Magnetic Flux Transport and Pressure VariMagnetic Flux Transport and Pressure Variations at Magnetotail Plasma Flow Bursts ations at Magnetotail Plasma Flow Bursts

during Geomagnetically Quiet Timesduring Geomagnetically Quiet Times

Motoharu Nowada (Motoharu Nowada ( 野和田 基晴野和田 基晴 : nowada@pku.edu.cn): nowada@pku.edu.cn)11

Sui-yan FuSui-yan Fu11, George K. Parks, George K. Parks22, Zu-yin Pu, Zu-yin Pu11, , Vassilis AngelopoulosVassilis Angelopoulos33, Charles W. Carlson, Charles W. Carlson22, ,

Hans-Ulrich AusterHans-Ulrich Auster44

1: ISPAT/SESS, Peking University1: ISPAT/SESS, Peking University2: SSL, University of California, Berkeley2: SSL, University of California, Berkeley

3: IGPP, University of California Los Angeles3: IGPP, University of California Los Angeles4: Technische Universität, Braunschweig, Deutsuland4: Technische Universität, Braunschweig, Deutsuland

EGU2012-1991

The fast plasma flows in the geomagnetotail are observed during both geomagnetically active and The fast plasma flows in the geomagnetotail are observed during both geomagnetically active and quiet times. However, it has been unclear about the fundamental difference in the plasma fast floquiet times. However, it has been unclear about the fundamental difference in the plasma fast flows between at two different geomagnetic conditions, that is, the generation mechanism of, and piws between at two different geomagnetic conditions, that is, the generation mechanism of, and pictures of the energy transport and balance at the fast plasma flows. Magnetic reconnection in the ctures of the energy transport and balance at the fast plasma flows. Magnetic reconnection in the magnetotail has been believed as one of the most possible mechanisms to generate the fast plasmagnetotail has been believed as one of the most possible mechanisms to generate the fast plasma flows regardless of the geomagnetic conditions. Recently, ma flows regardless of the geomagnetic conditions. Recently, Nowada et alNowada et al. [2012], however, de. [2012], however, demonstrated that the magnetotail magnetic reconnection does not always contribute to the generatimonstrated that the magnetotail magnetic reconnection does not always contribute to the generation of the fast plasma flows at geomagnetically quiet times based on the THEMIS measurements. on of the fast plasma flows at geomagnetically quiet times based on the THEMIS measurements. It is very important to reveal how the energy transport and balance in the magnetotail in associatioIt is very important to reveal how the energy transport and balance in the magnetotail in association with these plasma fast flows are on obtaining a clue to elucidate an essential difference in the pn with these plasma fast flows are on obtaining a clue to elucidate an essential difference in the plasma fast flows between during active and quiet geomagnetic conditions. lasma fast flows between during active and quiet geomagnetic conditions. Based on three events of the magnetotail plasma flow bursts, which are transient fast plasma floBased on three events of the magnetotail plasma flow bursts, which are transient fast plasma flows with the durations between 1 and 2 minutes, during geomagnetically quiet times, observed by ws with the durations between 1 and 2 minutes, during geomagnetically quiet times, observed by THEMIS, we examined detailed variations of the electric field as a proxy of the flux transport aspecTHEMIS, we examined detailed variations of the electric field as a proxy of the flux transport aspect, and associated pressure. The main characteristics of these events are shown as follows; 1) the t, and associated pressure. The main characteristics of these events are shown as follows; 1) the GSM-X component of the plasma velocity (VGSM-X component of the plasma velocity (Vxx) was higher than 300 km/s 2) associated parallel (V) was higher than 300 km/s 2) associated parallel (V//

//) and perpendicular (V) and perpendicular (V⊥⊥) velocities to the local magnetic field line were higher than 200 km/s 3) t) velocities to the local magnetic field line were higher than 200 km/s 3) the flow bursts were observed during which |he flow bursts were observed during which |ALAL| and | and AUAU indices were lower than 20 nT, and simulta indices were lower than 20 nT, and simultaneous neous KKpp index range was between -1 and 1. For almost events, the parallel (E index range was between -1 and 1. For almost events, the parallel (E////) and perpendicul) and perpendicular (Ear (E⊥⊥) components of the electric field to the local magnetic field line were much stronger than th) components of the electric field to the local magnetic field line were much stronger than the dawn-dusk electric field component (Ee dawn-dusk electric field component (Eyy). This result implies that a larger amount of the magnetic ). This result implies that a larger amount of the magnetic flux was transported into the parallel and perpendicular directions to the local magnetic field line tflux was transported into the parallel and perpendicular directions to the local magnetic field line than the dawn-dusk direction at the flow bursts. However, in the Ehan the dawn-dusk direction at the flow bursts. However, in the E yy component, the contribution fro component, the contribution from the dawn-to-dusk electric field (Vm the dawn-to-dusk electric field (VxxBBzz) was much greater than that from the dusk-to-dawn compon) was much greater than that from the dusk-to-dawn component (Vent (VzzBBxx). Furthermore, for two events, significant reduction of the plasma pressure, and enhance). Furthermore, for two events, significant reduction of the plasma pressure, and enhancement of the north-south magnetic field component (Bment of the north-south magnetic field component (B zz) were observed at/near the flow bursts. Sim) were observed at/near the flow bursts. Simultaneous total pressure was well-balanced, indicating that the magnetotail during the plasma floultaneous total pressure was well-balanced, indicating that the magnetotail during the plasma flow bursts was in the state of equilibrium. Based on these results, “bubble” might play a crucial role w bursts was in the state of equilibrium. Based on these results, “bubble” might play a crucial role for generating the plasma flow bursts at geomagnetically quiet times.for generating the plasma flow bursts at geomagnetically quiet times.

AbstractAbstract

Based on our previous results …Based on our previous results …[[Nowada et al.Nowada et al., 2012], 2012]

Under geomagnetically quiet conditions…Under geomagnetically quiet conditions… 1.1. “Magnetotail Magnetic Reconnection” might not “Magnetotail Magnetic Reconnection” might not

be necessary condition to generate the fast plasbe necessary condition to generate the fast plasma flows (plasma flow bursts).ma flows (plasma flow bursts).

2.2. The fast plasma flows (plasma flow bursts) occu The fast plasma flows (plasma flow bursts) occur in association with not only “pure (typical) substr in association with not only “pure (typical) substorm” but also “substorm-like phenomena”, such orm” but also “substorm-like phenomena”, such as pseudo-substorm.as pseudo-substorm.

Locations and Orbits of the THEMIS Locations and Orbits of the THEMIS probesprobes

Event I: January 31, 2008Event I: January 31, 2008- Plasma flow bursts are peri- Plasma flow bursts are periodically occurring. odically occurring.

- The magnetic field perturba- The magnetic field perturbations are observed in associtions are observed in association with the plasma flow bation with the plasma flow bursts. ursts. Significant enhancemSignificant enhancements of the ents of the BBzz components components (magnetotail dipolarization si(magnetotail dipolarization signature)gnature) are observed at/neare observed at/near the plasma flow bursts.ar the plasma flow bursts.

- Plasma density and temper- Plasma density and temperature are variable during the ature are variable during the plasma flow bursts.plasma flow bursts.

- The V- The Vx x component is almoscomponent is almost consistent with the Vt consistent with the V//// com component.ponent.

Event I: January 31, 2008Event I: January 31, 2008

Each electric field Each electric field component as a proxy component as a proxy parameter of the parameter of the magnetic flux transport magnetic flux transport aspect is derived by aspect is derived by following formulae: following formulae:

EEyy = V = VxxBBzz – V – VzzBBxx EE⊥⊥ = V = V⊥⊥BBzz

EE//// = V= V////BBzz

Variations of all electric Variations of all electric field components are field components are almost following those almost following those of the velocity of the velocity components, suggesting components, suggesting that the magnetic flux that the magnetic flux (magnetic energy) is (magnetic energy) is efficiently transported in efficiently transported in association with the association with the plasma flow bursts. plasma flow bursts.

EE//// >> E Eperpperp

EE//// >> EEperpperp

Parallel Parallel magnetic flux magnetic flux transport is the transport is the most dominant.most dominant.

Parallel Parallel magnetic flux magnetic flux transport is the transport is the most dominant.most dominant.

Event I: January 31, 2008Event I: January 31, 2008

Magnetic Pressure (PMagnetic Pressure (Pmm): ):

Plasma Pressure (PPlasma Pressure (Ppp): N): NppkTkTii

Total Pressure (PTotal Pressure (Ptottot): P): Pmm + P + Ppp

0

2

2tB

Both PBoth Ppp and and PPmm show significan show significant variations associated with the t variations associated with the plasma velocity. During the plasplasma velocity. During the plasma flow bursts, Pma flow bursts, Ppp shows shows REDUREDUCTION CTION and simultaneous and simultaneous PPmm indiindicatescates ENHANCEMENTENHANCEMENT..

In In THEMIS-DTHEMIS-D, , PPtottot has been alm has been almost ost CONSTANTCONSTANT. The . The PPtottot valuesvalues iin n THEMIS-ETHEMIS-E are also almost are also almost bacbackground levelkground level ((stablestable)), except fo, except for a plasma flow burst on r a plasma flow burst on ～～ 09:09:48 UT.48 UT.

Event II: March 27, 2009Event II: March 27, 2009- The first plasma flow burst is ob- The first plasma flow burst is observed by served by THEMIS-BTHEMIS-B, but is not o, but is not observed by THEMIS-C. bserved by THEMIS-C.

- During all plasma flow bursts, - During all plasma flow bursts, ththe e BBzz enhancements enhancements (dipolarizatio(dipolarization signatures)n signatures) are observed. are observed.

-The second plasma flow burst oThe second plasma flow burst observed by bserved by THEMIS-BTHEMIS-B is also see is also seen by THEMIS-C, but associated mn by THEMIS-C, but associated magnetic field and plasma variationagnetic field and plasma variations are different between the s are different between the THEMTHEMIS-BIS-B and THEMIS-C observations. and THEMIS-C observations.

-The third plasma flow burst is obThe third plasma flow burst is observed by only served by only THEMIS-BTHEMIS-B

-- The Beta (β) values at the secoThe Beta (β) values at the second plasma flow burst are different nd plasma flow burst are different between the two probes’ observatbetween the two probes’ observations.ions.

Event II: March 27, 2009Event II: March 27, 2009

The electric field The electric field varies in association varies in association with some plasma with some plasma flow burst events.flow burst events.

However, during However, during the other plasma the other plasma flow bursts, the flow bursts, the electric field does electric field does not show not show significant significant variationsvariations.TheThe E Eyy component is the lcomponent is the l

argest, althoughargest, although

EE//// >> E Eperpperp and and EE//// ≈ E ≈ Eperpperp arare observed during the plae observed during the plasma flow bursts.sma flow bursts.

Event II: March 27, 2009Event II: March 27, 2009

PPmm: : ReductionReduction

PPpp: : EnhancementEnhancement

PPtottot: : VariableVariable

PPmm: : EnhancementEnhancement

PPpp: : ReductionReduction

PPtottot: : Background Level Background Level

(stable)(stable)

In association In association with the plasma with the plasma flow bursts…flow bursts…

Event III: March 24, 2010Event III: March 24, 2010-- Plasma flow bursts are observed Plasma flow bursts are observed during the periodical plasma velocduring the periodical plasma velocity fluctuations.ity fluctuations.

- Gradual (- Gradual (THEMIS-DTHEMIS-D) and sharp ) and sharp ((THEMIS-ETHEMIS-E) enhancements of the ) enhancements of the BBzz components components are observed befo are observed before the plasma flow bursts. re the plasma flow bursts.

-- The magnetic field perturbations The magnetic field perturbations are observed in association with tare observed in association with the plasma flow burstshe plasma flow bursts

-- The plasma density and temperThe plasma density and temperature of ature of THEMIS-ETHEMIS-E are variable du are variable during the plasma flow burst. Howevring the plasma flow burst. However, their variationser, their variations inin THEMIS-D THEMIS-D arare almost stable.e almost stable.

-- The VThe Vxx component is almost con component is almost consistent with the Vsistent with the Vperpperp component. component.

Event III: March 24, 2010Event III: March 24, 2010

The electric field The electric field components in components in both both THEMIS-DTHEMIS-D and and THEMIS-ETHEMIS-E indicate indicate significant significant enhancements in enhancements in association with association with the plasma flow the plasma flow bursts.bursts. During the plasma flDuring the plasma fl

ow bursts, the case oow bursts, the case of Ef Eperpperp >> E E//// is domina is dominant.nt.

Event III: March 24, 2010Event III: March 24, 2010

During the plasma floDuring the plasma flow burst intervals, w burst intervals, PPmm s showshows significantsignificant enhaenhancementncement, and simulta, and simultaneous Pneous Ppp indicates indicates rereduction.duction.

AssociatedAssociated P Ptottot is is stabstablele (its value is (its value is backgrbackground levelound level).).

Contribution of Dawn-Dusk Oriented Electric Field (VContribution of Dawn-Dusk Oriented Electric Field (VxxBBzz) in the E) in the Eyy co componentmponent

EEyy = V = VxxBBzz – V – VzzBBxx

Dawn-Dusk and Dusk-DawDawn-Dusk and Dusk-Dawn oriented electric field con oriented electric field components mponents

Earth-Sunward and NorEarth-Sunward and North-Southward magnetic fluth-Southward magnetic flux transport aspectsx transport aspects

EEyy = V = VxxBBzz

Dawn-Dusk oriented electrDawn-Dusk oriented electric field componentic field component

Earth-Sunward magnetiEarth-Sunward magnetic flux transport aspect (Coc flux transport aspect (Contribution by the plasma flntribution by the plasma flow bursts)ow bursts)

Large contributionLarge contribution by the plasma flow by the plasma flow burstsbursts

Large contributionLarge contribution by the plasma flow by the plasma flow burstsbursts

Large Large contributioncontribution

Little Little contributioncontribution

Conclusion (I)Conclusion (I)

We investigated the magnetic flux transport aspects We investigated the magnetic flux transport aspects and pressure variations/balance during the plasmand pressure variations/balance during the plasma flow bursts at geomagnetically quiet times…a flow bursts at geomagnetically quiet times…

- In Events I and III, - In Events I and III, EE////, E, Eperpperp > > E Eyy was seen, suggesti was seen, suggesting that the magnetic flux (magnetic energy) is dong that the magnetic flux (magnetic energy) is dominantly transported to the field-aligned and perpminantly transported to the field-aligned and perpendicular directions to the local magnetic field linendicular directions to the local magnetic field line.e.

- In almost cases, the plasma flow bursts play an im- In almost cases, the plasma flow bursts play an important role for the transport of the magnetic flux iportant role for the transport of the magnetic flux in the magnetotail.n the magnetotail.

Conclusion (II)Conclusion (II)

- Significant enhancements of the B- Significant enhancements of the Bzz component were obser component were observed at/near the plasma flow bursts.ved at/near the plasma flow bursts.

- In Events I and III, significant reduction (enhancement) of t- In Events I and III, significant reduction (enhancement) of the plasma pressure (the magnetic pressure) was seen in he plasma pressure (the magnetic pressure) was seen in association with the plasma flow bursts. association with the plasma flow bursts.

- Simultaneous total pressure was almost constant (was co- Simultaneous total pressure was almost constant (was consistent with the background level), suggesting that the pnsistent with the background level), suggesting that the plasma flow bursts were occurring under the state of equililasma flow bursts were occurring under the state of equilibrium.brium.

From these results, “bubble” might play a crucial role for the From these results, “bubble” might play a crucial role for the

generation of the plasma flow bursts during the geomagngeneration of the plasma flow bursts during the geomagnetically quiet times.etically quiet times.

Back Up SlidesBack Up Slides

Plasma Flow Bursts in magnetotail…Plasma Flow Bursts in magnetotail…

1.1. The sun-earthward plasma velocity component (The sun-earthward plasma velocity component (VVxx) and th) and the perpendicular/parallel plasma velocity components to the e perpendicular/parallel plasma velocity components to the local magnetic field line (local magnetic field line (VV⊥⊥or or VV////), whose ranges are whose ranges are higher higher than 300 km/sthan 300 km/s,, are frequently observed aroundare frequently observed around -10 Re ~-10 Re ~ -3-30 Re0 Re in the magnetotail plasma sheet. in the magnetotail plasma sheet.

2.2. The durations for these fast plasma flows are typically The durations for these fast plasma flows are typically ~ ~ 10 min.10 min.,, which are identified as Bursty Bulk Flow (BBF), but which are identified as Bursty Bulk Flow (BBF), but the fast plasma flows with much shorter duration (within the fast plasma flows with much shorter duration (within 5 5 min.min.) are also observed. These transient fast plasma flows ) are also observed. These transient fast plasma flows are called as “Plasma Flow Burst”.are called as “Plasma Flow Burst”. 3.3. Interestingly, these fast plasma flows are observed durin Interestingly, these fast plasma flows are observed duringg geomagnetically both active and quiet timesgeomagnetically both active and quiet times.

Fast Plasma flows during geomagnetically quiet timesFast Plasma flows during geomagnetically quiet times

Result of the GEOTAIL observations froResult of the GEOTAIL observations from January 1997 to April 1998m January 1997 to April 1998 (1.4 year (1.4 years)s). Only 4 fast plasma flows from 41 geo. Only 4 fast plasma flows from 41 geomagnetic quiet conditions, which were idmagnetic quiet conditions, which were identified by absence of significant auroral entified by absence of significant auroral brightening with POLAR UVI observations, brightening with POLAR UVI observations, were selected [Ieda et al., 2003].were selected [Ieda et al., 2003].

Also statistical result with the GEOTAIL Also statistical result with the GEOTAIL observations from September 1993 to Dobservations from September 1993 to December 1994ecember 1994 (1.4 years) (1.4 years). The duration. The durations for the fast plasma flows at geomagents for the fast plasma flows at geomagentically quiet times, identified as |AL| < 10ically quiet times, identified as |AL| < 100 nT, were 446 hours (corresponding to 0 nT, were 446 hours (corresponding to about 19 days) [Ohtani et al., 2002].about 19 days) [Ohtani et al., 2002].

Main characteristics of these plasma flow bursts Main characteristics of these plasma flow bursts at geomagnetically quiet timesat geomagnetically quiet times

- THEMIS- THEMIS1. The 1. The VVxx component is higher than component is higher than 300 km/s300 km/s, and as, and as

sociated parallel (sociated parallel (VV////)) and perpendicular (and perpendicular (VV⊥⊥) velocit) velocities to the local magnetic field line are higher than ies to the local magnetic field line are higher than 200 km/s200 km/s. The fast flow duration is . The fast flow duration is betweenbetween 1 and 1 and 2 minutes2 minutes..

2. 2. GSM-X <GSM-X < 0 [Re] (Nightside)0 [Re] (Nightside) and and -10 < GSM-Y < 10 [Re]-10 < GSM-Y < 10 [Re] (to avoid the MPCL crossing (to avoid the MPCL crossing

data).data).3. The 3. The ββ value value is higher than or nearly is higher than or nearly 0.50.5..

- Ground- Ground4.4. KKpp index index range is betweenrange is between -1 and +1-1 and +1 andand ALAL//AUAU indi indi

cesces areare lower than ±20 nTlower than ±20 nT..

3 Events of Magnetotail plasma flow bursts at geomag3 Events of Magnetotail plasma flow bursts at geomagnetically quiet timesnetically quiet times

Event Event ##

DateDate Time Intervals (UT)Time Intervals (UT) Flow Flow OrientationOrientation

THEMIS THEMIS ProbesProbes

II 2008/01/312008/01/31 09:45 – 10:0109:45 – 10:01 EarthwardEarthwardP3 (D) and P3 (D) and

P4 (E) P4 (E)

IIII 2009/03/272009/03/2700:10 – 00:19 (TH-B)00:10 – 00:19 (TH-B)

00:56:00 – 00:58:30 (TH-B)00:56:00 – 00:58:30 (TH-B)

00:59 – 01:02 (TH-C)00:59 – 01:02 (TH-C)EarthwardEarthward

P1 (B) and P1 (B) and

P2 (C)P2 (C)

IIIIII 2010/03/242010/03/24 04:25:40 – 04:30:3004:25:40 – 04:30:30 EarthwardEarthward P3 (D) and P3 (D) and P4(E)P4(E)

Contribution of Dawn-Dusk Oriented Electric Field (VContribution of Dawn-Dusk Oriented Electric Field (VxxBBzz) in the E) in the Eyy co component and comparison with the direct measurementmponent and comparison with the direct measurement

EEyy = V = VxxBBzz – V – VzzBBxx

Dawn-Dusk and Dusk-Dawn Dawn-Dusk and Dusk-Dawn oriented electric field compooriented electric field componentsnents

Earth-Sunward and North-Earth-Sunward and North-Southward magnetic flux traSouthward magnetic flux transport aspectsnsport aspects

EEyy = V = VxxBBzz

Dawn-Dusk oriented electric Dawn-Dusk oriented electric field componentfield component

Earth-Sunward magnetic fEarth-Sunward magnetic flux transport aspect (Contriblux transport aspect (Contribution by the plasma flow burution by the plasma flow bursts)sts)

Ey: A direct measurement wiEy: A direct measurement with EFI onboard THEMISth EFI onboard THEMIS