Electric Skies - Thunderstorms and Lightning

The analysis of the electromagnetic signal for individual lightnings can also be used to explore the properties of the ionosphere which is the upper boundary of the Earth-ionosphere waveguide. Recent comparisons of measurements between Hungary (by our collaborator Dr. Gabriella Satori) have shown small but systematic increases in the Schumann resonance frequencies at both stations which can be attributed to the changes in ionization in the upper D region of the ionosphere on the 11 year solar cycle. We are presently near the maximum of this cycle, and so the resonant frequencies are also near their peak values.

Studies on severe weather in Florida are also underway with MIT Lincoln Laboratory and NASA Marshall Space Flight Center. The main interest at present is the behavior of total lightning flash rate that may signal the occurrence of a tornado. We have found already that strong upsurges in total flash rate, dominated by intracloud lightning, tend to precede all forms of severe weather on the ground (hail, wind, tornadoes) by 5-15 minutes. One challenge at present is to identify features that may distinguish a tornado from another form of severe weather.

FS: How do you measure the volts in lightning?

EW: Measuring the voltage of lightning itself is probably a near impossible task, because in general we are unable to predict where a lightning will occur to make the appropriate measurement. One can however estimate the voltage difference developed in a thundercloud before it produces lightning by measuring the vertical variation of electric field from the ground to the center of electric charge in the storm with balloon-borne measuring equipment. The integral of this vector electric field is the total voltage available to drive the lightning. The values one obtains are in the range of ten to several hundred megavolts.

FS: Can we make use of lightning in terms of power?

EW: If lightning occurred in one place in a predictable manner day in and day out, the harnessing of its energy might be seriously considered. Such is not the case. Lightning does strike twice in the same place, but extremely infrequently. To harness the energy, the lightning must strike an electrode connected to a very robust bank of electrical capacitors. One captured strike would deliver at most 10^8 joules. This would provide enough energy to power one electric hairdryer for about ten hours. So clearly, a large number of captured flashes would be needed to supply the energy needs of just a single household.

FS: What is the ‘global circuit’ and what have you learnt from this?