The figure, unveiled at the European Geosciences Union meeting in Vienna, is substantially lower than numbers that have been used for nearly a century. The new research uses a global network of monitoring stations that detect the electromagnetic pulses produced by major bolts of lightning. It confirms that thunderstorms are mainly a tropical phenomenon – and the Congo basin is the global hotspot. Thunderstorms also track the passage of sunlight across the world, with sunny conditions producing greater convection in the air.
“The monitoring stations might miss some bolts of lightning, but we think we’re getting the big ones – and that’s enough to tell you where the thunderstorms are,” said Colin Price, head of the Geophysics and Planetary Sciences department at Tel Aviv University in Israel.”And so with this global network we’re able to improve on numbers that have been in standard use since the 1920s.“
The first attempt to estimate thunderstorm numbers is thought to have been made by CEP Brooks in 1925. At that time, it was customary for weather stations to note days when thunderstorms occurred nearby. Collecting records where he could, the British climatologist calculated there were around 1,800 per hour on average across the world.
But his research suffered from incomplete data and mistaken assumptions – including that storms were equally distributed over land and sea, whereas the vast majority occur over land. In the 1950s, OH Gish and GR Wait flew over the top of 21 thunderstorms in the US in aeroplanes carrying equipment capable of measuring voltages and currents in the air. Extending their readings to the rest of the world, they came up with a global figure of 2,000-3,600 per year.
More recently, satellites have been deployed – but they do not see the whole world. The new research uses a completely different technique, with more than 40 stations around the world geared up to detect electromagnetic pulses produced by strong lightning bolts.
Triangulating from groups of stations enables the World Wide Lightning Location Network (wwlln.net) to pinpoint flashes. When they are clustered, a computer algorithm is deployed to assign flashes to their separate parent storms. Analysing this data for September 2010 produced the average hourly figure of 760.
Each continent shows peaks during its daytime – and globally, the peak time is around noon GMT. Thunderstorms cluster in the centre of continents in the tropics, with the Congo basin standing out. The network is looking to add new observation points to improve results, and recently initiated a programme to detect explosive volcanic eruptions via the lightning flashes that occur in the ascending plumes of hot ash. (BBC)
A thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth’s atmosphere known as thunder. The meteorologically assigned cloud type associated with the thunderstorm is the cumulonimbus. Thunderstorms are usually accompanied by strong winds, heavy rain and sometimes snow, sleet, hail, or no precipitation at all. Those which cause hail to fall are known as hailstorms. Thunderstorms may line up in a series or rainband, known as a squall line. Strong or severe thunderstorms may rotate, known as supercells. While most thunderstorms move with the mean wind flow through the layer of the troposphere that they occupy, vertical wind shear causes a deviation in their course at a right angle to the wind shear direction.
Thunderstorms result from the rapid upward movement of warm, moist air. They can occur inside warm, moist air masses and at fronts. As the warm, moist air moves upward, its cools, condenses, and forms cumulonimbus clouds that can reach heights of over 20 km. As the rising air reaches its dew point, water droplets and ice form and begin falling the long distance through the clouds towards the Earth’s surface. As the droplets fall, they collide with other droplets and become larger. The falling droplets create a downdraft of air that spreads out at the Earth’s surface and causes strong winds associated with thunderstorms.
Thunderstorms can generally form and develop in any geographic location, perhaps most frequently within areas located at mid-latitude when warm moist air collides with cooler air. Thunderstorms are responsible for the development and formation of many severe weather phenomena. Thunderstorms, and the phenomena that occur along with them, pose great hazards to populations and landscapes. Damage that results from thunderstorms is mainly inflicted by downburst winds, large hailstones, and flash flooding caused by heavy precipitation. Stronger thunderstorm cells are capable of producing tornadoes and waterspouts.
There are four types of thunderstorms: single-cell, multicell cluster, multicell lines, and supercells. Supercell thunderstorms are the strongest and the most associated with severe weather phenomena. Mesoscale convective systems formed by favorable vertical wind shear within the tropics and subtropics are responsible for the development of hurricanes. Dry thunderstorms, with no precipitation, can cause the outbreak of wildfires with the heat generated from the cloud-to-ground lightning that accompanies them. Several methods are used to study thunderstorms, such as weather radar, weather stations, and video photography. Past civilizations held various myths concerning thunderstorms and their development as late as the Eighteenth Century. Other than within the Earth’s atmosphere, thunderstorms have also been observed on Jupiter and Venus.
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