Transcript DUSEL_RS2 - New Mexico Tech

Opportunities for Atmospheric
Electricity and Lightning studies at
DUSEL
Richard Sonnenfeld
Physics Department
New Mexico Tech
Kenneth Eack
Los Alamos National Laboratory
Lightning Facts
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100 strikes/second on Earth.
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Peak current I=105 Amps
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Voltage drop V=108 V
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Charge transfer Q=20 Coul.
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Energy E= 109 J
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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.
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Lightning research has lead to improved lightning rods,
lightning warning systems, lightning hardening, and global
lightning location networks
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How do storms electrify?
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Where exactly are the charges found?
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What is their magnitude?
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What sort of particles do they attach to?
Collisional Inductive Charging
(Elster-Geitel charging)
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High electric fields polarize
water drops
Cloud droplets scatter off of
raindrops or graupel
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Mechanism can occur in
warm clouds or cold (subfreezing) clouds
Collisional Non-Inductive Charging
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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
Evidence for Non-Inductive Charging
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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
Other Mechanisms
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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.
Warm lightning – Annoyance or Message?
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Warm cloud lightning has been reported in the
tropics by reputable observers. [Moore60]
Most “accepted” charging mechanisms involve
glaciation.
How can this be?
Tool and Techniques of lightning
research
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Electric field measurement devices
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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
- In Situ
Measurement of
Cloud Top Properties
Blower
Width and Depth ~3 to 5 m
In Situ
Measurement of
Mid-Cloud
Properties
Access to the cloud is attained
at various points throughout its
depth using numerous side-shafts,
each providing power and ethernet
connections
Aerosol Filter
- In Situ Measurement of
Below-Cloud Properties
- Upward-looking remote
sensing instruments
- Measurement of Precip
Aerosol Generation
Active Grid
Turbulence Generator
Addition of Trace Gases
Total vertical extent ~500 to 1000+ m
Moveable
instrument
platform
SCHEMATIC OF A
VERTICAL
SHAFT CLOUD
LABORATORY
Advantages of DUSEL - I
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Total control of boundary conditions
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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.
Advantages of DUSEL - II
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Instrumentation may be affixed to walls rather
than flown on balloons.
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Allows multiple sensors at once to be brought to bear,
allows observing time-dependence of charging and
field.
Particle measurements easier than balloon flights.
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Collected charged hydro-meteors may be taken to
microscopes much sooner after they are trapped.
Problems DUSEL can probably tackle
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Do warm clouds electrify? How?
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Can ice-water mechanism occur in a more
realistic circumstance than a typical laboratory?
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Where are the charges in warm clouds?
Where will the charges go?
If can generate “steady state” electrification, then
can measure the charges BEFORE the matter is
confused by lightning strokes.
Problems DUSEL may not be able to
tackle
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Will lightning be produced?
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It is likely that a glaciated cloud must be created to
have any hope of seeing lightning.
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Still not obvious – in nature, 3-4 km column of
convection is often needed to produce lightning.
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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.
References
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[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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