Weather and climate, Year 7: more practice

A rain gauge

HintIt collects the water in a container.

The whyRainfall is measured in millimetres (mm) of depth collected over a period such as a day.

Millimetres (mm)

HintIt is a depth, not a volume.

The whyOne millimetre of rain is a layer of water one millimetre deep over the ground.

So direct sunlight does not heat it and give a false reading

HintAir temperature is not the same as how hot a thermometer in the sun gets.

The whyWeather stations use a screen that lets air through but blocks the sun, so the reading reflects the air itself.

Convectional rainfall

HintCommon on hot summer afternoons.

The whyThe rising warm air cools, water vapour condenses into cloud, and heavy showers or thunderstorms often follow.

Frontal rainfall

HintNamed after the boundary between the two air masses.

The whyThe lighter warm air rides up over the heavier cold air, cools and condenses. Many UK wet spells are frontal.

The leeward side

HintThe air has already lost its moisture by then.

The whyAir rises on the windward side and drops its rain. Descending on the other side, it warms and holds its moisture. This is the rain shadow.

Rise and cool

HintWater vapour only condenses when it is cooler.

The whyRising air cools, vapour condenses into droplets, and clouds form. When the droplets grow heavy enough, they fall as rain.

Cold

HintThink where it began its journey.

The whyPolar maritime air is cold and showery. It crosses the sea on its way south, picking up moisture.

Hot and dry

HintIt begins over warm land, far from the sea.

The whyContinental means it has formed over land, so it carries little moisture. In summer it can bring heatwaves.

Different air masses with different temperatures and moisture keep arriving

HintEach air mass brings its own character.

The whyBritain sits where polar and tropical, sea and land air meet, so conditions can change within days or hours.