<Tr> <Td> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloudy . Most weather phenomena occur in the lowest level of the atmosphere, the troposphere, just below the stratosphere . Weather refers to day - to - day temperature and precipitation activity, whereas climate is the term for the averaging of atmospheric conditions over longer periods of time . When used without qualification, "weather" is generally understood to mean the weather of Earth . </P> <P> 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 with latitude . The strong temperature contrast between polar and tropical air gives rise to the largest scale atmospheric circulations: the Hadley Cell, the Ferrel Cell, the Polar Cell, and the jet stream . Weather systems in the mid-latitudes, such as extratropical 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 . </P>

Most of earth's weather events take place in the