Transcript ++ (?) Non-thermal heating

The EUV impact on ionosphere:
What do observations indicate for
atmospheric evolution of early
Earth and Exo-Earths?
J.-E. Wahlund and M. Yamauchi
Swedish Institute of Space Physics (IRF)
ON3 Response of atmospheres and magnetospheres of
terrestrial planets to extreme solar/stellar conditions
Various escape processes
process
Jeans escape
Mechanism
Explanation
thermal,
Thermal tail exceeds escape
light neutral/ion velocity
Hydrodynamic blow-off thermal,
Extreme EUV condition at
neutral/ion
early Sun/Star.
Photochemical heating chemical, light Release of energy in the
neutral
excited atomic state.
non-thermal,
Ion pickup & subNewly exposed ions to SW is
light ion
sequent sputtering
subject to SW DC field.
non-thermal,
Non-thermal ion
Local deposit of SW energy to
energization by E// & EM light/heavy ion ionosphere causes EM field
wave
that energizes ions.
non-thermal,
Large-scale
SWDP & EM forces push bulk
light/heavy ion plasma anti-sunward at the
momentum transfer
boundary region.
Today's keyword : Ionosphere
1. As source of non-thermally escaping ions.
2. As protector to keep "neutrals to be escape" inside
ionosphere (Jeans escape + ion pick-up).
3. As a modifier of large-scale momentum transfer.

(a) The evolution of the planetary atmosphere might be dependent on
the ionospheric condition and its activity.
(b) Consider dependence of escape on
solar EUV/FUV & solar wind (SW).
 hints for extreme conditions at early Sun/star
EUV & SW dependence of
ionospheric contribution: 1. as source
As:
Source
of
Protect
from
Magnetized Unmagnetized
waverelated
heating
(Jeans)
Amplify O+-related
by
instability
?
Key word
localized energy
deposit to
ionosphere
(Jeans)
relative height of
ionopause &
ion pick-up
exosphere
(interaction
bulk momentum
area increase)
transfer
Fact 1: high rate of non-thermal ion escape
Escape at solar maximum
Mars: 0.5 kg/s (O+, O2+)
Venus: 2kg/s (O+)
Earth: 1 kg/s (O+)
Cluster/CIS
H+
O+
Lundin et al., 2004
(Nilsson et al., 2004)
Fact 2a: Ion escape increases with F10.7 flux
Between solar max & min (factor 3 difference in F10.7 flux):
Earth: a factor of 102 (or 3) change for O+ (or H+) outflow.
 largest contribution & high O/H ratio at early Earth
?
(Cully et al., 2003)
Venus: a factor of 20 change
in ionotail density.
Mars: a factor of 102
difference between MEX and
Phobos-2 (but need revision).
Fact 2b: Non-thermal ion escape increases
with geomagnetic activity
Akebono/DE/Polar
Freja@h=1700km (Norqvist et al., 1998)
(Cully et al., 2003)
H+
O+
(Broad-Band Electrostatic Low Frequency wave)
(Lower Hybrid or Electro-Magnetic Ion Cyclotron wave)
(1) in various forms
(2) depend strongly on Kp, SWDP, and IMF
EUV & SW dependence of
ionospheric contribution: 2. as protector
As:
Source
of
Protect
from
Magnetized Unmagnetized
waverelated
heating
(Jeans)
Amplify O+-related
by
instability
?
Key word
localized energy
deposit to
ionosphere
(Jeans)
relative height of
ionopause &
ion pick-up
exosphere
(interaction
bulk momentum
area increase)
transfer
SW wind interaction with atmosphere
present/ancient Earth? present Mars/Venus?
ancient Mars/Venus?
ancient Earth?
SW is stopped by the
magnetic pressure of
the dipole field
Interplanetary magnetic
field (IMF) is enhanced
around the ionosphere
due to induction current
For reference
Protection by ionosphere
In both magnetized/unmagnetized planets, strong Bfield lies between the ionosphere and (shocked) SW.
1. Thick ionosphere means higher ionization rate by
the electron impact ionization.
 Extra ionization of neutrals with escape velocity,
while these ions cannot escape beyond the
magnetized ionopause/magnetopause.
 Reduction of Jeans escape (of mainly H, He)
2. Higher ionopause location means less neutrals
(corona) beyond the ionopause.
 Reduction of ion pick-up (of mainly H, He)
Fact 3: Ionopause is EUV/FUV dependent
Solar cycle variation of the ionopause height:
Venus : 1700 km difference between solar maximum (high) and
solar minimum (low) (Zhang et al., 2007). The same tendency for
Mars (Zhang et al., 1990).
 Therma/non-thermal ratio = out-of-phase of solar cycle
cf. SW dependence of ionopause height
We expect:
(a) strong (stable) IMF  no change
(b) variable IMF  lower balance altitude (by cancellation of B)
(c) strong SWDP  lower balance altitude
 Therma/non-thermal ratio = out-of-phase of SW activity
Fact 4a: extra ionization (cold case)
high ionization (by
electron impact) &
subsequent escape
are observed at
Titan
(Wahlund et al., 2005)
Fact 4b: extra ionization (hot case)
Critical ionization velocity (CIV)
Possible extra ionization by, e.g., critical ionization
velocity mechanism
EUV & SW dependence of ionospheric
contribution
As:
Source
of
Protect
from
Magnetized Unmagnetized
waverelated
heating
(Jeans)
Amplify O+-related
by
instability
?
Key word
localized energy
deposit to
ionosphere
(Jeans)
relative height of
ionopause &
ion pick-up
exosphere
(interaction
bulk momentum
area increase)
transfer
Magnetized planet
increase in EUV/FUV SWDP
(IMF)
+
+
Non-thermal heating
+++
Jeans + photochemical
Ion pick-up
++
same same same
same
same same same
Large-scale
momentum transfer
O/H ratio
++
IMF
+ (?)
+
+ (?)
+ (?)
(#1)
++
+
+
(#1) Increase or decrease depending on the relative
importance of non-thermal heating
Unmagnetized planet
increase in EUV/FUV SWDP
Non-thermal heating
Jeans + photochemical
Ion pick-up
Large-scale
momentum transfer
O/H ratio
++ (?)
++
+ (?)
IMF
(IMF)
same
+
same same same
(#2)
++
same
+
++
+
same
++
(#1)
++
same
+
#1) depending on relative importance of non-thermal heating.
#2) depending on relative extent of ionosphere and exosphere
Since ancient Earth's ionosphere is
* Most likely High EUV/FUV
* More likely High SWDP
* Probably strong/active IMF
 much higher O escape
& much higher O/H ratio of escape
than present.
 The ancient atmosphere can be
chemically quite reduced
Unclear parameters : Magnetized or non-magnetized,
atmospheric composition, internal condition
End
Extra slides for Q & A
Budget above the Earth's
ionosphereH+/O+ in major return route
ion escape
< 10 eV (2~3 Re)
> 10 eV (3~4 Re)
H+
2~5
2~8
O+
1~3
1.5~20
ion precipitation
ion
electron
> 10 eV (DMSP)
0.2~0.9
9~60
in 1025 /s
mass budget
out
in
in kg/s
H+
O+
meteors
0.05~0.2
< 0.02
0.5~5
?
0.5
After Moore et al., 1999
Magnetized planet (Earth, Mercury)
Magnetopause : balance between SW PD  Planetary magnetic
field
(a) stronger but stable IMF  lower altitude of magnetopause
but more return flow
(b) more variable IMF  more internal process (non-thermal
escape)
(c) stronger SW PD  lower altitude of magnetopause + escape
How about UV dependence ?
(important for ancient condition)
Height and density of the ionosphere
(1) Ionization (source) = Chapman model
One-component atmosphere (scale height = H  1/gravity)
s: cross section, F0:incoming solar flux, n0:density at z=0
Peak altitude : zmax(c , F0, H) = H ln(n0sH/cos(c))
 does not depends on F0 , but on H (i.e., gravity)
Peak production : qmax (c , F0 , H) = F0cos(c)/H exp(1)
 depends on F0 and H (i.e., gravity)
(2) Transport (recombination loss is ignorable)
Moves peak of ne(z) much higher with less sharp ne(z) profile
Transport (convection) is mainly driven by heating ( q)
 Ionospheric extent depends on both F0 and gravity
Escape from
the cusp
Earth ?
Mars ?
Venus ?
Io & other
Satellites?