Observations of an enhanced convection channel in the cusp ionosphere

Transient or patchy magnetic field line merging on the dayside magnetopause, giving rise to flux transfer events (FTEs), is thought to play a significant role in energizing high-latitude ionospheric convection during periods of southward interplanetary magnetic field. Several transient velocity patterns in the cusp ionosphere have been presented as candidate FTE signatures. Instrument limitations, combined with uncertainties about the magnetopause processes causing individual velocity transients, mean that definitive observations of the ionospheric signature of FTEs have yet to be presented. This paper describes combined observations by the PACE HF backscatter radar and the DMSP F9 polar-orbiting satellite of a transient velocity signature in the southern hemisphere ionospheric cusp. The prevailing solar wind conditions suggest that it is the result of enhanced magnetic merging at the magnetopause. The satellite particle precipitation data associated with the transient are typically cusplike in nature. The presence of spatially discrete patches of accelerated ions at the equatorward edge of the cusp is consistent with the ion acceleration that could occur with merging. The combined radar line-of-sight velocity data and the satellite transverse plasma drift data are consistent with a channel of enhanced convection superposed on the ambient cusp plasma flow. This channel is at least 900 km in longitudinal extent but only 100 km wide. It is zonally aligned for most of its extent, except at the western limit where it rotates sharply poleward. Weak return flow is observed outside the channel. These observations are compared with and contrasted to similar events seen by the EISCAT radar and by optical instruments.

[1]  C. Meng,et al.  Ion acceleration at the equatorward edge of the cusp: Low altitude observations of patchy merging , 1991 .

[2]  Wolfgang Baumjohann,et al.  The Magnetospheric Response to 8-Minute Period Strong-Amplitude Upstream Pressure Variations , 1989 .

[3]  G. Caudal,et al.  A SAFARI-EISCAT comparison between the velocity of F region small-scale irregularities and the ion drift , 1985 .

[4]  M. Gussenhoven,et al.  Precipitating Electron and Ion Detectors (SSJ/4) for the Block 5D/flights 6-10 DMSP (Defense Meteorological Satellite Program) Satellites: Calibration and Data Presentation , 1984 .

[5]  R. Greenwald,et al.  Mapping high-latitude plasma convection with coherent HF radars , 1989 .

[6]  R. Greenwald,et al.  Simultaneous HF-radar and DMSP observations of the cusp , 1990 .

[7]  M. Smith,et al.  the pulsating cusp , 1990 .

[8]  R. Livingston,et al.  Polar cap F layer patches: Structure and dynamics , 1986 .

[9]  Lou‐Chuang Lee,et al.  Magnetic Flux Transfer at the Earth’s Magnetopause , 1986 .

[10]  J. M. Ruohoniemi,et al.  Drift motions of small‐scale irregularities in the high‐latitude F region: An experimental comparison with plasma drift motions , 1987 .

[11]  Mike Lockwood,et al.  The ionospheric signatures of flux transfer events and solar wind dynamic pressure changes , 1990 .

[12]  M. Lockwood,et al.  OBSERVATIONS AT THE MAGNETOPAUSE AND IN THE AURORAL IONOSPHERE OF MOMENTUM TRANSFER FROM THE SOLAR WIND , 1988 .

[13]  Manfred Scholer,et al.  Magnetic flux transfer at the magnetopause based on single X line bursty reconnection , 1988 .

[14]  C. R. Clauer,et al.  Ionospheric traveling convection vortices observed near the polar cleft: A triggered response to sudden changes in the solar wind , 1988 .

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

[16]  M. Freeman,et al.  The determination of time‐stationary two‐dimensional convection patterns with single‐station radars , 1991 .

[17]  R. Greenwald,et al.  Polar Anglo‐American Conjugate Experiment , 1989 .

[18]  M. Smith,et al.  Low-altitude signatures of the cusp and flux transfer events , 1989 .

[19]  M. Saunders.  Origin of the cusp Birkeland currents , 1989 .

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

[21]  R. Greenwald,et al.  An ionospheric signature of possible enhanced magnetic field merging on the dayside magnetopause , 1991 .

[22]  R. Greenwald,et al.  Simultaneous conjugate observations of dynamic variations in high‐latitude dayside convection due to changes in IMF By , 1990 .

[23]  Patrick T. Newell,et al.  The cusp and the cleft/boundary layer: Low‐altitude identification and statistical local time variation , 1988 .

[24]  M. Greenspan,et al.  Characteristics of the Thermal Plasma Monitor (SSIES) (Special Sensor for Ions, Electrons, and Scintillation) for the Defense Meteorological Satellite Program (DMSP) Spacecraft S8 through S10 , 1986 .

[25]  R. Heelis,et al.  Origin of density enhancements in the winter polar cap ionosphere , 1988 .

[26]  N. Maynard,et al.  Empirical high‐latitude electric field models , 1987 .

[27]  P. Newell.  Comment on “Low‐altitude signatures of the cusp and flux transfer events” by Lockwood and Smith , 1990 .

[28]  Per Even Sandholt,et al.  IMF control of polar cusp and cleft auroras , 1988 .