The Arctic Oscillation: Cold Heralds Hot

TERRADAILY

Arctic Oscillation: Cold Heralds Hot

The AO index describes the relative intensity of a semipermanent low-pressure center over the North Pole. A band of upper-level winds circulates around this center, forming a vortex. When the AO index is positive and the vortex intense, the winds tighten like a noose around the North Pole, locking cold air in place.

Boulder - Mar 05, 2003
Why has the Arctic warmed so dramatically in recent years? How does the Arctic's circulation keep frigid air over the poles and sometimes allow it to spill across the United States? And how might global change affect the behavior of this circulation?

Clara Deser, from the National Center for Atmospheric Research (NCAR), addressed these and other questions in a presentation in Denver on February 17 at the annual meeting of the American Association for the Advancement of Science. Deser gave a summary if the structure and effects of the Arctic Oscillation (AO) as part of the symposium "El Nino, Monsoon, Arctic Oscillation, and Global Warming."

Although the AO has been recognized by various names for many years, it has become a topic of keen research interest only in the last decade. The AO index describes the relative intensity of a semipermanent low-pressure center over the North Pole. A band of upper-level winds circulates around this center, forming a vortex. When the AO index is positive and the vortex intense, the winds tighten like a noose around the North Pole, locking cold air in place.

A negative AO and weak vortex (as has been the case most of this winter) allow intrusions of cold air to plunge southward into North America, Europe, and Asia. Apart from variations like this winter's, the index has been mostly positive in wintertime since the late 1980s.

"The Arctic Oscillation has strengthened in recent decades, contributing to the unusual warmth over the Northern Hemisphere land masses," says Deser. "This has led to the speculation that the AO may be affected by increasing greenhouse gas concentrations and that it may, in turn, enhance global warming."

Deser also discussed recent computer-model simulations that support this view, and the relationship between the AO and ozone, which has been measurably depleted across the region in recent years.

TERRADAILY

NASA Begins New Year With International Arctic Ozone Study

Greenbelt - Jan 13, 2003
NASA researchers, and more than 350 scientists from the United States, European Union, Canada, Iceland, Japan, Norway, Poland, Russia and Switzerland, are working together this winter to measure ozone and other atmospheric gases. The scientists will use aircraft, large and small balloons, ground-based instruments and satellites.

Exploring The Unknown World Of "Cloud Nine"

Boulder - Jul 08, 2002
Ball Aerospace has won a contract to build a NASA spacecraft that will explore the little understood 100 kilometers above the arctic in the mesosphere where polar clouds form and drift southward. Selected as part of NASA's Small Explorer (SMEX) program the mission will increase our understanding of what surely must be "cloud nine" at the edge of space.

Last Mid Ocean Ridge Explored

Washington - Nov 28, 2001
Contrary to their expectations, scientists on a research cruise to the Arctic Ocean have found evidence that the Gakkel Ridge, the world's slowest spreading mid-ocean ridge, may be very volcanically active. They also believe that conditions in a field of undersea vents, known as "black smokers," could support previously unknown species of marine life.

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