El Niños and La Niñas Rearrange Antarctic Sea Ice
Scientists have been mystified by observations that when sea ice on one side of the South Pole recedes, it advances farther out on the other side, a phenomena referred to as the Antarctic sea ice dipole. New findings utilizing the GISS GCM suggest for the first time that this is the result of El Niños and La Niñas driving changes in the subtropical jet stream, which then alter the path of storms that move sea ice around the South Pole.
The results have important implications for understanding global climate change better because sea ice contributes to the Earth's energy balance. The sea ice, which is generated around each pole when the water gets cold enough to freeze, reflects solar energy back out to space, cooling the planet. When there is less sea ice, the ocean absorbs the sun's heat and that amplifies climate warming. Understanding why variations occur in the current climate can help us estimate how they may change as climate warms.
During El Niño years, when the waters of the Eastern Pacific heat up, warm air rises. As the air rises it starts to move toward the South Pole, but the earth's rotation turns the winds eastward. The Earth's rotation is just strong enough to cause this rising air to strengthen the subtropical jet stream, a band of atmospheric wind near the equator that also blows eastward.
When the subtropical jet stream gets stronger over the Pacific basin, it diverts storms away from the Pacific side of the South Pole. Since there are fewer storms near the Pacific-Antarctic region during El Niño years, there are less winds to blow sea ice farther out into the ocean, and ice stays close to shore.
At the same time, the rising air in the tropical Pacific forces the air in the tropical Atlantic to sink instead of rising. That sinking air weakens the subtropical jet stream over the Atlantic, allowing storm to progress towards the South Pole. The storms, which intensify as they meet the cooler Antarctic air, then blow sea ice away from the pole farther into the Atlantic.
During La Niña years, when the Eastern and central Pacific waters cool, there is an opposite effect, where sea ice retreats on the Atlantic side, and advances on the Pacific side.
The results show that in order to understand how sea ice may change as climate warms, we must also learn what will happen to tropical temperatures, and El Niño / La Niña occurrences. This is one more example of how very disparate components of the climate system are connected, requiring that they all be understood before we can properly estimate future climate sensitivity.
Yuan, X., and D.G. Martinson 2001. The Antarctic dipole and its predictability. Geophys. Res. Lett. 28, 3609-3612.
Rind, D., M. Chandler, J. Lerner, D.G. Martinson, and X. Yuan 2001. Climate response to basin-specific changes in latitudinal temperature gradients and implications for sea ice variability. J. Geophys. Res. 106, 20161-20173.
Please address all inquiries about this research to Dr. David Rind.