Agrometeorology and Solar Radiation Quiz

Study Notes

Probability: Initial probability is the amount of rainfall at a specific probability (50% or 75%) during a week or month in a region. Conditional probability is the level of a particular amount of rainfall projected for a specific period.
Rainy Days: A meteorological rainy day is at least 2.5 mm of rainfall in a day, while a crop rainy day is above 5mm. Effective rainfall is 5 mm per day.

Sun: The sun is the source of all energy for Earth's physical and biological processes. Its diameter is 1.39 x 10⁶ km, and the average distance from Earth is 1.5 x 10⁸ km. Earth is closest to the sun on December 31st and farthest on July 1st.
Temperature: The sun's central interior temperature is between 8 x 10⁶ and 40 x 10⁶ °C, and its surface temperature is 5778°K (5505°C).
Time: It takes 8.3 minutes or 500 seconds for solar radiation to reach Earth.
Solar Radiation Units: Solar radiation is measured in watts per square meter (W/m²). 1 watt= 1 Joule/sec. 1 cal/cm²/min = 697.93 W/m²/ and 1 feet candle = 10.764 lux.
Solar Constant: The energy falling on a 1 cm² surface at the outer atmosphere for one minute is known as the solar constant and is 1.94 cal/cm²/min or 1353 W/m².
Cloud Cover: Approximately 80% of incoming solar radiation is reflected back into the atmosphere by clouds.

Albedo: The portion of incident solar energy reflected back is called albedo. It is calculated as (amount of visible light reflected / total incident light) * 100.
Light Intensity: The minimum light intensity where the rate of photosynthesis equals the rate of respiration is known as the compensation point. It's directly proportional to temperature. The light saturation point is the maximum light intensity where photosynthesis reaches a maximum. Most crops reach light saturation at about 2500-10000 ft candles.

Infrared radiation: Means "below red". Longer wavelengths that are often absorbed by atmospheric water and CO2.
Ultraviolet (UV) radiation: Above violet, shorter wavelengths.
- UV-A: Reaches Earth's surface, less harmful.
- UV-B: Harmful to skin, causes burns, genetic damage, and skin cancer.
- UV-C: Very harmful; absorbed by ozone in the atmosphere.
Visible radiation (PAR): Most effective in heating Earth. Visible light is about 50-60% of total solar radiation.
Near Infrared Radiation: Important for photoperiodism, seed germination, flowering, and fruit color development. Wavelength range is 0.76-0.92 μ.

C3 and C4 plants: C4 plants have higher light saturation points than C3 plants.
Day Length: Day and night lengths are equal on March 21st and September 23rd, and day length increases/decreases from those points to other solstice days.