• The atmosphere is a gaseous envelope surrounding Earth and other planets.
  • Air is composed mainly of nitrogen (78.08%) and oxygen (20.95%).
  • Water vapor makes up about 0.25% of the atmosphere by mass.
  • The atmosphere is divided into five layers based on temperature variations.
  • The troposphere (up to 18 km) hosts weather phenomena like clouds and fog.
  • The stratosphere (8–50 km) contains the protective ozone layer.
  • The mesosphere (50–80 km) experiences a strong temperature drop.
  • The thermosphere (80–400 km) enables long-distance radio communication.
  • The exosphere (400 km and beyond) gradually merges with space.
  • The ozone layer absorbs harmful UV radiation from the sun.
  • CFCs from air conditioners and sprays deplete the ozone layer.
  • Satellites orbit the Earth in the exosphere.
  • Weather describes atmospheric conditions over a short period.
  • Climate is the long-term statistical analysis of weather patterns.
  • Clouds are minute water droplets suspended in the air at high altitudes.
  • Cloud types include cirrus (hair-like), cumulus (heap-like), stratus (layered), and nimbus (rain-bearing).
  • Cumulonimbus clouds cause thunderstorms, heavy rain, and hail.
  • Nimbostratus clouds are dark, thick, and bring prolonged precipitation.
  • High clouds include cirrus, cirrocumulus, and cirrostratus.
  • Middle clouds include altocumulus and altostratus.
  • Low clouds include stratus, stratocumulus, and nimbostratus.
  • Silver iodide is used for seeding cold clouds, while sodium chloride seeds warm clouds.
  • Precipitation includes rain, sleet, snow, hail, and drizzle.
  • Rain droplets range from 0.5 to 4 mm in size.
  • Drizzle consists of fine rain droplets less than 0.5 mm.
  • Fog is a thick cloud near the surface, limiting visibility to less than 1 km.
  • Mist is a cloud with visibility greater than 1 km.
  • Rime is freezing fog.
  • Snow forms when water vapor freezes into ice crystals.
  • Sleet is partly melted snow falling with rain.
  • Hail consists of ice balls that fall like rain, occurring in warm weather.
  • India gets 75% of its rainfall from the Southwest Monsoon (June–September).
  • The South-West monsoon begins on 1st June.
  • Coastal Andhra Pradesh and Tamil Nadu experience the North-East monsoon (October–December).
  • Mawsynram (11,871 mm) receives the highest annual rainfall in India, followed by Cherrapunji (11,777 mm).
  • India's annual average rainfall is 1,120 mm, while the global mean is 990 mm.
  • A rainy day has at least 2.5 mm of rainfall.
  • A cyclone is a low-pressure system with inward-spiraling winds, leading to storms.
  • Cyclones are known as hurricanes in North America and typhoons in East Asia.
  • An anticyclone is a high-pressure system with outward-spiraling winds, bringing calm weather.
  • A tornado is a violent funnel-shaped storm occurring in spring and early summer.
  • Absolute humidity is the actual water vapor in air, measured in g/m³.
  • Relative humidity is the percentage of water vapor in air compared to its saturation limit.
  • Saturation deficit is the extra water vapor required for full saturation at a given temperature.
  • The solar constant is approximately 1.366 kW/m², representing solar radiation received per unit area.
  • Palmer’s Drought Severity Index (PDSI) measures dryness based on rainfall and temperature.
  • Maximum-Minimum thermometer measures temperature.
  • Wet and dry bulb thermometer, hygrometer, psychrometer measure relative humidity.
  • Rain gauge measures rainfall.
  • Anemometer measures wind speed/velocity.
  • Wind vane measures wind direction.
  • Cambel-Stokes sunshine recorder measures sunshine duration.
  • Open pan evaporimeter measures evaporation.
  • Lysimeter measures evapotranspiration.
  • Aneroid barometer measures air pressure.
  • Ceilometer measures cloud height.
  • Pyranometer measures total incoming radiation.
  • Pyrometer measures high temperatures from a distance.
  • Cryometer measures low temperatures.
  • Pycnometer measures specific gravity of soil.
  • Tensiometer measures soil moisture tension.
  • Peizometer measures depth of the water table.
  • Fathometer measures depth of sea/water.
  • Automatic Weather Station (AWS) automates weather measurements like temperature, wind, humidity, and radiation.
  • Isotherms connect points of equal temperature.
  • Isobars connect points of equal atmospheric pressure.
  • Isohyets connect points of equal rainfall/precipitation.
  • Isotachs connect points of equal wind speed.
  • Isohels connect points of equal sunshine duration.
  • Isochrone connects points of the same time.
  • Isobath connects points of equal water table elevation.
  • Evapotranspiration is the combined water loss from plant transpiration and soil evaporation.
  • Crop water use, consumptive use, and evapotranspiration (ET) describe the water consumed by crops.
  • Potential evapotranspiration (PET) measures the water required for optimal vegetation growth.
  • Hyper-arid areas have a P/PET ratio of <0.05.
  • Arid areas have a P/PET ratio of 0.05–0.20.
  • Semi-arid areas have a P/PET ratio of 0.20–0.50.
  • Dry subhumid areas have a P/PET ratio of 0.50–0.65.
  • Dryland agriculture is crop cultivation under rainfed conditions.
  • Dry farming occurs in areas with less than 750 mm annual rainfall.
  • Dryland farming occurs where rainfall is above 750 mm annually.
  • Rainfed farming takes place in areas receiving more than 1,150 mm rainfall.
  • Climate Smart Agriculture (CSA) enhances productivity, adaptation, and mitigation.
  • The Indian Meteorological Department (IMD) is located in New Delhi.
  • The Agricultural Meteorology Division of IMD is based in Pune.