More lightning curiosities
From Norway's
Birkeland Centre for Space Science:
Unique observations of optical lightning and terrestrial gamma flash
In a study by Nikolai �stgaard and Thomas Gjesteland at the Birkeland Centre for Space Science (BCSS), University of Bergen, together with researchers from USA and South Africa, the first simultaneous detection of a terrestrial gamma flash (TGF) and the optical signal from lightning is presented. This result may be a breakthrough in the understanding of the enigmatic terrestrial gamma flash that was discovered in the 90s. The study has recently been accepted for publication in Geophysical Research Letters.
"Our study shows that the TGF was produced deep in the thundercloud at the initial stage of an intracloud (IC) lightning before the leader reached the cloud top and extended horizontally" says professor Nikolai �stgaard, leader of BCSS. "A strong radio pulse was produced by the TGF itself. This is the first time the sequence of radio pulses, TGF and optical emissions have been identified" �stgaard adds.
By fortuitous coincidence two independent satellites passed less than 300 km from a thunderstorm that developed over Lake Maracaibo in Venezuala, October 27, 2006 and produced a TGF lasting only 70 ms . This is a region known for its powerful and frequent lightning. The RHESSI satellite detected a TGF that lasted only 70 ms and TRMM recorded optical emissions as well as the cloud temperature.
"Together with two independent measurements of radio emissions we have an unprecedented coverage of the event" says scientist Thomas Gjesteland. Both timing and location show clearly that the radio signals, the TGF and optical lightning came from the same IC discharge that lasted for about 300 ms.
It was recently suggested that TGFs could be dark lightning, that is, the gammas are produced by relativistic electrons that also make a strong electric current that again produces a strong radio pulse, and that this can occur without any following optical lightning to discharge the cloud. "Our results confirm that the TGF produces a strong radio signal, but the �dark lightning�(TGF) is followed by a �bright lightning� and indicates that both phenomena are intrinsic processes in the lightning discharge" says Nikolai �stgaard.
This comes on the heels of the Florida Institute of Technology's comments on
Dark Lightning.
For something as simple as an electric spark, there is a lot we do not know. Fun time to be alive!
Kristian Olaf Birkeland was a
fascinating character -- the first space scientist. He was the first person to figure out the causation of the Aurora. He invented the
electromagnetic cannon (AKA coil gun).
More
here and
here.
Posted by DaveH at April 26, 2013 12:29 PM