Weather is a set of all the phenomena occurring in a given
atmosphere at a given time. Weather phenomena lie in the
troposphere. Weather refers, generally, to day-to-day
temperature and precipitation activity, whereas climate is the
term for the average atmospheric conditions over longer periods
of time. When used without qualification, "weather" is
understood to be the weather of Earth. Weather occurs due to
density (temperature and moisture) differences between one place
and another. These differences can occur due to the sun 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 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 (100 °F t