MESSENGER observations of a flux‐transfer‐event shower at Mercury

[1] Analysis of MESSENGER magnetic field observations taken in the southern lobe of Mercury's magnetotail and the adjacent magnetosheath on 11 April 2011 indicates that a total of 163 flux transfer events (FTEs) occurred within a 25 min interval. Each FTE had a duration of ∼2–3 s and was separated in time from the next by ∼8–10 s. A range of values have been reported at Earth, with mean values near ∼1–2 min and ∼8 min, respectively. We term these intervals of quasiperiodic flux transfer events “FTE showers.” The northward and sunward orientation of the interplanetary magnetic field during this shower strongly suggests that the FTEs observed during this event formed just tailward of Mercury's southern magnetic cusp. The point of origin for the shower was confirmed with the Cooling model of FTE motion. Modeling of the individual FTE-type flux ropes in the magnetosheath indicates that these flux ropes had elliptical cross sections, a mean semimajor axis of 0.15RM (where RM is Mercury's radius, or 2440 km), and a mean axial magnetic flux of 1.25 MWb. The lobe magnetic field was relatively constant until the onset of the FTE shower, but thereafter the field magnitude decreased steadily until the spacecraft crossed the magnetopause. This decrease in magnetic field intensity is frequently observed during FTE showers. Such a decrease may be due to the diamagnetism of the new magnetosheath plasma being injected into the tail by the FTEs.

[1]  M. Hidalgo,et al.  Elliptical cross‐section model for the magnetic topology of magnetic clouds , 2002 .

[2]  E. W. Hones,et al.  ISEE 3 observations of traveling compression regions in the Earth`s magnetotail , 1993 .

[3]  Lou‐Chuang Lee,et al.  A theory of magnetic flux transfer at the Earth's magnetopause , 1985 .

[4]  S. Fuselier,et al.  Properties of Near-Earth Magnetic Reconnection from In-Situ Observations , 2011 .

[5]  C. Owen,et al.  The structure of flux transfer events recovered from Cluster data , 2006 .

[6]  Joachim Raeder,et al.  Flux Transfer Events: 1. generation mechanism for strong southward IMF , 2006 .

[7]  A. Summers,et al.  Hydromagnetic flow around the magnetosphere , 1966 .

[8]  C. J. Owen,et al.  Role of the magnetosheath flow in determining the motion of open flux tubes , 2001 .

[9]  Richard D. Starr,et al.  Mercury's Magnetosphere After MESSENGER's First Flyby , 2008, Science.

[10]  Daniel N. Baker,et al.  Mercury’s magnetospheric magnetic field after the first two MESSENGER flybys , 2010 .

[11]  C. Russell,et al.  Initial results of high-latitude magnetopause and low-latitude flank flux transfer events from 3 years of Cluster observations , 2005 .

[12]  A. Vaivads,et al.  Retreat and reformation of X‐line during quasi‐continuous tailward‐of‐the‐cusp reconnection under northward IMF , 2008 .

[13]  L. Burlaga,et al.  Magnetic field structure of interplanetary magnetic clouds at 1 AU , 1990 .

[14]  C. Cid,et al.  A non‐force‐free approach to the topology of magnetic clouds in the solar wind , 2002 .

[15]  C. T. Russell,et al.  Initial ISEE magnetometer results: magnetopause observations , 1978 .

[16]  C. Owen,et al.  Motion of flux transfer events: a test of the Cooling model , 2007 .

[17]  George Gloeckler,et al.  MESSENGER Observations of the Spatial Distribution of Planetary Ions Near Mercury , 2011, Science.

[18]  Christopher T. Russell,et al.  A survey of dayside flux transfer events observed by ISEE 1 and 2 magnetometers , 1984 .

[19]  B. Sonnerup,et al.  Magnetopause reconnection rate , 1974 .

[20]  M. Dunlop,et al.  Cluster observations of crater flux transfer events at the dayside high-latitude magnetopause , 2008 .

[21]  M. Kivelson,et al.  Modeling a force‐free flux transfer event probed by multiple Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft , 2008 .

[22]  C. Russell,et al.  Flux transfer events at Mercury , 1985 .

[23]  James A. Slavin,et al.  The effect of erosion on the solar wind stand-off distance at Mercury , 1979 .

[24]  S. Solomon,et al.  MESSENGER Mission Overview , 2007 .

[25]  S. Solomon,et al.  MESSENGER Observations of Magnetic Reconnection in Mercury’s Magnetosphere , 2009, Science.

[26]  G. Morfill,et al.  The formation of the plasma sheet resulting from plasma mantle dynamics , 1978 .

[27]  Haje Korth,et al.  The Global Magnetic Field of Mercury from MESSENGER Orbital Observations , 2011, Science.

[28]  H. Auster,et al.  THEMIS observations of the dayside traveling compression region and flows surrounding flux transfer events , 2008 .

[29]  J. Dungey.  Interplanetary Magnetic Field and the Auroral Zones , 1961 .

[30]  S. Solomon,et al.  MESSENGER observations of large flux transfer events at Mercury , 2010 .

[31]  B. Anderson,et al.  The Magnetometer Instrument on MESSENGER , 2007 .

[32]  James A. Slavin,et al.  The Structure of Mercury's Magnetic Field from MESSENGER's First Flyby , 2008, Science.

[33]  S. Solomon,et al.  Plasma pressure in Mercury's equatorial magnetosphere derived from MESSENGER Magnetometer observations , 2011 .

[34]  H. Zhang,et al.  Plasmoid in the high latitude boundary/cusp region observed by Cluster , 2005 .

[35]  J. Slavin,et al.  On the origin of reverse polarity TCRs , 2001 .

[36]  C. Owen,et al.  A SIMPLE ILLUSTRATIVE MODEL OF OPEN FLUX TUBE MOTION OVER THE DAYSIDE MAGNETOPAUSE , 1989 .

[37]  Mike Lockwood,et al.  On the quasi‐periodic nature of magnetopause flux transfer events , 1993 .

[38]  M. F. Marcucci,et al.  TC-1 observations of a flux rope: Generation by multiple X line reconnection , 2011 .

[39]  E. Kobel,et al.  A model of the steady state magnetic field in the magnetosheath , 1994 .

[40]  Nancy U. Crooker,et al.  Dayside merging and cusp geometry , 1979 .

[41]  O. D. Constantinescu,et al.  Evidence for a flux transfer event generated by multiple X‐line reconnection at the magnetopause , 2010 .