![]() ![]() Despite its lethal nature, the exact cause and nature of the killer fog has largely remained a mystery. Researchers now estimate that the total death count was likely more than 12,000 people, as well as thousands of animals. By the time the dense fog cover lifted, more than 150,000 people had been hospitalized and at least 4,000 people had died. Strong winds- these can cause turbulence within the fog and disperse the water droplets.London may be known for its drizzly weather, but in 1952 the city’s quintessential fog cover turned deadly, and no one knew exactly why - until now.įor five days in December 1952, a fog that contained pollutants enveloped all of London. ![]() ![]() This is often called ‘burning off the fog’.Ģ. This effect spreads up through the fog and the fog dissipates. Morning sunrise- the sun’s rays heat the ground beneath the fog and the water droplets evaporate to become water vapour. The photo shown was taken in the Canadian province of Quebec.ġ. Because of the convection, the water appears to ‘steam’. This convection causes the mixed air to rise a metre or more, thus enhancing the process of fog formation. However, convection also occurs, because the water is so much warmer than the overlying air. What is the science behind this type of fog?Ĭondensation results mainly from the cold air mixing with the air that is in contact with the water surface. Over sea water, steam fog is called sea smoke. This kind of fog forms when cold air flows over water that is more than 9° or 10☌ warmer than the air. The fog then dissipates (disappears), often very quickly. Most of the rays are actually reflected from the top of the fog but some reach the surface, otherwise it would not be daylight in the fog! The ground is gradually heated until the dew-point temperature is exceeded. During the day, the sun’s rays heat the ground beneath the fog. This type of fog does not form over the sea because the temperature of the sea’s surface stays much the same day and night. If there is a very gentle breeze, the tiny water droplets are stirred upwards to form a shallow layer of radiation fog, as in the picture of fog at Cardiff shown. If there is no wind, droplets of dew form on, for example, grass. If the air in contact with a surface is cooled to its dew-point temperature, small water droplets form (condensation). When the sky is clear at night, land surfaces radiate heat to space and therefore cool.Sea and lake surfaces do not, however, cool by more than a small amount overnight (much less than 1☌). What is the science behind this type of fog? ![]() Radiation fog is particularly common in autumn and winter in the UK. It commonly forms in the dips with sources of moisture such as streams and rivers. In mid-winter, however, particularly in latitudes where the sun is low in the sky (e.g. This type of fog usually forms at night and dissipates (disappears) during the day. This kind of fog forms when the sky is clear and the wind speeds are low (1-5 kilometres per hour). In fog the distance you can see (known as visibility) is less than 1km, but in mist the visibility distance can be 1km-2km. The density of fog and mist are different. Fogs seen over the sea are different to those found in valley lowland areas and over mountains for example.ĭownload fog fact file for printing, or have a look at our Experiments and Demonstrations page for experiments which demonstrate how clouds can look dark from below but white from above, or how to make a hygrometer to measure air humidity.For a deeper understanding of how and where clouds form, have a look at our exercise using height/ temperature graphs to investigate atmospheric stability, lapse rates and cloud formation with a worksheet for students with an introductory PowerPoint or this paper. It can cover vast areas and comes in a variety of types, just like clouds do. ![]()
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