Precipitation

1. Humidity and precipitation:
All air masses contain a certain amount of water vapor or atmospheric humidity. Has a mass of air rises, its temperature decreases. The humidity it contains is transformed into a liquid state and falls to the earth’s surface in the form of presentation. There are three main causes of precipitation:

2. Types of rainfall

Convectional Rainfall

• This happens as the sun heats the earth. The earth heats the air above it which causes it to start rising. As it rises it cools, condenses and rains.
• On a sunny day clouds often form in the afternoon due to this process and can lead to heavy downpours.

Relief Rainfall

• This is caused by physical features causing the air to rise.
• Mountains cause the air to rise, it cools and condenses. They often have clouds around the tops and have higher rainfall totals.

Frontal rainfall

• This occurs when two air masses meet. The warmer air mass rises above the cooler one.
• As it rises it cools and condenses and then rains.
• Common in the UK where there are several air masses often meeting.

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