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High-latitude ground-based observations of the thermospheric ion-drag time constant

Research output: Contribution to journalJournal article


  • M. J. Kosch
  • K. Cierpka
  • M. T. Rietveld
  • T. Hagfors
  • K. Schlegel
Journal publication date04/2001
JournalGeophysical Research Letters
Number of pages4
Original languageEnglish


From previous studies, it has been conclusively demonstrated that F-region thermospheric winds follow, but generally lag behind, the ion drift pattern of magnetospheric convection. Analysis of the ion-neutral momentum exchange equation shows that ion-drag and thermal pressure are the major contributors to neutral momentum forcing at F-region heights with relatively minor effects from coriolis, advection and viscous forces. An ion-neutral coupling time constant (e-folding time) has been defined which describes the time taken for the neutral gas velocity to approach the ion velocity after a step change in convection. In this study, F-region ion drift and neutral winds have been observed by the EISCAT tristatic incoherent scatter facility and a ground-based Fabry-Perot interferometer, respectively, from northern Scandinavia. The e-folding time varies in the range 0.5 - 6.5 hours, with an average of 1.8 and 3.3 hours for a geomagnetically active and quiet period, respectively, which compares well with previous satellite measurements of 0.5 - 3.5 hours.