Antarctica influencing weather in tropics

February 14, 2016 09:00 am | Updated 08:12 pm IST

Antarctica acts as a global heat sink.

Antarctica acts as a global heat sink.

Scientists are coming to grips with how weather in Antarctica is influencing climate as far away as the tropics. For example, researchers at Ohio State's Byrd Polar Research Center have discovered an influence of atmospheric circulation in the Wilkes Land and Ross Sea regions of Antarctica on precipitation from the East Asian monsoon.

In this context, the Atmospheric Radiation Measurement West Antarctic Radiation Experiment (AWARE) project gains importance as it studies the skies above Antarctica for answers to questions such as how climate change and associated atmospheric physics are affecting Antarctica and how the ripple effects of these phenomena are being felt thousands of miles away in the mid latitudes and the tropics. The temperature gradient between the equator and the poles essentially drives the atmospheric circulation in the southern hemisphere in the form of three north-south systems: the polar cell, the mid-latitude Ferrel cell and the tropical Hadley cell. These cells are dynamically linked together.

The AWARE project by the United States located at Mc Murdo station in Antarctica will observe how climate change affects the polar region as it has been determined that when the polar region warms, the location of the boundary between the polar and Ferrel cells will change, along with the strength of circulation in both cells.

This in turn will influence the strength of tropical circulation on the other side of the Ferrel cell. These linkages between polar regions and mid- and tropical latitudes are known as teleconnections.

Dr. Dan Lubin, Principal Investigator of the project, Research Physicist at Scripps Institution of Oceanography, U.S., noted in an email to this Correspondent: “In an early climate model experiment done with my colleagues, we discovered that a change in Antarctic cloud properties that led to a warming of Antarctica weakened the Southern Hemisphere Ferrel cell, and allowed the Hadley Cell on the other side to strengthen, which in turn resulted in more rainfall due to increased latent heat release over Southern Hemisphere tropical regions.

“An expanding Hadley cell is generally expected to result from a globally warming atmosphere, so the Antarctic warming from cloud property change is a positive feedback on a warming climate,” he said..

The study examines the physics of the clouds over Antarctica. “By physics we mean several things, including how much of the cloud is comprised of ice particles versus liquid water drops (liquid water can exist in temperatures colder than -30 centigrade in very clean air), how much total water content is in the cloud, how the cloud is formed (e.g., from evaporation in the lower atmosphere, or being carried long-distance by moving air masses), how much solar radiation the cloud allows to reach the surface, and how much thermal radiation that the cloud radiates to warm the surface.”

Antarctica acts as a global heat sink. Near the equator the Sun is highest in the sky and insolation (solar radiation reaching the surface) is larger than thermal radiation loss to space. At the South Pole during winter there is no insolation and the Antarctic continent loses energy to space. Energy and warmth transported over the Antarctic continent by global circulation patterns is lost to space by radiative cooling.

Another important feature being studied are the winds that traverse in the form of storm tracks across Antarctica’s atmosphere and their effect on Antarctica’s climate. However, one established trend due to global warming is the slight southward shift of the storms and the intrusion of warm air which led to the breaking away of a large ice-shelf. Also, the frequency of warm and moist air intrusions over West Antarctica generated by storms in the Ross and western Amundsen Seas, is a hypothesis under study by AWARE.

Another wind system is the circumpolar westerlies which prevents warm air from the northern latitudes of the southern ocean from reaching the interior of eastern Antarctica which remains a cold, isolated desolate region, losing energy to space.

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