AbstractThe electromagnetic field measurement at the band-pass of extremely low frequency (ELF) is the only way to monitor the long-term lightning activities globally. In addition to the single event analysis, huge amount data collected by this continuous recording system become a challenge to pick up and process the transients’ signal buried in systemmatically. In this work, we develop an efficient, adaptive and real-time algorithm to extract and process the transient events from the raw sferic data and to construct a transient event database with their electromagnetic parameters for further analysis.
The data recorded by the NCKU Lulin ELF station between March 2010 and February 2011 is used in this work. After the ELF transient database is construced, we find that the transient occurrence rate recorded by Lulin station shows a strong association with the features of local, not global, climate. This result also hints that the detection efficiency of Lulin station is distance dependent, and it is also verified by direct comparison with the WWLLN database.
The polarity of the TLEs are dertermined by analyzing coincident events with the ISUAL TLE database. We notice that there is a highly correlation between the sprite and the +CG as literatures reported, and 4 –CG sprites out of 107 are recognized respectively. This ratio of 4.4% is greater than the previous result of less than 1% obtained by ground observations in the past years. The ratio of –CG and +CG elves derived in this work is approximately 45:55, but the ratio of –CG and +CG of lightning is about 1:10 generally. This interesting result implies that the average intensity of +CG is probably greater than –CG owing to elves are triggered by the lightning with high peak current typically. We also find that 2/3 halos are associated with –CG strokes. Therefore, it might exist a dependency between halos and –CG lightnings.
|Date of Award||2012|
|Supervisor||Bing-Chih Chen (Supervisor)|
- ELF electromagnetic field measurement
- Transient Luminous Events(TLEs)
- Imager of Sprite and Upper Atmospheric Lightning(ISUAL)