M. Galand (1), I.C.F. Müller-Wodarg (1), L. Moore (2), M. Mendillo (2), S. Miller (3) , L.C. Ray (1)
(1) Department of Physics, Imperial College London, London, U.K. (2) Center for Space Physics, Boston University, Boston, MA, USA(3) Department of Physics and Astronomy, University College London, U.K.
Thermosphere - Ionosphere - Magnetosphere Coupling
1. Energy crisis at giant planets2. TIM coupling3. Modeling of IT system4. Comparison with observations5. Outstanding questions
(Gladstone et al., 2007) Cassini/UVIS
[UVIS team]
JUPITER
Credit: J. Clarke (BU), NASA
Credit: NASA/JPL/Space Science Institute
Cassini/ISS (false color)
SATURN
Canada
Cassini/VIMS (IR)[VIMS team/JPL, NASA, ESA]
Cassini/UVIS(Pryor et al., 2011)
1. SETTING THE SCENE: THE ENERGY CRISIS AT THE GIANT PLANETS
Exosphere
Thermosphere
Mesosphere
Stratosphere
85 km
50 km
~ 15 km
500 km
Troposphere
TexoTHERMAL PROFILE (EARTH)
Ionosphere
Key transition region between the space environment and the lower atmosphere
ion, e-
ion, e-
Solar photons
Neutral
Suprathermalelectrons
SOLAR ENERGY DEPOSITION IN THE UPPER ATMOSPHERE
Thermal e-
B
Ionospherice- heating
+
Ther
mos
pher
e
Ne, NionSP, SH
TeAirglow
Neutral atmospheric heating
*
Exothermic reactions
[after Mendillo et al., 2002]
Outer planetsEarth
CO2 atmospheres
W
Exos
pher
ic te
mpe
ratu
re (K
) Main energy source:UV solar radiation Main energy source?
IS THE SUN THE MAIN ENERGY SOURCE OF PLANERATY THERMOSPHERES?
[After Yelle and Miller, 2004; Melin et al., 2011 (+poster)]
Observed values at low to mid-latitudes
Modeled values (Sun only)
ENERGY CRISIS AT THE GIANT PLANETS
solstice
equinox
ENERGY BUDGET OF THE THERMOSPHERE
HEATING SOURCES
Solar heating through excitation/dissociation/ionization + exothermic chemical reactions
Auroral particle heating via collisions + chemistry [Grodent et al., 2001]
“Ionospheric Joule heating” via auroral electrical currents and ion-drag heating [Vasyliũnas and Song, 2005]
Dissipation of upward, propagating waves (such as gravity waves, …)
- Solar EUV/FUV heating*: 0.5 TW (Earth), 0.8 TW (Jupiter), 0.2 TW (Saturn)- Auroral part./Joule heating*: 0.08 TW (Earth), 100 TW (Jupiter), 5-10 TW (Saturn)
[*: Strobel, 2002]
2. THERMOSPHERE-IONOSPHERE-MAGNETOSPHERECOUPLING
MAGNETOSPHERE-IONOSPHERE-THERMOSPHERE COUPLING
Examples of ITM coupling:• Angular momentum transfer• Ion outflow, particle precipitation
MAGNETOSPHERE
Exchange ofparticles, momen-tum & energy
AURORALTHERMOSPHERE
IONOSPHERE
• Overall, at high latitudes:the magnetosphere extracts angular momentum from the upper atmosphere through the magnetic field-aligned currents [e.g., Hill, 1979]
The magnetosphere “swims” on the ionosphere.
MAGNETOSPHERE-IONOSPHERE-THERMOSPHERE COUPLING
MAGNETOSPHERE
IONOSPHERE
MAGNETOSPHERE-IONOSPHERE-THERMOSPHERE COUPLING
Examples of ITM coupling:• Angular momentum transfer• Ion outflow, particle precipitation
MAGNETOSPHERE
Exchange ofparticles, momen-tum & energy
AURORALTHERMOSPHERE
IONOSPHERE
S
Pedersen
current
Field-alignedcurrent
Fiel
d-al
igne
dcu
rren
t
AURORAL THERMOSPHERE
TO MAGNETOSPHERE
IONOSPHERE
Ionospheric Joule heating(resistive + frictional heating)[Vasyliũnas and Song, 2005]
TIM coupling through current system
FROM MAGNETOSPHERE
QJ = J . Ei
MAGNETOSPHERE-IONOSPHERE-THERMOSPHERE COUPLING
Energy redistribution towards lower
latitudes?
MAGNETOSPHERE
ATMOS
STIM
Strongercooling
Local time averaged
Ion drag fridge mechanism [Smith et al., 2007; Smith and Aylward, 2009]
wind direction
Polar sub-corotation due to auroral forcing (westward ion velocities due to ambient E fields) drives equator-to-pole circulation
[Mueller-Wodarg et al., 2011]
Strongerheating
EXOSPHERICTEMPERATURE
Does the ion drag fridge mechanism rule out auroral energy in solving the global energy crisis at Giant Planets?
3. MODELING THE THERMOSPHERE/IONOSPHERE SYSTEM
Electron and ion densities & temperaturesElectrical conductances
Beer-Lambert Lawapplied to the solar flux
Ionospheric densities (Ne, Ni) , drifts, &
temperatures (Te, Ti)[Moore et al., JGR, 2008]
Boltzmann Equationapplied to suprathermal
electrons
3D Thermosphere-Ionosphere Model
Thermospheric densities (Nn), winds, & temp.
[Müller-Wodarg et al., Icarus, 2006]
1D Energy Deposition Model[Galand et al., JGR, 2009, 2011]
Nn
Ne, TePe, Pi, Qe
Pe, Pi
Incident AuroralElectron
Distribution
Solar Flux
Flexible model which allows us to explore the parameter space and assess the effect of it on ionospheric/thermospheric quantities, such as Ne, S, Tn.
Neutral temperatures
COUPLED FLUID/KINETIC STIM MODEL
* Full ion-neutral dynamical coupling
*
Electric field
with Dt = 25 min
STIM RESULT 1: Ionospheric conductances in auroral regions
-Pedersen conductivities peak at the homopause conductances peak near 2.5 keV- At low energies, conductances are driven by the solar source
Q0 = 0.2 mW m-2
SOLAR VALUES
12 LT
[Galand et al., 2011]
€
Q0(t − Δt)
€
SP
Ped
erse
n co
nduc
tanc
e (m
ho)
with Dt = 25 min
STIM RESULT 1: Ionospheric conductances in auroral regions
-Pedersen conductivities peak at the homopause conductances peak near 2.5 keV- At low energies, conductances are driven by the solar source
Q0 = 0.2 mW m-2
12 LT
[Galand et al., 2011]
€
Q0(t − Δt)
€
SP
Ped
erse
n co
nduc
tanc
e (m
ho)
Sun only12 LT
78°S LAT
EquinoxSolar min
EquinoxSolar max
SummerSolar min
Pedersen conductances
0.7 mho 1.6 mho 2.6 mho
Auroral electron mean energy &
energy flux
Earth[Fuller-Rowell and
Evans, 1987]
Saturn[Galand et al.,
2011]
Jupiter[Millward et al.,
2002]
10 keV1 mW m-2
SP = 4-6 mho
SP = 11-12 mho
SP = 0.1-0.2 mho
Composition Altitude range
SP=max(SP)/10 over 70 km (E) and 500 km (S)
Strength of B fieldB field 20 times
stronger at J cp w/ S
Slippage parameter(1) for Jupiter(2) & Saturn(3):
€
k =Ω −ωn
Ω −ω i
= ~ 0.5
(1) Bunce et al. [2003]; (2) Cowley et al. [2004]; (3) Galand et al. [2011]
STIM RESULT 1: Ionospheric Conductances in auroral regions
• Charge exchange reaction H+ + H2(v≥4) H2+ + H(1)
controls the abundance of H3+ as it is quickly followed by:
H2+ + H2 H3
+ + H
• Reaction rate k1* = k1 [H2(v≥4)]/[H2]
– Low k1* means less charge exchange reaction and increase in ionospheric densities
k1 = 10-9 cm3 s-1 [Huestis, 2008]
At low- and mid-latitudes: Moore et al. (2010) found best match between model and Cassini RSS data for a reduction of ([H2(v≥4)]/[H2]) from Moses and Bass [2000]
In the auroral regions, expected to be larger: Galand et al. (2011) assumed 2 x ([H2(v≥4)]/[H2]) from Moses and Bass [2000]
• How does this affect thermospheric circulation?
STIM RESULT 2: sensitivity to vibrationally excited H2 rate
Local time averaged[Mueller-Wodarg et al., 2011]
3 cells
STIM RESULT 2: sensitivity to vibrationally excited H2 rate
wind direction
EXOSPHERICTEMPERATURE
4. OBSERVATIONS OF THE THERMOSPHERE/IONOSPHERE SYSTEM
(1) STIM, 3 cells(2) STIM, 1 cell(3) Voyager UVS(Vervack and Moses, 2011)(4) Voyager UVS (Smith et al., 1983)(5) Cassini UVIS (Nagy et al., 2009)(6) UKIRT (Melin et al., 2007)
3
4
5
1
26
Implication for exospheric temperatures
[Mueller-Wodarg et al., 2011]
+
Type of observat.
Radio occultations
H3+ IR
emissionsUV
emissionsRadio
emissions
Physical quantities
Electron density
Effective H3+
column density, temp, and velocity
vector
Auroral e- energy flux & energy
(generating aurora)
Auroral e- energy flux and energy
(within accele region)
Which observations can help constrained the problem?
Sample of relevant observations: Earth-based + space missions
UV occultations In situ measurements(particle, fields)
Atmosph. densities,Texospheric
Down/upgoing auroral particles (if conditions allows),
Magnetic field strength/direction, Electric
currents
Combine as many as possible to better constrain the problem [e.g., Melin, talk]
JUNO over the polar regions
Credit: Juno Team
Credit: Juno Team
JUNO observations through the magnetic field lines connected to the auroral ionosphere, close/within the acceleration region (expected to be 2-3 RJ from center [Ray et al., 2009]):- Electric currents along magnetic field lines- Plasma/radio waves revealing processing responsible for particle acceleration [see Hess, tutorial]- Energetic particles precipitating into atmosphere creating aurora- Ultraviolet/IR auroral emissions regarding the morphology of the aurora
• Can the energy crisis be solved via auroral forcing alone as proposed here?– Is the mechanism proposed efficient at Jupiter, Uranus (seasonal
asymmetry [Melin et al., 2011 + poster]), and Neptune?– At Saturn, beside the solar contribution which is dominant [Moore et al.,
2010], are they additional energy sources at low- and mid-latitudes?[e.g., break-down in co-rotation of the ions in the ionosphere [Stallard et al., 2010; Tao, poster; Ray, talk], molecular neutral torus of Saturn through charge-exchange (ENA) [e.g., Jurak & Johnson, 2001], wave heating (super-rotat≠IR)]
Further constraints on ionospheric densities at different LT [dawn/dusk RSS, Max Ne SEDs, ground-based IR in H3
+ (noon!)]
• What drive the hemispheric differences observed at Saturn in the magnetosphere and auroral, ionospheric regions?– Asymmetry in B field? Hemispheric (seasonal) differences in the
atmosphere? If the latter, should reverse now as going out of equinox?• Is the variable rotation rate observed in the magnetosphere linked
to atmospheric dynamics? [e.g., Jia/Kivelson talk] (two-way MI coupling)
Outstanding questions
EXTRA SLIDES
Ionospheres in the solar system
Mendillo et al. (2002)
PLANETARY IONOSPHERES in the SOLAR SYSTEM
[LASP, TIMED/SEE]
Ionization Heating of thermosphere
ORIGIN of the soft X-RAY and UV SOLAR SPECTRUM
SP P z dzionosphere
SH H z dzionosphere
Pedersen (SP) & Hall (SH)conductances:
Pedersen (sP) & Hall (sH)conductivities:
with
eBm
H z nieB
e2
en2 e
2 i
2
in2 i
2
i
n
P z nieB
ene
en2 e
2 in i
in2 i
2
i
n
IONOSPHERIC CONDUCTIVITIES IN THE AURORAL REGION
Sun only (0.1 mW m-2 including 4x10-3 mW m-2 for photoe-)Sun + Soft e- (500 eV, 0.2 mW m-2)Sun + Hard e- (10 keV, 0.2 mW m-2)
12 LT
IONOSPHERIC CONDUCTANCES IN THE AURORAL REGION
€
αP Q0(t − ΔtP )
Em = 10 keV<Q0> = 0.2 mW m-2
LT-dependence based on HST/UV brightness analysis [Lamy et al., 2009]
[Galand et al., 2011]
0800 UT
0400 – 1400 UT
DtP = 23 min
Pedersen
Electrical conductances proportional to but shifted in time
€
Q0
• Polar sub-corotation due to auroral forcing (westward ion velocities due to ambient E fields) drives equator-to-pole circulation
• NOTE: this is not simply the return-flow of thermally driven pole-to-equator winds higher up!
• Therefore, the poleward flow cools the equatorial regions• Does this rule out magnetospheric energy in solving the Gas Giant energy
crisis?
Pole-to-equator flow
Equator-to-pole flow
Smith et al., Nature (2007)Smith and Aylward (2009)
Subcorotating Region
ENERGY REDISTRIBUTION FROM HIGH TO LOWER LATITUDESThe “Ion Drag Fridge”