AGROMETEOROLOGY: COMPLETE LECTURE NOTES
Unit 1: Introduction & History
1. Basics & Etymology
Meteorology: Derived from Greek words "Meteoron" (meaning 'above the earth's surface' or 'things in the air') and "Logos" (meaning 'study').
Climate: Derived from Greek word "Klima" (meaning slope or inclination).
Weather vs. Climate:
Weather: State of atmosphere at a specific time and place (Short-term).
Climate: Summation of weather over a long period (Long-term average of >30 years).
2. Fathers of the Field
Meteorology (World): D.N. Walia.
Agrometeorology (India): L.A. Ramdas.
Agroclimatology: Koppen.
3. Important Institutions & Timeline
1643: Barometer discovered by Torricelli.
1875: IMD (India Meteorological Department) established at Calcutta.
IMD Headquarters Shift (Trick: C-S-P-D):
Calcutta (1875) > Shimla (1905) > Pune (1928) > New Delhi (1944).
1932: Division of Agricultural Meteorology established at Pune.
1950: WMO (World Meteorological Organization) established in Geneva, Switzerland.
1983: AICRP on Agrometeorology started at Hyderabad.
1988: NCMRWF (National Centre for Medium Range Weather Forecasting) established in New Delhi.
Unit 2: Atmosphere Structure & Composition
1. Composition of Air
Nitrogen (N_2): 78.08% (Volume), 75.52% (Weight).
Oxygen (O_2): 20.95% (Volume), 23.14% (Weight).
Argon (Ar): 0.93% (Volume).
Carbon Dioxide (CO_2): 0.033% (Volume) or 421 ppm (Current global average).
Exam Point: Soil air contains 8-10 times more CO_2 than atmospheric air.
2. Structure of Atmosphere (Vertical Layers)
Total Mass: 99% of atmospheric mass is within 40 km of earth.
Layers (Trick: T-S-M-T):
Exosphere: >600 km. Contains Hydrogen and Helium.
Unit 3: Solar Radiation & Heat
1. Key Values
Solar Constant: Energy received at the top of Earth's atmosphere. Value = 1.94 cal/cm²/min or 1353 Watts/m².
Albedo: Percentage of reflected radiation.
Fresh Snow: 80-95% (Highest).
Crops: 15-25%.
Black Soil: Low albedo (absorbs more heat).
Earth's Average: 30%.
Moon: 7%.
2. Radiation Types
PAR (Photosynthetically Active Radiation): 0.4 to 0.7 Micro meter (400-700 nm). Essential for photosynthesis.
Forms:
Direct Radiation: 42% of PAR.
Diffused Radiation: Sky radiation (Blue sky due to scattering). Better for crop canopies.
3. Temperature Basics
Lapse Rate: Vertical temperature decrease = 6.5°C/km (3.5 F/1000 ft),.
Adiabatic Lapse Rate: Change in temp without heat exchange.
Dry: 10 C/km.
Wet/Moist: 6 C/km.
Inversion: Temp increases with height (Negative lapse rate). Occurs in long winter nights.
Coolest Time: Just before sunrise.
Warmest Time: 2:00 PM.
Unit 4: Rainfall & Monsoon
1. Rainfall Terminology
Rainy Day: Rainfall > 2.5 mm in 24 hours.
Crop Rainy Day: Rainfall > 5 mm in 24 hours.
Drizzle: Droplets < 0.5 mm.
Rain: Droplets 0.5 to 6 mm.
2. Monsoons in India
South-West Monsoon (Grand Period of Rainfall):
Duration: June – September.
Contribution: >75% (80%) of total rainfall,.
Onset: 1st June (Kerala).
Withdrawal: 1st-15th September (Rajasthan).
North-East Monsoon (Retreating Monsoon):
Duration: October – December.
Contribution: 10-15%.
Benefits: Tamil Nadu and Andhra Pradesh.
3. Global Phenomena
El Nino: Warming of sea surface in Pacific Ocean. Causes Drought in India.
La Nina: Cooling of sea surface. Causes Good Rainfall in India.
4. Artificial Rain (Cloud Seeding)
Father: Vincent Schaefer (1946).
Cold Clouds: Use Silver Iodide (AgI) or Dry Ice (CO_2).
Warm Clouds: Use Sodium Chloride (NaCl) (Common Salt).
Unit 5: Humidity & Clouds
1. Humidity Types
Absolute Humidity: Mass of water vapor per unit volume of air (g/m3).
Specific Humidity: Mass of water vapor per unit weight of air (g/kg).
Relative Humidity (RH): Most used in agriculture. Ratio of actual vapor to saturation point (%).
Equation:{Water Vapour present}/{Water Vapour required for saturation} x 100.
Optimum RH for crops: 40-60%.
2. Clouds
Cirrus: Highest, fibrous, silky ("Feather like").
Cumulonimbus: Thunderstorms, hail, and heavy rain.
Nimbus: Rain-bearing clouds.
Unit 6: Climatic Classification
1. Major Systems
De Candolle (1900): First based on vegetation.
Koppen (1936): Most widely accepted. Based on weather elements.
Troll (1965): Based on temperature and humid months. Used by ICRISAT.
Hargreaves: Based on MAI (Moisture Availability Index).
2. India's Climate
Classification: Tropical Monsoon Climate.
Semi-arid: Largest climatic type area in India (57%), mainly Maharashtra.
Arid: 17% area.
Unit 7: Instruments (Exam Hack: Match the Meter)
Unit 8: Weather Forecasting
Types of Forecasts
Short Range:
Duration: 0-3 days (Validity).
Use: Irrigation, Pesticide spray.
Medium Range:
Duration: 3-10 days.
Use: Sowing, Harvesting.
Issued by: NCMRWF (Noida/Delhi).
Long Range:
Duration: 10-30 days (or seasonal).
Use: Cropping pattern selection.
Issued by: IMD (Pune/Delhi).
Unit 9: Important Facts & Tricks
Blue Color of Sky: Due to scattering of short wave (blue) radiation.
Red Sunset: Due to scattering.
Greenhouse Gases: CO_2 is the most important gas.
Freezing Mixtures: Ice + Salt (NaCl) or NH_4Cl.
Frost Control: Spray 0.1% Sulphuric Acid (H2SO4) or use smoke/irrigation.
Iso-Lines (Map Tricks):
Isotherm: Equal Temperature.
Isobar: Equal Pressure.
Isohyet: Equal Rainfall.
Isohel: Equal Sunshine.
Isotach: Equal Wind Speed.
Isopluvial: Equal Depth of Rainfall.
Unit 10: Crop-Specific Climate Data
Optimal Temps:
Rice/Maize: 30-32°C.
Wheat: 20-25°C.
Sugarcane: 25-26°C.
Base Temperature: Min temp below which crop doesn't grow.
Wheat: 4.5°C.
Rice/Maize: 10°C.
