Transcript GlobalElectricCircuit

Global Lightning Activity and the
Atmospheric Electric Field
Prepared by Marek Gołkowski and Morris Cohen
Stanford University
and
Marek Kubicki
Institute of Geophysics (IGF)
Polish Academy of Sciences
IHY Workshop on
Advancing VLF through the Global AWESOME Network
Outline
 Global Atmospheric Circuit
 Stanford-IGF Correlation Study
 Atmospheric Electric Field Measurements
(Polish Academy of Sciences)
 Global Lightning Activity Using VLF
(Stanford AWESOME VLF Network)
 Results for March and May 2007
 Summary
 References
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Global Electric Circuit
 Global thunderstorms charge ionosphere and current returns to ground through fair weather
conduction
 Fair weather electric field 100-300 V/m measured on the surface
 Circuit looks simple but shows complex variations with latitude, longitude, magnetopheric &
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ionospheric processes, also pollution and climate change
Global Effects: Carnegie Curve
 The Carnegie Curve is
daily variation of fair
weather electric field with
universal time (UT).
 Global Lightning Activity
and the Carnegie Curve
show general correlation
Lightning
Activity
Source:
Whipple and Scrase, 1936
 However, several
differences remain, most
notably, Carnegie Curve
does not show a maxima
for strong lightning
activity in Africa/Europe
 Exact role of lightning and
other variables still not
well understood need
for more global
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measurements
America vs. Africa
Two hypothesis for the American
dominance over Africa in the
Carnegie Curve
1) Current control by position of magnetic dip equator [Kartalev et al.,
2006]
2) Electrified shower curves in South America dominate over Africa
[Rycroft et al., 2007 and others]
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Lightning activity assessment
 Atmospheric electric field
 Pros – global measurement
 Cons – affected by fair weather conditions
 ELF/VLF measurements
 Pros – can be measured anywhere, anytime
 Cons – affected by ELF/VLF propagation
 Measures mostly lightning stroke activity
Stanford - IGF Joint Study
Goal:
 Investigate role of global lightning activity on fair weather electric field
Approach:
 Lightning releases large amount of energy into VLF band that propagates
for long distances
 Use VLF data to estimate global lightnting activity
 Fair weather electric field (Ez) can be measured with standard scientific
equipment
 Capture seasonal variation by looking at 2 months: March 2007 and May
2007
VLF Receiver
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E-Field Collector
Atmospheric Electric Field
Measurements
Hornsund - Polish Polar Station
Świder Observatory
HO
SW
 Atmospheric electricity measurements are made with standard radioactive collectors
 The Polish Academy of Sciences operates a mid-latitude collector in Świder, Poland
and a polar latitude collector at the Polish Polar Station in Hornsund on Spitsbergen
 Measurements were made in “Fair Weather” conditions including low aerosol 8content
confirmed from other instruments
Fair Weather Conditions
 Fair Weather Conditions are defined to involve:
 No precipitation (rain, snow, hail, fog, etc,)
 Minimal clouds < 4/8 (8/8 = complete cloud cover)
 Slow wind speed < 6 m/s
 No thunderstorms in ~75 km radius from measurement
 Additionally it is important to have conditions with small concentrations of
aerosols. This concentration can be measured with additional instruments
 Only observations made during Fair Weather Conditions are considered to
be measurements of the Global Atmospheric Electric Field
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VLF Measurements
Group 1
CH: Chistochina,
Alaska
CH
SW
PA: Palmer Station,
Antarctica
TA
MI
AD: Adelaide,
Australia
AD
Group 2
TA: Taylor, Indiana
PA
SW: Swider, Poland
MI: Midway Island
 For the study global lightning activity was estimated by looking at VLF data from three
sites with Stanford Awesome receivers
 Sites were chosen to cover all global areas of lightning activity
 Total EM energy in a narrow band around 2 frequencies 325 Hz and 10 kHz was
calculated every 15 minutes
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Day-Night Propagation Effects
Palmer (PA) March
5:00
PA
 VLF Waves propagate more
efficiently at night
PA
 Sites show greater activity when
station it is nighttime at station
 Local time effects need to be taken
corrected for in VLF data
PA
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Lightning vs. Ez
Atmospheric electric field measurements (bottom panels) observed at SW and HO.
Top panel plots show lightning activity derived from sites AD, CH, and PA using the
propagation scalar method.
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Lightning vs. Ez
 ELF/VLF estimate of global
lightning activity and
atmospheric electric field
observed at SW for 25 March
2007
 General similarity is observed
on this day
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Summary
 Fair weather electric field thought to be linked to
thunderstorm activity
 Strokes? Rainfall? Something else?
 Ez field difficult to measure in “fair weather” conditions
 ELF/VLF measurements require propagation
adjustments
 Combination of ELF/VLF and Ez presents
complementary measurements
 Measurements sometimes correlated, sometimes not.
 Why? More analysis to come…
 ELF/VLF measurements combined with other
instruments can yield exciting new results
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References
B A. Tinsley, L. Zhou (2006). Initial results of a global circuit model with variable stratospheric and
tropospheric aerosol. Journal of Geophysical Research , vol. 11, D16205, doi:10.1029/2005JD006988.
Kartalev, M.D., M.J. Rycroft, M. Fuellekrug, V.O. Papitashvili, V.I. Keremidarska ., (2006). A possible
explanation for the dominant effect of South American thunderstorms on the Carnegie curve. Journal
of Atmospheric and Solar-Terrestrial Physics, 68, 457-468.
Rycroft, M.J., Israelsson, S. and Price, C., (2000) The global atmospheric electric circuit, solar activity and
climate change. Journal of Atmospheric and Solar-Terrestrial Physics, 62, 1563–1576.
Harrison, R. G. (2004), The global atmospheric electric circuit and climate, Surveys in Geophysics, 25, 441484.
Whipple, F.J.W., Scrase, F.J., (1936). Point discharge in the electric field of the earth. Geophysical
Memoirs of London VII, 68, 1–20.
Williams E.R., S.J Heckman, (1993). The local diurnal variation of cloud electrification and the global
diurnal variation of negative charge on the Earth. Journal of Geophysical Research , 98, D3, 52215234.
Williams, E.R. (1993), Global Circuit response to Seasonal variations in global surface air temperature.
Monthly Weather Review, 122,1917-1929.
Williams, E. R. G. Satori, (2004). Lighting, thermodynamic and hydrological comparison of the two tropical
continental chimneys. Journal of Atmospheric and Solar-Terrestrial Physics, 66, 1213-1231. 15