Global Control of Merging by the IMF Cluster

Global Control of Merging by the IMF: Cluster Observations of Dawnside Flank Magnetopause Reconnection S. Eriksson, S. R. Elkington, T. D. Phan, S. M. Petrinec, H. Reme, M. W. Dunlop, M. Wiltberger, A. Balogh, R. E. Ergun, and M. Andre Contact information: eriksson@lasp. colorado. edu

Outline n Introduction On the “MHD sash” and antiparallel magnetic fields n Methodology How to find Cluster events near the sash? n Observations and MHD simulations Northern Hemisphere dawnside flank on 2001 -06 -30 Southern Hemisphere dawnside flank on 2001 -05 -29 n Summary & Conclusions

MHD Sash & Antiparallel Merging Top left: MHD sash as defined by the magnetic field minima on the magnetopause from the ISM model [Siscoe et al. , 2001] for two different directions of the IMF. Right: Regions of near antiparallel magnetic fields (black) in vacuum [Luhmann et al. , 1984] for various directions of the IMF.

Methodology: Two Cluster sc 1 Events Predicted magnetopause crossings near the MHD “sash” (black) for two events on the dawnside flank. Dashed lines illustrate search volume.

Methodology: ACE IMF Data for 2001 -06 -30 (a) Cluster sc 1 clock angle and radial position in the GSM YZ plane. (b) ACE IMF data and clock angle corresponding to Cluster interval in (a). (c) Clock angles of the IMF, Cluster sc 1 position, and the estimated sash location using expression above (only valid in X=0 plane) [e. g. Siscoe et al. , 2001]

Methodology: ACE IMF Data for 2001 -06 -30 …. using ACE IMF data as input to the expression of the antiparallel separator line [e. g. Yeh, 1976], we predict that Cluster sc 1 is within 10 deg of the sash when marked by vertical bars along the time axis …. 03: 00 UT 09: 00 UT

Cluster Data 2001 -06 -30/04: 00 – 12: 00 UT Speed enhancements

MVAB Transformation Minimum variance analysis interval: 0827: 30 UT to 0918: 30 UT (2001 -06 -30)

LMN Transformed Data and Eight Walen Analysis Intervals Positive Vm changes and negative Vl changes in velocity, indicating a merging site sunward and northward of Cluster sc 1 ….

Walen Analyses Mostly negative Walen slopes, indicating a merging site north of Cluster sc 1.

MHD Simulation (LFM code) The Cluster sc 1 location at 06: 00 UT is indicated by red diamond symbols. It is passing through the MHD sash region on the Northern Hemisphere dawnside flank ….

Topological 3 D MHD View Flux tubes: open-open-closed-closed Equatorward and tailward directed plasma jets are consistent with the relaxation of the kink in the open-closed fields connected to the Southern Hemisphere Cluster sc 1

Southern Hemisphere Event: ACE IMF Data for 2001 -05 -29 (a) Cluster sc 1 clock angle and radial position in the GSM YZ plane. (b) ACE IMF data and clock angle corresponding to Cluster interval in (a). (c) Clock angles of the IMF, Cluster sc 1 position, and the estimated sash location using expression above (only valid in X=0 plane) [e. g. Siscoe et al. , 2001]

Southern Hemisphere Event: ACE IMF Data for 2001 -05 -29 …. using ACE IMF data as input to the expression of the antiparallel separator line [e. g. Yeh, 1976], we predict that Cluster sc 1 is within 10 deg of the sash when marked by vertical bars along the time axis …. 01: 00 UT 05: 00 UT

Cluster Data 2001 -05 -29/02: 30 – 04: 30 UT Plasma acceleration

MVAB Transformation Minimum variance analysis interval: 0321: 30 UT to 0341: 30 UT (2001 -05 -29)

LMN Transformed Data and Two Walen Analysis Intervals Positive and smaller negative Vm changes during positive Vl changes in velocity, indicating a merging site mostly southward of Cluster sc 1 ….

Walen Analyses Positive Walen slopes, indicating a merging site south of Cluster sc 1.

MHD Simulation (LFM code) The Cluster sc 1 location at 03: 10 UT is indicated by black diamond symbols. It is passing through the equatorward part of the MHD sash region on the Southern Hemisphere dawnside flank ….

Modeled Antiparallel and Component Merging Regions Estimated regions of antiparallel and component merging projected onto the magnetopause using the Tsyganenko T-96 model. The component merging line incorporates a draped magnetosheath field [S. M. Petrinec]. The effect of the By component is clearly seen.

Summary of Plasma Acceleration 2001 -06 -30 Event Using the LM velocities to transform into GSM, we note that the plasma is accelerated tailward and southward along the magnetopause. Note that the average Mach numbers during the jet intervals are super-Alfvenic. The directions agree well with the direction of the MHD sash.

Summary of Plasma Acceleration 2001 -05 -29 Event Using the LM velocities to transform into GSM, we note that the plasma is accelerated sunward and northward along the magnetopause. Note that the average Mach numbers during the jet intervals are Alfvenic. The directions agree well with the direction of the MHD sash.

Summary n The Walen test and the analysis of plasma acceleration in the magnetopause plane at Cluster together with MHD simulations confirm the presence of an X-line in the direction of the MHD sash.

Summary n n The Walen test and the analysis of plasma acceleration in the magnetopause plane at Cluster together with MHD simulations confirm the presence of an X-line in the direction of the MHD sash. The magnetic field shear angle ranges between 162 deg and 168 deg at times of clear crossings into the magnetosheath. Note that the shear angle at the poleward X-line location may be different.

Summary n n n The Walen test and the analysis of plasma acceleration in the magnetopause plane at Cluster together with MHD simulations confirm the presence of an X-line in the direction of the MHD sash. The magnetic field shear angle ranges between 162 deg and 168 deg at times of clear crossings into the magnetosheath. Note that the shear angle at the poleward X-line location may be different. Antiparallel merging where MHD predicts the location of the sash may likely be the source of these plasma jets. However, since the modeled antiparallel and component merging regions both lie poleward of Cluster, we cannot rule out a component merging process.

Summary n n The Walen test and the analysis of plasma acceleration in the magnetopause plane at Cluster together with MHD simulations confirm the presence of an X-line in the direction of the MHD sash. The magnetic field shear angle ranges between 162 deg and 168 deg at times of clear crossings into the magnetosheath. Note that the shear angle at the poleward X-line location may be different. Antiparallel merging where MHD predicts the location of the sash may likely be the source of these plasma jets. However, since the modeled antiparallel and component merging regions both lie poleward of Cluster, we cannot rule out a component merging process. The Alfvenic magnetosheath plasma flow on 29 May 2001 made the detection of sunward jets possible.