Atmospheric winds: formation, measurement, and global circulation

Winds are the large-scale flow of gases through the atmosphere and the mass movement of air is characteristic when considering Earth. The masses know very little about winds in spite of the fact that they are one of the most important concepts keeping the world function normally. Solar energy warms air and makes it rise, thus making it possible for cool air to move into its place creating wind. The fact that Earth's surface is composed out of a multitude of materials means that it absorbs energy at different rates. In contrast to land, water takes longer to heat or to cool because it has different properties, but this does not mean that winds move faster over the water, as the fact that there is less friction over water makes it possible for wind to travel faster there.

Body

Even with the fact that one cannot see wind moving, the respective person can still measure it by calculating the force that it applies on particular objects. In order to get a better understanding of this concept one simply needs to think about how trees move as a result of wind -- this would enable a meteorologist to approximate the wind's speed. The official measuring tools for wind are wind vanes (for measuring wind direction) and anemometers (measuring wind speed). The Beaufort Wind Scale is used to translate data retrieved from anemometers.

A wind vane points toward the direction in which wind moves and wind direction is meant to relate to the direction from which the wind comes. A west wind thus blows from the west to the east. One of the most common types of anemometers is an object with three arms that rotate on top of a shaft. Each arm ends in a cup and the cups are spun as wind blows and spin the shaft. The device is equipped with other measuring tools that count the number of rotations per minute and convert this speed in miles per hour (Wind Energy).

Local winds are more likely to form rapidly in areas where land meets water, as while air on land loses its density and expands, air over the water is denser and moves in to replace hot air on land. Winds typically move horizontally, with vertical winds only being present in extreme conditions such as when a thunderstorm occurs. Wind was used throughout history as a tool to generate energy, as people discovered its properties thousands of years ago. "Wind is called a renewable energy source because the wind will blow as long as the sun shines" (Wind Energy).

Global Circulation

The tropical belt and lower latitudes on Earth are the principal input areas that gather solar energy. Higher latitudes and the poles are areas that have a negative energy balance because thermal radiation makes it possible for Earth to lose energy in these regions. "Ocean currents and atmospheric heat conduction are not sufficient to compensate for this differential heating of the globe. The global atmospheric circulation has to take over as well" (Emeis 9).

The Hadley cell, the Ferrel cell, and the polar cell are the main traits of global circulation and they make it possible for meteorologists to observe a longitude of winds present in the troposphere and the stratosphere. In the case of the Hadley cell, direct thermal circulation involves air rising in the vicinity of the equator, moving through the poles, and going down in the subtropics. The descending motion involves large anticyclones in surface pressure fields and deserts. The polar cell is relatively similar, as it also puts across direct thermal circulation and it involves cold air descending at the poles and rising to higher altitudes. The Ferrel cell is localized between the Hadley and the polar cells and it involves cold air rising at higher altitudes and hot air sinking in the subtropics (Emeis 9-10).

Pressure Gradient Force

Pressure gradient involves the change in pressure measured across a particular distance. Many surface maps meant to relate to atmospheric matters involve H's and L's that are meant to represent high and low pressure centers. These H's and L's are surrounded by isobars, lines that display equal pressure. Areas of equal pressures are connected with a line in order for them to show were constant pressure is located. "Pressure gradient is the difference in pressure between high and low pressure areas. Wind speed is directly proportional to the pressure gradient. This means the strongest winds are in the areas where the pressure gradient is the greatest" (Origin of Wind).

The pressure gradient force attempts to equalize pressure differences by using high pressure with the purpose of pushing air in the direction of low pressure. If the pressure gradient force is the only force acting on air, air would flow from high pressures to low pressures. Even with this, Earth's rotation makes it possible for a second force to exist: the Coriolis force. This force has a strong influence on the direction toward which wind flows. "Named after Gustav-Gaspard Coriolis, the French scientist who described it mathematically in 1835, this force is what causes objects in the northern hemisphere to turn to the right and objects in the southern hemisphere to turn to the left" (Origin of Wind).

Winds in general

There are a series of questions that people have difficulty answering regarding winds and it is important for society to provide more complex education concerning these weather phenomena in order for the masses to gain a better understanding concerning what happens around them. Humanity has always been interested in winds and while people in the present have access to a wide range of information concerning winds, individuals in the past knew very little concerning what causes them and how they operate.

Greek mythology promoted the belief that Aeolus was the king of the winds and that he lived on an island named Aeolia. Zeus provided him with the task of looking after winds and with the chance to control them however he pleased. The legend of Odysseus also relates to Aeolus, as the Greek hero visited Aeolia and was given a leather sack holding the Storm Winds in order to be sure that he would have a safe journey home. However, his crew thought that the sack held great treasures, opened the bag, and thus set free all of the Storm Winds, this making it even more difficult for them to be able to reach their home. Even with the fact that Ancient Greeks obviously had a limited understanding of winds, it is nonetheless intriguing to look at how they perceived conditions in which winds are more likely to occur.

Wind speed is faster above the ground because it encounters less friction and winds move very fast when there is nothing to slow them down. This is why wind turbines are mounted on top of towers. Anemometers connected to control boxes are mounted on top of turbines with the purpose of providing data to the turbine. This makes it possible for turbines to start when wind speeds are useful and to stop when winds are slow.

Works cited:

Ahrens, Donald C., Jackson, Peter L., Jackson, Christine, E.O., "Meteorology Today: An Introduction to Weather, Climate, and the Environment," (Cengage Learning, 01.07.2011)

Emeis, Stefan, "Wind Energy Meteorology," (Springer, 2013)

"Geostrophic Wind," retrieved February 20, 2013, from the University of Illinois Website: http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fw/geos.rxml

"Origin of Wind," Retrieved February 20, 2013, from the National Weather Service Website: http://www.srh.noaa.gov/jetstream//synoptic/wind.htm

"Wind Energy," Retrieved February 20, 2013, from the NEED Website: http://www.need.org/needpdf/infobook_activities/IntInfo/WindI.pdf