Statistical study of non-reconnection plasma jets as observed by the DOUBLE STAR spacecraft E. Amata 1, S. Savin 2, D. Ambrosino 1, L. Trenchi 1, M.F. Marcucci 1 1) Istituto di Fisica dello Spazio Interplanetario, INAF, Roma, Italia 2) IKI RAN, Moscow, Russian Federation Istituto di Astrofisica e Planetologia Spaziali: IAPS

A vast literature has been produced in the last decades on the observation of accelerated jets close to the Earth’s magnetopause, which have been commonly ascribed to magnetic reconnection at the magnetopause between the magnetic field convected by the shocked solar wind and the magnetic field of the magnetosphere. Nemecek et al. (1998) described abrupt strong ion flux increases or decreases in the flank magnetosheath, which they called Transient Flux Events (TFE). Savin et al. (2008) presented observations of non reconnection jets, argued that such jets are accompanied by plasma super-diffusion and suggested that they are important for energy dissipation and plasma transport. Shue et al. (2009) presented an event during which a fast magnetosheath jet impinged on the subsolar magnetopause and produced an indentation of the magnetopause which resulted in the reflection of the jet so as to produce a sunward flow in the magnetosheath. Finally, non reconnection jets have been described by Amata et al. (2008), Hietala et al. (2009, 2011), Savin et al. (2011).

Outline Some examples: - Nemecek et al. - March 17, 2001, Cluster - March 2, 2004, Double Star - March 17, 2005, Cluster + Double Star Statistical study of DS jets Conclusions

Nemecek et al (GRL,1998) found a number of events, in the Interball data set, when unusually large flow fluxes were observed in the MSH. Transient Flux Enhancement: TFE. F (t) > 1.5 (t-5min,t) WIND ion flux. N ~ 6cm -3 ; V ~ 490 km/s WIND clock angle WIND M A I.Ball ion flux I.Ball mag. field v - At all latitudes of the flank MSH. - Steady solar wind flow. - Highly supercritical SW (M A >7). - Not correlated with magnetic field changes (thus, no link with the slow mode transitions reported by Song et al. [1992]).

Cluster SC1 (red lines) and ACE (black lines) magnetic field data. Cluster (HIA SC1) omni-directional ion energy spectrograms from 09:10 to 12:10 UT on March 17, IMP 8 (dots), WIND (blue solid line) and SC1 ion density (red line). SC1 T // (black line) and T ┴ (red line). Solar wind V x measured by IMP 8 (dots) and by ACE (solid line). Bulk ion kinetic energy density, measured by IMP 8 (dots), WIND (blue) and SC1 (red). SC1 magnetosonic Mach number.

Possible interaction of the A and B jets with the magnetopause (GSM XZ plane): -Shue et al., 1998, magnetopause (dashed curve), - deformed magnetopause (thin solid line), - jet peak velocity vectors, - Cluster orbit (solid thick line), - the H jet and the bow shock are also shown.

XZ GSE XY GSE March 17, 2005, Cluster + Double Star

ACE V z ~ -30 km/s ACE V x ~ -690 km/s

(km/s) DS VxDS VyDS VzCl VxCl VyCl Vz Jet MSH XZ GSEXY GSE MSH/Jet flow Angle Double Star Cluster 10° 14° W k_jet ~ 3. W k_MSH ~ 1.5 W k_SW β MSH β jet M ms_MSH M ms_jet D.Star Cluster

Outline Some examples: - Nemecek et al. - March 17, 2001, Cluster - March 2, 2004, Double Star - March 17, 2005, Cluster + Double Star Statistical study of DS jets Conclusions

Triggered bt the previous results, we decided to look at the whole DS data base. We identified jets in the DS MSH data in the period (winter and spring tiimes)

We considered all cases when Pdyn_msh > Pdyn_omni Alternatively, we considered all cases when Mms_msh > 1. The results I will describe in the following slides did not change.

Clock angle

Plasma data provided by the HIA were examined searching for high dynamic pressure plasma jets in the Earth’s magnetosheath (Pdyn > Pdyn_SW). The study was limited to portions of the spacecraft orbit such that the angle between the position vector in GSE and the Sun-Earth line was steadily below 20°. More than 500 such jets were identified. Therefore, we can suggest that such jets are a permanent feature of MSH dynamics. We found that: 1)such jets occur at all distances from the bow shock and from the magnetopause; suggesting that they are somehow generated at the bow shock and propagate in the MSH, 2)they are not due to magnetic reconnection; 3)about 1/3 of jets occur without changes in the solar wind conditions (TD, RD etc.); 4)they have Mms > Mms_msh: usually, Mms > 1. 5)no clear dependence is observed on the average IMF Bz component 6)no dependence is observed on the average IMF clock angle. 7)dependence on the average IMF Bx component to br further investigated. Further studies are required to fully explain the mechanism(s) by which they are generated Summary and conclusions