2001/02/08 T E Moore - SW Interactions via LENA 1

Solar Wind-Magnetosphere Interactionsvia Low Energy Neutral Atom Imaging

• T E Moore[1], M R Collier[1], M-C Fok[1], S A Fuselier[2], D. G. Simpson[1], G. R. Wilson[3], M. O. Chandler[4]• 1. NASA’s Goddard Space Flight Center, Interplanetary Physics Branch, Code 692, Greenbelt, MD 20771 • 2. Lockheed Martin Advanced Technology Center, Dept. H1-11, Bldg. 255, Palo Alto, CA 94304 • 3. Mission Research Corporation, 589 W. Hollis St., Suite 201, Nashua, NH 03062 • 4. National Space Science and Technology Center, NASA MSFC SD50, Huntsville AL 35805

• LENA was motivated by need for time-resolved ionospheric outflow observations. • Also responds to neutral atoms with energies up to a few keV (from sputtering). • As a result, we have been able to:

- Show that ionospheric outflow responds to solar wind dynamic pressure variations.

- Observe that the response is prompt.

- Infer a heating source below 1000 km altitude for the larger flux events.

- Use neutral atom emissions to reveal the magnetosheath, with cusp-related structures.

- Infer dayside structure in the geocorona. .

- Measured the annual variation of the neutral solar wind.

- Probe the interstellar gas and dust in the inner solar system.

- Directly observe the interstellar neutral atom focusing cone at 1 AU.

• LENA imaging has thus proven to be a promising new tool for studying the interplanetary medium and its interaction with the magnetosphere, even from inside the magnetosphere.

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Low Energy Neutral Atoms (LENA) CME/Storm Onset and Response

• Solar Wind LENA increase marks CME arrival at 0915 hrs.

• Earth sector LENA respond within travel time of 35eV O0.

Hr Before Hr After Snap Perigee

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Comparison with Ion Outflows

• Preliminary comparisons:- Some spatial correspondence (day - night here)- Flux comparison indicates low altitude source region - Best correspondence w/ auroral oval from transverse views (not shown)- Posters AGUsm01: SM72A-14 (Coffey et al.), -15(Wilson et al.)

LENA H/O/Total Images TIDE Polar Ion Outflows Neutral Fraction vs

Source Altitude

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Simulated LENA EmissionsAuroral zone emissions Uniform polar emissions

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Sources of Indirect SW-LENA

Collier et al.Nov JGRp.24,893

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Solar LENA flux profile

Strong similarity to ram pressure profile observed at WIND.

Tracking observed at some time scales, not others.

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Simulation of Indirect LENAs

• Simulations performed by M.-C. Fok using MHD magnetosheath.• Analogous to ring current ENA simulations, using an CCMC

(BatsRUS) MHD model of the magnetosheath, and looking out. • LOS integration from 8 to 50 RE, excepting antisunward 90° cone.

Images collapsed in polar angle, for IMAGE. • No true solar LENAs assumed to arrive in solar wind here.

Dawn-Dusk Orbit

Noon-Midnight Orbit Noon-Midnight Orbit

Dawn-Dusk Orbit200 eV 4000 eV

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• Solar wind flux or dynamic pressure increases produce a big reaction in LENA.

• A brightening is seen especially between the sun pulse and the Earth (white line here).

• Is this the expected relation between solar wind intensity and ENA emission from this region?

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We expect a very strong dependence because so many factors are affected by solar wind flux (and Pd).

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Simulation of Magnetosheath CE

• CCMC Simulations based on BatsRUS Code

• LOS integration from IMAGE spacecraft by M-C Fok.

• Consider periods of enhanced Pd solar wind for compressed magnetopause.

• Remote sensing of cusp and cleft possible with sufficient sensitivity and-or Pd.

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Seeing Magnetosheath Structure

• LENA spin modulation near the peak of the 31 March 2001 event at about 0450UT:

• CCMC (BatsRUS) MHD simulation of the 31 March 2001 event, showing magnetosheath density distribution along LENA lines of sight at about 0450 UT

0

5

10

15

20

25

30

35

40

45

0 50 100 150 200 250 300 350

LENA bkg adjusted H counts

04:50:08-04:54:16

Sun

Earth

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Remote-Sensing the Magnetosheath

Sun

MS

Simulations indicate features of the magnetosheath should be visible and are visible from inside the magnetosphere.

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Evidence for Geocoronal Erosion?

5-50 RE

5-12 RE

Data: LENA background adjusted flux > 30 eVDeflectors

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0.1

1.0

10.0

100.0

0 100 200 300

sun_pulse_ltt_09.plt

IOC level (x4)

nominal ops level

ppsp level (x0.33)

ppsp stepping (x0.33)

ppsp level (x0.33)

Tsurutani et al., 1994 events

LENA H rate [counts/s](sun sector apogee)

day of year 2000/2001

radiation stormMexican Aurora

Storm

Observation: Annual Variation of Solar Wind ENA

Long term, seasonal variations reflect solar system distribution of neutral gas (interstellar and other sources)

Short term, storm variations reflect solar wind intensity variations, CMEs, and distribution of the geocorona.

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SW ENA Model of Bzowski et al.Icarus 1996

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Limit on Inner Solar System DustCollier et al., AGU SM2001

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Predicted Direct ISN Observations

Fuselier, 1997

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Direct ISNs, Interpreted?

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3D Interstellar Neutral Trajectories

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ISN Flux

12/1 1/1 2/1 3/1

12/1 1/1 2/1 3/1

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Conclusions

• We have been able to: - Validate earlier statistical inferences that ionospheric heating

responds to solar wind dynamic pressure variations.- Observe that the response is prompt, as fast as

hydromagnetic wave propagation speeds. - Infer that the heating source must lie lower than 1000 km

altitude for the larger flux events. - Use neutral atom emissions to reveal the magnetosheath,

with cusp-related structures.- Infer dayside structure in the geocorona, owing to solar wind

erosion by charge exchange. - Measure the annual variation of the neutral solar wind.- Interpret annual variation in terms of interstellar neutral gas

and dust in the inner solar system. - Directly observe the interstellar neutral atom focusing cone at

1 AU.

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Comparison with Dayside Aurora

• See Fuselier et al., GRL 15 March 2001.

• Before/After images of dayside aurora.

• IMF Bz generally Northward.

• Similar in many ways to 24 Sept 98 CME, with resultant Ionospheric Mass Ejection [Moore et al., GRL, 1999]

8 June 2000 CME Arrival

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Direct ISNs, Observed

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SWLENA: A Heliospheric Gas and Dust Probe

• Three chargeexchange media:– Heliospheric dust

generates constantbackground gas

– Interstellar neutralsenter from apex, lostby PI and CE.

– Geocoronal H nearEarth

• Three Response TimeScales:– Minimum flux is due

to dust-generated gas

– Annual variationreflects ISN anisotropy

– Solar wind responsereflects geocoronal gasinteraction