EISCAT-Cluster observations of quiet-time near-Earth magnetotail fast flows

and their signatures in the ionosphere

Nordic Cluster Meeting, Uppsala, Sweden, 24 – 25 August 2011

T. Pitkänen(1), A. T. Aikio(1), O. Amm(2), K. Kauristie(2), H. Nilsson(3), and K. U. Kaila(1)

(1) Department of Physics, University of Oulu, Oulu, Finland(2) Finnish Meteorological Institute, Helsinki, Finland(3) Swedish Institute of Space Physics, Kiruna, Sweden

• Cluster

• EISCAT

• MIRACLE all-sky camera (557 nm) and magnetometers

• Meridian-scanning photometer (Hβ 486 nm)

Introduction Case study of quiet-time bursty bulk flows (BBFs) on 17 Oct 2005

Focus on signatures of BBFs in the ionosphereIn this talk: plasma flow patterns

Observations:

Sergeev et al., 2000

Bursty bulk flows (BBFs)

Transient, localized, fast, Earthward plasma flows

• Convective in the central plasma sheet, field-aligned in the outer plasma sheet

• Typical duration of ~ 10 min with superimposed flow bursts of ~ 1 min

• V ~ 100 – 800 km/s (max. ~ 2000 km/s), cross-tail width 1 – 5 RE

• Only ~ 5 % contribution to the plasma flows, but 70 – 80 % to the total plasma and magnetic flux transport in the plasma sheet

• Tend to occur during substorm expansions, but appear during all levels of geomagnetic activity

• Ionospheric signatures of BBFs include auroral streamers, which are considered to represent upward field-aligned current flowing to the duskside flank of a BBF

Baumjohann et al., 1990; Angelopoulos et al., 1992, 1994

Sergeev et al., 2000

Geomagnetic conditions

After Walsh et al., 2009

17 Oct 2005

Between 18 – 19 UT, the near-Earth space was on quiet state

decrease of Bz

AE indices indicate gradually weakening convection electrojets after 17 UT

Cluster satellites

After Walsh et al., 2009

17 Oct 2005

18:00 – 19:00 UTCluster in the evening sector southern plasma sheet(plasma β > 0.5)XGSM ~ –12 to –14 RE

Sun

0012

06

18

Ground-based measurements 17 Oct 2005

Footpoints of Cluster (T96)

Field-of-view of the KEV ASC

Red: The mainland EISCAT VHF near Tromsø; The ESR 32m and 42m antennas on Svalbard

Yellow: MIRACLE Kevo all-sky camera (KEV ASC)

Blue: MIRACLE magnetometer stations

Green: Meridian-scanning photometer (KIL MSP) operated at Kilpisjärvi

KIL MSP

Svalbardgeomagn. north

After 18:15 UT a series of 3 flow events identified

• Deflection and compression of ambient plasma in front of an approaching plasma bubble(e.g. Sergeev et al., 1996; Snekvik et al., 2007)

• Tailward flows are consistent with return flow patterns around edges of a bubble (Pontius and Wolf, 1990)

Cluster C1Observations

17 Oct 2005

n reduction during duskside return flows,

BBF proper flows

Deflection burstsReturn flows

CIS HIA data

FGM data

CIS HIA data

Plasma compression

which could be signature of a wake behind the moving bubble suggested by Walsh et al. (2009)

Earthward

tailward

duskward

dawnward

Walsh et al., 2009

dawnside

duskside

no n reduction during dawnside return flows

Kevo all-sky camera 17 Oct 2005

MLTUT

18:25:00 – 18:57:00 UT, 3 frames/min

EISCAT vs.Cluster

17 Oct 2005 17 Oct 2005

MLTUT

PCB

PCB

Erec (mV/m)

equatorwards

polewards

line-of-sight

• Auroral streamers seen by VHF in Te can be directly associated to the BBFs by Cluster

• Streamers are associated with

- sharp velocity shear at the equat- orward edge of a streamer

- equatorward component in the plasma flow within the streamer

- reduced Ne and enhanced Ti in poleward flows

polar capboundary (PCB)

streamers

C1 CIS HIA

C4 CIS CODIF (proton)

equatorwards

pole-wards

21:00 21:30UT

MLT

BBF-streamer ( 2)geomagnetic north

proton oval

The streamer evolution in the optical EISCAT and ASC data is consistent with the Cluster data

streamer

Cluster sees the plasma deflection when mapped roughly in front of the streamer (frame c)

velocityshear

20:50 MLT

22:20 MLT

18:30 18:35

Earthward

tailward

C1 Vx, Vy

duskward

dawnward

Cluster in the tail and EISCAT in the ionosphere see the same BBF proper flow (frame d) Cluster and EISCAT see dawnside and duskside return flows, respectively (frame e)

~18:31 – 18:34 UT(frame d)

2-D equivalentcurrents fromMIRACLE data(Amm, 1997;Amm and Viljanen, 1999)

BBF-streamer ( 3)geomagnetic north

21:00 MLT

22:30 MLT

streamer

velocityshear

18:40 18:45 18:50

Earthward

tailward

~18:42 – 18:45 UT(frame b)

Summary and conclusions

After Walsh et al., 2009

17 Oct 2005

The BBFs at Cluster

auroral streamers and associated plasma flows agree with the simultaneous Cluster data (T96 mapping), which suggests that

EISCAT saw the ionospheric counterpart of BBF proper and return flows observed by Cluster in the magnetotail

a southeastward streamer-aligned plasma flow roughly poleward of the streamer is the ion- ospheric manifestation of the BBF proper flow channel. A northwestward low-density plasma flow on the equatorward side of a velocity shear corresponds to the duskside return flow

The duskside return flows were associated with decrease in plasma density. However, no similar feature was seen for the dawnside return flows, but rather an increase in density

See:Pitkänen et al., Ann. Geophys. 29, pp. 299–319, 2011

agree with the bubble model (Pontius and Wolf, 1990), including tailward return flows

tailward return flows show an interesting asymmetry in plasma density

decrease in plasma density in duskside return flows gives some support to the recent suggestion of formation of a depleted wake (Walsh et al., 2009)

The BBFs in the ionosphere

Walsh et al., 2009

Summary and conclusions

After Walsh et al., 2009

17 Oct 2005

The BBFs at Cluster

auroral streamers and associated plasma flows agree with the simultaneous Cluster data (T96 mapping), which suggests that

EISCAT saw the ionospheric counterpart of BBF proper and return flows observed by Cluster in the magnetotail

a southeastward streamer-aligned plasma flow roughly poleward of the streamer is the ion- ospheric manifestation of the BBF proper flow channel. A northwestward low-density plasma flow on the equatorward side of a velocity shear corresponds to the duskside return flow

The duskside return flows were associated with decrease in plasma density. However, no similar feature was seen for the dawnside return flows, but rather an increase in density

See:Pitkänen et al., Ann. Geophys. 29, pp. 299–319, 2011

agree with the bubble model (Pontius and Wolf, 1990), including tailward return flows

tailward return flows show an interesting asymmetry in plasma density

decrease in plasma density in duskside return flows gives some support to the recent suggestion of formation of a depleted wake (Walsh et al., 2009)

The BBFs in the ionosphere