Estimation of Global Lightning Activity and Observations of Atmospheric Electric Field
Abstract: Variations in the global atmospheric electric circuit are investigated using a wide range of globally spaced instruments observing VLF (∼10 kHz) waves, ELF (∼300 Hz) waves, Schumann resonances (4–60 Hz), and the atmospheric fair weather electric field. For the ELF/VLF observations, propagation effects are accounted for in a novel approach using established monthly averages of lightning location provided by the Lightning Image Sensor (LIS) and applying known frequency specific attenuation parameters for daytime/nighttime ELF/VLF propagation. Schumann resonances are analyzed using decomposition into propagating and standing waves in the Earth-ionosphere waveguide. Derived lightning activity is compared to existing global lightning detection networks and fair weather field observations. The results suggest that characteristics of lightning discharges vary by region and may have diverse effects upon the ionospheric potential.
Summary (2 min read)
- The relationship between atmospheric currents and ionospheric potentials on a planetary scale is known as the global electric circuit.
- Many questions remain and even fundamental assertions are often contended.
- It is clear that the link between the DC phenomena of the equipotential global ionosphere and the AC phenomena of lightning discharges and their related effects are still poorly understood.
- Thus, although both LIS and OTD instruments provide extremely valuable long term averages of lightning frequency and distribution, they are unable to quantify lightning activity at any given instant.
2.1 ELF/VLF measurements and analysis
- Stanford University operates a network of global receiving sites that record data in the band from 300 Hz to 47 kHz using aircore magnetic field antennas.
- Cohen et al. (2009) provide a description of the receiver hardware.
2.3 Atmospheric electric field observations
- The fair weather atmospheric electric field (vertical electric field measured at the ground) Figure 4a, adapted from Fig. 5 of Kubicki et al. (2007), shows the normalized daily variation of electric field over select summer and winter days during the years 1965-2000.
- Since the conductivity and electric field exhibit an inverse relationship only for the late evening and night hours, diurnal observations of Ez at SW can be interpreted as measures of global ionospheric potential (Kubicki et al. 2007).
- For lightning detection networks, of which WWLLN is an example, the observable is the flash rate scaled by the detection efficiency α, which will depend on the location of receiving stations and the specifics of the algorithm employed.
- The high peak currents of lightning associated with the oceans and the maritime continent are expected predominantly to influence VLF observations, while the high charge moment strikes of the Congo Basin can be expected to be observed in Schumann resonance measurements.
3. OBSERVATIONS AND ANALYSIS
- Seven days each in the months of March and May 2007.the authors.
- During this time, ELF/VLF data were available from at least 3 sites and SR data were obtained for 31 March Brought to you by | Koc University Authenticated Download Date | 5/5/17 9:33 AM.
3.1 Data from 31 March and 20 May
- The days 31 March and 20 May were those for which the most measurements were available.
- The SR derived lightning activity for both of these days, as shown in Fig. 3, is found to exhibit a central peak between 10:00-18:00 UT, which is classically associated with lightning activity in the African sector as established by thunder days (Whipple and Scrase 1936).
- It is worth mentioning a recent study by Nieckarz et al. (2009) who examined two years of fair weather Ez data from SW with SR data using the identical receiving station (HY) and technique as the authors use here.
- An examination of data from the WWLLN network for 20 May 2007 corroborates this view.
- It is clear that increasing the observation station requirement causes the number of geolocated flashes attributed to the African sector to decrease more substantially than for the other two regions and thereby changes the shape of the diurnal world total flash detection curve.
3.4 Multi-day averages
- Figure 13 shows averages of ELF/VLF and Ez for the seven days in March and seven days in May separated by month.
- The ELF/VLF data were computed using the three sites, AD, CH and PA, which recorded data on all days of the study.
- The averaged ELF and VLF data for March and the VLF data for May exhibit resemblance to the classic Carnegie curve (Whipple and Brought to you by | Koc University Authenticated Download Date | 5/5/17 9:33 AM.
4. SUMMARY AND DISCUSSION
- The authors have analyzed widely spaced ELF, VLF, SR and Ez for select days in March and May 2007.
- A theme of their work has been the integration of different globally spaced measurements and investigating the regional differ- Brought to you by | Koc University Authenticated Download Date | 5/5/17 9:33 AM.
Did you find this useful? Give us your feedback
Cites background from "Estimation of Global Lightning Acti..."
...An ELF station with a single antenna enables measuring electrical lightning activity in the storm centers at a broad range of distances, starting at 0.15 Mm [Nieckarz et al., 2009b; Gołkowski et al., 2011]....
"Estimation of Global Lightning Acti..." refers methods in this paper
...On global scales, the value of α for WWLLN does not exceed 5% (of cloud to ground lightning) (Rodger et al. 2005)....
...Figure 6 shows the number of geolocated flashes from the WWLLN network for 20 May 2007 for the world (top panels) and also for global regions divided by longitude to represent roughly the three major lightning centers of Africa, Asia (Maritime Continent), and the Americas....
...For lightning detection networks, of which WWLLN is an example, the observable is the flash rate scaled by the detection efficiency α, which will depend on the location of receiving stations and the specifics of the algorithm employed....
...However, neither the WWLLN network on this day nor on other days examined in May 2007 does exhibit the dominance of the African sector for flash rates as has been reported elsewhere (Boccipio et al. 2000)....
...Since WWLLN receivers monitor the VLF band (6-22 kHz), the network is most sensitive to discharges with high peak currents....
"Estimation of Global Lightning Acti..." refers background in this paper
...Elves are a product of the electromagnetic pulse (EMP) emitted by lightning strokes (Fukunishi et al. 1996) making them an indicator of high peak current of lightning discharges....
...Acta Geophysica vol. 59, no. 1, Feb. 2011, pp. 183-204 DOI: 10.2478/s11600-010-0035-4 ________________________________________________ © 2010 Institute of Geophysics, Polish Academy of Sciences...
Related Papers (5)
Frequently Asked Questions (1)
Q1. What are the contributions in "Estimation of global lightning activity and observations of atmospheric electric field" ?
For the ELF/VLF observations, propagation effects are accounted for in a novel approach using established monthly averages of lightning location provided by the Lightning Image Sensor ( LIS ) and applying known frequency specific attenuation parameters for daytime/nighttime ELF/VLF propagation. The results suggest that characteristics of lightning discharges vary by region and may have diverse effects upon the ionospheric potential.