What Causes Weather?
Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers to day-to-day temperature and precipitation activity, whereas climate is the term for the statistics of atmospheric conditions over longer periods of time. When used without qualification, “weather” is generally understood to mean the weather of Earth.
Weather processes such as wind, clouds, and precipitation are all the result of the atmosphere responding to uneven heating of the Earth by the Sun. Because the Earth is round and not flat, the Sun’s rays don’t fall evenly on the land and oceans. The Sun shines more directly near the equator bringing these areas more warmth.
However, the Polar Regions are at such an angle to the Sun that they get little or no sunlight during the winter, causing colder temperatures. These differences in temperature create a restless movement of air and water in great swirling currents to distribute heat energy from the Sun across the planet.
When air in one region is warmer than the surrounding air, it becomes less dense and begins to rise, drawing more air in underneath. Elsewhere, cooler denser air sinks, pushing air outward to flow along the surface and complete the cycle.
Weather is driven by air pressure, temperature and moisture differences between one place and another. These differences can occur due to the sun’s angle at any particular spot, which varies by latitude from the tropics. The strong temperature contrast between polar and tropical air gives rise to the jet stream.
Weather systems in the mid-latitudes, such as extra tropical cyclones, are caused by instabilities of the jet stream flow. Because the Earth’s axis is tilted relative to its orbital plane, sunlight is incident at different angles at different times of the year.
On Earth’s surface, temperatures usually range ±40 °C (−40 °F to 100 °F) annually. Over thousands of years, changes in Earth’s orbit can affect the amount and distribution of solar energy received by the Earth, thus influencing long-term climate and global climate change.
Surface temperature differences in turn cause pressure differences. Higher altitudes are cooler than lower altitudes due to differences in compression heating. Weather forecasting is the application of science and technology to predict the state of the atmosphere for a future time and a given location.
The system is a chaotic system; so small changes to one part of the system can grow to have large effects on the system as a whole. Human attempts to control the weather have occurred throughout human history, and there is evidence that human activities such as agriculture and industry have modified weather patterns.