Transcript Slide 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
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
Sergeev et al., 2000
• MIRACLE all-sky camera (557 nm) and magnetometers
• Meridian-scanning photometer (Hβ 486 nm)
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
Sergeev et al., 2000
• 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
17 Oct 2005
Geomagnetic conditions
 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
17 Oct 2005
Cluster satellites
18:00 – 19:00 UT
06
Cluster in the evening
sector southern
plasma sheet
(plasma β > 0.5)
XGSM ~ –12 to –14 RE
00
12
18
After Walsh et al., 2009
Sun
17 Oct 2005
Ground-based measurements
geomagn.
north
Svalbard
 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
Footpoints of
Cluster (T96)
Field-of-view of
the KEV ASC
KIL MSP
 Green: Meridian-scanning photometer
(KIL MSP) operated at Kilpisjärvi
17 Oct 2005
BBF proper flows
Earthward
duskward
tailward
dawnward
Deflection bursts
CIS HIA
data
After 18:15 UT a series of
3 flow events identified
dawnside
Return flows
Cluster C1
Observations
duskside
FGM data
Walsh et al., 2009
Plasma compression
CIS HIA
data
• 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)
no n reduction during
dawnside return flows
n reduction during
duskside return flows,
which could be signature of a wake behind the moving bubble
suggested by Walsh et al. (2009)
Kevo all-sky camera
18:25:00 – 18:57:00 UT, 3 frames/min
UT
MLT
17 Oct 2005
17 Oct 2005
17 Oct 2005
C1 CIS HIA
C4 CIS CODIF
(proton)
equatorwards
equatorwards
line-ofsight
polewards
polewards
streamers
polar cap
boundary (PCB)
Erec
(mV/m)
PCB
UT
MLT
• 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 equatorward edge of a streamer
- equatorward component in the
plasma flow within the streamer
PCB
UT
MLT
EISCAT vs.
Cluster
21:00
21:30
- reduced Ne and enhanced Ti in
poleward flows
BBF-streamer ( 2)
geomagnetic
north
velocity
shear
20:50 MLT
streamer
2-D equivalent
currents from
MIRACLE data
(Amm, 1997;
Amm and
Viljanen, 1999)
proton oval
22:20 MLT
~18:31 – 18:34 UT
(frame d)
C1 Vx, Vy
Earthward
duskward
tailward
dawnward
18:30
18:35
 The streamer evolution in the optical EISCAT and ASC data is consistent with the Cluster data
 Cluster and
EISCAT
dawnside
and
duskside
return
respectively
(frame
e) d)c)
sees
in
the
the
tail plasma
andsee
EISCAT
deflection
in thewhen
ionosphere
mappedsee
roughly
theflows,
same
in front
BBF
of proper
the streamer
flow (frame
(frame
BBF-streamer ( 3)
geomagnetic
north
velocity
shear
21:00 MLT
streamer
22:30 MLT
~18:42 – 18:45 UT
(frame b)
Earthward
tailward
18:40
18:45
18:50
17 Oct 2005
Summary and conclusions
 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
After Walsh et al., 2009
 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 ionospheric 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
Walsh et al., 2009
See:
Pitkänen et al., Ann. Geophys. 29, pp. 299–319, 2011
17 Oct 2005
Summary and conclusions
 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
After Walsh et al., 2009
 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 ionospheric 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
See:
Pitkänen et al., Ann. Geophys. 29, pp. 299–319, 2011