2 Atmospheric Moisture and Cloud Formation Free Online FlashCards

What does humidity describe?

Humidity describes the amount of water vapor in the air.

What does relative humidity compare?

Relative humidity compares the water vapor present with the amount needed to saturate the air at its current temperature. Air at 100% relative humidity is saturated.

How can temperature change relative humidity without changing water vapor?

Warming raises the amount of water vapor needed for saturation, so relative humidity can fall. Cooling can raise relative humidity even when the water-vapor content stays the same.

What is the dew point?

The dew point is the temperature air must reach by cooling, at constant pressure and with no change in water-vapor content, to become saturated.

What happens during evaporation, and what does it require?

Evaporation changes liquid water into water vapor. It requires energy, commonly supplied by sunlight and the surrounding air.

How do plants add water vapor to the atmosphere?

Transpiration is the release of water vapor from plants; it adds moisture to the atmosphere.

What role do condensation nuclei play in cloud formation?

When air becomes saturated, water vapor can condense onto tiny particles called condensation nuclei, such as dust, sea salt, or smoke. The resulting droplets or ice crystals can form clouds.

What happens to energy when water vapor condenses?

Condensation changes water vapor into liquid water and releases energy to the surrounding air.

What may clouds contain below freezing?

At temperatures below freezing, clouds may contain ice crystals as well as, or instead of, liquid droplets.

How do maritime tropical and continental polar air masses differ?

An air mass takes on characteristics of the region where it forms. Maritime tropical air is generally warm and humid, while continental polar air is generally cold and dry.

How can a front contribute to cloud formation?

Where air masses meet, fronts can force air upward and contribute to cloud formation.

Why does rising air cool higher in the atmosphere?

Higher in the atmosphere, pressure is lower. Rising air expands in this lower pressure and cools.