Ocean currents are like rivers that flow through the water around them. They are quite distinct. "Kuroshio" means "black water" and the Kuroshio Current is clearly visible as a stream less than 50 miles (80 km) wide moving at up to 7 MPH (11 km/h).
When an ocean current moves toward or away from the equator, the Coriolis effect influences its direction. Currents start to turn as they approach continents. The Coriolis effect intensifies as currents move farther from the equator. This makes them turn more, until they are flowing across the ocean. This brings the currents close to the continent on the opposite side. They are deflected again, this time toward the equator, so that eventually they follow an approximately circular path, called a gyre. There is a gyre in each of the major oceans. They turn clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.
Gyres also affect the climate by transporting heat away from the equator. They pass close to the continents on either side of each ocean as boundary currents. Boundary currents on the western side of the ocean carry
Vostok is the name of a Russian research station in Antarctica, located at about 78.75° S. Qaanaaq is a small town in northern Greenland (Kalaallit Nunaat), at 76.55° N. The maps show their locations.
They are in similar latitudes, but they have very different climates. At Vostok, January is the warmest month, when the average temperature is -26°F (-32°C). The coldest month is August, with an average temperature of -90°F (-68°C). At Qaanaaq, the average temperature ranges from a high of 46°F (8°C) in July to a low of -2I°F (-29°C) in Februar y.
warm water away from the equator in both hemispheres. The magnitude of the Coriolis effect increases with distance from the equator. Combined with the increased force of the wind driving the currents as they enter the belt of middle-latitude westerlies and the friction between the currents and the adjacent water, the strengthening of the Coriolis effect makes western boundary currents narrow and fast-moving. This effect is known as western intensification. The Gulf Stream, for example, is about 50 miles (80 km) wide and flows at about 1.3-2.2 MPH (2.1-3.5 km/h), transporting about 1,942 million cubic feet of water per second (55 x 106 m3 s-1).
Eastern boundary currents flow toward the equator. They move out of the influence of the westerly winds, the Coriolis effect decreases with increasing distance from the pole, and friction with the adjacent water decreases as the current slow. This makes the currents broad and slow-moving. The Canary Current is 600 miles (1,000 km) wide and flows at
Both places are dry, despite all the snow and ice. Qaanaaq has an annual rainfall (it falls as snow in winter, of course, but is converted to the equivalent amount of rainfall) of 2.5 inches (64 mm). Vos-tok has 0.2 inch (4.5 mm).
The temperature range is similar for both: 64°F (36°C) at Vostok and 67°F (37*C) at Qaanaaq. The difference is that Vostok is much colder than Qaanaaq. This is because Qaanaaq is on the coast, albeit the coast of an ocean that is frozen over for much of the year, while Vostok is in the interior of a large continent. The North Pole is located in the Arctic Ocean, and the Arctic Basin is sea surrounded by Eurasia, North America, and Greenland (Kalaallit Nunaat).
A large ice sheet covers East Antarctica, where Vostok is located. Air subsiding into the permanent Antarctic high-pressure region flows outward as a bitterly cold, extremely dry wind that blows almost incessantly. This combined with its elevation—Vostok is 13,000 feet (3,950 m) above sea level, on top of the thick ice—is what gives Vostok its cold, dry climate.
The continent also receives 7 percent less solar radiation than the Arctic does, because in the middle of winter (June) the South Pole is 3 million miles (4.8 million km) farther from the Sun than the North Pole is in the middle of its winter (December).
Qaanaaq is at sea level, but that is not the principal reason for its warmer climate. It is warmer because of the sea. Ocean currents carry warm water into the Arctic Basin. The sea is frozen for most of the year, but there are gaps in the ice— called leads—that appear and disappear. Winds move the ice, piling it up in some places and leaving it thin in others. Heat escapes from the ocean where there are open water surfaces, but ice insulates the areas it covers. The sea temperature never falls below 29°F (-l.6°C); below this temperature the water approaches its greatest density and sinks below warmer water that flows in at the surface to replace it. When the air temperature over the water falls below the temperature of the sea surface, heat passes from the water to the air. This warmer air then moves across the ice. Consequently, air temperatures over the entire Arctic Basin are much higher than they would be if there were land rather than sea beneath the ice. The coldest temperature recorded over the ice in the Arctic is -58°F (-50°C), and over most of the Arctic Basin the average temperature ranges between about 4°F (-20°C) and -40°F (-40°C). On July 21, 1983, the temperature at Vostok fell to -128.6'F (-89.2°C).
about 0.22-0.67 MPH (0.35-1.08 km/h), carrying 565 million cubic feet of water per second (16 x 106 m3 s-1).
Air that crosses a boundary current is affected by the contact. If it is a western boundary current, the air becomes warmer and gathers more moisture. If it is an eastern boundary current, the air cools and some of its moisture condenses to form cloud or fog. The frequent fogs of San Francisco are due to the condensation of moisture in warm Pacific air that crosses the nearby California Current. Western boundary currents produce less effect in middle latitudes, because there the weather systems usually travel from west to east, so they move from land to sea on the eastern sides of the continents.
EVAPORATION AND CONDENSATION AND HOW THEY PRODUCE OUR WEATHER
Weather consists mainly of water, or the lack of it. Water moves into the air from the oceans and from the surface of lakes, rivers, and wet ground. It falls from the air as precipitation—rain, drizzle, sleet, snow, hail, fog, frost, and dew. Its constant movement between the surface of the land and sea and the atmosphere constitutes the hydrologic cycle. The diagram illustrates this.
A staggering amount of water is involved. Each year, approximately 89 million billion (89 x 1015) gallons (336 x 1015 liters) evaporate from the ocean surface and 17 x 1015 gallons (64 x 1015 liters) evaporate from the land surface or from plants (transpiration). About 79 x 1015 gallons (300 x 1015 liters) fall as precipitation over the oceans and 26 x 1015 gallons (100 x 1015 liters) over land. About 9.5 x 1015 gallons (36 x 1015 liters) flow from the land back to the sea.
This is a very large quantity of water, but it amounts to only a small proportion of the total amount of water on Earth. The oceans hold 97 percent of all the water on the planet. Of the remaining 3 percent, more than half is frozen and held in the polar icecaps and glaciers and about 0.5 percent is held in the ground, but either bound firmly to mineral particles or located so deep below the surface as to be beyond our reach. The moisture in the air and clouds, together with the water or ice falling at any given time as precipitation and the water flowing through rivers and streams, in ground water, and stored in lakes, amounts to about 4 billion billion (4 x 1018) gallons (15 x 1018 liters). That is approximately 0.005 percent of the total.
Despite sometimes feeling so wet, in fact the air contains very little water. Over a desert, the very dry air often contains almost no water vapor, and even in the wettest places, such as the humid Tropics, it seldom accounts for more than about 4 percent of the air by volume. Knowing the amount of water that is moving through the cycle at any particular time and its location in the cycle makes it possible to calculate the length of time an individual water molecule spends in each part of the cycle. It remains in the ocean for about 4,000 years. Once it falls onto land, the molecule spends around 400 years at or close to the land surface. It spends a much shorter time traveling between sea and land, however. A water molecule remains in the atmosphere for an average of only 10 days.
The water molecule and the hydrogen bond
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