Weather is the condition of the Earth’s atmosphere at a given place and time in regard to sunshine, dryness, precipitation, heat, wind, temperature, cloud cover, and air pressure. Low pressure often triggers cloudy weather and precipitation. High pressure typically generates fair or pleasant weather in which there is no precipitation, visibility is optimal, cloud coverage of the immediate sky area is less than 3/8, and there are no extremes in temperature or winds.
The three principal factors behind weather changes are heat, wind, and moisture. Variations in temperature, moisture, and pressure between atmospheric air masses that encompass the entire planet lead to weather changes.
Heat comes primarily from the sun. Geothermal energy from the planet itself plays a lesser role in weather formation. Land areas and bodies of water receive uneven amounts of solar rays because of the Earth’s round shape. Equatorial locations receive more solar heat than locations near the North and South Poles because they get the most exposure to direct sunlight. The polar regions in the Earth’s northern and south regions undergo more frigid temperatures since they receive little direct sunlight during the winter season. Land areas heat up more rapidly than bodies of water. Conversely, water areas retain heat longer because land masses cool more quickly. Weather is also influenced by seasonal changes that are brought about by the planet’s rotation around the sun.
The resulting variations in temperatures lead to constant air and water movements across the world, which circulate solar heat energy worldwide and generate ocean currents and jet streams. The unbalanced heating and cooling of scattered locations on the Earth creates winds. Clouds are moved by winds and they deposit moisture that becomes rain or snow depending on the temperature. Warm air tends to carry more moisture than cooler air.
The atmosphere in a given area thins out and begins to rise when it becomes hotter than the air that surrounds it. When colder, more dense air settles over the region and drives the thinner air away, air circulates across the globe and completes the weather cycle.
Atmospheric pressure is the single most important factor that affects weather change as high pressure induces air to gradually flow downward and dissipate, while low pressure prompts air to rise where water vapor collects and condenses to form clouds. High pressure weather systems often lead to clear and cloudless days because the sinking air prevents the formation of clouds. Alternately, air cools as it rises into low pressure systems, causing water vapor to form into clouds and be released eventually as precipitation.
The atmosphere of the Earth consists of different air masses, which perpetually move at varying speeds relative to each other. Air masses in the Earth’s northern hemisphere circulate clockwise while air masses in the Earth’s southern hemisphere circulate in an opposing, counterclockwise direction. The movement and collision of these masses of air triggers the formation of wind and storms, which lead to changes in weather patterns across the entire world.