Image credit: NASA/JPL

Transcription

1 Image credit: NASA/JPL Aleia Paan Dr. Carol Pat Dr. Kurt Retherford 1

2 Motivation Investigation of the connection between the variabilit in Ganmede footprint brightness and in Ganmede s auroral emissions brightness through local processes occurring at Ganmede, using a 3D multi fluid simulation model Auroral Emissions Brightness Calculation Main Parameters Assumptions Results Conclusions and Future Work 2

3 Latitudinal position depends on: Position of Ganmede relative to the Jovian plasma sheet Brightness characteried b three periodic variations: Long timescale: 5 hour period Co rotation of the Jovian plasma with Jupiter flu ering of the Jovian plasma sheet over Ganmede Medium timescale: minute period Non sstema c energe c magnetospheric injection events in the vicinit of Ganmede? Short timescale: ~100 second quasi period Burst reconnections on Ganmede s magnetopause Footprint Footprint Footprint 3 [Grodent et al., 2009], Image credit: NASA Photojournal

4 HST STIS observations of ogen emissions (λ = nm) Brightness contours in Raleighs Over 4 orbits of Ganmede Emissions from Ganmede s trailing side Mostl located > 40 N/S latitude To Jupiter Spin Ais Jovian Plasma Longitudinal non uniformit of brightness emissions Brightness range: R 4 [Hall et al., 1997], Image credit: [Feldman, 2000]

5 HST ACS/SBC observation of ogen emissions (λ = nm and λ = nm) Brightness contours in Raleighs Emissions from Ganmede s Jovian facing side Latitudes of emission are uncertain b Spin Ais Jovian Plasma To Jupiter 5 [Retherford, 2009], MOP conference

6 Use a 3D multi fluid simulation model to: Stud the periodicities in the brightness of the aurora at Ganmede and the responsible local processes occurring at Ganmede Relate the above to the observed short and long period variabilit of Ganmede s auroral footprint at Jupiter 6

7 Emission from ecited ogen O* generated b electron impact dissociation of O 2 (λ = nm, forbidden line of O: 3s 5 S 0 2p 43 P): Brightness: where O 2 + e O* + O + e O + hν + O + e B(R) = n e. C(T e ). N(O 2 ) B(R) is the brightness of the aurora, in Raleigh (R) n e is the electron number densit of electrons responsible for the aurora, in cm 3 C(T e ) is the emission rate of O* generated b electron impact dissociative ecitation of O 2 which depends on electron temperature T e, in cm 3 /s N(O 2 ) is the atmospheric column densit of O 2 at Ganmede, in cm 2 7 [Hall et al., 1997], [Eviatar et al., 2000], [Retherford, 2002]

8 Range of values considered for the atmospheric column densit of molecular ogen N(O 2 ) (a,b) : N(O 2 ) (cm 2 ) From To 7.4* * *10 12 cm 2 Value used in the model for C(T e ) (c,d,e) : Electron temperature of 100 ev (average Jovian plasma electron temperature) C(100 ev) = 1.3*10 8 cm 3 /s Values used in the model for n e : Provided b a 3D multi fluid simulation code (f) Mapped onto a spherical surface above Ganmede s ionosphere where aurora occurs 8 (a) [Eviatar et al., 2000], (b). [Hall et al., 1997], ( (c). [Cosb, 1993], (d). [Marconi 2007], (e). [Burger et al., 2010], (f). [Pat and Winglee, 2004]

9 Considered 3 of the 6 Galileo flbs: Galileo Flb Position of Ganmede relative to the Jovian plasma sheet Flow speed (km/s) Mv A B (nt) B (nt) B (nt) G2 ABOVE G8 CENTER G28 BELOW [Kivelson et al., 2002]

10 Observed for different positions of Ganmede with respect to the Jovian plasma sheet: Position of Ganmede relative to the Jovian plasma sheet ABOVE CENTER BELOW Trailing Side Spin Ais To Jupiter Jovian Facing Side Flow Spin Ais Maimum Brightness (R) : direction of co rotational Jovian plasma flow : direction to Jupiter : direction of the Jovian spin ais 10

11 Observed for different positions of Ganmede with respect to the Jovian plasma sheet: Position of Ganmede relative to the Jovian plasma sheet ABOVE CENTER BELOW Trailing Side Spin Ais To Jupiter Jovian Facing Side Flow Spin Ais Maimum Brightness (R) : direction of co rotational Jovian plasma flow : direction to Jupiter : direction of the Jovian spin ais 11

12 Observed for different positions of Ganmede with respect to the Jovian plasma sheet: Position of Ganmede relative to the Jovian plasma sheet ABOVE CENTER BELOW Trailing Side Spin Ais To Jupiter Jovian Facing Side Flow Spin Ais Maimum Brightness (R) : direction of co rotational Jovian plasma flow : direction to Jupiter : direction of the Jovian spin ais 12

13 Observed for a given position of Ganmede with respect to the Jovian plasma sheet (in this case, Ganmede in below the plasma sheet): Time (s) t t t t Trailing Side Spin Ais To Jupiter Jovian Facing Spin Ais Side Flow Maimum Brightness (R) Brightness (R) : direction of co rotational Jovian plasma flow : direction to Jupiter : direction of the Jovian spin ais 13

14 Considering onl the electrons from the Jovian plasma precipitating into Ganmede s atmosphere (Ganmede in below the plasma sheet): Time (s) t t t t Trailing Side Spin Ais To Jupiter Jovian Facing Spin Ais Side Flow Maimum Brightness (R) Brightness (R) : direction of co rotational Jovian plasma flow : direction to Jupiter : direction of the Jovian spin ais 14

15 The present stud: Agrees well with the HST observations of Ganmede s aurora Suggests the presence of short and long period variabilities in the auroral brightness at Ganmede due to local processes Supports the hpothesis of a correlation between the variabilit of Ganmede s auroral footprint on Jupiter s ionosphere and the variabilit in brightness and morpholog of the aurora at Ganmede Provides evidence for the need to account for the electron temperature in the calculation of the auroral brightness 15

16 Investigation of the electron temperature dependence: Constrain the temperature of the electrons responsible for the aurora Cold electrons trapped in the closed field lines region near the equator Hot electrons accelerated through reconnection and precipitating along open field lines near the polar caps Incorporate the electron temperature dependence in the calculation of the auroral brightness through the emission rate C(T e ) 16

17 17 Image credit: Outer Planet Flagship Mission/JPL

18 18

19 Investigation of the electron number densit for the G1 and G2 flbs: 19 Left picture credit: [Eviatar et al., 2000]

20 Plots of magnetic field components obtained b 3D multi fluid model for G2 flb compared to Galileo MAG data 20

21 Plots of magnetic field components obtained b 3D multi fluid model for G8 flb compared to Galileo MAG data 21

22 Plots of magnetic field components obtained b 3D multi fluid model for G28 flb compared to Galileo MAG data 22

23 Densities of e (ionospheric and Jovian) obtained b 3D multi fluid model for the G28 flb 23

24 Temperatures of e (ionospheric and Jovian) obtained b 3D multifluid model for the G28 flb 24

25 Densities and temperatures of H + obtained b 3D multi fluid model for the G28 flb 25

26 Densities and temperatures of O + obtained b 3D multi fluid model for the G28 flb 30 26

27 Investigation of the electron number densit for the G1 and G2 flbs: Log of Electron densit (cm-3) G1 Inbound Outbound Radial Distance from Ganmede (Rg) G2 27 Left picture credit: [Eviatar et al., 2000]

28 Ion species s Conservation of mass: Conservation of momentum: Pressure evolution equation: Evolution of magnetic field: Current: 28

29 Electron velocit: Modified Ohm s law: Resistivit term Onl in the ionosphere Ions species modeled: Jovian magnetospheric plasma (H +, S +, S 2+, O + and O 2+ ) treated as a single fluid of light ions Ion populations in Ganmede s ionosphere: H +, O + Calibration with Galileo magnetometer data and Plasma Wave Eperiment 29

30 Jovian magnetospheric plasma Speed = 140/180 km/s Bulk mass = 13 amu Ganmede s ionospheric plasma 2:1 H + to O + ionospheric outflows (sputtering of water ice) 2000 H + ions/cm 3 and 1000 O + ions/cm 3 at the base of the ionosphere Scale height = 263 km Temperatures = 9 ev for equatorial region to 0.1 ev for polar regions Resistivit = 1.2*10 4 Ω/m 30

31 3.0 Ganmede s UV aurora Jovian Magnetospheric Plasma temperature Ganmede s ionospheric O + temperature Ganmede s ionospheric H + temperature Jovian Magnetospheric Plasma Has access to Ganmede s ionosphere through the cusps Eperiences heating to the kev range reconnection Ionospheric O + and H + Ver little acceleration Warmer temperatures in the closed field line region 31 Images credit: [Pat and Winglee, 2004]

32 Jovian Magnetospheric Plasma bulk pressure Ganmede s ionospheric O + bulk pressure Ganmede s ionospheric H + bulk pressure Jovian Magnetospheric Plasma Has access to Ganmede s ionosphere through the cusps Ver little access to Ganmede s magnetosphere Eception for highl energetic ions Ionospheric O + Largel populate Ganmede s inner magnetosphere and magnetotail Ionospheric H + Mostl populate Ganmede s inner magnetosphere 32 Images credit: [Pat and Winglee, 2004]

33 Magnetic field morpholog at Ganmede + ions species densities Ion species densities + flow velocities in the plane Ion species densities + flow velocities in the equatorial plane 33 Asmmetric flow Images credit: [Pat et al., 2008]

34 Jovian Magnetospheric Plasma loss to Ganmede s ionosphere: ~1.5*10 27 amu/s Higher energ ions and electrons driving sputtering, aurora, and airglow can also gain access into Ganmede s ionosphere Ionospheric loss rates at ~ 24 R G (magnetotail): ~4*10 26 H + ions/s ~1*10 26 O + ions/s 34 Image credit: NASA/JPL (False Color from Galileo)

35 Previous model: + Provides evidence of magnetic reconnection at the origin of the trailing hemisphere aurora at Ganmede + Provides energ distribution in Ganmede s magnetosphere + Provides repartition of ion populations in Ganmede s magnetosphere Does not eplain auroral brightness, morpholog, and periodicit 35

36 Future stud will: + Treat each ion species in the Jovian Magnetospheric Plasma separatel + Account for electron precipitations and relates them to the aurora Brightness (electrons energ, ionospheric densit) Morpholog Variabilit Periodicit 36