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World Thunderstorm "Map" Key To Assessing Climate Change
10th February 2015 | reportingclimatescience.com
The Doomsday Clock, which measures the likelihood of global catastrophe, last month ticked a minute closer to "midnight" — the apocalypse. The symbolic clock was set to 11:57 by a board of atomic scientists featuring 17 Nobel Laureates, who warned that the planet, beset by climate change and nuclear proliferation, faced extraordinary and undeniable threats to its continued existence.

New research by Prof. Colin Price of Tel Aviv University's Department of Geosciences and published in Environmental Research Letters will likely be crucial to measuring the impact of climate change on thunderstorms - one of the weather occurrences most problematic for human life on the planet. The varying frequency and intensity of thunderstorms have direct repercussions for the public, agriculture, and industry. "To date, satellites have only provided snapshots of thunderstorm incidence," said Prof. Price, whose new map of thunderstorms around the world is the first of its kind. "We want to use our algorithm to determine how climate change will affect the frequency and intensity of thunderstorms. According to climate change predictions, every one percent rise in global temperature will lead to a 10 percent increase in thunderstorm activity. This means that we could see 25 percent more lightning by the end of the century."

Keeping track of lightning

To draft a global thunderstorm map, Prof. Price and TAU graduate student Keren Mezuman used a vast global lightning network of 70 weather stations capable of detecting radio waves produced by lightning - the main feature of a thunderstorm - from thousands of miles away. The World Wide Lightning Location Network (http://wwlln.net) is run by atmospheric scientists at universities and research institutes around the world. The TAU team harnessed this ground-based system to cluster individual lightning flashes into "thunderstorm cells." Every hour the exact GPS time of every detected lightning pulse was registered. Prof. Price and his colleagues then calculated the difference in arrival times of signals, using data from four to five different stations to locate individual lightning strokes anywhere on the globe. Finally, the researchers grouped the detected flashes into clusters of thunderstorm cells. The WWLLN station in Israel has the ability to detect lightning as far away as central Africa.

Climate change and thunderstorms

"When we clustered the lighting strikes into storm cells, we found that there were around 1,000 thunderstorms active at any time somewhere on the globe," said Prof. Price. The researchers, pooling seven years of data analysis, found that every day lightning activity on earth peaked at 1900 GMT, with low activity at 0300 GMT every day. While previous studies had estimated that 90 percent of lightning flashes occurred over land areas, the TAU team found that only 50 percent of the thunderstorms cells existed over land areas, implying that land storms have much more lightning than ocean storms. "How lightning will be distributed in storms, and how the number and intensity of storms will change in the future, are questions we are working on answering," Prof. Price said.

Abstract

Estimates of global thunderstorm activity have been made predominately by direct measurements of lightning discharges around the globe, either by optical measurements from satellites, or using ground-based radio antennas. In this paper we propose a new methodology in which thunderstorm clusters are constructed based on the lightning strokes detected by the World Wide Lightning Location Network (WWLLN) in the very low frequency range. We find that even with low lightning detection efficiency on a global scale, the spatial and temporal distribution of global thunderstorm cells is well reproduced. This is validated by comparing the global diurnal variations of the thunderstorm cells, and the currents produced by these storms, with the well-known Carnegie Curve, which represents the mean diurnal variability of the global atmospheric electric circuit, driven by thunderstorm activity. While the Carnegie Curve agrees well with our diurnal thunderstorm cluster variations, there is little agreement between the Carnegie Curve and the diurnal variation in the number of lightning strokes detected by the WWLLN. When multiplying the number of clusters we detect by the mean thunderstorm conduction current for land and ocean thunderstorms (Mach et al 2011 J. Geophys. Res. 116 D05201) we get a total average current of about 760 A. Our results show that thunderstorms alone explain more than 90% in the variability of the global electric circuit. However, while it has been previously shown that 90% of the global lightning occurs over continental landmasses, we show that around 50% of the thunderstorms are over the oceans, and from 00-09UTC there are more thunderstorm cells globally over the oceans than over the continents. Since the detection efficiency of the WWLLN system has increased over time, we estimate that the lower bound of the mean number of global thunderstorm cells in 2012 was around 1050 per hour, varying from around 840 at 03UTC to 1150 storms at 19UTC.

Citation

On the spatial and temporal distribution of global thunderstorm cells by Keren Mezuman, Colin Price and Eli Galanti published in Environmental Research Letters Volume 9 Number 12, Keren Mezuman et al 2014 Environ. Res. Lett. 9 124023 doi:10.1088/1748-9326/9/12/124023 Read the abstract and get the paper here.

Source

Tel Aviv University news release here.

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