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Solar System Physics Group
Grande et al, Venus, RAS 2010
Solar wind interactions and Solar wind interactions and Ionospheric loss mechanisms Ionospheric loss mechanisms
at Venusat Venus
M Grande, A G Wood, I C Whittaker, G Guymer and A BreenM Grande, A G Wood, I C Whittaker, G Guymer and A Breen
S BarabashS BarabashSwedish Institute of Space PhysicsSwedish Institute of Space Physics
T ZhangT ZhangAustrian Academy of SciencesAustrian Academy of Sciences
Solar System Physics Group
Grande et al, Venus, RAS 2010
• Boundaries and effect of Solar Cycle.• Atmospheric loss• Flux tubes and transition parameter• Trans-terminator flow.• CME• CIR structure observed by IPS and in
situ at Venus
11
Outline
Solar System Physics Group
Grande et al, Venus, RAS 2010r
(Rv)
x (Rv)
BoundaryBoundary locationslocations identified by algorithm identified by algorithm
Blue points – Blue points – Bow ShockBow Shock
Red points – ICBRed points – ICB
Solar System Physics Group
Grande et al, Venus, RAS 2010
Bow Shock modelBow Shock model
Fitted curve Fitted curve agrees closely agrees closely with previous with previous resultsresults
But Aber curve But Aber curve is the lowest is the lowest altitude at the altitude at the sub-solar pointsub-solar point
Whittaker et al JGR 2010
Solar System Physics Group
Grande et al, Venus, RAS 2010
Sub solar Sub solar points vary points vary linearly linearly with with average average sunspot sunspot numbernumber
Compare solar conditions of different modelsCompare solar conditions of different models
Bow Shock modelBow Shock model
Whittaker et al JGR 2010
Solar System Physics Group
Grande et al, Venus, RAS 2010D
iffer
ence
fro
m f
itted
po
sitio
n (R
v)
Dynamic pressure indicator 7 day averaged EUV
r (R
v)
x (Rv)
Boundary locationsBoundary locations
In agreement with Martinecz et al. (2009) the bow shock position does In agreement with Martinecz et al. (2009) the bow shock position does not correlate with either;not correlate with either;
• the solar wind dynamic pressurethe solar wind dynamic pressure
• or the solar EUV fluxor the solar EUV flux
The same analysis for the ICB also shows no correlationThe same analysis for the ICB also shows no correlation
Solar System Physics Group
Grande et al, Venus, RAS 2010
Water Loss at Venus
• Spatial distribution of the escaping plasma. The measured O +
(a), and H+ (b) flux distributions in the tail region from 33 orbits were integrated over XVse [20.5, 23.0] and are shown in a YVse–ZVse plane across the tail. The geometrical eclipse of Venus is shown by the thin grey circle. To ensure that no solar-wind protons affect the mass composition measurements inside the IMB, we restrict the area of the analysis to R,1.2RV. Blank circles show measurements with zero flux. The plasma sheet region is identified by red dashed lines and labelled PS, the boundary layer at the IMB is identified by black dashed lines and labelled BL, and the direction of the convection electric field is labelled E.
• S. Barabash et al Nature Vol 450|29 November 2007
Escaping ions leave Venus through theplasma sheet and in a boundary layer of the induced magnetosphere. The escape rate
ratios are Q(H+1)/Q(O+)=1.9implying that the escape of H+ and O+, together with the estimated escape of neutral hydrogen and oxygen, currently takes place near the stoichometric ratio corresponding to water.
Solar System Physics Group
Grande et al, Venus, RAS 2010
H+He++He+• X-R(signed) plot H+ This cylindrical plot shows that the data fits the bow shock in all three dimensions.
•The wake can also be seen to flow at an angle towards positive y. This is associated with the 5° angle the solar wind makes with Venus.
X-Y plot of O+The main ion concentration is found over the pole, corresponding to low altitude
The planetary wake is the clear escape route for O+
Solar System Physics Group
Grande et al, Venus, RAS 2010
Double energy populations occur in conjunction with flux ropes in the Venusian ionosphere with ionosheric oxygen and SW protons on the same flux tube,The small number of cases studied so far do not preclude a chance association
Solar System Physics Group
Grande et al, Venus, RAS 2010
1.
2.
4.
3.
Mean electron energy
Log
elec
tron
den
sity 1. Solar wind
2. Magnetosheath
3. Boundary Layer
4. Magnetopause
(Hapgood & Bryant 1990 GRL 17(11))
Transition parametersTransition parameters
Solar System Physics Group
Grande et al, Venus, RAS 2010
Solar System Physics Group
Grande et al, Venus, RAS 2010
• Traditionally a transition parameter is defined by anti-correlation between electron density and mean electron energy (perpendicular to the electric field) The parameter has been used previously to characterise boundary crossings at Earth based on electron data.(Hapgood & Bryant 1990 GRL 17(11))
• Once defined, the transition parameter can be used to reveal ordering in other, independent data sets.
•We are using it to decide whether flux rope events offer a small scale mechanism for atmospheric loss at Venus
r (R
v)
Transition parametersTransition parameters
Solar System Physics Group
Grande et al, Venus, RAS 2010
Ion energies below the ICBIon energies below the ICB
Lowest Lowest energies near energies near
periapsisperiapsis
Low energies Low energies in the tailin the tail
Higher Higher energies energies close to close to
boundary with boundary with shocked solar shocked solar
windwind
Solar System Physics Group
Grande et al, Venus, RAS 2010
Ion energies below the ICBIon energies below the ICB
Showing only Showing only those ions those ions
with energies with energies above the above the
escape escape velocityvelocity
Solar System Physics Group
Grande et al, Venus, RAS 2010
Transport of higher energy ionsTransport of higher energy ions
Photoelectrons caused by Photoelectrons caused by photoionisation of oxygenphotoionisation of oxygen
Observed on dayside and nightside Observed on dayside and nightside (Coates et al., 2008)(Coates et al., 2008)
Inferred that these are transported Inferred that these are transported from day to nightfrom day to night
Suggest that they set up an E fieldSuggest that they set up an E field
Suggest that this can accelerate Suggest that this can accelerate O+O+
This would then be lost to the solar This would then be lost to the solar wind (Coates et al., 2009)wind (Coates et al., 2009)
Solar System Physics Group
Grande et al, Venus, RAS 2010
Day-to-night flow at Day-to-night flow at solar maximumsolar maximum
From Brace et al. (1995) (left) and Miller and Whitten (1991) (right)
Ion TransportIon Transport
Solar System Physics Group
Grande et al, Venus, RAS 2010
Ion TransportIon Transport
At solar minimum ionopause at a lower altitudeAt solar minimum ionopause at a lower altitude
Inhibits transport processInhibits transport process
Remote sensing experiments suggestRemote sensing experiments suggest
that transport strongly reduced / shut off that transport strongly reduced / shut off
(Knudsen et al., 1987)(Knudsen et al., 1987)
Venus Express conducting first in situ measurements at solar miniumumVenus Express conducting first in situ measurements at solar miniumum
Solar System Physics Group
Grande et al, Venus, RAS 2010
One Venus year of observations from 4 August 2008One Venus year of observations from 4 August 2008
Cover all LT sectors, once in each directionCover all LT sectors, once in each direction
Solar flux approximately constant, around 70 sfuSolar flux approximately constant, around 70 sfu
Ion Counts and PositionIon Counts and PositionIntegrated Ion Counts, 4th August 2008 – 17th March 2009
Solar System Physics Group
Grande et al, Venus, RAS 2010
Ion Counts and PositionIon Counts and Position
One Venus year of observations from 4 August 2008One Venus year of observations from 4 August 2008
Cover all LT sectors, once in each directionCover all LT sectors, once in each direction
Solar flux approximately constant, around 70 sfuSolar flux approximately constant, around 70 sfu
Integrated Ion Counts, 4th August 2008 – 17th March 2009
Solar System Physics Group
Grande et al, Venus, RAS 2010
AssymetriesAssymetries
Can have significant counts Can have significant counts nightward of terminatornightward of terminator
Maintenance of nightside ionsMaintenance of nightside ions
Higher peak counts on dusk side Higher peak counts on dusk side
Could be dawn-dusk asymmetry in dayside Could be dawn-dusk asymmetry in dayside ion density (Miller and Knudsen, 1987)ion density (Miller and Knudsen, 1987)
Solar System Physics Group
Grande et al, Venus, RAS 2010
Ion Transport in Noon-Midnight PlaneIon Transport in Noon-Midnight Plane
Energy of peak countsEnergy of peak counts MedianMedian 1st quartile1st quartile 3rd quartile3rd quartile
Noon-Midnight orbits:Noon-Midnight orbits: 15 eV15 eV 13 eV13 eV 20 eV20 eV
Midnight-Noon orbits:Midnight-Noon orbits: 25 eV25 eV 20 eV20 eV 29 eV29 eV
NoonNoonMidnightMidnight NoonNoonMidnightMidnight
Suggests nightward ion flow of ~4 km/sSuggests nightward ion flow of ~4 km/s
Solar System Physics Group
Grande et al, Venus, RAS 2010
Ion Transport in Noon-Midnight PlaneIon Transport in Noon-Midnight Plane
Suggests Suggests antisunward flow of antisunward flow of several km/sseveral km/s
At the highest At the highest altitudes altitudes approaches the approaches the escape velocityescape velocity
Solar System Physics Group
Grande et al, Venus, RAS 2010
Transport of lower energy ionsTransport of lower energy ionsTransterminator Transterminator
ion flow driven by ion flow driven by pressure gradientpressure gradient
Transterminator Transterminator ion flux greater ion flux greater than required to than required to
populate populate nightside nightside
ionosphere ionosphere (Brace et al., (Brace et al.,
1995)1995)
Suggest that Suggest that some of these some of these
ions could be lost ions could be lost to the solar windto the solar wind
Solar System Physics Group
Grande et al, Venus, RAS 2010
An image taken by the inner camera HI-1A on STEREO A more than a day after the CME launch.
The front and core of the CME are visible in this image and labeled A and B respectively.
The bright body on the left hand-side of the figure is Mercury.
A. P. Rouillard et al 2008
Solar System Physics Group
Grande et al, Venus, RAS 2010
Solar Wind periodicity CIR
Identified with Slow/Fast stream CIR structures
in Solar Wind near solar minimum Note repeat of structure when repeated on 28 day periodSame is also currently seen at Earth with ACEThree stream structure is a feature of current cycleLong term pattern of coronal holesNote ability of STEREO to image associated CIRs
3
Solar System Physics Group
Grande et al, Venus, RAS 2010
Separation of orbits by initial Solar Wind mean energy
Wake differences fast/slow stream
5
Fast Slow
All
Heavy
Solar System Physics Group
Grande et al, Venus, RAS 2010
Solar System Physics Group
Grande et al, Venus, RAS 2010
CIRs Identified by IPS
Solar System Physics Group
Grande et al, Venus, RAS 2010
• The ion composition plots match the bow shock model well and show tail-ward cold O+ escape.
• Trans terminator flow identified as possible ion loss mechanism
• The CME arriving on the 25th/26th May produces a relaxation and compression of the bow shock and unusual energization patterns in the inner magnetosphere.
• The solar wind ion densities show periodicities related to CIR structure
• These correlate with IPS observations11
Conclusions
Solar System Physics Group
Grande et al, Venus, RAS 2010
Solar System Physics Group
Grande et al, Venus, RAS 2010
• Note repeat of structure when repeated on 28 day period
• Same is also currently seen at Earth with ACE
• Three stream structure is a feature of current cycle
• Long term pattern of coronal holes• Note ability of STEREO to image
associated CIRs
Solar System Physics Group
Grande et al, Venus, RAS 2010
STEREO for Venus – Solar Wind studies
Solar System Physics Group
Grande et al, Venus, RAS 2010a: the radial component of the
magnetic field in VSO coordinates measured by the Venus Express magnetometer before the arrival of the first front (blue), during the pas sage of front A (green) (and the associated flux rope) and after the passage of front A (red).
b, The magnitude of the magnetic field vector before the passage of front A.
c, The magnitude of the magnetic field vector during the passage of front A.
d: The magnitude of the magnetic field vector after the passage of front A.
e: the radial distance between VEX and Venus. The time of inbound and outbound crossing of the bow shock are shown by vertical lines for each of the passages shown in the above panels.
A. P. Rouillard et al 2008
Solar System Physics Group
Grande et al, Venus, RAS 2010
• The event caused the bow shock to relax outward before strongly compressing it inwards then relaxing back to close to its original position for the outbound crossing. • The location of the bow shock as determined by the VEX magnetometer was confirmed by ASPERA4. • The range of variation of the shock distance seen during both inbound and outbound passes is roughly 0.5RV •The ion populations in the inner magnetosphere, including the ionosphere, are enhanced and energised