Download Venus Ek

On the possibility of sprites
on other planets
Yoav Yair and Roy Yaniv
Lightning Activity in our solar system





Earth, Jupiter, Saturn - definite
Venus – probable, debatable
Uranus, Neptune – probable, partly confirmed
Mars, Titan - theoretically possible
Moon, Mercury, Pluto - impossible
If there are planetary lightning flashes,
should there also be planetary TLEs?


1
1
Es  Q 

2
2
  Z  Z s   Z  Z s  
Computing conventional breakdown thresholds for
various atmospheric compositions
Ek is the critical electric field, where ionization
exactly balances attachment.




Ionization –
  Bi 
 Ai  exp 

P
E
/
P


Attachment –

2
  Ba 
E
 Aa     exp 

P
P
E/P
E/p is the electric field normalized to pressure, and Ek (the critical electric
field) been expressed in normalized form of E/p. To find Ek at other
pressures, we multiplied by the pressure (in torr units).
Parameters (Sentman, 2004)
Determination of Electrical Fields

we assumed 3 different Electrical charges that a
Lightning can produce.

For Earth and Venus we assumed 100 Coulomb,
500 Coulomb and 1000 Coulomb values produced
by Lightning discharge.
For the Gas Giants we assumed 100 Coulomb,
1000 Coulomb and 10000 Coulomb values
produced by Lightning discharge.

Verification: Earth Electrical Fields
(10km cloud)
Calculations for Venus
Clouds heights: 48, 55, 70 km
Ionospheric height is ~ 300 km
Venus Electrical Fields (48km cloud)
Venus Electrical Fields (55km cloud)
Venus Electrical Fields (70km cloud)
Titan Electrical Fields
The Clouds of Jupiter

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Permanent global coverage organized
in belts and zones
Lower cloud - probably water - 5 bar
pressure level, convective, mixedphase
Middle cloud - NH4SH at the 2 bar
pressure level, stratiform
Upper cloud - Ammonia Ice, Cirrus-like
•Ionospheric height is 1600 km above
the 1-bar level
Clouds: H2O 2 bar (-20km), 3 bar (-33
km), 4 bar (-44km).
Jupiter Electrical Fields (-20km cloud)
Jupiter Electrical Fields (-33km cloud)
Jupiter Electrical Fields (-44km cloud)
Saturn’s cloud layers (Atreya, 1986)


Weaker convection, water
clouds deeper and warmer:
probably no ice
H2O 4 bar (-90km), 6 bar (120 km), 8 bar (-150km).
Saturn Electrical Fields (-90km cloud)
Saturn Electrical Fields (-120km cloud)
Saturn Electrical Fields (-150km cloud)
Summary
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The huge surface atmospheric pressure on Venus (~9 MPa)
means that no cloud-to-ground discharge from the high-level
sulfuric acid clouds (Zs ~ 50 to 70 km) are possible.
Sprites can be produced by IC discharges (van der Velde et al.,
2006), so even if all lightning activity in Venus is entirely intracloud discharges, sprites and Elves are still possible.
Venusian IC discharges would be slow to build-up and would
exhibit different characteristics compared to their terrestrial
analogues (Gurnett et al., 2001).
Potential emission bands from CO2 between 290 and 500 nm,
with prominent lines near 288, 410 and 427 nm (Smyth, 1931).
Also OI (777.7 nm).
In Jupiter and Saturn, the amount of charge required to initiate
sprites is of the order of 104 C. Although these may seem highly
unrealistic values, it has already been shown that lightning in
these planets are far more energetic than on earth.