Weather Watch

Feeling Under Pressure?: What are barometers?

We tend to think that the air around us doesn’t weigh anything, but in fact a cubic metre of air weighs over a kilogram. This air presses down on the Earth’s surface exerting a force we call air pressure. And if you add all those cubic metres of air sitting above our heads, it roughly equates to the force of an elephant balancing on a desk! This is equivalent to 1000 hectopascals (hPa), which is the unit used by meteorologists.

Damp or dry? Measuring humidity

Humidity is the amount of water vapour, an invisible gas, in the air. Warm air can ‘hold’ more water vapour than cold air; in fact air at 35°C can hold six times more water vapour as air at 5°C. All meteorological instruments measure the relative humidity (RH); this is the amount of water vapour in the air compared to the amount required to saturate it, given as a percentage - so completely saturated air has a RH of 100%.

How the OPAL Climate Survey is enlisting the observatory powers of the British public: The OPAL Climate Survey and roadshow

Turn off the lights. Half fill the kettle. Have a shower instead of a bath. Whatever you do in your daily life, you probably don't feel like you're making all that much of a difference in the fight against the relentless march of climate change – which is where the OPAL Climate Survey steps in.

Ashes to ashes: How the Tamboro volcano eruption wreaked havoc on Europe's weather

Six months after the end of the Eyjafjallajökull volcano eruption, we look back almost 200 years to examine how ash from the biggest volcanic eruption in recorded history played havoc with the weather, with utterly devastating effects

This an extract from the launch issue of theWeather magazine. Join theWeather Club to read the whole article. The Winter issue of theWeather is out now.