Weather Watch

Nacreous clouds

Image: Nacreous clouds over Aberdeen on 29th January  
Credit: Stephane Gentile, Associate Fellow of the Royal Meteorological Society

Several rare sightings of nacreous clouds have been reported over the last few days, delighting cloudspotters, with photographs of the clouds coming from England and Scotland.

Dark Lightning

This 'dark opponent' discharges from storm clouds and flings antimatter into space. Astrophysicists and meteorologists are now trying to understand what they have termed ‘dark lightning’. 

Lightning occurs due to charge separation in a cloud. When negatively charged electrons build up at the base of a thundercloud, anything it passes over becomes   positively charged. If the cloud passes over a tall object, like a tall building or tree, these electrons jump, creating the ‘pitchfork’ of light you see streaking across the sky.

Catatumbo ‘Everlasting’ Lightning

It occurs over the mouth of the Catatumbo River where it empties into Lake Maracaibo in Venuzuela, South America. Each year, over 1.2 million bolts of lightning are confined to the mouth of the Catatumbo River - the single highest concentration of lightning in the world.

The Catatumbo lightning, whilst not rare or unusual, is a  remarkable feature in that it persists in the same place night after night. Indeed, the reliability of the storms means that they have historically been used as a maritime navigational aid.

Measuring Wind Speed : What is anemometer?

Wind is simply movement of air, but sometimes this movement can be pretty fast! Those of us in the South of England have recent memories of the St Jude’s Day storm on 28 October, and the disruption caused by gusts of up to 99mph. As well as meteorologists, lots of other people are interested in how fast the wind is blowing, ranging from sportsmen such as parachutists and sailors, to those concerned with hazardous winds, such as air traffic controllers and crane operators. But how do we measure its speed?

Winds of Change

Image: Some of the local wind names and their location. 

In many areas of the world, regional conditions give rise to winds that have been identified by the locals as having a special effect or occurring during a particular season. Quite often these winds are given a name by local inhabitants.

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.