Solar wind Alfvén waves: a source of pulsed ionospheric convection and atmospheric gravity waves

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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Observations of polar patches generated by solar wind Alfvén wave coupling to the dayside magnetosphere

Annales Geophysicae ◽

10.1007/s00585-999-0463-0 ◽

1999 ◽

Vol 17 (4) ◽

pp. 463-489 ◽

Cited By ~ 30

Author(s):

P. Prikryl ◽

J. W. MacDougall ◽

I. F. Grant ◽

D. P. Steele ◽

G. J. Sofko ◽

...

Keyword(s):

Solar Wind ◽

Electric Field ◽

Alfven Waves ◽

Alfven Wave ◽

Alfvén Waves ◽

Convection Cell ◽

Convection Flow ◽

Vhf Radar ◽

Sky Imager ◽

The Imf

Abstract. A long series of polar patches was observed by ionosondes and an all-sky imager during a disturbed period (Kp = 7- and IMF Bz < 0). The ionosondes measured electron densities of up to 9 × 1011 m-3 in the patch center, an increase above the density minimum between patches by a factor of \\sim4.5. Bands of F-region irregularities generated at the equatorward edge of the patches were tracked by HF radars. The backscatter bands were swept northward and eastward across the polar cap in a fan-like formation as the afternoon convection cell expanded due to the IMF By > 0. Near the north magnetic pole, an all-sky imager observed the 630-nm emission patches of a distinctly band-like shape drifting northeastward to eastward. The 630-nm emission patches were associated with the density patches and backscatter bands. The patches originated in, or near, the cusp footprint where they were formed by convection bursts (flow channel events, FCEs) structuring the solar EUV-produced photoionization and the particle-produced auroral/cusp ionization by segmenting it into elongated patches. Just equatorward of the cusp footprint Pc5 field line resonances (FLRs) were observed by magnetometers, riometers and VHF/HF radars. The AC electric field associated with the FLRs resulted in a poleward-progressing zonal flow pattern and backscatter bands. The VHF radar Doppler spectra indicated the presence of steep electron density gradients which, through the gradient drift instability, can lead to the generation of the ionospheric irregularities found in patches. The FLRs and FCEs were associated with poleward-progressing DPY currents (Hall currents modulated by the IMF By) and riometer absorption enhancements. The temporal and spatial characteristics of the VHF backscatter and associated riometer absorptions closely resembled those of poleward moving auroral forms (PMAFs). In the solar wind, IMP 8 observed large amplitude Alfvén waves that were correlated with Pc5 pulsations observed by the ground magnetometers, riometers and radars. It is concluded that the FLRs and FCEs that produced patches were driven by solar wind Alfvén waves coupling to the dayside magnetosphere. During a period of southward IMF the dawn-dusk electric field associated with the Alfvén waves modulated the subsolar magnetic reconnection into pulses that resulted in convection flow bursts mapping to the ionospheric footprint of the cusp.Key words. Ionosphere (polar ionosphere). Magneto- spheric physics (magnetosphere-ionosphere interactions; polar wind-magnetosphere interactions).

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On nonlinear circularly polarized Alfvén waves

Journal of Plasma Physics ◽

10.1017/s0022377800013271 ◽

1988 ◽

Vol 40 (2) ◽

pp. 281-287 ◽

Cited By ~ 6

Author(s):

G. Mann

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Periodic Solutions ◽

Type Equation ◽

Finite Amplitude ◽

Alfven Waves ◽

Alfvén Waves ◽

Circularly Polarized ◽

Ambient Magnetic Field ◽

Nonlinear Schrödinger

Finite-amplitude circularly polarized Alfvén waves propagating along the ambient magnetic field are described by a derivative nonlinear Schrödinger-type equation. It leads to stationary, solitary and periodic solutions with phase modulations. The amplitude–width relation for these solitons is shown to be an inequality. The relevance of the results is briefly discussed for particular phenomena in the solar wind.

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FRB coherent emission from decay of Alfvén waves

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa774 ◽

2020 ◽

Vol 494 (2) ◽

pp. 2385-2395 ◽

Cited By ~ 10

Author(s):

Pawan Kumar ◽

Željka Bošnjak

Keyword(s):

Magnetic Field ◽

Wave Packet ◽

Electric Field ◽

Static Magnetic Field ◽

Strong Electric Field ◽

Alfven Waves ◽

Alfven Wave ◽

Alfvén Waves ◽

Radio Waves ◽

Electron Positron

ABSTRACT We present a model for fast radio bursts (FRBs) where a large-amplitude Alfvén wave packet is launched by a disturbance near the surface of a magnetar, and a substantial fraction of the wave energy is converted to coherent radio waves at a distance of a few tens of neutron star radii. The wave amplitude at the magnetar surface should be about 1011 G in order to produce an FRB of isotropic luminosity 1044 erg s−1. An electric current along the static magnetic field is required by Alfvén waves with non-zero component of transverse wave vector. The current is supplied by counter-streaming electron–positron pairs, which have to move at nearly the speed of light at larger radii as the plasma density decreases with distance from the magnetar surface. The counter-streaming pairs are subject to two-stream instability, which leads to formation of particle bunches of size of the order of c/ωp, where ωp is the plasma frequency. A strong electric field develops along the static magnetic field when the wave packet arrives at a radius where electron–positron density is insufficient to supply the current required by the wave. The electric field accelerates particle bunches along the curved magnetic field lines, and that produces the coherent FRB radiation. We provide a number of predictions of this model.

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Ionospheric cusp flows pulsed by solar wind Alfvén waves

Annales Geophysicae ◽

10.5194/angeo-20-161-2002 ◽

2002 ◽

Vol 20 (2) ◽

pp. 161-174 ◽

Cited By ~ 14

Author(s):

P. Prikryl ◽

G. Provan ◽

K. A. McWilliams ◽

T. K. Yeoman

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Surface Waves ◽

Alfven Waves ◽

Alfven Wave ◽

Mhd Waves ◽

Alfvén Waves ◽

Propagation Time ◽

Short Period ◽

The Imf

Abstract. Pulsed ionospheric flows (PIFs) in the cusp foot-print have been observed by the SuperDARN radars with periods between a few minutes and several tens of minutes. PIFs are believed to be a consequence of the interplanetary magnetic field (IMF) reconnection with the magnetospheric magnetic field on the dayside magnetopause, ionospheric signatures of flux transfer events (FTEs). The quasiperiodic PIFs are correlated with Alfvénic fluctuations observed in the upstream solar wind. It is concluded that on these occasions, the FTEs were driven by Alfvén waves coupling to the day-side magnetosphere. Case studies are presented in which the dawn-dusk component of the Alfvén wave electric field modulates the reconnection rate as evidenced by the radar observations of the ionospheric cusp flows. The arrival of the IMF southward turning at the magnetopause is determined from multipoint solar wind magnetic field and/or plasma measurements, assuming plane phase fronts in solar wind. The cross-correlation lag between the solar wind data and ground magnetograms that were obtained near the cusp footprint exceeded the estimated spacecraft-to-magnetopause propagation time by up to several minutes. The difference can account for and/or exceeds the Alfvén propagation time between the magnetopause and ionosphere. For the case of short period ( < 13 min) PIFs, the onset times of the flow transients appear to be further delayed by at most a few more minutes after the IMF southward turning arrived at the magnetopause. For the case of long period (30 – 40 min) PIFs, the observed additional delays were 10–20 min. We interpret the excess delay in terms of an intrinsic time scale for reconnection (Russell et al., 1997) which can be explained by the surface-wave induced magnetic reconnection mechanism (Uberoi et al., 1999). Here, surface waves with wavelengths larger than the thickness of the neutral layer induce a tearing-mode instability whose rise time explains the observed delay of the reconnection onset. The compressional fluctuations in solar wind and those generated in the magnetosheath through the interaction between the solar wind Alfvén waves and the bow shock were the source of magnetopause surface waves inducing reconnection.Key words. Interplanetary physics (MHD waves and turbulence) – Magnetospheric physics (magnetosphere-ionosphere interactions; solar wind-magnetosphere interactions)

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A guiding centre Vlasov equation and its application to Alfvén waves

Journal of Plasma Physics ◽

10.1017/s0022377800004438 ◽

1969 ◽

Vol 3 (3) ◽

pp. 331-351 ◽

Cited By ~ 36

Author(s):

Jules A. Fejer ◽

Joseph R. Kan

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Collisionless Plasma ◽

Alfven Waves ◽

Landau Damping ◽

Alfvén Waves ◽

Dielectric Tensor ◽

Equilibrium Plasma ◽

Warm Plasma ◽

The Magnetic Field

Guiding centre approximations are used to derive the dielectric tensor of a collisionless plasma. This approximate dielectric tensor is used to obtain the dispersion relation of Alfvén waves in a warm plasma. In a ‘low/ β’ equilibrium plasma Alfvén waves are shown to suffer considerable Landau damping if the propagation vector is almost perpendicular to the magnetic field. In a non- equilibrium plasma Alfvén waves can be generated by ‘negative Landau damping’ even if β is low. For sufficiently high β the well-known ‘garden hose’ instability can occur and is then probably dominant. The importance of these two instabilities in the magnetosphere and in the solar wind is discussed.

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On the direction of the velocity and magnetic field fluctuations in undisturbed solar wind

Open Astronomy ◽

10.1515/astro-2021-0024 ◽

2021 ◽

Vol 30 (1) ◽

pp. 184-190

Author(s):

Dmitry V. Erofeev

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Solar Activity ◽

Alfven Waves ◽

High Solar Activity ◽

Slow Solar Wind ◽

Alfvén Waves ◽

Velocity Fluctuations ◽

Field Fluctuations

Abstract Measurements of velocity and magnetic field in near-Earth heliosphere is analized in order to investigate systematical deflection from transversality of the velocity and magnetic field fluctuations in undisturbed solar wind. Fluctuations occurred in the meridional plain of heliosphere (RN plain of the RTN reference system) are transversal with respect to mean magnetic field during periods of high solar activity, but they become non-transversal close to solar cycle minima. This phenomenon is investigated focusing on a role of Alfvén waves. It is shown that deflections from transversality is mostly expressed by fluctuations in slow solar wind streams with low contribution of Alfvén waves, whereas strongly Alfvénic turbulence undergo such deflection in a less degree. In addition, we consider orientation of velocity fluctuations in the azimuthal (RT) plain of heliosphere, which also indicates some interesting features.

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