What are ‘highs’ and ‘lows’?
Air pressure varies across different parts of the Earth’s surface, and this difference causes winds. Air moves from an area of high pressure, or an anticyclone, to an area of low pressure, or a depression. Depressions are usually associated with worsening weather conditions and rain. These changes in air pressure can be measured by an instrument called a barometer. In a mercury barometer the air pressure pushes down on the mercury, which is forced up the barometer to give an accurate reading.
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Why do we get thunder and lightning?
Lightning is a huge spark of electricity that is produced in a cloud. Thunder is the loud noise made by the lightning as it rips through the air.
During thunderstorms, enormous electrical charges build up inside a cloud. Eventually the charges seem to flow down to the ground when lightning strikes. In fact, the electrical charges flow up from the ground and down from the cloud at the same time. The tremendous heat generated by the lightning causes the explosive noise of thunder. Lightning frequently strikes in the same place repeatedly, and along the same path through the air. It can also strike between two clouds.
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