future effects of seismic activity
on people and structures. Data generated in the Lab studies can
provide perspective with which to interpret anecdotal historical
accounts of small earthquakes with large effects, described as
far back as the 1800s in England. The Lab's sensitive instruments
and population density have given scientists information about
the recent seismic events that might otherwise have been misinterpreted.
Ultimately, the information will contribute to efforts to improve
safety during seismic events.
"Engineers are the consumers of the information that geoscientists
come up with," Gardner said. "It's their job to predict
how structures will be affected by seismic activity. Our job is
really public safety, and predicting the probable effects from
a local quake on facilities at the Laboratory and in Northern
New Mexico."
--Kay Roybal
Administrative nonexempt employees receive
cash award
PHOTO
Don Cobb, associate Laboratory director for threat
reduction and chair of the Salary Policy Committee, welcomes administrative
nonexempt employees and the OS/GS Subcommittee of the Salary Policy
Committee to the Los Alamos Award Program team awards celebration,
held last Thursday in the Otowi Building Cafeteria [see the Nov. 8 Newsbulletin].
PHOTO
Alex Gancarz, right, of the Quality Improvement Office (QIO) and
project leader of the SPC project team, hands Bennie Glover, left,
of Nuclear Weapons-Stockpile Systems (NW-SS) a piece of cake at
the Los Alamos Award Program team awards celebration. Photos
by Sandi Embry
November weather
Last month was one of the warmest and driest Novembers on record
in Los Alamos and White Rock, due largely to so-called "La
Niña" conditions, according to Laboratory meteorologist
George Fenton of Air Quality (ESH-17).
The mean temperature in Los Alamos in November was 44.1 degrees
Fahrenheit, while the average daily high temperature of 58 degrees
F was 3 degrees F higher than the average record for the month,
established in 1942. The mean minimum temperature of 29 degrees
F also was 2 degrees higher than average, he said.
A La Niña occurs when equatorial waters off the South
American coast cool, affecting the storm track that steers weather
disturbances over the United States. When a La Niña occurs,
the storm track rises over the northern United States bringing
warmer temperatures and reduced precipitation to the southern
United States.
Conversely, the so-called El Niño phenomenon causes
those same equatorial waters to warm, steering storms over the
southern United States and bringing more moisture and colder temperatures,
he said.
Fenton said eight high temperature records were established
including a string of seven consecutive days, Nov. 11 through
17. On eight other days, the high temperature was within 3 degrees
F of tying a daily record, he said.
Only .02 of an inch of precipitation was recorded at the Technical
Area 6 measuring station last month, a full one inch below normal
for November and the driest in Los Alamos since 1956. A cold front
that passed through the area between Nov. 22 and 24 brought snow
showers that accounted for all the recorded precipitation, Fenton
said.
It was much the same in White Rock in November, with the average
high temperature of 61 degrees F well above normal and 3 degrees
F greater than the previous average high temperature of 58 degrees
F established in 1966.
The mean temperature in White Rock last month was 42 degrees
F, slightly below the November mean record, Fenton added.
Eight high temperature records were tied or established in
White Rock in November, with six other days within 3 degrees F
of also tying daily records. On Nov. 25, the low temperature of
7 degrees F tied a record established in 1993.
Only .05 of an inch of precipitation was recorded at the Technical
Area 54 measuring station in White Rock last month, the driest
November since 1989.
--Steve Sandoval
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