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Ann. Geophys., 23, 401-417, 2005
www.ann-geophys.net/23/401/2005/
© European Geosciences Union 2005
Solar wind Alfvén waves: a source of pulsed ionospheric convection and atmospheric gravity waves
P. Prikryl1, D. B. Muldrew1, G. J. Sofko2, and J. M. Ruohoniemi3
1Communications Research Centre, Ottawa, ON, Canada
2University of Saskatchewan, Saskatoon, Canada
3The Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA
Abstract. A case study of medium-scale travelling ionospheric
disturbances (TIDs) that are correlated with solar wind Alfvén waves is
presented. The HF radar ground-scatter signatures of TIDs caused by
atmospheric gravity waves with periods of 20-40min are traced to a source
at high latitudes, namely pulsed ionospheric flows (PIFs) due to bursts in
the convection electric field and/or the associated ionospheric current
fluctuations inferred from ground magnetic field perturbations. The
significance of PIFs and TIDs in the context of solar-terrestrial
interaction is that Alfvénic fluctuations of the interplanetary magnetic
field (IMF) observed in the solar wind plasma streaming from a coronal hole
correlate with PIFs and TIDs. The link between the solar wind Alfvén
waves and TIDs is corroborated by the ground magnetic field signatures of
ionospheric current fluctuations that are associated with the IMF-By
oscillations and TIDs. The observed PIFs and the associated
negative-to-positive deflections of the ground magnetic field X component
are interpreted as ionospheric signatures of magnetic reconnection pulsed by
solar wind Alfvén waves at the dayside magnetopause. Although the
clarity of the radar line-of-sight velocity data may have been affected by
anomalous HF propagation due to intervening TIDs, the application of a pure
state filtering technique to analyze the radar data time series reveals a
one-to-one correspondence between PIFs, TIDs and solar wind Alfvén
waves. The spectra of solar wind and ground magnetic field perturbations are
similar to those of PIFs and TIDs. The ground-scatter signatures indicate
TID wavelengths, phase velocities and travel times that are consistent with
ray tracing, which shows a subset of possible gravity wave group paths that
reach the F region from a source in the E region after the wave energy first
travel downward to the upper mesosphere where the waves are reflected
upward. The observed one-to-one correspondence between the convection
electric field bursts and TIDs is consistent with the modeling results for
large-scale TIDs by Millward et al. (1993a,b). The correlation with
solar wind Alfvén waves points to very direct coupling of energy in the
solar wind into the subauroral atmosphere.
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