Science Lesson

Atlantic Meridional Overturning Circulation

Generalised model of thermohaline circulation, adapted from NASA.

The Atlantic Meridional Overturning Circulation (AMOC) is a system of currents in the Atlantic Ocean, including the Gulf Stream that circulates a vast amount of heat from the tropics towards the North Pole disseminating the cold, saline, dense waters towards the Tropics and even further south towards the South Pole. The figure above captures that in a generalised worldwide model of thermohaline (thermo- referring to temperature and –haline referring to salt content) circulation.

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.

Aurora Borealis

The Aurora Borealis, also known as the Northern Lights, and Aurora Australis (Southern Lights) in the Southern Hemisphere, are a spectacular natural phenomenon. They light up a night sky, dancing around in fantastic colours. There are few places in the Northern Hemisphere where you can see them, but they can be elusive if you are really unlucky. Here we explain the science behind the Northern Lights and share few tips on how to maximise your chances of witnessing this wonderful spectacle. 

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.


Jetstreams are discontinuous, narrow currents of strong winds in the upper atmosphere. The polar jetstream is of special interest to meteorologists because of its association with the regions where warm and cold air masses meet, and weather systems develop bringing wind and rain.

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%.

Heat Stress

Heat stress occurs when the body’s means of controlling its internal temperature starts to fail. Some cultures have adapted to avoid heat stress – the Mediterranean siesta signals a work break during the hottest part of the day, or in the tropics where work begins earlier, ends later and is carried out at a slower pace. Heat stress is not something we experience very often in the UK, especially after recent summers, but if we do experience a heatwave – a prolonged spell when daytime and overnight temperatures are elevated and humidity is high - we need to be prepared.