Abstract
Abstract. On 5 January 2003, the footprint of the Cluster spacecraft, then orbiting in the dayside magnetosphere near the magnetopause, was in the close vicinity of the EISCAT Svalbard Radar (ESR) in the dayside afternoon sector. This configuration made possible the study of the magnetopause motion and its direct consequences on the ionospheric plasma at high latitude. Cluster observed multiple magnetopause crossings despite its high latitude, while on the ground the magnetic activity was very low, whereas the ionospheric plasma sounded by the ESR exhibited poleward moving plasma density structures. In this paper, we compare the satellite and radar data, in order to show that the plasma density structures are directly related to the magnetopause motion and its associated pulsed ionospheric flow. We propose that the variations in electric field make the convection velocity vary enough to alter the electron population by accelerating the chemistry in the F-region and act as a source of electron depletion. The magnetopause motion is in this case, a source of plasma density structures in the polar dayside ionosphere.
Highlights
Polar patches in the high-latitude dayside ionosphere are commonly defined as regions of enhanced electron density compared to the “background” density
We find wave-like patterns in the ground magnetograms, suggesting that the information travels by means of ultra low-frequency (ULF) waves
We have reported a peculiar case of observations of ionospheric density structures in the polar cap. The analysis of both EISCAT Svalbard Radar (ESR) and Cluster data suggest that another process may exist, namely the formation of density structures by pulsed ionospheric flows associated to ULF waves
Summary
Polar patches in the high-latitude dayside ionosphere are commonly defined as regions of enhanced electron density compared to the “background” density. A similar idea was proposed by Rodger et al (1994) According to these authors, zonal flow changes in the ionospheric convection due to variations in the y-component of the IMF could lead to polar patch formation by bringing high-density plasma from the afternoon sunlit ionosphere for intervals when IMF By is positive. The region between two vortices, where the plasma flow is fast, favors ion frictional heating and would act as a source of electron depletion (Valladares et al, 1999) All in all, it appears that periodic or pseudo-periodic variations of precipitation and/or convection electric field may potentially lead to the formation of density structures in the polar ionosphere. These features lead us to consider another possibility: the patch formation by ULF waves
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