Inversion of Multi-Station Schumann Resonance Background Records for Global Lightning Activity in Absolute Units

Tuesday, 16 December 2014: 5:45 PM
Earle R Williams1, Vadim C Mushtak1, Anirban Guha2, Robert A Boldi3, Jozsef Bor4, Tamas Nagy4, Gabriella Satori4, Ashwini Kumar Sinha5, Rahul Rawat5, Yasuhide Hobara6, Mitsuteru Sato7, Yukihiro Takahashi7, Colin Gregory Price8, Mariusz Neska9, Koloskov Alexander10, Yuri Yampolski10, Robert C Moore11, Michael F. Mitchell11 and Antony C Fraser-Smith12, (1)Massachusetts Institute of Technology, Cambridge, MA, United States, (2)Tripura University, Physics, Agartala, India, (3)Zayed University, Dubai, United Arab Emirates, (4)Research Center for Astronomy and Earth Sciences, Sopron, Hungary, (5)Indian Institute of Geomagnetism, UAS, Navi Mumbai, India, (6)The Univ. of Electro-Comms, Chofu-City, Tokyo, Japan, (7)Hokkaido University, Sapporo, Japan, (8)Tel Aviv University, Tel Aviv, Israel, (9)Institute of Geophysics Polish Academy of Sciences, Warsaw, Poland, (10)Institute of Radio Astronomy National Academy of Sciences of Ukraine, Kharkov, Ukraine, (11)University Florida, Gainesville, FL, United States, (12)Stanford University, Stanford, CA, United States
Every lightning flash contributes energy to the TEM mode of the natural global waveguide that contains the Earth’s Schumann resonances. The modest attenuation at ELF (0.1 dB/Mm) allows for the continuous monitoring of the global lightning with a small number of receiving stations worldwide. In this study, nine ELF receiving sites (in Antarctica (3 sites), Hungary, India, Japan, Poland, Spitsbergen and USA) are used to provide power spectra at 12-minute intervals in two absolutely calibrated magnetic fields and occasionally, one electric field, with up to five resonance modes each. The observables are the extracted modal parameters (peak intensity, peak frequency and Q-factor) for each spectrum. The unknown quantities are the geographical locations of three continental lightning ‘chimneys’ and their lightning source strengths in absolute units (C2 km2/sec). The unknowns are calculated from the observables by the iterative inversion of an evolving ‘sensitivity matrix’ whose elements are the partial derivatives of each observable for all receiving sites with respect to each unknown quantity. The propagation model includes the important day-night asymmetry of the natural waveguide. To overcome the problem of multiple minima (common in inversion problems of this kind), location information from the World Wide Lightning Location Network has been used to make initial guess solutions based on centroids of stroke locations in each chimney. Results for five consecutive days in 2009 (Jan 7-11) show UT variations with the African chimney dominating on four of five days, and America dominating on the fifth day. The amplitude variations in absolute source strength exceed that of the ‘Carnegie curve’ of the DC global circuit by roughly twofold. Day-to-day variations in chimney source strength are of the order of tens of percent. Examination of forward calculations performed with the global inversion solution often show good agreement with the observed diurnal variations at individual receiving sites, lending confidence to the 3-chimney model for global lightning.