Post on 08-Feb-2016
description
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