Weather
Weather refers to the short-term atmospheric conditions at a specific place and time, encompassing temperature, humidity, precipitation, wind speed and direction, cloud cover, and atmospheric pressure. It is driven by the uneven heating of Earth's surface by solar radiation, the rotation of the Earth (Coriolis effect), and the redistribution of energy and moisture by atmospheric circulation. Weather is distinct from climate, which describes the average patterns of weather over a region across 30 or more years; meteorologists predict weather using numerical weather prediction models, radiosonde data, satellite imagery, and surface observation networks.
Key Weather Parameters and Their Measurement Instruments
| Parameter | Unit | Instrument | Typical Range | Weather Significance |
|---|---|---|---|---|
| Temperature | °C / °F / K | Thermometer | −50°C to +50°C (surface) | Air mass identity and comfort |
| Atmospheric pressure | hPa / mbar | Barometer | 870–1,085 hPa | High = fair, Low = stormy |
| Relative humidity | % | Hygrometer | 0–100% | Moisture, fog, precipitation risk |
| Wind speed | m/s / km/h / knots | Anemometer | 0–100+ m/s | Energy transport, storm force |
| Wind direction | Degrees (0–360°) | Wind vane | 0–360° | Air mass source region |
| Precipitation | mm / in | Rain gauge | 0–500 mm/day (extreme) | Water cycle, flooding |
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Related Terms
Troposphere
The troposphere is the lowest layer of Earth's atmosphere, extending from the surface to approximately 8–9 km at the poles and 16–18 km at the equator, and containing about 80% of the atmosphere's total mass and virtually all of its water vapor and weather. Temperature generally decreases with altitude at the environmental lapse rate of approximately 6.5°C per 1,000 m (the standard atmosphere value), until reaching the tropopause, a temperature inversion that caps the troposphere. All significant weather phenomena — clouds, precipitation, thunderstorms, cyclones, and jet streams — occur within the troposphere, making it the most meteorologically active layer.
Atmosphere (Earth)
The Earth's atmosphere is the layer of gases retained by Earth's gravity surrounding the planet, extending from the surface to approximately 10,000 km altitude where it gradually merges with the interplanetary medium. It consists primarily of nitrogen (78.09%), oxygen (20.95%), argon (0.93%), and carbon dioxide (0.04%), plus trace gases and variable amounts of water vapor. The atmosphere performs critical functions including regulating surface temperature through the greenhouse effect, protecting life from harmful ultraviolet radiation via the ozone layer, enabling weather and climate systems, and providing the oxygen and carbon dioxide essential for respiration and photosynthesis.
Ozone Layer
The ozone layer is a region of Earth's stratosphere, concentrated approximately 15–35 km above the surface, where ozone (O₃) molecules are present at relatively high concentrations (2–8 ppm), absorbing 97–99% of the Sun's medium-frequency ultraviolet radiation. Ozone is continuously formed when UV radiation (wavelength < 240 nm) splits O₂ molecules into oxygen atoms that then react with other O₂ molecules, and destroyed by catalytic cycles involving chlorine, bromine, nitrogen, and hydrogen radicals. Depletion of the ozone layer by synthetic chlorofluorocarbons (CFCs) — culminating in the discovery of the Antarctic ozone hole in 1985 — led to the Montreal Protocol (1987), which has successfully reduced stratospheric chlorine loading and begun the layer's recovery.
From Old English "weder" (air, sky, breeze, storm), related to Old Norse "veðr" and Proto-Germanic "*wedraz". The word is cognate with the Russian "vedro" (fair weather) and traces to a Proto-Indo-European root "*we-dhro-" linked to wind. The verb "to weather" (to endure conditions) and "weather" as a noun for atmospheric conditions have been in continuous English use since before the 12th century.