THE WAKE OF FLUX TRANSFER EVENTS AT THE DAYSIDE

The effects of flux transfer events (FTE) on the dayside auroral ionosphere are studied, using a simple twin-vortex model of induced ionospheric plasma flow. It is shown that the predicted and observed velocities of these flows are sufficient to drive nonthermal plasma in the F region, not only within the newly opened flux tube of the FTE, but also on the closed, or "old" open, field lines around it. In fact, with the expected poleward neutral wind, the plasma is more highly nonthermal on the flanks of, but outside, the open flux tube: EISCAT observations indicate that plasma is indeed driven into nonthermal distributions in these regions. The nonthermal plasma is thereby subject to additional upforce due to the resulting ion temperature anisotropy and transient expansion due to Joule heating and also to ion accelerations associated with the FTE field aligned current system. Any upflows produced on closed field lines in the vicinity of the FTE are effectively bunched-up in the "wake" of the FTE. Observations from the AMPTE-UKS satellite at the magnetopause reveal ion upflows of energy ~100 eV flowing out from the ionosphere on closed field lines which are only found in the wake of the FTE. Such flows are also only found shortly after two, out of all the FTEs observed by AMPTEUKS. The outflow from the ionosphere is two orders of magnitude greater than predicted for the "classical" polar wind. It is shown that such ionospheric ion flows are only expected in association with FTEs on the magnetopause which are well removed from the sub-solar point-either towards dusk or, as in the UKS example discussed here, towards dawn. It is suggested that such ionospheric ions will only be observed if the center of the FTE open flux tube passes very close to the satellite. Consequently, we conclude the ion upflows presented here are probably driven by the second of two possible source FTEs and are observed at the satellite with a laq 1Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, England. 2Also Visiting Honorary Lecturer, Blackett Laboratory, Imperial College, London. $Mullard Space Science Laboratory, Department of Physics and Astronomy, University College

[1]  C. Farrugia,et al.  A multi‐instrument study of flux transfer event structure , 1988 .

[2]  Charles J. Farrugia,et al.  What are flux transfer events , 1988 .

[3]  M. Lockwood,et al.  Flow in the high latitude ionosphere: measurements at 15s resolution made using the EISCAT ‘Polar’ experiment , 1988 .

[4]  M. Lockwood,et al.  Scattered power from non-thermal, F-region plasma observed by EISCAT - Evidence for coherent echoes? , 1988 .

[5]  M. Dunlop,et al.  A magnetic boundary signature within flux transfer events , 1987 .

[6]  T. Killeen,et al.  Effects of thermospheric motions on the polar wind: A time‐dependent numerical study , 1987 .

[7]  M. Lockwood,et al.  The modelled occurrence of non-thermal plasma in the ionospheric F-region and the possible consequences for ion outflows into the magnetosphere , 1987 .

[8]  David J. Southwood,et al.  The ionospheric signature of flux transfer events , 1987 .

[9]  Charles J. Farrugia,et al.  Field and flow perturbations outside the reconnected field line region in flux transfer events: Theory , 1987 .

[10]  Mike Lockwood,et al.  Non-Maxwellian ion velocity distributions observed using EISCAT , 1987 .

[11]  Per Even Sandholt,et al.  Signatures in the dayside aurora of plasma transfer from the magnetosheath , 1986 .

[12]  M. Lockwood,et al.  EISCAT observations of bursts of rapid flow in the high latitude dayside ionosphere , 1986 .

[13]  M. Lockwood,et al.  The geomagnetic mass spectrometer— mass and energy dispersions of ionospheric ion flows into the magnetosphere , 1985, Nature.

[14]  K. Glassmeier,et al.  Observations of a possible ground signature of flux transfer events , 1985 .

[15]  R. Schunk,et al.  Effect of hot electrons on the polar wind , 1984 .

[16]  Daan Hubert.  Non-Maxwellian velocity distribution functions and incoherent scattering of radar waves in the auroral ionosphere , 1984 .

[17]  L. Lyons,et al.  Generation of ion‐conic distribution by upgoing ionospheric electrons , 1981 .

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

[19]  C. Darwin,et al.  Note on hydrodynamics , 1953, Mathematical Proceedings of the Cambridge Philosophical Society.

[20]  R. Schunk.  An updated theory of the polar wind , 1986 .

[21]  T. Moore.  Acceleration of low-energy magnetospheric plasma , 1986 .

[22]  M. Lockwood.  Low-energy ion flows into the magnetosphere , 1986 .

[23]  David J. Southwood,et al.  Theoretical aspects of ionosphere-magnetosphere-solar wind coupling , 1985 .