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Opportunities for Atmospheric Electricity and Lightning studies at DUSEL

Richard Sonnenfeld Physics Department New Mexico Tech Kenneth Eack Los Alamos National Laboratory. Opportunities for Atmospheric Electricity and Lightning studies at DUSEL. Lightning Facts. 100 strikes/second on Earth. Peak current I=10 5 Amps Voltage drop V=10 8 V

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Opportunities for Atmospheric Electricity and Lightning studies at DUSEL

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  1. Richard Sonnenfeld Physics Department New Mexico Tech Kenneth Eack Los Alamos National Laboratory Opportunities for Atmospheric Electricity and Lightning studies at DUSEL

  2. Lightning Facts • 100 strikes/second on Earth. • Peak current I=105 Amps • Voltage drop V=108 V • Charge transfer Q=20 Coul. • Energy E= 109 J • Channel radius r=1 cm. Lightning Effects • Costs $4-5 Billion/yr in disrupted power lines, destroyed electronics. Sets off ammunition dumps, kills hundreds of people. • Lightning research has lead to improved lightning rods, lightning warning systems, lightning hardening, and global lightning location networks

  3. How do storms electrify? • Where exactly are the charges found? • What is their magnitude? • What sort of particles do they attach to?

  4. Collisional Inductive Charging(Elster-Geitel charging) • High electric fields polarize water drops • Cloud droplets scatter off of raindrops or graupel • Mechanism can occur in warm clouds or cold (sub-freezing) clouds

  5. Collisional Non-Inductive Charging • Contact potential difference of ~100 mV observed between wet ice and dry ice. • Ice crystals and cloud droplets scatter off of riming graupel and acquire charge • Mechanism requires cold (sub-freezing) clouds

  6. Evidence for Non-Inductive Charging • The negative charge center in storms is always found around the –10C Isotherm. • Inverted polarity storms can be explained in terms of differing temperature profiles

  7. Other Mechanisms • Several other charge transfer mechanisms have been suggested. • Many, but not all require ice in the cloud. • At an average density of 1-10 Coulombs/km^3, 1 g/kg of LWC and for 7 micron cloud droplets, only need 20 e-/droplet to produce needed charge for lightning. • Even a very inefficient process could produce this.

  8. Warm lightning – Annoyance or Message? • Warm cloud lightning has been reported in the tropics by reputable observers. [Moore60] • Most “accepted” charging mechanisms involve glaciation. • How can this be?

  9. Tool and Techniques of lightning research • Electric field measurement devices • Slow antennae / field mills • Inductive loop charge sensors – combined with cameras – Need single charge sensitivity. • Meteorological radar • Arrays for mapping RF pulses caused by lightning

  10. Advantages of DUSEL - I • Total control of boundary conditions • Should allow the production of a “steady state” storm • Allows the “same storm” to be recreated over and over-again to test different hypothesis. • Easy to create a desired temperature profile. Negative charge region should reside at –10 C. • Can vary updraft rate and LWC and see effect on charging. • Effect of contaminants (salt, soot, SO4) is easy to observe by direct injection.

  11. Advantages of DUSEL - II • Instrumentation may be affixed to walls rather than flown on balloons. • Allows multiple sensors at once to be brought to bear, allows observing time-dependence of charging and field. • Particle measurements easier than balloon flights. • Collected charged hydro-meteors may be taken to microscopes much sooner after they are trapped.

  12. Problems DUSEL can probably tackle • Do warm clouds electrify? How? • Where are the charges in warm clouds? • Can ice-water mechanism occur in a more realistic circumstance than a typical laboratory? • Where will the charges go? • If can generate “steady state” electrification, then can measure the charges BEFORE the matter is confused by lightning strokes.

  13. Problems DUSEL may not be able to tackle • Will lightning be produced? • It is likely that a glaciated cloud must be created to have any hope of seeing lightning. • Still not obvious – in nature, 3-4 km column of convection is often needed to produce lightning. • Perhaps artificially intensive the convection or updrafts can lead to sufficient fields in a shorter air column. • The cosmic rays which may trigger lightning will be absent.

  14. References • [Krehbiel86] “The Electrical Structure of Thunderstorms” Paul R. Krehbiel, in The Earth’s Electrical Environment, National Academy Press, 263 pages (1986). • [Marshall91] “Electric field soundings through thunderstorms” T.C. Marshall and W.D. Rust, J. Geophys. Res., Vol 96, 22297-306 (1991). • [Moore60] “Observations of Electrification and Lightning in Warm Clouds” C.B.Moore, et al., J. Geophys. Res., Vol 65, 1907-1910 (1960). • [Rakov03] “Lightning: Physics and Effects” V.A.Rakov and M. Uman., Cambridge Univ. Press, 687 pages. (2003). • [Saunders98] “Laboratory studies of Rime accretion rate …” C.P.R. Saunders and S.L. Peck., J. Geophys. Res., Vol 103, 13949-56 (1998).

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