1. Solar Radiation & The Water Cycle

2. What is the water cycle?
The water cycle is the continuous movement of water (H2O) on, below and above Earth’s surface.

3. What drives the water cycle?
The water cycle is driven by solar radiation.

4. What is solar radiation & radiant energy?
Solar radiation is radiant energy emitted by the sun, particularly electromagnetic energy.
About half of the radiation is in the visible short-wave part of the electromagnetic spectrum
Radiant energy is the energy of electromagnetic waves.

5. How does solar radiation drive the water cycle?
Solar radiation is energy that is absorbed by either absorb or reflected by the atmosphere.
The energy that isn’t reflected enters Earth’s atmosphere where it heats up the gases.
This energy heats the atmosphere which we refer to as heat.
Energy from the sun heats the water and when the water has heated enough it changes states of matter: liquid to a gas (evaporation or transpiration).

6. What changes are caused in the water cycle by solar radiation?
Evaporation
Transpiration
Condensation
Precipitation
Dew/Frost
Humidity

7. What is evaporation?
Evaporation is the heating of water causing it to change from a liquid state (water) to a gaseous state (water vapor).

8. What is transpiration?
Transpiration is the evaporation of water (liquid) to a water vapor (gas).

9. What is condensation?
Condensation occurs in the upper levels of the atmosphere.
It occurs when the water vapor, from evaporation and transpiration, reaches a high enough level in the atmosphere that the heat (energy) absorb from solar radiation is lost and it changes back to a liquid (water).

10. What is precipitation?
Precipitation is the falling of water, ice, snow, sleet, or hail back to the Earth.
When the cooling occurs from condensation water vapor turns to one of the following forms of precipitation and it depends upon the temperature of the upper atmosphere and the amount of heat (energy) lost by the water vapor.

11. What is dew and frost?
Dew and frost are the condensing of water vapor on the ground due to a significant temperature change during the night.
Dew forms above freezing temperatures.
Frost forms below freezing temperatures.

12. What is humidity?
Humidity is the amount of water that has been evaporated during the day.
Relative humidity is the percentage of water vapor in the air in comparison to how much it can hold (saturated). As temperature increase the amount of water vapor increases. If it reaches 100% you get precipitation.
Ex: Air can hold 20 grams of water vapor at 90oF, then if it was holding 18 grams it would be 18/20=90% humidity.