Weather is the day-to-day fluctuation of temperature, moisture, and wind currents. It is driven by nuclear energy received from the sun. As the oceans and continents as well as atmospheric elements like methane and carbon dioxide heat up or cool down, high and low temperatures create atmospheric pressure, resulting in wind or the air movement of atmospheric constituents like water vapor, dust, and gases.
Earth's Tilt and the Sun
Over approximately 40,000 years, the Earth's axial tilt ranges from 22.1 degrees to 24.5 degrees. As the angle of the Earth in respect to the sun changes, so too does the available energy received from its nuclear furnace. The current axial tilt of roughly 23.4 degrees creates six major wind belt zones divided by five lines of latitude. As the Earth orbits the sun, the angle of the sun's rays changes across the globe as a direct result of the Earth's axial tilt.
As the rays of electromagnetic energy from the sun enter the Earth's atmosphere, they are either reflected back out to space, absorbed by atmospheric gases or stored in ocean waters or continental surfaces. The closer the ray's angel of entry is to 90 degrees, the greater the amount of energy that is retained. As a result, latitudes nearer the equator receive more of the sun's energy throughout the year than do higher and lower latitudes.
The equator, at 0 degrees latitude, divides the northeast trade wind zone in the Northern Hemisphere from the southeast trade wind zone in the Southern Hemisphere. In respect to the wind belts, the equator is known as the equatorial doldrums. The horse latitudes are located at 30 degrees north latitude and 30 degrees south latitude, and divide the northeast and southeast trade wind zones from the zones known as the prevailing westerlies.
Above and below the prevailing westerlies at 60 degrees north latitude and 60 degrees south latitude are the polar fronts dividing the prevailing westerlies from the polar easterlies.
Wind Belts and Wind Direction
Simply put, the direction of wind flow associated with wind belt zones flows from the direction indicated within its name. The northeast trade winds flow from northeast to southwest. The southeast trade winds flow from the southeast to the northwest.
The Coriolis Effect
If it were not for the Earth's rotation, the winds would simply flow in relatively straight paths from north to south or from south to north respectively. But the Earth does rotate, and as a result, the wind and weather patterns are deflected to the right in the northern hemisphere and to the left in the southern hemisphere.
This effect is known as the Coriolis effect and adds greatly to the atmospheric airflow mixture and weather variability.
Sea and Canyon Breezes
Localized winds like those found along a coastline are created by similar forces. As the sun rises, the water and the land absorb the sun's heat at different rates. As a result, high and low pressure systems are created. In the morning, the land will heat up faster than the water. As the land heats up it, radiates heats to the surrounding area.
Hot air is less dense than cold air, so the warming air begins to rise, pulling the cooler air over the water inland. As the heated air rises, it begins to cool, flowing out to sea until it grows cold and dense and falls. This cycle reverses as the day closes and sun begins to set.
Not only does the land warm faster, but it also cools faster than does water. As a result, the circle of air flow reverses as the warmer air above the water flows toward the cooler air above the land.
Wind and Weather
As a result of the movement of atmospheric materials transported by wind, driven by the energy from the sun, climates are created and weather occurs. Without wind, weather would not exist. Wind, in its interdependent relationship with the other cycles of the Earth, like ocean currents, is the vehicle by which water vapor and, by consequence, temperature variations are moved from one area of the globe to another, creating weather variations within specific climate zones.
- wind image by hanna kreis from Fotolia.com