Association of Pi2 pulsations and pulsed reconnection: ground and Cluster observations in the tail lobe at 16 R E

Simultaneous measurements from the Cluster spacecraft and several ground stations (SAMNET, IMAGE, Kakioka, Hermanus) provide evidence for an association of Pi2 pulsations and pulsed reconnection in the magnetotail. On 8 September 2002, substorm-related Pi2 pulsations were recorded with the same waveform (same frequency) in the tail lobe at 16 R E and time-delayed on the ground (both nightside and dayside) spanning L values from 1.23 to 6.11. The tail lobe Pi2 pulsations were a series of nightside flux transfer event (NFTE) pulses propagating at a speed of 600–800 km/s towards Earth, which for the first time relates these two magnetospheric phenomena. NFTEs have previously been considered as the remote signature of tail reconnection. The first ground onset of the Pi2 pulsations occurred at high- and midlatitude ground stations with a time delay of ~30 s with respect to the tail lobe Pi2, followed by lower latitude ground stations. The largest pulsations were observed at high latitude (ten times larger than at low latitude) near the polar cap boundary. The polarization pattern of the ground Pi2s in the H-D plane was consistent with a periodically driven field-aligned current (FAC) system. In addition, fast mode waves must have also played a role in the inner magnetosphere because of propagation effects among ground stations and because of the simultaneous occurrence of dayside low-latitude Pi2. Auroral brightening occurred in the region of upflowing FAC, and the auroral electrojet expanded poleward together with the auroral bulge both of which are typical substorm signatures. Hence, we conclude that the substorm-related Pi2 pulsations in space at 16 R E and on the ground were remotely driven by pulsed reconnection in the magnetotail, that is, reconnection not only provided the energy but its temporal variations also determined the characteristic Pi2 frequency. Scenarios are discussed that address the connection of pulsed reconnection and the driven current system in the ionosphere. These results show that reconnection can be coupled to the ionosphere through what is phenomenologically known as Pi2 pulsations. As a corollary, it is shown that the time history of events fits within the modified NENL model of substorms.

[1]  R. Nakamura,et al.  Reconstruction of the reconnection rate from Cluster measurements: First results , 2005 .

[2]  V. Angelopoulos,et al.  Transition from substorm growth to substorm expansion phase as observed with a radial configuration of ISTP and Cluster spacecraft , 2005 .

[3]  Wolfgang Baumjohann,et al.  Electric current and magnetic field geometry in flapping magnetotail current sheets , 2005 .

[4]  Kazue Takahashi,et al.  Pi2 pulsations associated with poleward boundary intensifications during the absence of substorms , 2004 .

[5]  A. Vaivads,et al.  Structure of the magnetic reconnection diffusion region from four-spacecraft observations. , 2004, Physical review letters.

[6]  C. Meng,et al.  Propagation characteristics of Pi 2 magnetic pulsations observed at ground high latitudes , 2004 .

[7]  A. Viljanen,et al.  One-dimensional upward continuation of the ground magnetic field disturbance using spherical elementary current systems , 2003 .

[8]  J. Slavin,et al.  Simultaneous observations of earthward flow bursts and plasmoid ejection during magnetospheric substorms , 2002 .

[9]  K. Kauristie,et al.  Ionospheric Signatures Of Bursty Bulk Flows , 2002 .

[10]  T. Nagai,et al.  Tailward electrons at the lobe-plasma sheet interface detected upon dipolarizations , 2001 .

[11]  Wolfgang Baumjohann,et al.  Flow bursts and auroral activations: Onset timing and foot point location , 2001 .

[12]  Kiyohumi Yumoto,et al.  Flow bursts, braking, and Pi2 pulsations , 2001 .

[13]  J. Olson,et al.  Characteristics of energy transfer of Pi 2 magnetic pulsations: Latitudinal dependence , 2000 .

[14]  V. Angelopoulos,et al.  Ionospheric current signatures of transient plasma sheet flows , 2000 .

[15]  Y. Yamade,et al.  Field‐aligned currents generated in magnetotail reconnection: 3D Hall‐MHD simulations , 2000 .

[16]  J. Sauvaud,et al.  Multiple‐spacecraft observation of a narrow transient plasma jet in the Earth's plasma sheet , 2000 .

[17]  R. Lysak,et al.  MHD waves in a three‐dimensional dipolar magnetic field: A search for Pi2 pulsations , 1999 .

[18]  Larry Kepko,et al.  Generation of Pi2 pulsations by bursty bulk flows , 1999 .

[19]  Wolfgang Baumjohann,et al.  Flow braking and the substorm current wedge , 1999 .

[20]  John V. Olson,et al.  Pi2 pulsations and substorm onsets: A review , 1999 .

[21]  Kihong Kim,et al.  Compressional MHD waves in the magnetosphere: A new approach , 1999 .

[22]  J. C. Samson,et al.  Association between Geotail plasma flows and auroral poleward boundary intensifications observed by CANOPUS photometers , 1999 .

[23]  D. J. Webster,et al.  Properties and sources of low and very low latitude Pi2 pulsations , 1998 .

[24]  Wolfgang Baumjohann,et al.  Braking of high‐speed flows in the near‐Earth tail , 1997 .

[25]  Daniel N. Baker,et al.  Neutral line model of substorms: Past results and present view , 1996 .

[26]  Frederick W. Menk,et al.  Are low‐latitude Pi2 pulsations cavity/waveguide modes? , 1996 .

[27]  Brian J. Anderson,et al.  Statistical analysis of Pi 2 pulsations observed by the AMPTE CCE Spacecraft in the inner magnetosphere , 1995 .

[28]  J. Sauvaud,et al.  A two satellite study of nightside flux transfer events in the plasma sheet , 1992 .

[29]  G. Paschmann,et al.  Bursty bulk flows in the inner central plasma sheet , 1992 .

[30]  M. Lester,et al.  Polarization, propagation and MHD wave modes of Pi2 pulsations : SABRE/SAMNET results , 1991 .

[31]  K. Yumoto,et al.  dayside Pi 2 pulsations at low latitudes , 1989 .

[32]  W. Hughes,et al.  A comparison of magnetic signatures and DMSP auroral images at substorm onset: Three case studies , 1987 .

[33]  Wolfgang Baumjohann,et al.  The transient response mechanism and Pi2 pulsations at substorm onset-review and outlook , 1984 .

[34]  M. Lester,et al.  LONGITUDINAL STRUCTURE IN PI-2 PULSATIONS AND THE SUBSTORM CURRENT WEDGE , 1984 .

[35]  Mark Lester,et al.  Polarization patterns of Pi 2 magnetic pulsations and the substorm current wedge , 1983 .

[36]  J. Samson,et al.  Polarization characteristics of Pi 2 pulsations and implications for their source mechanisms: Influence of the westward travelling surge , 1983 .

[37]  W. Hughes.  The effect of the atmosphere and ionosphere on long period magnetospheric micropulsations , 1974 .

[38]  Takao Saito,et al.  Geomagnetic pulsations , 1969 .

[39]  H. E. Kallmann,et al.  Transient Response , 1945, Proceedings of the IRE.