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 ionosphere In 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 R E 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., 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., Oct :00 – 19:00 UT Cluster in the evening sector southern plasma sheet (plasma β > 0.5) X GSM ~ –12 to –14 R E Sun

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 Svalbard geomagn. 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 C1 Observations 17 Oct 2005 n reduction during duskside return flows, BBF proper flows Deflection bursts Return 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 MLT UT 18:25:00 – 18:57:00 UT, 3 frames/min

EISCAT vs. Cluster 17 Oct 2005 MLT UT PCB E rec (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 cap boundary (PCB) streamers C1 CIS HIA C4 CIS CODIF (proton) equatorwards pole- wards 21:0021:30 UT 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) velocity shear 20:50 MLT 22:20 MLT 18:30 18:35 Earthward tailward C1 V x, V y 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 equivalent currents from MIRACLE data (Amm, 1997; Amm and Viljanen, 1999)

BBF-streamer ( 3) geomagnetic north 21:00 MLT 22:30 MLT streamer velocity shear 18:4018:45 18:50 Earthward tailward ~18:42 – 18:45 UT (frame b)

Summary and conclusions After Walsh et al., 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., 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