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Arctic Ocean Circulation Does An About-Face
ScienceDaily (Nov. 14, 2007) - A team of NASA and university scientists has
detected an ongoing reversal in Arctic Ocean circulation triggered by
atmospheric circulation changes that vary on decade-long time scales. The
results suggest not all the large changes seen in Arctic climate in recent
years are a result of long-term trends associated with global warming. The
team, led by James Morison of the University of Washington's Polar Science
Center Applied Physics Laboratory, Seattle, used data from an
Earth-observing satellite and from deep-sea pressure gauges to monitor
Arctic Ocean circulation from 2002 to 2006. They measured changes in the
weight of columns of Arctic Ocean water, from the surface to the ocean
bottom. That weight is influenced by factors such as the height of the
ocean's surface, and its salinity. A saltier ocean is heavier and circulates
differently than one with less salt. The very precise deep-sea gauges were
developed with help from the National Oceanic and Atmospheric
Administration; the satellite is NASA's Gravity Recovery and Climate
Experiment (Grace). The team of scientists found a 10-millibar decrease in
water pressure at the bottom of the ocean at the North Pole between 2002 and
2006, equal to removing the weight of 10 centimeters (four inches) of water
from the ocean. The distribution and size of the decrease suggest that
Arctic Ocean circulation changed from the counterclockwise pattern it
exhibited in the 1990s to the clockwise pattern that was dominant prior to
1990. Reporting in Geophysical Research Letters, the authors attribute the
reversal to a weakened Arctic Oscillation, a major atmospheric circulation
pattern in the northern hemisphere. The weakening reduced the salinity of
the upper ocean near the North Pole, decreasing its weight and changing its
circulation. "Our study confirms many changes seen in upper Arctic Ocean
circulation in the 1990s were mostly decadal in nature, rather than trends
caused by global warming," said Morison. "While some 1990s climate trends,
such as declines in Arctic sea ice extent, have continued, these results
suggest at least for the 'wet' part of the Arctic -- the Arctic Ocean --
circulation reverted to conditions like those prevalent before the 1990s,"
he added. The Arctic Oscillation was fairly stable until about 1970, but
then varied on more or less decadal time scales, with signs of an underlying
upward trend, until the late 1990s, when it again stabilized. During its
strong counterclockwise phase in the 1990s, the Arctic environment changed
markedly, with the upper Arctic Ocean undergoing major changes that
persisted into this century. Many scientists viewed the changes as evidence
of an ongoing climate shift, raising concerns about the effects of global
warming on the Arctic. Morison said data gathered by Grace and the bottom
pressure gauges since publication of the paper earlier this year highlight
how short-lived the ocean circulation changes can be. The newer data
indicate the bottom pressure has increased back toward its 2002 level. "The
winter of 2006-2007 was another high Arctic Oscillation year and summer sea
ice extent reached a new minimum," he said. "It is too early to say, but it
looks as though the Arctic Ocean is ready to start swinging back to the
counterclockwise circulation pattern of the 1990s again." Morison cautioned
that while the recent decadal-scale changes in the circulation of the Arctic
Ocean may not appear to be directly tied to global warming, most climate
models predict the Arctic Oscillation will become even more strongly
counterclockwise in the future. "The events of the 1990s may well be a
preview of how the Arctic will respond over longer periods of time in a
warming world," he said. Grace monitors tiny month-to-month changes in
Earth's gravity field caused primarily by the movement of water in Earth's
land, ocean, ice and atmosphere reservoirs. As such it can infer changes in
the weight of columns of ocean water. In contrast, the pressure gauges
installed on the sea floor in 2005-2006 directly measured water pressure at
the bottom of the ocean. Gauge data were remotely recovered during the first
year of the study.
"The close agreement between the North Pole pressure gauges and Grace data
demonstrates Grace's potential for tracking world ocean circulation," said
study co-author John Wahr of the University of Colorado, Boulder.
"Satellite altimeters, such as NASA's Jason, are ideal for studying ocean
circulation but can't be used at Earth's poles due to ice cover," said study
co-author Ron Kwok of NASA's Jet Propulsion Laboratory, Pasadena, Calif.
"Our results show Grace can be a powerful tool for tracking changes in the
distribution of mass in the Arctic Ocean, as well as its circulation."
Grace is a partnership between NASA and the German Aerospace Center (DLR).
The University of Texas Center for Space Research, Austin, has overall
mission responsibility. JPL developed the twin satellites. DLR provided the
launch, and GeoForschungsZentrum Potsdam, Germany, operates Grace. For more
on Grace: http://www.csr.utexas.edu/grace/ .
The study was funded by the National Science Foundation.
Adapted from materials provided by NASA/Jet Propulsion Laboratory.
--
Quote Of The Week
"The Clintons Are A Terminally Unethical And Vulgar Couple, And They?ve
Betrayed Everyone Who Has Ever Believed In Them." - Bob Herbert, Columnist
NY Times Clinton
ScienceDaily (Nov. 14, 2007) - A team of NASA and university scientists has
detected an ongoing reversal in Arctic Ocean circulation triggered by
atmospheric circulation changes that vary on decade-long time scales. The
results suggest not all the large changes seen in Arctic climate in recent
years are a result of long-term trends associated with global warming. The
team, led by James Morison of the University of Washington's Polar Science
Center Applied Physics Laboratory, Seattle, used data from an
Earth-observing satellite and from deep-sea pressure gauges to monitor
Arctic Ocean circulation from 2002 to 2006. They measured changes in the
weight of columns of Arctic Ocean water, from the surface to the ocean
bottom. That weight is influenced by factors such as the height of the
ocean's surface, and its salinity. A saltier ocean is heavier and circulates
differently than one with less salt. The very precise deep-sea gauges were
developed with help from the National Oceanic and Atmospheric
Administration; the satellite is NASA's Gravity Recovery and Climate
Experiment (Grace). The team of scientists found a 10-millibar decrease in
water pressure at the bottom of the ocean at the North Pole between 2002 and
2006, equal to removing the weight of 10 centimeters (four inches) of water
from the ocean. The distribution and size of the decrease suggest that
Arctic Ocean circulation changed from the counterclockwise pattern it
exhibited in the 1990s to the clockwise pattern that was dominant prior to
1990. Reporting in Geophysical Research Letters, the authors attribute the
reversal to a weakened Arctic Oscillation, a major atmospheric circulation
pattern in the northern hemisphere. The weakening reduced the salinity of
the upper ocean near the North Pole, decreasing its weight and changing its
circulation. "Our study confirms many changes seen in upper Arctic Ocean
circulation in the 1990s were mostly decadal in nature, rather than trends
caused by global warming," said Morison. "While some 1990s climate trends,
such as declines in Arctic sea ice extent, have continued, these results
suggest at least for the 'wet' part of the Arctic -- the Arctic Ocean --
circulation reverted to conditions like those prevalent before the 1990s,"
he added. The Arctic Oscillation was fairly stable until about 1970, but
then varied on more or less decadal time scales, with signs of an underlying
upward trend, until the late 1990s, when it again stabilized. During its
strong counterclockwise phase in the 1990s, the Arctic environment changed
markedly, with the upper Arctic Ocean undergoing major changes that
persisted into this century. Many scientists viewed the changes as evidence
of an ongoing climate shift, raising concerns about the effects of global
warming on the Arctic. Morison said data gathered by Grace and the bottom
pressure gauges since publication of the paper earlier this year highlight
how short-lived the ocean circulation changes can be. The newer data
indicate the bottom pressure has increased back toward its 2002 level. "The
winter of 2006-2007 was another high Arctic Oscillation year and summer sea
ice extent reached a new minimum," he said. "It is too early to say, but it
looks as though the Arctic Ocean is ready to start swinging back to the
counterclockwise circulation pattern of the 1990s again." Morison cautioned
that while the recent decadal-scale changes in the circulation of the Arctic
Ocean may not appear to be directly tied to global warming, most climate
models predict the Arctic Oscillation will become even more strongly
counterclockwise in the future. "The events of the 1990s may well be a
preview of how the Arctic will respond over longer periods of time in a
warming world," he said. Grace monitors tiny month-to-month changes in
Earth's gravity field caused primarily by the movement of water in Earth's
land, ocean, ice and atmosphere reservoirs. As such it can infer changes in
the weight of columns of ocean water. In contrast, the pressure gauges
installed on the sea floor in 2005-2006 directly measured water pressure at
the bottom of the ocean. Gauge data were remotely recovered during the first
year of the study.
"The close agreement between the North Pole pressure gauges and Grace data
demonstrates Grace's potential for tracking world ocean circulation," said
study co-author John Wahr of the University of Colorado, Boulder.
"Satellite altimeters, such as NASA's Jason, are ideal for studying ocean
circulation but can't be used at Earth's poles due to ice cover," said study
co-author Ron Kwok of NASA's Jet Propulsion Laboratory, Pasadena, Calif.
"Our results show Grace can be a powerful tool for tracking changes in the
distribution of mass in the Arctic Ocean, as well as its circulation."
Grace is a partnership between NASA and the German Aerospace Center (DLR).
The University of Texas Center for Space Research, Austin, has overall
mission responsibility. JPL developed the twin satellites. DLR provided the
launch, and GeoForschungsZentrum Potsdam, Germany, operates Grace. For more
on Grace: http://www.csr.utexas.edu/grace/ .
The study was funded by the National Science Foundation.
Adapted from materials provided by NASA/Jet Propulsion Laboratory.
--
Quote Of The Week
"The Clintons Are A Terminally Unethical And Vulgar Couple, And They?ve
Betrayed Everyone Who Has Ever Believed In Them." - Bob Herbert, Columnist
NY Times Clinton
