Temperature

1. Temperature is a measure of the degree of hotness or coldness of a body.
2. The instrument used to measure temperature is a Thermometer.
3. Maximum thermometer (Mercury-in-glass) records highest temperature of the day.
4. Minimum thermometer (Alcohol-in-glass) records lowest temperature of the day.
5. Six’s Thermometer measures both maximum and minimum temperatures.
6. The unit of temperature is °C (Celsius) or Kelvin (K).
7. 0°C = 273 K (Kelvin scale).
8. The average surface temperature of the Earth is 15°C.
9. Temperature decreases with altitude at an average rate of 6.5°C per km.
10. The difference between daily maximum and minimum temperature is called Diurnal range.

Air Pressure

11. Atmospheric pressure is the weight of air exerted per unit area.
12. The instrument used to measure air pressure is a Barometer.
13. Mercury barometer was invented by Evangelista Torricelli (1643).
14. The standard atmospheric pressure at sea level is 1013.25 mb or 760 mm Hg.
15. Aneroid barometer does not use liquid and is portable.
16. The line joining equal pressure points on a weather map is called an Isobar.
17. Pressure decreases with height at an average rate of 1 mb per 10 m.
18. Low pressure is associated with cloud formation and rainfall.
19. High pressure is associated with clear sky and dry weather.
20. A Cyclone is a system of low pressure with inward-spiraling winds.

Wind

21. Wind is the horizontal movement of air caused by pressure differences.
22. Anemometer measures wind speed.
23. Wind vane indicates wind direction.
24. Wind direction is named from the direction it blows from.
25. The difference in pressure between two points is called Pressure gradient.
26. Coriolis force causes deflection of winds due to Earth’s rotation.
27. Trade winds blow from subtropical high pressure to equatorial low pressure.
28. Westerlies blow from 30°–60° latitudes.
29. Jet streams are high-altitude, fast-moving air currents found in the tropopause.
30. Sea breeze occurs during the daytime, while land breeze occurs during the night.

Solar Radiation

31. Solar radiation is the primary energy source driving all weather processes.
32. The total solar energy received per unit area outside the Earth’s atmosphere is the Solar Constant = 1367 W/m².
33. Pyranometer measures global solar radiation.
34. Pyrheliometer measures direct solar radiation.
35. Albedo is the percentage of reflected radiation.
36. Fresh snow has the highest albedo (~80–90%).
37. Water surfaces have low albedo (~5–10%).
38. The Earth’s albedo averages around 30%.
39. Net radiation is the balance between incoming and outgoing radiation.
40. Stevenson Screen houses thermometers and protects them from radiation and precipitation.

Humidity and Evaporation

41. Humidity is the amount of water vapour present in the air.
42. Absolute humidity is the actual mass of water vapour in a given volume of air (g/m³).
43. Relative humidity (RH) = (Actual vapour pressure / Saturation vapour pressure) × 100.
44. Hygrometer measures humidity.
45. Psychrometer uses wet and dry bulb thermometers to determine humidity.
46. The temperature at which air becomes saturated is called the Dew point.
47. Evaporation is the process of converting liquid water into vapour.
48. Evaporimeter (Piche or Class A Pan) measures evaporation rate.
49. Evapotranspiration = Evaporation + Transpiration.
50. Potential evapotranspiration (PET) is the maximum possible loss of water by evapotranspiration.

Rainfall and Precipitation

51. Rainfall is measured using a Rain gauge.
52. The standard non-recording rain gauge used in India is the Symons type.
53. Tipping bucket rain gauge is an automatic recording instrument.
54. The minimum rainfall required for agriculture is about 500 mm annually.
55. Mawsynram (Meghalaya) receives the highest rainfall in the world (~11,872 mm/year).
56. Leh (Ladakh) receives the lowest rainfall in India.
57. Precipitation includes rain, snow, hail, sleet, and dew.
58. Nimbostratus and Cumulonimbus are major rain-bearing clouds.
59. Orographic rainfall occurs when moist air is lifted over mountains.
60. Cyclonic rainfall is associated with low-pressure systems.

Weather Observation and Instruments

61. Weather is the day-to-day condition of the atmosphere.
62. Climate is the average weather condition over a long period (30+ years).
63. Meteorological Observatory is a place equipped with instruments for recording weather data.
64. Automatic Weather Station (AWS) records all weather parameters digitally.
65. Stevenson’s Screen is painted white to reflect solar radiation.
66. Barograph records continuous changes in air pressure.
67. Thermograph records temperature continuously.
68. Hygrograph records humidity continuously.
69. Wind rose shows the frequency of wind direction at a station.
70. Ceilometer measures the height of cloud base.