Climate And Ice: Cold In All Its Brutal Guises
During the mid to late Tertiary Period, or 25-30 million years ago, Antarctica moved away from South America and Australia, and the great circumpolar ocean current
flowed eastward unimpeded around the now isolated continent. This mighty river of water, driven by the westerly tropospheric circulation, the West Wind Drift,
blocked the influx of warm northern ocean currents from transporting and transferring heat to these cooler waters to the south.
The west-flowing Antarctic coastal current is the result of winds blowing down from the Polar Plateau to merge with more localized katabatic, or gravity, winds.
Unequal surface heating is one of the driving mechanasdasdasdisms that causes the atmosphere to circulate, but forces such as air pressure and Earth’s rotation also contribute.
Westerly winds dominate the swath of ocean from the 40s to the Antarctic Circle at 66º33' South. Weather in Antarctica is dominated by these sea and air circulating systems.
Significant temperature gradients between the continent and vast unencumbered circumpolar seas create persistent low-pressure systems over the water.
These cyclones churn southeastward to spiral into the continent with clock-like precision every three to five days, depending on the season.
Between latitudes 60º and 65º South, a particularly nasty band of circumpolar low pressure is the bane of ship-board passengers who soon realize that the latitudinal
name “Screaming Sixties” is not without justification.
During winter, the cooling of the stratosphere over Antarctica causes a stable cyclonic system to remain above the Polar Plateau. This strong air mass swirls around a
circumpolar vortex of dense cold air like winds around the eye of a hurricane. The return
of spring and its warming influence weakens the westerly winds and opens a route for
warmer air to flow in.
Variations in ozone concentration are linked with the overall behavior of this vortex. During the winter, low ozone levels remain constant in association with the very
stable air mass circling the vortex because of the lack of ultra-violet radiation required to initiate the necessary molecular changes.
Also, the strength of the vortex repels the flow of ozone-rich air masses from lower latitudes. The reporting of an ozone "hole" in the 1980s grabbed the world's attention,
for Ozone absorbs ultraviolet (UV) light energy; fewer ozone molecules allow more cancer-causing UV radiation to reach Earth.
Ice-crystal clouds form in the frigid stratosphere and chlorine compounds react with other chemicals on the surface of the ice particles.
Spring sunlight triggers the release of free-roving chlorine atoms which interact with ozone — a molecule consisting of three oxygen atoms — to form chlorine monoxide.
This new molecule then acts as a catalytic agent that spurs the destruction of more ozone molecules. The size of the hole reaches its
maximum in late September and closes in late November when ozone-rich air from the north moves over Antarctica.
The movement of air from high pressure areas to lower pressure cells produces wind. Certain regions of Antarctica are notorious for sustained, high-velocity blows called katabatic,
or gravity, winds with speeds up to 200 mph. These dense rivers of cold air roll down from the Polar Plateau and reach maximum speeds near the coasts where descents are steepest.
For this reason East Antarctic shores, ice cliffs, and ice shelves are the windiest regions on Earth. Such strong winds are the stuff of nightmares for scientists and explorers.
Katabatic winds paired with surface snow, or drift, produce ferocious blizzards that add to the misery of field researchers. Drift snow is as fine and gritty as baking soda and
reduces the landscape into a murky void of screaming winds and stinging facial abrasions. Even worse is the suffocating sensation of being unable to breathe as drift clogs the nose
and throat. These tiny but powerful wind-blown ice granules sculpt the surface into ice formations called sastrugi. When the wind blows persistently from one direction,
the sastrugi resemble a just-plowed frozen field; multidirectional winds carve a chaotic surface that looks like a sea of frozen whitecaps.
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