4 Humidity, Clouds, and Precipitation Free Online FlashCards

What is water vapor?

Water vapor is water in its invisible gaseous state.

What does relative humidity measure?

Relative humidity is the water vapor in the air compared with the amount needed for saturation at the same temperature, expressed as a percentage.

What happens during evaporation?

Evaporation changes liquid water into water vapor as some molecules gain enough energy to escape from the water surface.

What role do condensation nuclei play?

Condensation nuclei are tiny airborne particles, such as dust, sea salt, or smoke, on which condensation usually begins.

Why can we see clouds but not water vapor?

Clouds are visible because their droplets and ice crystals scatter light; water vapor itself is invisible.

How do droplets grow in relatively warm clouds?

In relatively warm clouds, droplets collide and merge into larger drops through collision and coalescence.

Why might a cloud produce no precipitation at the ground?

Not every cloud produces precipitation: particles may stay suspended, evaporate, or melt before reaching the surface.

What is transpiration?

Transpiration is the release of water vapor by plants.

Why can relative humidity change when temperature changes?

Warmer air can hold more water vapor before saturation, so relative humidity can change with temperature even if the amount of vapor stays the same.

What is the dew point?

The dew point is the temperature air must cool to, at its current pressure and water-vapor content, to become saturated.

What happens during condensation?

Condensation changes water vapor into liquid water, often when air cools to saturation.

What is deposition in the water cycle?

Deposition is the direct change of water vapor into ice.