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Electrodynamics of the Martian Dynamo Region The M 4 Approach er´ emy A. Riousset, 1,2 Carol S. Paty, 1 Robert J. Lillis, 3 Matthew O. Fillingim, 3 Scott L. England, 3 Paul G. Withers, 4 and John P. M. Hale 1 1 School of Earth and Atmospheric Sciences, Georgia Tech, Atlanta, GA, 30306, USA 2 Institut f¨ ur Theoretische Physik, TU-BS, Braunschweig, D-38106, Germany ([email protected]) 3 Space Sciences Lab, UC Berkeley, Berkeley, CA, 94720, USA 4 Astronomy Department, Boston U, Boston, MA, 02215, USA January 21, 2014 TU-BS, ITP-NPS, Braunschweig, DE

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Page 1: Electrodynamics of the Martian Dynamo Region - Rioussetriousset.com/jeremy/wp-content/uploads/RioussetTUBS2014... · Electrodynamics of the Martian Dynamo Region ... Introduction

Electrodynamics of the Martian Dynamo RegionThe M4 Approach

Jeremy A. Riousset,1,2 Carol S. Paty,1 Robert J. Lillis,3 Matthew O. Fillingim,3

Scott L. England,3 Paul G. Withers,4 and John P. M. Hale1

1School of Earth and Atmospheric Sciences, Georgia Tech, Atlanta, GA, 30306, USA2Institut fur Theoretische Physik, TU-BS, Braunschweig, D-38106, Germany ([email protected])3Space Sciences Lab, UC Berkeley, Berkeley, CA, 94720, USA4Astronomy Department, Boston U, Boston, MA, 02215, USA

January 21, 2014

TU-BS, ITP-NPS, Braunschweig, DE

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Electrodynamics of the Martian Dynamo RegionThe M4 Approach

Jeremy A. Riousset,1,2 Carol S. Paty,1 Robert J. Lillis,3 Matthew O. Fillingim,3

Scott L. England,3 Paul G. Withers,4 and John P. M. Hale1

1School of Earth and Atmospheric Sciences, Georgia Tech, Atlanta, GA, 30306, USA2Institut fur Theoretische Physik, TU-BS, Braunschweig, D-38106, Germany ([email protected])3Space Sciences Lab, UC Berkeley, Berkeley, CA, 94720, USA4Astronomy Department, Boston U, Boston, MA, 02215, USA

January 21, 2014

TU-BS, ITP-NPS, Braunschweig, DE

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Electrodynamics of Mars’ dynamo region

Keypoints:

• Mars is neither magnetized like Earth,Jupiter, Saturn, or Uranus, nor demagne-tized like Venus: hence it is curious.

• Our work is a collaboration between intru-mentalists (at SSL), and modelers (BU, GT,SSL).

30”

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Introduction Motivations The M4 Approach Results Conclusions References

Outline

Introduction

Modeling of Mars’ Ionosphere: Why?

Modeling of Mars’ Ionosphere: How?

Modeling of Mars’ Ionosphere: And?

Conclusions

Riousset et al. | Electrodynamics of Mars’ dynamo region | 3/32

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Introduction Motivations The M4 Approach Results Conclusions References

Outline

Introduction

Modeling of Mars’ Ionosphere: Why?

Modeling of Mars’ Ionosphere: How?

Modeling of Mars’ Ionosphere: And?

Conclusions

20

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Electrodynamics of Mars’ dynamo region

Introduction

Outline

Keypoints:

• Mars is fascinating. ‘‘He [Dave Brain] can’tbelieve that someone is willing to pay himto think about Mars all day.’’ About DaveBrain as a Lecturer at Berkeley.

• Here my goal is to explain to you why westudy Mars’ ionosphere, how our group doesit, and what our recent results are.

1’00”

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Introduction Motivations The M4 Approach Results Conclusions References

Objectives of the Study

Figure : Model ~B-field configuration near a magnetic cusp.

The M4 approach [Riousset et al., 2013a]:

Mars (CO2, & O)Multifluid (O+

2 , CO+2 , O+, & e)

MagnetoHydroDynamic (MHD)Model

Two case studies [Riousset et al., 2013b]:

Cusp: case of the isolated buried mag-netic dipoleArcades: Terra Sirenum Analogy

Riousset et al. | Electrodynamics of Mars’ dynamo region | 4/32

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Introduction Motivations The M4 Approach Results Conclusions References

Objectives of the Study

Figure : Model ~B-field configuration near a magnetic cusp.

The M4 approach [Riousset et al., 2013a]:

Mars (CO2, & O)Multifluid (O+

2 , CO+2 , O+, & e)

MagnetoHydroDynamic (MHD)Model

Two case studies [Riousset et al., 2013b]:

Cusp: case of the isolated buried mag-netic dipoleArcades: Terra Sirenum Analogy2

01

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Electrodynamics of Mars’ dynamo region

Introduction

Objectives of the Study

Keypoints:

• We are using a Multifluid, i.e., not parti-cle approach to study the macroscopic dy-namics of the atmospheric plasma, due toelectromagnetic effects, and hydrodynamic(classic fluid mechanic effects) via MHDapproach.

• Our work is based on observations of theplanet’s atmosphere and ionosphere (Viking)and magnetic fields (MGS/MagnetoMeter)to propose and explain of observable effects:Mars is losing its atmosphere.

1’45”

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Introduction Motivations The M4 Approach Results Conclusions References

Follow the Water!

Mars Facts:

g≈3.7 m/s2

T≈210 K (130–308 K)

P≈0.006P=600 Pa

Atmosphere: &95% CO2, O

Neutral winds

Dense atmosphere⇓

Greenhouse effect⇓

Temperature ⇓

Liquid water

List of missions to Mars (wiki).

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Introduction Motivations The M4 Approach Results Conclusions References

Follow the Water!

Mars Facts:

g≈3.7 m/s2

T≈210 K (130–308 K)

P≈0.006P=600 Pa

Atmosphere: &95% CO2, O

Neutral winds

Dense atmosphere⇓

Greenhouse effect⇓

Temperature ⇓

Liquid water

List of missions to Mars (wiki).

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Electrodynamics of Mars’ dynamo region

Modeling of Mars’ Ionosphere: Why?

‘‘Atmosphere? Atmosphere? Est-ce que j’ai une gueuled’atmosphere?’’ (Hotel du Nord, Marcel Carne, 1938)

Follow the Water!

Keypoints:

• Mars is one of the most studies planet in thesolar system. The Martian canals were ini-tially believed to be artefacts and thereforeevidences of the existence of extraterrestrialintelligent life.

• The recent space exploration programadopted the so-called ‘‘Follow the waterapproach’’. It started by exploring the cur-rent reservoirs of H2O and the next missionMAVEN will focus on the Martian atmo-sphere/ionosphere down to 120 km.

• The presence of a dense atmosphere (muchdenser than it currently is) is absolutely nec-essary to maintain water in liquid form atthe surface, a condition which is closely as-sociated with the possibility of life.

2’30”

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Introduction Motivations The M4 Approach Results Conclusions References

‘‘The Thin Red Line’’

Figure : Earth’s atmosphere today. Image cour-tesy: http://thebarometer.podbean.com/.

Figure : Mars’ atmosphere today. Image courtesy:NASA.

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Introduction Motivations The M4 Approach Results Conclusions References

‘‘The Thin Red Line’’

Figure : Earth’s atmosphere today. Image cour-tesy: http://thebarometer.podbean.com/.

Figure : Mars’ atmosphere today. Image courtesy:NASA.

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Electrodynamics of Mars’ dynamo region

Modeling of Mars’ Ionosphere: Why?

‘‘Atmosphere? Atmosphere? Est-ce que j’ai une gueuled’atmosphere?’’ (Hotel du Nord, Marcel Carne, 1938)

‘‘The Thin Red Line’’

Keypoints:

• It all happens in this very thin line observedin these zenith pictures. Blue on Earth dueto Rayleigh scaterring, and red one Mars.

• Mars’ atmosphere is much thinner thanEarth’s (the pictures are not to scale), be-cause it has lost most of it (∼96%).

3’15”

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Introduction Motivations The M4 Approach Results Conclusions References

‘‘The Great Escape’’

Mars Facts:

No dipolar, ‘‘Earth-like’’magnetic-field

Remanent crustal fields

Ionosphere: e & 71% O+2 , 25%

CO+2 , 4% O+

Figure : Mars Atmospheric VolatileEvolutioN (MAVEN). Image courtesy:NASA.

Figure : Image Courtesy: [Jedrich, 2012].

Riousset et al. | Electrodynamics of Mars’ dynamo region | 8/32

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Introduction Motivations The M4 Approach Results Conclusions References

‘‘The Great Escape’’

Mars Facts:

No dipolar, ‘‘Earth-like’’magnetic-field

Remanent crustal fields

Ionosphere: e & 71% O+2 , 25%

CO+2 , 4% O+

Figure : Mars Atmospheric VolatileEvolutioN (MAVEN). Image courtesy:NASA.

Figure : Image Courtesy: [Jedrich, 2012].20

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Electrodynamics of Mars’ dynamo region

Modeling of Mars’ Ionosphere: Why?

‘‘Atmosphere? Atmosphere? Est-ce que j’ai une gueuled’atmosphere?’’ (Hotel du Nord, Marcel Carne, 1938)

‘‘The Great Escape’’

Keypoints:

• The loss of the Martian atmosphere is be-lieved to be related to the shutoff of itscore-dynamo (∼4 Gyr ago). It is proba-bly not the only mechanisms, but is worthinvestigating it, we think.

• Earth is protected by its magnetosphere,but Mars is not and there are many wayin which this absence of a magnetospherecould lead to a loss of the atmosphere.

4’15”

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Introduction Motivations The M4 Approach Results Conclusions References

Mars’s Magnetic Environment

Figure : Image courtey: DTU Space, [Luhmann and Russell, 1997].

Bow shock: Supersonic/superalfvenic speed→ VSW=γPi

ρi

Magnetic Pile-up Boundary: Local deflection of solar wind protons → VSW=0

Ionopause: Pressure balance:ρSWV 2

SW

2=P

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Introduction Motivations The M4 Approach Results Conclusions References

Mars’s Magnetic Environment

Figure : Image courtey: DTU Space, [Luhmann and Russell, 1997].

Bow shock: Supersonic/superalfvenic speed→ VSW=γPi

ρi

Magnetic Pile-up Boundary: Local deflection of solar wind protons → VSW=0

Ionopause: Pressure balance:ρSWV 2

SW

2=P

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Electrodynamics of Mars’ dynamo region

Modeling of Mars’ Ionosphere: Why?

‘‘Atmosphere? Atmosphere? Est-ce que j’ai une gueuled’atmosphere?’’ (Hotel du Nord, Marcel Carne, 1938)

Mars’s Magnetic Environment

Keypoints:

• At Mars, the bow shock still exists due tothe planet’s traveling at high speed throughthe solar wind.

• The absence of a magnetic dipole to shieldthe planet reveals a drapping effect. Onthe dayside, the solar wind magnetic field isparallel to the surface, and ‘‘wraps around’’the planet to end up almost perpendicularto the surface on the nightside.

4’15”

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Introduction Motivations The M4 Approach Results Conclusions References

Mars’ Magnetic Map

Figure : Radial magnetic field (Br ) computed at 200 km altitude in color, overlain on gray-shaded topographic gradient map of Mars (MOLA data). The dark grey bands show regionsof inadequate data coverage [Purucker et al., 2000, Plate 1].

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Introduction Motivations The M4 Approach Results Conclusions References

Mars’ Magnetic Map

Figure : Radial magnetic field (Br ) computed at 200 km altitude in color, overlain on gray-shaded topographic gradient map of Mars (MOLA data). The dark grey bands show regionsof inadequate data coverage [Purucker et al., 2000, Plate 1].

20

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Electrodynamics of Mars’ dynamo region

Modeling of Mars’ Ionosphere: Why?

‘‘Atmosphere? Atmosphere? Est-ce que j’ai une gueuled’atmosphere?’’ (Hotel du Nord, Marcel Carne, 1938)

Mars’ Magnetic Map

Keypoints:

• There is another major component of themagnetic field on Mars: the remanentcrustal field, which are embedded in thecrust and do not depend on the day/nightside.

• The intrinsic magnetic field at Mars variestherefore temporarily (day-/nighttime) andgeographically (south hemisphere anomaly)on a scale of a few 10–100 km (representa-tion obtained with the model of Puruckeret al. [2000]).

5’00”

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Introduction Motivations The M4 Approach Results Conclusions References

Mars’ Magnetic Environment: A Unique Plasma Lab

Figure : Image courtesy: NASA/JPL.

Complex magnetic field configuration from re-manent crustal fields with:

open/closed magnetic loopstrong/weak magnetic field magnitude

Daytime/nighttime asymmetry with respect tothe solar wind interaction

Figure : The percent occurrence of openmagnetic field lines (i.e., connecting theIMF to the Martian atmosphere) at ∼400km altitude on the nightside and dayside[Brain et al., 2007].

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Introduction Motivations The M4 Approach Results Conclusions References

Mars’ Magnetic Environment: A Unique Plasma Lab

Figure : Image courtesy: NASA/JPL.

Complex magnetic field configuration from re-manent crustal fields with:

open/closed magnetic loopstrong/weak magnetic field magnitude

Daytime/nighttime asymmetry with respect tothe solar wind interaction

Figure : The percent occurrence of openmagnetic field lines (i.e., connecting theIMF to the Martian atmosphere) at ∼400km altitude on the nightside and dayside[Brain et al., 2007].

20

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Electrodynamics of Mars’ dynamo region

Modeling of Mars’ Ionosphere: Why?

‘‘Atmosphere? Atmosphere? Est-ce que j’ai une gueuled’atmosphere?’’ (Hotel du Nord, Marcel Carne, 1938)

Mars’ Magnetic Environment: A Unique Plasma Lab

Keypoints:

• We can map the connection between thesolar wind magnetic field and the crustalmagnetic field to retrieve the topology ofthe magnetic field. This picture is fromMGS/MG measurements, and was used tovalidate the model of the previous slide.

• The complexity of the structure of the Mar-tian magnetic field can be broken down tothe dipole scale. We can use many magneticdipole, each creating a piece of the Martiancurstal field, to reproduce the map of Brainet al. [2007] [Langlais et al., 2004; Puruckeret al., 2000].

6’30”

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Introduction Motivations The M4 Approach Results Conclusions References

Auroras

Figure : Aurora Australis as captured by NASA’sIMAGE satellite, overlaid onto NASA’s satellite-based Blue Marble image. Image courtesy:NASA.

Figure : Mars’ aurora? Image courtesy:ESA/Mats Holmstrom.

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Introduction Motivations The M4 Approach Results Conclusions References

Auroras

Figure : Aurora Australis as captured by NASA’sIMAGE satellite, overlaid onto NASA’s satellite-based Blue Marble image. Image courtesy:NASA.

Figure : Mars’ aurora? Image courtesy:ESA/Mats Holmstrom.

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Electrodynamics of Mars’ dynamo region

Modeling of Mars’ Ionosphere: Why?

‘‘Atmosphere? Atmosphere? Est-ce que j’ai une gueuled’atmosphere?’’ (Hotel du Nord, Marcel Carne, 1938)

Auroras

Keypoints:

• The magnetic field on Earth is directly visi-ble on Earth. Auroras forms at the boundarybetween open and closed magnetic field line:this is the aurora circle.

• At Mars, the complexity of the magneticfield topology yields many small ‘‘magneticcusp’’ similar to Earth’s cusp, and an auroraon Mars is expected to follow a more intri-cated path. Particle precipitation modelssuggest that a Martian aurora could looklike the left-hand side picture. In this plot,particle precipitations are shown in green(the sensibility of our instruments has not al-lowed to record them in the visible yet), andone can think of it as a false color image.

7’00”

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Introduction Motivations The M4 Approach Results Conclusions References

Mars’ Dynamo Region (I)

Definition: A dynamo current is generated by differential motions of positive andnegative species.Mars’ case:

positive ions → governed by collision with neutrals (demagnetized)

electrons → governed by gyromotion (magnetized)

Estimates based on:O+

2 : most abundant ionCO2: most abundant neutralelectron

Altitudes:HL: lower boundary of the dynamo regionHU: upper boundary of the dynamo region

ΩO+2

= νO+2 −CO2

(HU) & Ωe = νe−CO2 (HL)

z&HUνO+

2 −CO2ΩCO2 Magnetized ions ⇒ No dynamo current

νe−CO2Ωe Magnetized electrons

HL.z.HUνO+

2 −CO2&ΩCO2 Demagnetized ions ⇒ Ionospheric current

νe−CO2Ωe Magnetized electrons

z.HLνO+

2 −CO2&ΩCO2 Demagnetized ions ⇒ No differential current

νe−CO2&Ωe Demagnetized electrons

Riousset et al. | Electrodynamics of Mars’ dynamo region | 13/32

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Introduction Motivations The M4 Approach Results Conclusions References

Mars’ Dynamo Region (I)

Definition: A dynamo current is generated by differential motions of positive andnegative species.Mars’ case:

positive ions → governed by collision with neutrals (demagnetized)

electrons → governed by gyromotion (magnetized)

Estimates based on:O+

2 : most abundant ionCO2: most abundant neutralelectron

Altitudes:HL: lower boundary of the dynamo regionHU: upper boundary of the dynamo region

ΩO+2

= νO+2 −CO2

(HU) & Ωe = νe−CO2 (HL)

z&HUνO+

2 −CO2ΩCO2 Magnetized ions ⇒ No dynamo current

νe−CO2Ωe Magnetized electrons

HL.z.HUνO+

2 −CO2&ΩCO2 Demagnetized ions ⇒ Ionospheric current

νe−CO2Ωe Magnetized electrons

z.HLνO+

2 −CO2&ΩCO2 Demagnetized ions ⇒ No differential current

νe−CO2&Ωe Demagnetized electrons20

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Electrodynamics of Mars’ dynamo region

Modeling of Mars’ Ionosphere: Why?

‘‘Atmosphere? Atmosphere? Est-ce que j’ai une gueuled’atmosphere?’’ (Hotel du Nord, Marcel Carne, 1938)

Mars’ Dynamo Region (I)

Keypoints:

• A dynamo current is generated by differen-tial motions of positive and negative species.Between ∼100–200 km, ion motion is drivenby collisions and electrons driven by themagnetic field.

• Above the dynamo regions, both electronsand ions are driven by the magnetic field (gy-romotions), and below, there either absent(very low density) or guided by collisions.

8’30”

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Introduction Motivations The M4 Approach Results Conclusions References

Mars’ Dynamo Region (II)

Figure : Expected locations of nighttime ionospheric currents (a) ~B=20 nT iz (typical);

(b) ~B=2000 nT iz (near ne peak).

Riousset et al. | Electrodynamics of Mars’ dynamo region | 14/32

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Introduction Motivations The M4 Approach Results Conclusions References

Mars’ Dynamo Region (II)

Figure : Expected locations of nighttime ionospheric currents (a) ~B=20 nT iz (typical);

(b) ~B=2000 nT iz (near ne peak).20

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Electrodynamics of Mars’ dynamo region

Modeling of Mars’ Ionosphere: Why?

‘‘Atmosphere? Atmosphere? Est-ce que j’ai une gueuled’atmosphere?’’ (Hotel du Nord, Marcel Carne, 1938)

Mars’ Dynamo Region (II)

Keypoints:

• In this graphical representation of the mech-anisms described before, one can see thatthe altitude of the dynamo regions is di-rectly dependent of the magnitude of themagnetic field.

• The collision frequency couples the chargecarriers (ions and electrons) to the neutrals,while the gyrofrequency couples the chargecarriers to the magnetic field. The green-shadowed region shows where ions and elec-trons are coupled to different processes.

10’00”

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Introduction Motivations The M4 Approach Results Conclusions References

Previous Modeling of Mars’ E-M Environment

Hybrid [Boesswetter et al., 2010; Brechtand Ledvina, 2010; Brecht and Thomas,1988]

Individual ions/neutralizing electronsSingle fluid, multispecies [Ma et al.,2002, 2004]

1 ion fluid/neutralizing electronsMultifluid, multispecies [e.g., Harnett,2009; Harnett and Winglee, 2006; Saueret al., 1997]

Multiple ion fluids/neutralizing electrons

Figure : Magnetic field strength from a hybridsimulation of Mars [Ledvina et al., 2008].

Riousset et al. | Electrodynamics of Mars’ dynamo region | 16/32

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Introduction Motivations The M4 Approach Results Conclusions References

Previous Modeling of Mars’ E-M Environment

Hybrid [Boesswetter et al., 2010; Brechtand Ledvina, 2010; Brecht and Thomas,1988]

Individual ions/neutralizing electronsSingle fluid, multispecies [Ma et al.,2002, 2004]

1 ion fluid/neutralizing electronsMultifluid, multispecies [e.g., Harnett,2009; Harnett and Winglee, 2006; Saueret al., 1997]

Multiple ion fluids/neutralizing electrons

Figure : Magnetic field strength from a hybridsimulation of Mars [Ledvina et al., 2008].2

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Electrodynamics of Mars’ dynamo region

Modeling of Mars’ Ionosphere: How?

Previous models

Previous Modeling of Mars’ E-M Environment

Keypoints:

• There are numerous models focused on theMartian electrodynamics. Some use a fluidapproach (single fluid/multi-species MHD,true multifluid MHD), other a ‘‘particular’’approach (hybrid models, which uses super-particles). All requires assumptions. Noneis good-for-everything.

• The model have focus on the planetary scale,but we look at a smaller domain (600 kmvs. 2-5×R, R=3390 km).

11’00”

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Introduction Motivations The M4 Approach Results Conclusions References

Multifluid Model Formulation (I)

Based on Paty and Winglee [2006] for Ganymede published in [Riousset et al., 2013a]

Conservation of matter (O+2 , CO+

2 , & O+)

Plasma approximation (e)

Equation of state (O+2 , CO+

2 , O+, & e)

Conservation of momentum (O+2 , CO+

2 , &O+)

Plasma current definition (e)

∂ni

∂t= −∇ ·

(ni~Vi

)ne =

∑i

ni

∂Pi

∂t= −∇ ·

(Pi~Vi

)+ (γ − 1)~Vi · ∇Pi

∂Pe

∂t= −∇ ·

(Pe~Ve

)+ (γ − 1)~Ve · ∇Pe

ρi∂~Vi

∂t= −ρi

(~Vi · ∇

)~Vi + qini

(~E + ~Vi × ~B

)−∇Pi −

ρiGMM

(RM + r)2 r

+∑n

ρiνi−n

(~Vn − ~Vi

)~Ve =

∑i

ni ~Vi

ne−

~J

ene

Riousset et al. | Electrodynamics of Mars’ dynamo region | 17/32

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Introduction Motivations The M4 Approach Results Conclusions References

Multifluid Model Formulation (I)

Based on Paty and Winglee [2006] for Ganymede published in [Riousset et al., 2013a]

Conservation of matter (O+2 , CO+

2 , & O+)

Plasma approximation (e)

Equation of state (O+2 , CO+

2 , O+, & e)

Conservation of momentum (O+2 , CO+

2 , &O+)

Plasma current definition (e)

∂ni

∂t= −∇ ·

(ni~Vi

)ne =

∑i

ni

∂Pi

∂t= −∇ ·

(Pi~Vi

)+ (γ − 1)~Vi · ∇Pi

∂Pe

∂t= −∇ ·

(Pe~Ve

)+ (γ − 1)~Ve · ∇Pe

ρi∂~Vi

∂t= −ρi

(~Vi · ∇

)~Vi + qini

(~E + ~Vi × ~B

)−∇Pi −

ρiGMM

(RM + r)2 r

+∑n

ρiνi−n

(~Vn − ~Vi

)~Ve =

∑i

ni ~Vi

ne−

~J

ene20

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Modeling of Mars’ Ionosphere: How?

The M4 approach

Multifluid Model Formulation (I)

Keypoints:

• ‘‘Fluid variables’’ (densities, pressure, andvelocities) are calculated using classic fluidequations (conservations of matter, momen-tum, and equation of state).

• Our model is specific in that it does notdefine a conductivity coefficient but trullymodel its effects via the collisions.

Comments:

• Fundamental equations

• Elastic ion–neutral collision

11’00”

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Multifluid Model Formulation (II)

Maxwell–Faraday equation (~B)

Maxwell–Ampere equation (~J)

Generalized Ohm’s law (~E)

∂~B

∂t= −∇× ~E

~J =∇× ~Bµ0

~E =~J × ~Bene

−∑i

ni ~Vi × ~Bne

− ∇Pe

ene+me

e

∑n

νn−e

(~Vn − ~Ve

)

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Multifluid Model Formulation (II)

Maxwell–Faraday equation (~B)

Maxwell–Ampere equation (~J)

Generalized Ohm’s law (~E)

∂~B

∂t= −∇× ~E

~J =∇× ~Bµ0

~E =~J × ~Bene

−∑i

ni ~Vi × ~Bne

− ∇Pe

ene+me

e

∑n

νn−e

(~Vn − ~Ve

)

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Electrodynamics of Mars’ dynamo region

Modeling of Mars’ Ionosphere: How?

The M4 approach

Multifluid Model Formulation (II)

Keypoints:

• ‘‘Electromagnetic variables’’ (magnetic field,current, and electric field) are calculated us-ing Maxwell-Faraday and Maxwell-Ampereequations and the generalized Ohm’s law.

• Here again appears the collisions of elec-trons with neutrals. In the absence of suchcollisions, there is no dynamo region possi-ble.

Comments:

• Fundamental equations (implemented)

• Electron–neutral collisions (implemented)

12’00”

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Initial Conditions

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Initial Conditions

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Electrodynamics of Mars’ dynamo region

Modeling of Mars’ Ionosphere: How?

The M4 approach

Initial Conditions

Keypoints:

• The only records of ion density profile wehave come from Viking I and II landers in...1976.

• We use a bit of ingeniosity to derive thefraction of each ion in the ionosphere anduse the well-known electron density profilesto create our initial ionosphere. We topthat with known temperature and neutraldensities, complete it with the perfect gaslaw to create a full set of initial conditions.

Comments:

• Nighttime ionosphere (no photoionization)

• Non-uniform 3-D Cartesian grid:

-- 800 km×800 km×300 km-- Horizontal resolution: 10.0–∼35 km-- Vertical resolution: 4.0–∼22 km

• 2-step Runge-Kutta method [Balay et al.,1997; Pacheco, 1996; Press et al., 1992]

-- δt.1 ms

Comments (cont.):

• Initial conditions:

-- Horizontally uniform atmo-spheric/ionospheric profiles at t=0 s

-- ~Vn=100 m/s x

-- ~Vi=100 m/s y

Figure : 100 nT surface levels of Mars’ crustalfields using Purucker et al.’s [2000] magnetic fieldmodel [Brecht and Ledvina, 2010].

13’30”

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Magnetic Field

Isolated dipole

Vertical, upward, buried at –20 km

Magnetic moment: ~µ=1016 A·m2 z

Analog to cusp (e.g., at(15 N;15 E) and (10 S;110 E))

Building block for complex structure(loop, arcades)

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Magnetic Field

Isolated dipole

Vertical, upward, buried at –20 km

Magnetic moment: ~µ=1016 A·m2 z

Analog to cusp (e.g., at(15 N;15 E) and (10 S;110 E))

Building block for complex structure(loop, arcades)

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Electrodynamics of Mars’ dynamo region

Modeling of Mars’ Ionosphere: And?

Magnetic cusp

Magnetic Field

Keypoints:

• We simplify the problem into two fundamen-tal cases: a magnetic cusp, and magneticarcades. The first is both representative oflocal geometry, and building block of thesecond.

• In this first case, a single dipole is embed-ded at −20 km, and produces the cusp con-figuration, with reasonable magnetic fieldmagnitudes.

14’15”

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Electric Field

Generalized Ohm’s law:

~E = ~E1 + ~E2 + ~E3 + ~E4

~E1 =~J × ~Bene

~E2 = −∑i

ni ~Vi × ~Bne

~E3 = −∇Pe

ene

~E4 =me

e

∑t=i,n

νte(~Vt − ~Ve

)

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Electric Field

Generalized Ohm’s law:

~E = ~E1 + ~E2 + ~E3 + ~E4

~E1 =~J × ~Bene

~E2 = −∑i

ni ~Vi × ~Bne

~E3 = −∇Pe

ene

~E4 =me

e

∑t=i,n

νte(~Vt − ~Ve

)

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Electrodynamics of Mars’ dynamo region

Modeling of Mars’ Ionosphere: And?

Magnetic cusp

Electric Field

Keypoints:

• The effects of each component of the gen-eralized Ohm’s law can be visualized in thisprojection of the electric field in 3 planes (2vertical planes and 1 horizontal at 112 km,in the dynamo region).

• The uniform neutral winds break the cylin-drical symmetries creating the differencesobserved in the figure.

~Eα Direction of ~Eα

~E1 =~J × ~Bene

−z & outward directed from the cusp

~E2 = −∑i

ni ~Vi × ~Bne

+y &

+z if y ≤ 0−z if y ≥ 0

~E3 = −∇Pe

ene

−z if z ≤ 130 km+z if 130 ≤ z ≤ 160 km

~E4 = mee

∑t=i,n νte

(~Vt − ~Ve

) ' ~0 away from the cusphorizontal, CCW else

17’00”

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Dynamo Current

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Dynamo Current

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Electrodynamics of Mars’ dynamo region

Modeling of Mars’ Ionosphere: And?

Magnetic cusp

Dynamo Current

Keypoints:

• The ions are deviated into the neutral winddirections by collisions. Therefore, the torus-

shaped current forms due to the ~E×~B-driftof electrons.

• One can verify that the direction of thecurrent can also be retrieved from the right-

hand rule: ~J=∇× ~Bµ0

Comments:

• solid black arrows indicate the direction ofthe dynamo current

• solid magenta lines indicate the magneticfield lines

18’00”

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Magnetic Field of Terra Sirenum

Figure : Image courtesy Michael E. Purucker

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Magnetic Field of Terra Sirenum

Figure : Image courtesy Michael E. Purucker

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Modeling of Mars’ Ionosphere: And?

Terra Sirenum

Magnetic Field of Terra Sirenum

Keypoints:

• The magnetic map of Mars [Brain et al.,2007] and the models [Langlais et al., 2004;Purucker et al., 2000] show a striped mag-netic field region in Terra Sirenum (60S,180E). This region is likely to display mag-netic ‘‘arcades’’.

• Magnetic striped structure can be efficientlymodel using a dipole equivalent approach.

20’00”

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Magnetic Field

9 dipoles

Vertical, upward and downward, buried at –20 km

Magnetic moment: ~µ=±1016 A·m2 z

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Magnetic Field

9 dipoles

Vertical, upward and downward, buried at –20 km

Magnetic moment: ~µ=±1016 A·m2 z20

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Electrodynamics of Mars’ dynamo region

Modeling of Mars’ Ionosphere: And?

Terra Sirenum

Magnetic Field

Keypoints:

• For illustrative/descriptive purposes, onecan use as few as 9 dipoles to create rea-sonable magnetic arcades.

• We use three rows of dipoles evenly spaced,100 km-apart. The central row is consti-tuted of inverted diples, and flanked of tworows of upward dipoles just like the one weuse to produce the previous example.

• Inverted dipoles act exactly as upward dipoleexcept that they reverse the asymmetry in~E .

22’00”

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Dynamo Current

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Dynamo Current

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Modeling of Mars’ Ionosphere: And?

Terra Sirenum

Dynamo Current

Keypoints:

• The organized pattern of the modeled dy-namo current can be straightforwardly ex-plained using the results magnetic dipoles,and the principle of superposition.

• There is a current developing above theregions of converging field lines, but notabove the magnetic loops.

Results:

• The solid black arrows indicate the directionof the dynamo current.

• The colormap shows the amplitude of thecurrent density with blue representing thelower values, and red the more intense cur-rents.

• The solid magenta lines indicate the mag-netic field lines.

23’00”

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Fluxes of Ions at z≈300 km

Fi (z=300 km) =x

ni ~Vi · z dx dy

Fi≥0 ⇒ ion move toward the upper ionosphere

Fi≤0 ⇒ ion move downward (toward the lower atmosphere)

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Fluxes of Ions at z≈300 km

Fi (z=300 km) =x

ni ~Vi · z dx dy

Fi≥0 ⇒ ion move toward the upper ionosphere

Fi≤0 ⇒ ion move downward (toward the lower atmosphere)

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Electrodynamics of Mars’ dynamo region

Modeling of Mars’ Ionosphere: And?

Charge carrier dynamics

Fluxes of Ions at z≈300 km

Keypoints:

• We compare the dynamics of ions through ahorizontal plane at 300 km altitude. Whilewe use 9 sources to produce the magneticfield of the arcades, and only one for thecusp, it appears that the magnetic cuspfavors upwards motions over the magneticarcades.

• Strongly magnetized regions of Mars (e.g.,Terra Sirenum) can efficiently shield thelocal atmosphere and alter the motion ofcharged particles from the lower to the up-per atmosphere.

• This motions of charge carriers from thelower ionosphere to the upper atmosphereoffer a preferred path towards the escape ofions to space and therefore directly pertainsto the question of the atmospheric losses atMars.

Comments:

• Blue, red, and green lines distinguish O+2 ,

CO+2 , and O+ fluxes, respectively.

• Solid lines→ Cusp; Dashes lines→ Arcades

25’00”

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Principal Contributions

The principal results and contributions following from this work can be summarized asfollows:

1. The dynamo current forms in a doughnut shape around the base of an isolatedmagnetic cusp due to the ~E×~B-drift of electrons;

2. The asymmetry in the horizontal component of the electric field is explained bythe dependence of ~E on the collision-driven ion dynamics;

3. The organized pattern of the dynamo current produced by a striped magneticfield topology can be straightforwardly explained using the results from isolatedvertically oriented, upward and downward magnetic dipoles, and the principle ofsuperposition;

4. Strongly magnetized regions of Mars (e.g., Terra Sirenum) can efficiently shieldthe local atmosphere and alter the motion of charged particles from the lower tothe upper atmosphere.

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Acknowledgments

Thank You For Your AttentionQuestions?

This work is available online at:

http://www.jeremy.riousset.com/

Riousset et al. (2013), Three-dimensional multifluid modeling of atmosphericelectrodynamics in Mars’ dynamo region, J. Geophys Res., 118(6), 3647–3659,doi: 10.1002/jgra.50328.Riousset et al. (2013), Electrodynamics of the Martian dynamo region nearmagnetic cusps and loops using the Martian Multifluid MagnetohydrodynamicModel (M4), Geophys. Res. Lett., doi: 10.1029/2013GL059130, in press.

This work was supported by the National Aeronautics and Space Administration under grant NNX10AM88G-

MFRP to the Georgia Institute of Technology.

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References I

S. Balay, W. D. Gropp, L. C. McInnes, and B. F. Smith. Efficient management of parallelism in object oriented numerical soft-ware libraries. In E. Arge, A. M. Bruaset, and H. P. Langtangen, editors, Modern Software Tools in Scientific Computing,pages 163--202, Boston, MA, 1997. Birkhauser Press. ISBN 978-1-4612-7368-4. doi: 10.1007/978-1-4612-1986-6 8.

A. Boesswetter, H. Lammer, Y. Kulikov, U. Motschmann, and S. Simon. Non-thermal water loss of the early Mars: 3Dmulti-ion hybrid simulations. Planet. Space Sci., 58:2031--2043, 12 2010. doi: 10.1016/j.pss.2010.10.003.

D. A. Brain, R. J. Lillis, D. L. Mitchell, J. S. Halekas, and R. P. Lin. Electron pitch angle distributions as indicators of magneticfield topology near Mars. J. Geophys. Res., 112(A9):A09201, 2007. ISSN 0148-0227. doi: 10.1029/2007JA012435.

S. H. Brecht and S. A. Ledvina. The loss of water from Mars: Numerical results and challenges. Icarus, 206(1):164--173, 32010. ISSN 0019-1035. doi: 10.1016/j.icarus.2009.04.028.

S. H. Brecht and V. A. Thomas. Multidimensional simulations using hybrid particles codes. Comput. Phys. Commun., 48:135--143, 1 1988. doi: 10.1016/0010-4655(88)90031-8.

E. M. Harnett. High-resolution multifluid simulations of flux ropes in the Martian magnetosphere. J. Geophys Res., 114(A01208), 1 2009. ISSN 0148-0227. doi: 10.1029/2008JA013648.

E. M. Harnett and R. M. Winglee. Three-dimensional multifluid simulations of ionospheric loss at Mars from nominal solarwind conditions to magnetic cloud events. J. Geophys Res., 111(A09213), 9 2006. ISSN 0148-0227. doi: 10.1029/2006JA011724.

N. Jedrich. Instrument design for the mars atmospheric and volatile evolution mission. In Aerospace Conference, 2012 IEEE,pages 1--14, 2012. doi: 10.1109/AERO.2012.6187022.

B. Langlais, M. E. Purucker, and M. Mandea. Crustal magnetic field of Mars. J. Geophys Res., 109(E2), 2 2004. ISSN2156-2202. doi: 10.1029/2003JE002048. URL http://dx.doi.org/10.1029/2003JE002048.

S. A. Ledvina, Y. J. Ma, and E. Kallio. Modeling and simulating flowing plasmas and related phenomena. Space Sci. Rev., 139(1–4):143--189, 8 2008. ISSN 0038–6308. doi: 10.1007/s11214-008-9384-6. Workshop on Comparative Aeronomy,ISSI, Bern, CH, Jun 25–29.

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References II

J. G. Luhmann and C. T. Russell. Mars: Magnetic field and magnetosphere. In J. H. Shirley and R. W. Fainbridge, editors,Encyclopedia of Planetary Sciences, pages 454--456. Chapman and Hall, New York, NY, 9 1997.

Y.-J. Ma, A. F. Nagy, K. C. Hansen, D. L. DeZeeuw, T. I. Gombosi, and K. G. Powell. Three-dimensional multispecies MHDstudies of the solar wind interaction with Mars in the presence of crustal fields. J. Geophys. Res., 107:1282, 2002. doi:10.1029/2002JA009293.

Y.-J. Ma, A. F. Nagy, I. V. Sokolov, and K. C. Hansen. Three-dimensional, multispecies, high spatial resolution MHD studiesof the solar wind interaction with Mars. J. Geophys. Res., 109(A18):A07211, 2004. doi: 10.1029/2003JA010367.

P. S. Pacheco. Parallel programming with MPI. Morgan Kaufmann Publishers Inc., San Francisco, CA, 1996. ISBN1-55860-339-5.

C. Paty and R. Winglee. The role of ion cyclotron motion at Ganymede: Magnetic field morphology and magnetosphericdynamics. Geophys. Res. Lett., 33(10):L10106, 5 2006.

W. H. Press, B. P. Flannery, S. A. Teukolsky, and W. T. Vetterling. Numerical Recipes in C: The Art of Scientific Computing.Cambridge Univ. Press, Cambridge, UK; New York, NY, 2nd edition, 1992.

M. Purucker, D. Ravat, H. Frey, C. Voorhies, T. Sabaka, and M. Acuna. An altitude-normalized magnetic map of Mars andits interpretation. Geophys. Res. Lett., 27:2449--2452, 8 2000. doi: 10.1029/2000GL000072.

J. A. Riousset, C. S. Paty, R. J. Lillis, M. O. Fillingim, S. L. England, P. G. Withers, and J. P. M. Hale. Three-dimensionalmultifluid modeling of atmospheric electrodynamics in Mars’ dynamo region. J. Geophys Res., 118(6):3647--3659, 62013a. doi: 10.1002/jgra.50328.

J. A. Riousset, C. S. Paty, R. J. Lillis, M. O. Fillingim, S. L. England, P. G. Withers, and J. P. M. Hale. Electrodynamicsof the Martian dynamo region near magnetic cusps and loops using the Martian Multifluid Magnetohydrodynamic Model(M4). Geophys. Res. Lett., 2013b. doi: 10.1029/2013GL057589. in review.

K. Sauer, E. Dubinin, and K. Baumgartel. Bi-ion structuring in the magnetosheath of Mars–theoretical modeling. Adv. SpaceRes., 20:137, 1 1997. doi: 10.1016/S0273-1177(97)00523-1.

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Figure : Aurora making its way through the magnetosphere. Image courtesy:NASA.

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Figure : Aurora making its way through the magnetosphere. Image courtesy:NASA.

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Additional Material

Keypoints:

• This image is taken from ISS.

• It illustrates how during an aurora, precipi-tating particles make their way through themagnetosphere.

• It is absolutely beautiful!