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

2. Lightning Facts ● 100 strikes/second on Earth. ● Peak current I=10 5 Amps ● Voltage drop V=10 8 V ● Charge transfer Q=20 Coul. ● Energy E= 10 9 J ● Channel radius r=1 cm. ● 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 Lightning Effects

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) ● Mechanism can occur in warm clouds or cold (sub- freezing) clouds ● High electric fields polarize water drops ● Cloud droplets scatter off of raindrops or graupel

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

11. 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, SO 4 ) is easy to observe by direct injection.

12. 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.

13. 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.

14. 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.

15. 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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