Tony Salva, age 11, of Huntsville, Alabama, for his question:
Which is the biggest polar icecap and why?
The world's champion icecap spreads right over the South Pole. It is a massive shield of frozen snow that fits inside the Antarctic Circle at the very bottom of the globe. The arctic winter may freeze an icecap of about the same size. But the south polar ice field is a year round fixture and many times thicker.
Our polar icecaps are created because the earth's axis happens to be tilted 23 1/2 degrees toward the plane of its orbit. The axis, as you know, is a line from pole to pole through the exact center of the solid globe. It is the line around which the earth rotates like a spinning top, once every 24 hours. And this axis is tilted toward our yearly orbital path around the sun. The tilted axis naturally tilts the Northern and Southern Hemispheres, along with their Arctic and Antarctic Poles.
The direction of the axis remains fixed, its two poles pointed to opposite regions in the starry cosmos beyond the Solar System. But the planet's orbital circle changes the axis slant in relation to the sun. In January, the south polar axis is tipped towards the sun, in July the North Pole bows toward the sun. This operation in geometry brings alternating seasons to the two hemispheres. It brings more extreme changes to the Arctic and Antarctic Circles. These realms extend 23 1/2 degrees of latitude from the poles, a figure directly related to the 23 1/2 degree angle of the axis.
The yearly quota of sunlight hours is equal all. over the world. But the allocations are uneven. The polar circles get months of summer when the sun never sets and months of winter when the sun never rises. The Arctic and Antarctic Circles get equal shares of long summer daylight, and long winter nights. You would expect their polar icecaps to be equal. But the land and salt water make a great difference. Oceans are milder than land and salt water melts more easily than fresh water.
The North Pole lies about two miles below the Arctic Ocean.. Winters are cold enough to freeze its surface several feet thick. But the saltwater ice is cracked by tides and currents and spring breaks it into melting fragments. The South Pole is on the landmass of Antarctica under a massive icecap almost two miles thick. The ice is frozen fresh water from fallen snows and the frozen wasteland covers an area of 5,100,000 square miles. The icecap at the North Pole may cover roughly the same area, but its thin ice is merely a winter event.
There are no mild ocean waves under the Antarctic icecap and the warmth of the summer sun never reaches the ground below. The vast frozen wasteland breeds its own weather and the temperature rarely rises above freezing. Where the ice meets the sea, chunks are chewed off by the pounding waves. Meantime, new fields of frozen snow add their bulk to the monstrous icecap.
The Antarctic icecap works with the atmosphere to breed its own weather. The frozen expanse chills the air above it, summer and winter. Cold, heavy air masses push howling blizzards across the ice throughout the year. Such cold fronts also breed over the Arctic. They tend to push out to the Arctic Circle and beyond. There they are captured by the prevailing winds arid carried into our weather system. They bring us chilly storms but they are mild compared to the raging blizzards of Antarctica.