The Dependence of the PlasmaSheet on the Solar Wind

Joe BorovskyLos Alamos National Laboratory

1. The GEM Global-Interactions Campaign2. Why the Plasma Sheet Is Important3. Basic Properties of the Plasma Sheet4. The Sources of the Plasma Sheet5. The Dependence on the Properties of the Solar Wind6. What We Don't Know

The GEM Global InteractionsCampaign

Ultimate Goal of the Campaign:To determine the processes controlling plasmaentry and circulation within the magnetosphere.

This Talk:Look at one important pathway of the "entry andcirculation" picture-- The solar wind making its wayinto the plasma sheet and through themagnetosphere.

¿Why Is the Plasma Sheet Important?• Feeds plasma into the inner magnetosphere

Ring-current/partial-ring-current sourceAuroral-particle-precipitation sourceEnergetic-particle source

• Transports magnetic flux into the inner magnetosphere• Site of auroral currents and auroral Poynting flux• Site of nightside reconnection• Partakes in magnetospheric energy storage and release

What Is the Plasma Sheet?

-60-40-20020 RE

Northern Lobe

Solar Wind

Bow Shock

Southern Lobe

Plasma Sheet

Plasmasphere

(shocked solar wind)Magnetosheath

Dipole Magnetotail Solar Windn = 0.5-1.5 cm-3 n = 0.1-0.5 cm-3 n = 3-17 cm-3

Ti = 5-20 kev Ti = 2-10 kev Ti = 2-20 eVTi/Te > 6 Ti/Te ª 6 Ti/Te ~ 0.3

Mass of protons on nightside ~ 1 Ton

Cross Section of Magnetotail

PlasmaSheet

Plasma-SheetBoundary Layer

N o r t h e r nN o r t h e r nL o b eL o b e

S o u t h e r nS o u t h e r nL o b eL o b e

Plasma-SheetBoundary Layer

Mantle

Mantle

Low-LatitudeBoundary Layer

Low-LatitudeBoundary Layer

EmptyLobe

EmptyLobe

Convection in the Plasma Sheet

-70-60-50-40-30-20-10020

earthward-convectingplasma sheet

tailward-convectingplasma sheet

RE

Magnetotail convection is decoupled from the ionosphereFlows are turbulentMagnetic field is tangledSporadic reconnection events with BBFs

Plasma-Sheet Flows

-200

-100

0

100

200

-300 -200 -100 0 100 200

v y [k

m/s

ec]

vx [km/sec]

vx ave = -18.6 km/sec vy ave = 4.7 km/sec

Flow during a 2-hour interval

Fluctuations in the Magnetic-Field Direction

-20

-10

0

10

20

30

40

50

60

-10010203040506070

Elev

atio

n (S

outh

-Nor

th)

[d

eg]

Azimuth (Dusk-Dawn) [deg]

View ofthe Earth

2-Hours During SMC EventMarch 21, 1980

22.1 RE downtail

Suspected Plasma Sources for thePlasma Sheet

• Solar Wind Via the LLBL

• Solar Wind Via the Mantle

• Ionospheric Outflows

• Recirculation of the Outer Plasmasphere

Clues that the Solar Wind Is theDominant Source

1) CorrelationsProperties of the plasma sheet temporally track the properties of the solarwind [e.g. this talk].

2) Composition MeasurementsExcept when geomagnetic activity is very high, the plasma sheet has solar-wind composition [e.g. Lennartsson and Shelley, J.G.R., 91, 3061, 1986].

3) Temperature RatioIn the magnetotail plasma sheet Ti/Te ≈ 7 [e.g. Baumjohann, Space Sci. Rev.,64, 141, 1993] (as in the magnetosheath), and Ti and Te track each other (asin the magnetosheath).

The Properties of the Solar Wind and thePlasma Sheet Vary from Day to Day

(the flows vary from minute to minute)

0

2

4

6

8

10

-100

-50

0

50

100

120 130 140 150 160 170

n ps

[cm

-3]

nsw [cm

-3]

nps

nsw WIND

084

day.frac of 1995

Density

10

100

100

1000

120 130 140 150 160 170

T ps

[keV

]

vsw [km

/sec]

day.frac of 1995

Tps

vsw WIND

084

Speed, Temperature

Some Statistical Studies ofSolar-Wind/Plasma-Sheet Coupling

Magnetic FieldLui, A. T. Y., in Magnetospheric Currents, p. 158, AGU, 1984.Tsurutani et al., Geophys. Res. Lett., 11, 1082, 1984.Sergeyev, Geomag. Aeron., 27, 528, 1987.

PlasmaTerasawa et al., Geophys. Res. Lett., 24, 935, 1997.Borovsky et al., J. Geophys. Res., 102, 22089, 1987.Kletzing et al., J. Geophys. Res., 108, 1360, 2003.

Plasma & FieldsBorovsky et al., J. Geophys. Res., 103, 17617, 1998.

Example Correlation: nswÆ nps

0.1

1

1 10

n ps

[cm

-3]

Rcorr = +0.74

nps = 0.0785 ns w.62

nsw [cm-3]

magnetotail neutral-sheet crossingszero time lag

Correlations between the Solar-Wind and thePlasma Sheet in the Magnetotail

Relationship Rcorr

Rcorr

/Rrand

Function

nsw Æ nps +74% 5.6 nps µ nsw.62

vsw Æ Ti ps +54% 3.8 Ti ps µ vsw1

(rv2)sw Æ (nkT)ps +82% 6.1 (nkT)ps µ (rv2)sw.73

By sw Æ By ps +66%* 3.6 By ps µ By sw

Ey sw Æ Ey ps +36%* 1.6 ?

zero time lag*calm fields

Solar-Wind/Plasma-Sheet CouplingIs Via the Magnetosheath

1. nsw Æ nms Æ nps

2. vsw Æ Ti ms Æ Ti ps

3. By sw Æ By ms Æ By ps

4. Ey sw Æ Ey ms Æ Ey ps

5. vsw Æ Te ms Æ Te ps

6. Bow shock Æ (Ti/Te)ms Æ (Ti/Te)ps

Examining the Time Lag forSolar-Wind/Plasma-SheetCoupling

-0.1

0

0.1

0.2

0.3

0.4

0.5

-48 -36 -24 -12 0 12 24 36 48

Line

ar C

orre

latio

n Co

effic

ient

Time Lag [hr]

nsw´ nsw

1996 - 1998

nsw´ ne

084 + ACE + WIND

geosynchronous-orbit midnight

Density Pulses Can Be Seen Movingfrom the Solar Wind into the Plasma Sheet

100

101

102

8 10 12 14 16 18 20 22

n

[cm

-3]

Hour of April 30, 1998

WIND(time shifted to Earth)

084 (21 LT)

97A (19 LT)

080 (16 LT)

Mass-Transport Timescales from theSolar Wind into the Plasma Sheet

geosynchronousorbit

4 hr15 hr

8 hr

2 hrsolarwind 0 hr

neutral sheetat 20 RE

solar windat the nose

Bird's EyeBird's EyeV i e wV i e w

dusk

dawn

Rate of Flow of Solar-Wind Plasmathrough the Magnetosphere

Estimate 1: 1.1 tons of protons replaced every 4 hours:

4.6¥1025 protons/sec

Estimate 2: 15 km/s earthward flow of 0.5 cm-3 over 6¥20 RE

2 cross section: 3.6¥1025 protons/sec

Estimate 3: Transport rate through the dipole is twice the loss rate

Global proton aurora is 9¥1024 protons/secGlobal charge-exchange rate is >1¥1023 protons/sec

(thanks to Kunihiro Keika and Pontus Brandt) 1.8¥1025 protons/sec

Earth's Effective Cross Section forCapture of Solar-Wind Plasma

Proton transport rate through the magnetosphere is4¥1025 protons/sec

Solar-wind proton flux at 1 AU is3¥108 protons/cm2/sec

fiEffective entry area is1.3¥107 km2 (about twice the area of Australia)

This is one proton in 4000

**Note that the flow of plasma downtail may betwice the flow through the magnetosphere.

Summary (So Far) • Correlations between the plasma sheet's properties and

the solar wind are well established.

• Plasma sheet is largely magnetosheath plasma.

• Transport times from solar wind are (normal activity)2 hours to center of the tail4 hours to the nightside of the dipole15 hours to dayside magnetosphere

• Rate of solar-wind-plasma flow through magnetosphereis ~4¥1015 protons/sec.

What We Don't Know • Entry mechanisms: magnetosheath to plasma sheet • Pathways of magnetosheath entry • Understanding of solar-wind control of magnetosheath

entry • Quantification of magnetosheath entry and transport

from first principles • Whether the Ti/Te=7 ratio is (a) preserved through

capture or (b) recreated in the plasma sheet • Where the plasmaspheric plasma goes

We Have Not DiscussedThe Cold Dense Plasma Sheet

A northward-IMF interval, followed by southward IMF.Magnetosheath builds up in outer magnetosphere, then is

convected inFujimoto et al., Space Sci. Rev., 80, 325, 1997Thomsen Talk Today

Solar-Wind Control of Ionospheric OutflowsvBz (geomagnetic-activity) dependence

Yau and Andre, Space Sci. Rev., 80, 1, 1997Solar-wind-pressure dependence

Elliott et al., J. Geophys. Res., 106, 6067, 2001

To Get the Role of the Plasma Sheet Right,What Does a Model Need to Get Right?

First Order:• Location • Convection pattern• Density profile • Density-pulse movements• Temperature profile

Second Order:• Field disorder • Flow fluctuations*

*If flow fluctuations prove to be fundamental for transport,then getting their properties right becomes “First Order”.