Geography Topic
Types of rainfall
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Study focus - 3 things
- All rain needs the same basic process: warm moist air RISES, COOLS, CONDENSES into clouds, then falls
- Three types differ in WHY the air is rising: convectional (heated ground), orographic (mountains), frontal (meeting air masses)
- Jamaica gets all three at different times — convectional in summer afternoons is the most common
Section 1How rain forms (the shared steps)
Every type of rainfall follows the same basic recipe: 1) warm moist air rises, 2) it cools as it goes up, 3) water vapour condenses into tiny droplets forming clouds, 4) droplets join and grow heavy enough to fall as precipitation. The three types differ only in the REASON the air starts rising.
Section 2Convectional rainfall
Happens when the Sun heats the ground intensely; the warm ground heats the air above it, which rises rapidly. Common in tropical regions in the afternoon — Jamaica's summer afternoon thunderstorms are classic convectional rainfall. Often short, heavy, and accompanied by thunder.
Section 3Orographic (relief) rainfall
Happens when moist air is forced UP and OVER a mountain or highland. As it rises up the windward side, it cools and rain falls. By the time the air passes over the peak it's lost most of its moisture, so the leeward side is dry — this creates a "rain shadow." Common on mountain ranges across the Caribbean and beyond.
Section 4Frontal (cyclonic) rainfall
Happens when two air masses with different temperatures meet — typically a warm air mass and a cold air mass. The warmer, lighter air is forced up over the colder, denser air at the boundary (called a "front"). The rising warm air cools and rain falls. Common in temperate regions; a hurricane is an extreme tropical version of this kind of process.
Examples
It's 3 p.m. on a hot summer day in Kingston. Thick clouds build quickly and a short, heavy thunderstorm rolls through. What type of rainfall is this?
Convectional. The Sun heated the ground all day, the warm ground heated the air above it, the air rose rapidly, condensed, and produced a short heavy storm — the classic afternoon convectional pattern.
Moist trade winds blow into a Caribbean island and rise over its central mountain range. Heavy rain falls on the windward coast, and the leeward coast is much drier. What is this rainfall called?
Orographic rainfall. The air is forced up over the mountains, condenses, and dumps its moisture on the windward side, leaving a rain shadow on the leeward side.
Now let's water it
Session runs notes to flashcards to quiz back-to-back.