Born in Paris on May 21, 1792, Coriolis was a French engineer and mathematician who first described the force of motion on a rotating body, which has come to be called the Coriolis force. It is the apparent path of deflection of an object as it passes over the rotating Earth. If an object is launched, it will not land in a straight trajectory but be offset depending on the rate of movement of the object and the rate of movement of the Earth underneath. This concept was very important to the fields of meteorology, ballistics, and oceanography.
Coriolis showed that if the ordinary Newtonian laws of motion of bodies are to be used in a rotating frame of reference, an inertial force, acting to the right of the direction of body motion for counterclockwise rotation or to the left for clockwise rotation, must be included in the equations of motion. The effect of the Coriolis force is an apparent deflection of the path of an object that moves within a rotating coordinate system. In reality, the object does not actually deviate from its path, but it looks like it does because of the motion of the coordinate system.
When referring to the surface of the Earth, the Coriolis force is the most apparent in the path of an object moving longitudinally (from pole to pole) because this is where the greatest velocity and movement take place. On the Earth, an object that travels along a north-south path— or longitudinal line—will undergo apparent deflection to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, because as an object is traveling through the air, the Earth is constantly moving under the object. When the object lands, it is not at the point expected directly north (or south), but its path looks curved because of the deflection.
blow predominantly in one direction throughout the year and are associated with the rotation of the Earth. Over other areas of the Earth, the dominant wind direction changes with the seasons. Around the equator there is a belt of relatively low pressure, called the doldrums, where the heated air expands and rises.
Tropical heating fuels a huge tropical circulation pattern called the Hadley cell. Here, warm air rises in giant columns. This is the region
The other reason for the phenomenon is that the tangential velocity of a point on the Earth is a function of latitude (the velocity is basically 0 at the poles and it attains its maximum value at the equator). To illustrate this concept, think of a line of figure skaters in an ice show. If the line traces out a circle with one end as the pivot (not traveling across the ice, but turning in place), and the rest of the line rotates around it, a skater in the middle of the line will not have to skate nearly as fast as the skater on the far end. That skater will need to skate faster than the others because they have extra ground to cover in the same amount of time. As another example, if a cannon were fired northward from a point on the equator, the projectile would land to the east of its due north path. This variation would occur because the projectile was moving eastward faster at the equator than was its target farther north. Likewise, if the weapon were fired toward the equator from the North Pole, the projectile would again land to the right of its true path. This time, the target area would have moved eastward before the shell reached it because of its greater eastward velocity. A similar displacement occurs no matter the location from which the projectile is fired.
The Coriolis force is very significant in astrophysics and stellar dynamics. It is used to study the rotation of sunspots. It is also significant in Earth science, especially meteorology, physical geology, and oceanography because the Earth is a rotating frame of reference and the forces working on it affect everything else in the system. The Coriolis force is extremely important in the study of the dynamics of the atmosphere, such as the prevailing winds and the rotation of storms, and it has an effect on the ocean currents. Coriolis contributed immensely to many scientific disciplines.
The general circulation of the atmosphere: Heated air rises in the Tropics at the ITCZ and sinks in the Subtropics (30°). Additional heat flows toward the polar areas, while cold air circulates from the poles toward the equator. This transfer of heat creates major circulation cells that form the major wind systems, such as the trade winds, westerlies, and polar easterlies. These circulation patterns will be altered as global warming intensifies.
where towering cumulonimbus clouds created by the evaporation of water vapor from the tropical oceans occurs. The enormous amounts of water vapor are able to condense into the thick, puffy cloud formations common in the humid Tropics. This condensation produces a narrow zone of rainfall in the rising part of the Hadley cell near the equator. Huge amounts of heat are transported through the Hadley cell.
As the air rises and loses water vapor in the Tropics, it moves toward the subtropics in both hemispheres (a Hadley cell moves northward in the Northern Hemisphere and southward in the Southern Hemisphere). Once it reaches the subtropics, at a latitude of 30 degrees (north and south, respectively) the air in the cell cools and sinks back toward Earth. The sinking air is then warmed by the increasing pressure of the atmosphere at lower elevations, where it becomes even drier and able to hold more water vapor.
The Hadley cell flow prevents condensation from occurring in the subtropics, making these latitudes (30°N and 30°S) a zone of low precipitation and high evaporation. It is in this area that the Sahara is located. At this point, the trade winds from both the Northern and Southern Hemispheres blow from the subtropics back toward the Tropics and replace the rising air at the equator once again. As the warm, dry air is carried by the trade winds over the tropical ocean, it is able to pick up water vapor from the ocean's surface. The region near the equator where the northern and southern trade winds meet is called the Intertropical Convergence Zone (ITCZ). The ITCZ is a zone of abundant rainfall, due largely to the water vapor that the trade winds gather off the ocean on their way to the equator.
The Hadley cell is an extremely important component of the poleward transfer of heat to the Earth's polar areas. These large-scale movements of air also determine the pressure (the weight of the air) at the Earth's surface. When air moves up and away from the Tropics, it reduces the weight of the air mass over the ITCZ and causes a low surface pressure. The air that moves downward into the subtropics (30° latitude) has a higher surface pressure because the weight of air is pressing downward.
Because solar heating is the driving force behind the Hadley cell circulation, the seasonal shifts of the Sun between the hemispheres also affect the location of the ITCZ. It moves northward during the Northern Hemisphere's summer and southward during the Northern Hemisphere's winter (Southern Hemisphere's summer). The slow thermal response of the land and oceans causes the seasonal shifts of the ITCZ to lag about a month.
Important seasonal transfers of heat between the tropical ocean and land are called monsoons and happen because water takes much longer
Christopher Columbus (1451-1506), a Genoese seaman and explorer, is credited with the discovery of the trade winds. It was the trade winds that he used in order to sail his three ships across the Atlantic Ocean. He was able to sail from the Canary Islands to the Bahamas in 1492. An amazing accomplishment for the time, it was a distance of 5,400 miles (8,690 km), and he completed his voyage in only 36 days due to the force of the trade winds.
Much later, in 1970, Thor Heyerdahl, a Norwegian seaman and archaeologist, sailed a ship made of reeds from Morocco to the Caribbean, illustrating that the trade winds were capable of helping sailors accomplish this feat. He proposed that because it was possible to use the trade winds to accomplish this, that perhaps the idea of building pyramids could have been spread to Central America and Mesoamerica by Egyptians who may have traveled this same route long ago.
For centuries, the trade winds have been known to mariners as being consistent enough to provide transcontinental trade routes. They are the most steady, consistent wind systems on Earth. The expression the wind blows trade comes from navigating by the trade winds and means "the winds blows on track."
to heat up and cool down than land does. A monsoon is a major wind system that changes direction on a seasonal basis. In the summer monsoon, air flows from over the cooler ocean toward the land, where it quickly heats, rises, condenses, and produces heavy precipitation and releases huge amounts of heat. The strongest summer monsoon area in the world is in India where there is a strong, wet summer monsoon against the Himalaya Mountains. The winter monsoon is the reverse of the summer monsoon. The cold, dry air flows down and out over the land toward the ocean and precipitation occurs over the ocean.
Although monsoons are seasonal—giving areas a rainy season and a dry season—they have lasting effects on climate and affect many areas of the world, such as Asia, Africa, North America, and South America.
In the subtropical regions at 30° north and south, high pressure dominates. Also in this area the influence of the monsoonal flow of air from land to sea in summer produces oval-shaped cells of high pressure over the subtropical oceans. Air naturally flows away from higher pressure toward lower pressure, but, as the atmosphere circulates out of the high-pressure cells, it gets deflected by the Coriolis force. This creates the winds called the westerlies. The westerlies are a surface flow of warm air out of the subtropics that transport heat to the cooler high latitudes.
In the higher middle latitudes in both hemispheres, the circulation in the lower atmosphere is a complex zone of transition between the warm air flowing out of the subtropics and the cold flow from the polar latitudes toward the equator. The weather in this zone is dynamic, with a wide variety of climate conditions. The constant creation of high- and low-pressure cells that move from west to east (the westerlies) are separated by frontal zones. Frontal zones are regions near the Earth's surface where large changes in temperature occur over small areas due to fast-moving air. The poleward movement of warm air and the equatorward movement of cold air along the frontal systems that these provide serve to warm the polar latitudes and help maintain the Earth's energy budget. These midlatitude cyclones will be covered in chapter 6.
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