s.m.p. mckenna-lawlor 1 , e. kallio 2 , r. jarvinen 2 , m. alho 2 , and s. dyadechkin 2

4th SERENA-HEWG Meeting Key Largo, Florida,13-17 May, 2013 page 1

Success of the hybrid modelling technique Success of the hybrid modelling technique

in simulating the response of the Martian in simulating the response of the Martian

magnetosphere to solar energetic particle magnetosphere to solar energetic particle

irradiation and first steps in applying this irradiation and first steps in applying this

technique to study the response at technique to study the response at

Mercury to disturbed solar circumstancesMercury to disturbed solar circumstances

S.M.P. McKenna-Lawlor1, E. Kallio2, R. Jarvinen2, M. Alho2, and S. Dyadechkin2

1.Space Technology Ireland, Maynooth, Co. Kildare2.Finnish Meteorological Institute, Helsinki, Finland


The initial motivation of this study was to model data

composed of energetic protons with energies in the range

30 keV to a few tens of MeV recorded at Mars in March

1989 by the SLED particle detector aboard the Phobos-2

spacecraft.

Later the possibility to apply HYB modelling to extreme

conditions at Mercury was recognized and first steps to

achieve this were initiated.

Motivation


Encounter of Phobos-2 with Mars

Schematic of the encounter of Phobos-2 with Mars showing part of an elliptical orbit (E) and a circular orbit (C). Also represented are the Bow Shock (BS), the Magnetosheath, the Magnetic Pileup Boundary (MPB), the Magnetotail and the nominal interplanetary magnetic field (IMF). The two conical shapes illustrate the field of view of the SLED instrument when in an elliptical and circular orbit near the terminator plane.


SLED employed semiconductor detectors in two different telescopes directed at 55o westward of the Sun-Earth line (that is approximately in the nominal direction of the interplanetary magnetic field).

The front detector of Te1 was covered with a 15µg/cm2 Al foil. Te2 was fitted in addition with a 500 µg/cm2

Al foil which absorbed protons with energies < 350 keV while allowing the passage of electrons.

Subtraction of the counts of Te1 and Te2 allowed ions and electrons to be separated from each other.

The SLED instrument


Te 1 (without foil)Ch. 1 30-50 keV electrons + ionsCh. 2 50-200 keV electrons + ionsCh. 3 200-600 keV electrons + ionsCh. 4 0.6-3.2 MeV ionsCh. 5 3.2-4.5 MeV ionsCh. 6 > 30 MeV background rate

Te 2 (with foil)Ch. 1 30-50 keV electrons 350-400 keV ions Ch. 2 50-200 keV electrons 400-500 keV ions Ch. 3 200-600 keV electrons 0.5-1 MeV ions Ch. 4 0.6-3.2 MeV ionsCh. 5 3.2-4.5 MeV ionsCh. 6 > 30 MeV background rate

The SLED instrument - Energy channels


The SLED data modelled in the present study were measured

while Phobos-2 was executing circular orbits about Mars.

In these data it was found that, under extreme solar

conditions, the proton count rates measured by SLED were

significantly reduced behind the planet whenever the pitch

angle distribution of the particles remained relatively stable

during the integration time of the instrument (230s).

The SLED instrument


SLED Data

The plot shows particle data recorded by SLED in its Channel 3 (200-600 keV) and Channel 6 (> 30 MeV) of Te 1 from 1-26 March, 1989. Dashed vertical lines indicate recurrent records of depressions in flux (interpreted by McKenna-Lawlor et al. (1992) to be due to magnetic shadowing) as the spacecraft executed consecutive circular orbits around Mars. Particle enhancements due to recurrent bow shock crossings can also be discerned.


SLED data

Examples of particle data recorded by SLED in Te1, Channel 4 (0.6-3.2 MeV) in an MSO coordinate system; look direction of SLED top right. Mars is represented at the center of each plot. The relative number of counts recorded during particular orbits is indicated by the magnitude of vertical lines that represent individual readings made at successive locations during an orbit. Gaps correspond to operational switch offs due to telemetry constraints. The depressions are due to magnetic shadowing.


To model these observations, a 3-D, self-consistent, hybrid model

(HYB) supplemented by test particle simulations was developed.

This model allows the macroscopic properties of, solar related,

high energy ion populations near Mars to be investigated and

supports study of the motions of individual high energy ions at

the planet.

It is recalled that Mars neither possesses a significant, global,

intrinsic magnetic field nor a dense atmosphere.

Hybrid Modelling


Mars Hybrid Model (HYB) General features

•Quasineutral: Snion = nelectron • Hybrid: H+, O+, and O2

+ ions are particles, Electrons form a massless fluid

• Self-consistent model • Dynamics: - Electrons “carry” the magnetic field (E = - Ue x B) - Ions (H+, O+, O2

+) are accelerated by the Lorentz force

• Hierarchically refined cubic grid• Ion splitting and joining:

splitting: A → A1 + A2

joining: B1 + B2 + B3 → B1 + B2

(note: conserves E and p)

Note: Martial crustal magnetic fields are NOT included

See Kallio et al., 2010, for details of the HYB-Mars model

ne ,Ue

H+

O+

O2+


The Mars-centered Solar Orbital (MSO) coordinate system

The coordinate system used in the HYB Mars model is MSO where:

The x- axis points from the centre of Mars to the Sun.

The z -axis is perpendicular to the orbital plane of Mars pointing towards the north ecliptic pole.

The y-axis completes the right handed co-ordinate system.


HYB-Mars Model runs

In the present study, four different upstream parameters were utilized in order to analyze the response of the Martian plasma environment to different conditions:

1. NOMINAL RUN: Usw=485 km/s, nsw= 2.7 cm-3, IMF = [-1.634, 2.516, 0] nT

2. HIGH VELOCITY RUN: U=970 km/s, nsw= 2.7 cm-3, IMF = [-1.634, 2.516, 0] nT

3. HIGH DENSITY RUN: Usw=485 km/s, nsw= 10.8 cm-3, IMF = [-1.634, 2.516, 0] nT

4. HIGH DENSITY AND IMF RUN: Usw=485 km/s, n= 10.8 cm-3, IMF = [-6.536, 10.064, 0] nT


The nominal run was first compared with runs made when

the dynamic pressure of the solar wind was increased by a

factor of four (either by doubling the speed of the solar wind

or by increasing the solar wind density by a factor of four).

The role of the magnitude of the interplanetary magnetic

field (IMF) was then investigated in both the high density

and high IMF runs by increasing the magnetic field used in

the high density run by a factor of four.

Procedure


Next the motion of high energy proton populations was

studied with respect to each of the four upstream cases

selected. The energies of four high energy solar wind H+

beams were individually set at 50 keV, 200 keV, 600 keV

and 3.2 MeV, (corresponding to the highest particle energies

recorded in Te1 Channels 1-4 of SLED).

In the simulation process the high energy H+ ions were

injected into the simulation box using densities of a

sufficiently low value that the self consistent solution was

not affected.

Procedure contd.


The figures show the flow lines of the four high energy H+ ions near Mars in a nominal run. The 50 and 200 keV particles are disturbed by the magnetosphere. The colour in the z = 0 plane and on the r ~ RM sphere

indicates the normalized density of high energy ions, ñ. Note that some of the stream lines extend below the colour plane to the z < 0 hemisphere. An enhanced density (red colour), is created in Fig a because the v×B force impels ions toward the z < 0 hemisphere

Mars


Results of HYB modelling

Overall, the model indicated that:

During extreme SW conditions, the plasma environment at Mars affects the motion of high energy protons.

Ion scattering depends on (a) the energy of the incoming ions and (b) on upstream parameters (especially the SW speed and the IMF direction).

A magnetic shadow is formed which decreases in size as the particles increase in energy (keV to MeV range).


The properties of the high energy ions in the model runs were

qualitatively similar to the in situ measurements.

The quantitative results varied, however, from one run to another

and it therefore transpired to be necessary, in order to more fully

understand the in situ observations, to know the actual upstream

parameters that were present during the taking of the energetic

particle measurements.

Comparison of simulations with in situ measurements


An additional study was then mounted in which plasma and magnetic field data measured contemporaneously with the particle measurements aboard Phobos-2 were input to the HYB model.

Further, the model was itself upgraded through incorporating an High Energy Particle Tracing Mode in the global simulation such that energetic ions could be manually injected into the simulation using three different velocity distribution functions.

Upgrading the HYB model


1.“Beam” distributions composed of six, tight, discrete energy beams were launched along the IMF with energies corresponding to those of the SLED channels.

2.An energy scattered distribution based on SLED data was directed along the IMF in velocity space with a continuous energy distribution.

3. A fully scattered distribution around the IMF was utilized which included both angular and energy scattering.

Upgrading the HYB Model

a)


Several diagnostic tools were in addition developed and

incorporated into the hybrid model platform in order to

support one-to-one comparisons between the simulated and

observed particle fluxes.

In particular, a virtual SLED instrument was included in the

simulation to mimic how the instrument collected particles.

Diagnostics


View of the simulated magnetic field around Mars and several magnetic field lines which are connected to the orbit of Phobos2. The “cloud” in the figure is a volumetric plot of the magnitude of the magnetic field. The magnetic field lines are coloured in order to help the eye distinguish different lines from each other. The field lines are sourced from a hybrid model run with upstream parameters nSW = 3m-3, USW = [–600, 0, 0] km s-1 and Bsw = [–4, 4, 0] nT. The view point is on the +z axis.

Note that the draped magnetic field lines are three dimensional in the simulation and the figure only shows their projection on the xy plane.


Illustration of the motion of energetic protons near Mars. The “cloud” shows the strength of the magnetic field in 3-D (see the colour bar, top left). The circular white sphere represents the surface of Mars. The lines show trajectories of several energetic protons.The colour of a line represents the initial energy of an ion: The lowest energies (50 keV and 200 keV) are shown in green; the yellow trajectories represent 600 keV protons and the red trajectories 3.2MeV protons (see the colour bar, bottom left).

Mars

Note also that the colour of the initially green trajectories becomes grey or white when the trajectory is within or behind the strong magnetic field region.


Comparison of the simulated energetic proton fluxes and the particle fluxes measured by the SLED/Phobos-2 instrument along the circular orbit of Phobos-2 on 13 March 1989. The SLED ion data come from Telescope 1, from which the electrons were removed. The five panels display the normalized particle fluxes in five SLED energy channels compared with derived fluxes based on three different velocity distribution models: the beam, the energy scattered, and the fully scattered models

Two “fully scattered” fluxes are shown in cases where the particle fluxes were collected from 2 π space (green solid line) and when the fluxes were collected from the field-of-view (FoV) of the SLED telescopes, looking toward the nominal spiral angle of 55 at Mars. The fully scattered model resulted in the best agreement with the data.


Comparisons with the SLED Phobos-2 observations showed that the upgraded model successfully reproduced the key features of the observations. The best performance was obtained when using the fully scattered velocity distribution function.

Features successfully simulated included.

A particle flux enhancement near the bow shock recorded in the low energy SLED channels.

A particle flux decrease near the bow shock recorded in the high energy SLED channels.

Formation of a magnetic shadow and indication of how its size decreased with particle energy.

Results of the upgraded study


The success obtained through matching the Mars in situ energetic particle measurements with simulated data motivated an effort to apply hybrid modeling to simulate, for a BepiColombo application, the particle environment present at Mercury under extreme solar conditions.

In this case, instead of a draped magnetic field, Mercury has a dipole field which was shown by Mercury Messenger measurements to be offset from the geographic poles (Anderson et al., 2011).

Application of the methodology to Mercury


Application of the methodology to Mercury

FOUR RUNS were made using:

H+ from the SW ; nsw (H+) = 72 cm-3

NOMINAL RUN (Usw = 430 km/s)

1. “North IMF run”: IMF = [0, 0, 10] nT2. “Parker IMF run”: IMF = [32,10,0] nT

HIGH SPEED RUN (Usw = 1000 km/s)

3. “High speed north IMF run”: IMF = [0, 0, 10] nT4. “High speed Parker IMF run”: IMF = [32,10,0] nT


North IMF run (430 km/s) High speed Parker IMF run (1000 km/s)

n(H+) [m-3]

Note: The increase in Usw results in a more “compressed” magnetosphere

Magnetosphere and the solar wind density

n(H+) [m-3]


HIGH ENERGY (~0.5 MeV) PROTONS

An ~ 0.5MeV H+ population was injected into the solar wind in order to study how such high energy solar wind H+ ions are “shadowed” by Mercury’s magnetosphere. The population was assumed to move in the solar wind along –BIMF.

Two cases were studied:

1. “Nominal Parker IMF run”:

IMF = [32,10,0] nT, Usw = 430 km/s

2. “High speed Parker IMF run”:

IMF = [32,10,0] nT, Usw = 1000 km/s


Test particle simulations

50 keV H+ population 200 keV H+ population

“Parker IMF run”: IMF = [32,10,0] nT, Usw = 430 km/s High energy (> 50 keV) SW H+ ions launched along the IMF


Test particle simulations“Parker IMF run”: IMF = [32,10,0] nT, Usw = 430 km/s High energy (> 50 keV) SW H+ ions launched along the IMF

600 keV H+ population 3.2 MeV H+ population


High energy SW H+ ions: Y = 0 plane

High energy SW H+ population (~ 0.5 MeV) Main SW H+ populations (~400 km/s)

Log[n(H+)] [m-3]

Low density of SW population but not so low as on the left hand side

“Parker IMF run”: IMF = [32,10,0] nT, Usw = 430 km/s

Density of ~ 0.5 MeV H+ ions indicating shielding out of the H+ ions by the magnetic field.


High energy SW H+ ions: Z = 0 plane

Log[n(H+)] [m-3]

Log[n(H+)]Normalized so that the undisturbed value is ~ 1e-4


XY

XY



High energy SW H+ ions: X = 0 plane

Log[n(H+)] [m-3]



Z

Y

Z

Y



High energy SW H+ ions: Y = 0 plane

Log[n(H+)] [m-3]



“High speed Parker IMF run”: IMF = [32,10,0] nT, Usw = 1000 km/s


High energy SW H+ ions: Z = 0 plane

Log[n(H+)] [m-3]




XY

XY


High energy SW H+ ions: X = 0 plane

Log[n(H+)] [m-3]





A high solar wind (1000 km/s) results in a “compressed” Hermean magnetosphere.

This magnetosphere provides effective “shielding” against high energy (~0.5 MeV) H+ ions.

Upstream velocity changes affected all the parameters analyzed , namely, the:

size of the magnetosphere shielding of high energy SW H+ ions

As at Mars, knowledge of upstream conditions is essential in order to interpret the observations.

Results of applying HBY Modelling to Mercury


The 0.5 MeV case is for H+ ions launched in a beam along the IMF and is therefore similar to the beam case (a) used in the Mars SEP simulations In the future more realistic velocity distributions will be analyzed as in case b) [energy scattering] and case (c) [full scattering] at Mars.

The number of 0.5 MeV ions used in the simulation was low and we plan to include more ions in future runs and also a bigger simulation box. In this case the “cavity” might be at least partially filled with 0.5 MeV H+ ions.

Mercury’s dipole field was assumed to be 300 nT on the surface of Mercury at the magnetic equator. This is being upgraded, using Mercury Messenger data to ~190 nT and appropriately shifted as observed.

Also, energetic particle data recorded aboard Mercury Messenger can be input to the model with corresponding upstream parameters to derive the properties of an SEP along the orbit of Messenger.

Future Work


MPO/SIXS: (Solar intensity X-ray and particle spectrometer)

(Huovelin et al., 2010). X-ray (spectral range: 1–20 keV; including X-ray flare

parameters), Protons (spectral range: 1–30 MeV) and Electrons (spectral range: 100 keV–3MeV)

MMO/MPPE (Mercury plasma particle experiment) (Saito et al., 2008)

will observe: electrons (3 eV–700 keV), ions (5 eV–1.5 MeV), and energetic neutral atoms (25 eV–3.3 keV) (Milillo et al.,

2010)

Data ultimately available from BepiColombo for interpretation using HYB


Hybrid modeling has been successfully used to simulate the response of the Martian magnetosphere to solar high energy particle irradiation

Initial steps have been performed to develop a hybrid model to study the response of Mercury to extreme solar events.

This model can later be used to interpret data recorded aboard both Mercury Messenger and BepiColombo.

Conclusions

s.m.p. mckenna-lawlor 1 , e. kallio 2 , r. jarvinen 2 , m. alho 2 , and s. dyadechkin 2

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