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 In Focus

A triggered lightning

Published 2001-01-26

Thanks to a donation the lightning research program at Uppsala University was started in 1930 and since then it has been an active research area at this university. In addition to research work related to lightning, the research group working on this subject conducts studies related to all aspects of electrical discharges in the atmosphere. Indeed, this is the only university in Scandinavia where students can get educated in this subject.

In the United States there are several research groups located at different universities working on lightning research and the most successful research group on this subject is located at University of Florida in Gainesville. The lightning research program at University of Florida, Gainesville was initiated in the beginning of 1970’s and since then it has grown to be one of the most successful of its kind in the United States.

The groups at Uppsala and Florida were acquainted with each other for a long time but there were no collaborative studies conducted between them. In the beginning of 1990’s the Florida scientists created an international facility for lightning research and testing. This is a facility where lightning is triggered, and allowed to strike at objects of choice, by shooting rockets trailing a metal wire towards cloud.

The problem with lightning research is that, due to the random nature of lightning strikes, it is difficult to locate the lightning flashes and place the recording instruments at the correct place. These scientists have solved this problem by triggering lightning to a place that was decided beforehand. There is no possibility for a research group in Sweden to conduct such experiments both due to the financial difficulties and the scarcity of thunderstorms. Since 1990 many research groups from all over the world had collaborated with the Florida research group performing collaborative experiments at the International Center for Lightning Research and Testing (ICLRT).

In the beginning of 2001 the lightning research group at Uppsala started a research program on NOx production from lightning flashes. Initially, the research work was conducted using high voltage laboratory facilities at Uppsala University but soon it was realized that there was a strong need to conduct field experiments with real lightning.

During one of the international conference gatherings Prof. Vernon Cooray had a discussion with Prof. Vlad Rakov from University of Florida on the possibility of a joint cooperation on this topic. These discussions led to a submission of an application to STINT for funding for a international collaboration between Uppsala University and University of Florida. The application was granted and the collaboration was initiated in 2005.

After the initiation of the program Uppsala scientists conducted field measurements at ICLRT three times. Each time, the Uppsala University group consists of one student, one professor and one senior scientist. In addition one planning visit was conducted by Prof. Vernon Cooray. During the same time Prof. Rakov had visited Uppsala three times and each time he had given a seminar on lightning protection to scientists and engineers.

Thanks to this cooperation Uppsala scientists managed to solve one of the most important problems in atmospheric science. The problem was the following. As the public wait eagerly for the judgment of the scientific society on the devastating effects, such as the depletion of the Ozone layer and the global increase in temperature, caused by the man made modifications of the atmosphere and stratosphere, atmospheric modelers lean heavily in the complex computer simulations to understand the coupling between the human activities and the Earth’s atmosphere. In order to get reliable results such computer programs should take into account the concentration of various gases, such as Ozone, Nitrogen Oxides and Carbon Dioxide, and other chemicals introduced into the atmosphere both by natural and man made activities. One of the important sources of Ozone and Nitrogen Oxides in the atmosphere is the lightning flash and the other electrical activities that are associated with thunderstorms. Unfortunately, the exact amounts of these gases produced in the atmosphere by these electrical activities are not known.

Many researchers have made indirect estimations of the amount of nitrogen oxide generated by lightning flashes but no one has managed up to now to make a direct measurement of the nitrogen oxide production by lightning flashes. The problem is the difficulty to confine a part of the lightning channel into a closed chamber so that one can make a direct measurement of the nitrogen oxides generated by lightning flashes. However, working together with University of Florida researchers they forced the lightning flash to pass through a cylindrical air tight chamber and trapped the nitrogen oxides produced by the section of the lightning channel that pass through the chamber. The results of the study were published in Geophysical Research Letters and it was high lighted in the prestigious magazine ‘Nature’.

During this time, a research program was initiated between University of Florida and Florida Institute of Technology at Melbourne to study the X-ray production from lightning flashes. The scientists found strong bursts of X-rays emanating from lightning flashes but the mechanism by which X-rays was generated remained unknown. After seeing the high voltage facility at Uppsala University, Prof. Vald Rakov and Prof. Martin Uman at University of Florida suggested a cooperation between University of Florida, Florida Institute of Technology and Uppsala University to study the X-ray production from electrical discharges. Based on this cooperation two professors from Florida Tech. and one student from the University of Florida visited Uppsala to conduct measurements of X-rays from laboratory sparks. This work was successfully conducted and the results are now to be published.

During this cooperation it is realized that X-ray measurements should also be conducted from natural lightning together with electromagnetic field measurements and a collaborative research program was developed to use Marine laboratory of Florida Tech. located at the Atlantic coast of Melbourne to measure simultaneously the X-rays and electromagnetic fields generated by natural lightning. A group of scientists (one professor, two senior scientists and one student from Uppsala) spend one month at this facility studying natural lightning electromagnetic fields and lightning. This field measurement was successfully completed and plans are underway to conduct the field measurements with improved facilities in 2009. In addition to this Prof. Cooray visited Florida Tech. in 2008 to make arrangements for the 2009 campaign.

Thanks to our association with the Florida research group we have established collaborations with both University of Arizona (Prof. Philip Krider and Prof. Ken Cummings) and MIT (Prof. Earle Williams). Both groups are working on lightning related problems and research work is underway to perform common experiments together with these research groups. From the educational side in addition to the seminars conducted by Prof. Vlad Rakov, in 2008 in connection with a conference held in Uppsala, a lightning protection course was organized where Prof. Vlad Rakov and ten more world renowned lightning protection experts participated as teachers. Thirty five students from many countries attended the course. Several more visits are being planned for 2010: One visit to MIT, one visit to University of Arizona and the other to Florida Gainesville and Florida Tech.

Vernon Cooray

Division for Electricity and Lightning Research

Uppsala University

Senast uppdaterad: 08-12-22 13:57

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