Types of Rainfall

What is the key concept behind all types of rainfall?

Rainfall happens when moist air is forced upward into cooler zones, where it cools and condenses.

What is the basic rainfall process that all three types follow?

Air rises → Air cools → Water vapour condenses → Precipitation.

What is orographic rainfall (also called)?

Also called relief rainfall.

What causes orographic rainfall?

Warm, moist air is blocked by a mountain or hill and forced to rise over it.

Describe the process of orographic rainfall.

As the air rises it cools and releases moisture as rain on the windward (uphill) side. The air then descends on the other side, warming and drying out.

What is a rain shadow?

The dry area on the far (leeward) side of a mountain where all moisture has already fallen.

Give a New Zealand example of orographic rainfall.

Westward slopes of New Zealand's Southern Alps.

What is cyclonic rainfall (also called)?

Also called frontal rainfall.

What causes cyclonic rainfall?

Warm, moist air meets cold air during the passing of a low-pressure system (depression).

Describe the process of cyclonic rainfall.

The two air masses can't mix because they have different densities. Lighter warm air rises over denser cold air, cools, condenses, and falls as rain.

What is "the front" in cyclonic rainfall?

The boundary line where the warm and cold air masses meet.

Give a New Zealand example of cyclonic rainfall.

Most of the rain in the North and East of New Zealand.

What causes convectional rainfall?

Strong sunshine heats the ground surface, causing warm surface air to expand and rise rapidly.

Describe the process of convectional rainfall.

If the ground is wet or vegetated, rapid evaporation makes the rising air very moist. As it climbs into cooler altitudes it cools, condenses, and often creates heavy storms (cumulonimbus clouds).

Where does convectional rainfall most commonly occur?

Most common in equatorial regions near the tropics.

Give a New Zealand example of convectional rainfall.

Common in Auckland in summer.

What is the quick comparison between the three types of rainfall?

Orographic = forced up by mountains. Cyclonic = forced up by cold air. Convectional = forced up by heat.