EISCAT-Cluster observations

1
EISCAT-Cluster observations of quiet-time
near-Earth magnetotail fast flows and their
signatures in the ionosphere
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

Nordic Cluster Meeting, Uppsala, Sweden, 24 25
August 2011
2
Introduction

• Case study of quiet-time bursty bulk flows
  (BBFs) on 17 Oct 2005
• Focus on signatures of BBFs in the ionosphere
• In this talk plasma flow patterns

• Observations

• Cluster
• EISCAT
• MIRACLE all-sky camera (557 nm) and
  magnetometers
• Meridian-scanning photometer (Hß 486 nm)

Sergeev et al., 2000
3
Bursty bulk flows (BBFs)
Baumjohann et al., 1990 Angelopoulos et al.,
1992, 1994

• 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

Sergeev et al., 2000
4
Geomagnetic conditions
17 Oct 2005

• AE indices indicate gradually weakening
  convection electrojets after 17 UT

decrease of Bz
After Walsh et al., 2009
? Between 18 19 UT, the near-Earth
space was on quiet state
5
Cluster satellites
17 Oct 2005
1800 1900 UT Cluster in the evening sector
southern plasma sheet (plasma ß gt 0.5) XGSM
12 to 14 RE
06
00
12
18
After Walsh et al., 2009
Sun
6
Ground-based measurements
17 Oct 2005
Svalbard
geomagn. north

• 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

Footpoints of Cluster (T96)
Field-of-view of the KEV ASC
KIL MSP
7
17 Oct 2005
Cluster C1Observations
BBF proper flows
Earthward
CIS HIA data
duskward

• After 1815 UT a series of
• 3 flow events identified

tailward
dawnward
dawnside
Deflection bursts
duskside
Return flows
FGM data
Walsh et al., 2009
CIS HIA data
Plasma compression
n reduction during duskside return flows,
no n reduction during dawnside return flows
which could be signature of a wake behind the
moving bubble suggested by Walsh et al. (2009)
8
Kevo all-sky camera
17 Oct 2005
182500 185700 UT, 3 frames/min
UT
MLT
9
EISCAT vs.Cluster
17 Oct 2005
17 Oct 2005
C1 CIS HIA

• 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

C4 CIS CODIF (proton)
equatorwards
equatorwards
line-of- sight
pole- wards
polewards
streamers
PCB
polar cap boundary (PCB)
Erec (mV/m)
PCB
UT
MLT
2100
2130
UT
MLT
10
BBF-streamer ( 2)
geomagnetic north
velocity shear
2050 MLT
streamer
2-D equivalent currents from MIRACLE data (Amm,
1997 Amm and Viljanen, 1999)
proton oval
2220 MLT
1831 1834 UT (frame d)
C1 Vx, Vy
Earthward
duskward
tailward
dawnward

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

1830
1835

• Cluster and EISCAT see dawnside and duskside
  return flows, respectively (frame e)

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

• Cluster in the tail and EISCAT in the
  ionosphere see the same BBF proper flow (frame d)
  

11
BBF-streamer ( 3)
geomagnetic north
velocity shear
2100 MLT
streamer
2230 MLT
1842 1845 UT (frame b)
Earthward
tailward
1840
1845
1850
12
Summary and conclusions
17 Oct 2005

• The BBFs at Cluster

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

• tailward return flows show an interesting
  asymmetry in plasma density

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

• 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

• 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

After Walsh et al., 2009
Walsh et al., 2009
See Pitkänen et al., Ann. Geophys. 29, pp.
299319, 2011
13
Summary and conclusions
17 Oct 2005

• The BBFs at Cluster

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

• tailward return flows show an interesting
  asymmetry in plasma density

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

• 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

• 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

After Walsh et al., 2009
See Pitkänen et al., Ann. Geophys. 29, pp.
299319, 2011