The transformation of magnetoacoustic waves into Alfvén waves inside the magnetosphere

Abstract. A mechanism for the transformation of a magnetoacoustic wave into an Alfvén wave is proposed. During the compression of the magnetosphere by the solar wind the inner edge of the plasma sheet and the contours of B=const move in different ways. In the case of asymmetrical compression, the contours of B=const will cross the inner edge of the plasma sheet. To close the drift currents - that flow in the plasma sheet along the contours of B=const - the appearance of the field-aligned currents is necessary. This appearance corresponds to the generation of the Alfvén wave.

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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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Evolution of Alfvén wave-driven solar winds to red giants

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308014889 ◽

2007 ◽

Vol 3 (S247) ◽

pp. 201-207

Author(s):

Takeru K. Suzuki

Keyword(s):

Solar Wind ◽

Mode Conversion ◽

Alfven Waves ◽

Alfven Wave ◽

Alfvén Waves ◽

Stellar Winds ◽

Red Giants ◽

Giant Stars ◽

Solar Winds ◽

Red Giant

AbstractIn this talk we introduce our recent results of global 1D MHD simulations for the acceleration of solar and stellar winds. We impose transverse photospheric motions corresponding to the granulations, which generate outgoing Alfvén waves. The Alfvén waves effectively dissipate by 3-wave coupling and direct mode conversion to compressive waves in density-stratified atmosphere. We show that the coronal heating and the solar wind acceleration in the open magnetic field regions are natural consequence of the footpoint fluctuations of the magnetic fields at the surface (photosphere). We also discuss winds from red giant stars driven by Alfvén waves, focusing on different aspects from the solar wind. We show that red giants wind are highly structured with intermittent magnetized hot bubbles embedded in cool chromospheric material.

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Possible role of magnetosphere-ionosphere coupling in auroral arc generation

Annales Geophysicae ◽

10.1007/s00585-000-1108-5 ◽

2000 ◽

Vol 18 (9) ◽

pp. 1108-1117 ◽

Cited By ~ 5

Author(s):

W. Lyatsky ◽

A. M. Hamza

Keyword(s):

Growth Rate ◽

Plasma Sheet ◽

Alfven Waves ◽

The Other ◽

Alfven Wave ◽

Alfvén Waves ◽

Ionospheric Conductivity ◽

Model Based ◽

Field Aligned Current ◽

Auroral Arcs

Abstract. Three models for the magnetosphere-ionosphere coupling feedback instability are considered. The first model is based on demagnetization of hot ions in the plasma sheet. The instability takes place in the global magnetosphere-ionosphere system when magnetospheric electrons drift through a spatial gradient of hot magnetospheric ion population. Such a situation exists on the inner and outer edges of the plasma sheet where relatively cold magnetospheric electrons move earthward through a radial gradient of hot ions. This leads to the formation of field-aligned currents. The effect of upward field-aligned current on particle precipitation and the magnitude of ionospheric conductivity leads to the instability of this earthward convection and to its division into convection streams oriented at some angle with respect to the initial convection direction. The growth rate of the instability is maximum for structures with sizes less than the ion Larmor radius in the equatorial plane. This may lead to formation of auroral arcs with widths about 10 km. This instability explains many features of such arcs, including their conjugacy in opposite hemispheres. However, it cannot explain the very high growth rates of some auroral arcs and very narrow arcs. For such arcs another type of instability must be considered. In the other two models the instability arises because of the generation of Alfven waves from growing arc-like structures in the ionospheric conductivity. One model is based on the modulation of precipitating electrons by field-aligned currents of the upward moving Alfven wave. The other model takes into consideration the reflection of Alfven waves from a maximum in the Alfven velocity at an altitude of about 3000 km. The growth of structures in both models takes place when the ionization function associated with upward field-aligned current is shifted from the edges of enhanced conductivity structures toward their centers. Such a shift arises because the structures move at a velocity different from the E×B drift. Although both models may work, the growth rate for the model, based on the modulation of the precipitating accelerated electrons, is significantly larger than that of the model based on the Alfven wave reflection. This mechanism is suitable for generation of auroral arcs with widths of about 1 km and less. The growth rate of the instability can be as large as 1 s-1, and this mechanism enables us to justify the development of auroral arcs only in one ionosphere. It is hardly suitable for excitation of wide and conjugate auroral arcs, but it may be responsible for the formation of small-scale structures inside a wide arc.Key words: Ionosphere (auroral ionosphere) - Magnetospheric physics (auroral phenomena; magnetosphere-ionosphere interactions)

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Nonlinear interaction of obliquely propagating Alfvén waves and kinetic Alfvén waves in solar wind plasmas

Journal of Plasma Physics ◽

10.1017/s0022377813000767 ◽

2013 ◽

Vol 79 (5) ◽

pp. 927-931 ◽

Cited By ~ 2

Author(s):

NITIN YADAV ◽

R. P. SHARMA

Keyword(s):

Solar Wind ◽

Nonlinear Interaction ◽

Modulational Instability ◽

Alfven Waves ◽

Inertial Range ◽

Alfven Wave ◽

Alfvén Waves ◽

Dynamical Equations ◽

Turbulent Spectra ◽

Kinetic Alfvén Waves

AbstractThe nonlinear interaction of kinetic Alfvén waves (KAWs) with other possible plasma modes is considered to be responsible for the observed solar wind turbulent spectrum. In the present paper, a new channel of interaction between a KAW and an obliquely propagating Alfvén wave (AW) has been proposed. The governing dynamical equations are derived and the nonlinear interaction between the two wave modes KAW and AW is studied. The growth rate of modulational instability has been calculated. The nonlinear evolution of KAW filamentation and turbulent spectra has also been discussed. In the inertial range, energy cascade follows nearly Kolmogorov scaling, and after inertial range it follows −2.5 scaling in dispersive range. The obtained results indicate that the proposed mechanism may be responsible for transferring the energy from smaller wavenumbers to larger wavenumbers in the solar wind plasmas. The relevance of the present study with recent Cluster spacecraft observations has also been pointed out.

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Solar off-limb line widths with SUMER: revised value of the non-thermal velocity and new results

Annales Geophysicae ◽

10.5194/angeo-27-3551-2009 ◽

2009 ◽

Vol 27 (9) ◽

pp. 3551-3558 ◽

Cited By ~ 2

Author(s):

L. Dolla ◽

J. Solomon

Keyword(s):

Solar Wind ◽

Cyclotron Resonance ◽

Alfven Waves ◽

Stray Light ◽

Alfven Wave ◽

Alfvén Waves ◽

Thermal Velocity ◽

Line Profiles ◽

Lower Corona ◽

Ion Cyclotron

Abstract. Alfvén waves and ion-cyclotron absorption of high-frequency waves are frequently brought into models devoted to coronal heating and fast solar-wind acceleration. Signatures of ion-cyclotron resonance have already been observed in situ in the solar wind and in the upper corona. In the lower corona, one can use the line profiles to infer the ion temperatures. But the value of the so-called "non-thermal" (or "unresolved") velocity, potentially related to the amplitude of Alfvén waves propagating in the corona, is critical in firmly identifying ion-cyclotron preferential heating. In a previous paper, we proposed a method to constrain both the Alfvén wave amplitude and the preferential heating, above a polar coronal hole observed with the SUMER/SOHO spectrometer. Taking into account the effect of instrumental stray light before analysing the line profiles, we ruled out any direct evidence of damping of the Alfvén waves and showed that ions with the lowest charge-to-mass ratios were preferentially heated. We re-analyse these data here to correct the derived non-thermal velocity, and we discuss the consequences on the main results. We also include a measure of the Fe VIII 1442.56 Å line width (second order), thus extending the charge-to-mass ratio domain towards ions more likely to experience cyclotron resonance.

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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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Parametric instability, inverse cascade and the range of solar-wind turbulence

Journal of Plasma Physics ◽

10.1017/s0022377818000016 ◽

2018 ◽

Vol 84 (1) ◽

Cited By ~ 11

Author(s):

Benjamin D. G. Chandran

Keyword(s):

Solar Wind ◽

Nonlinear Evolution ◽

Parametric Instability ◽

Alfven Waves ◽

Turbulence Theory ◽

Alfven Wave ◽

Alfvén Waves ◽

Fast Solar Wind ◽

Parametric Decay ◽

Inverse Cascade

In this paper, weak-turbulence theory is used to investigate the nonlinear evolution of the parametric instability in three-dimensional low-$\unicode[STIX]{x1D6FD}$ plasmas at wavelengths much greater than the ion inertial length under the assumption that slow magnetosonic waves are strongly damped. It is shown analytically that the parametric instability leads to an inverse cascade of Alfvén wave quanta, and several exact solutions to the wave kinetic equations are presented. The main results of the paper concern the parametric decay of Alfvén waves that initially satisfy $e^{+}\gg e^{-}$, where $e^{+}$ and $e^{-}$ are the frequency ($f$) spectra of Alfvén waves propagating in opposite directions along the magnetic field lines. If $e^{+}$ initially has a peak frequency $f_{0}$ (at which $fe^{+}$ is maximized) and an ‘infrared’ scaling $f^{p}$ at smaller $f$ with $-1<p<1$, then $e^{+}$ acquires an $f^{-1}$ scaling throughout a range of frequencies that spreads out in both directions from $f_{0}$. At the same time, $e^{-}$ acquires an $f^{-2}$ scaling within this same frequency range. If the plasma parameters and infrared $e^{+}$ spectrum are chosen to match conditions in the fast solar wind at a heliocentric distance of 0.3 astronomical units (AU), then the nonlinear evolution of the parametric instability leads to an $e^{+}$ spectrum that matches fast-wind measurements from the Helios spacecraft at 0.3 AU, including the observed $f^{-1}$ scaling at $f\gtrsim 3\times 10^{-4}~\text{Hz}$. The results of this paper suggest that the $f^{-1}$ spectrum seen by Helios in the fast solar wind at $f\gtrsim 3\times 10^{-4}~\text{Hz}$ is produced in situ by parametric decay and that the $f^{-1}$ range of $e^{+}$ extends over an increasingly narrow range of frequencies as $r$ decreases below 0.3 AU. This prediction will be tested by measurements from the Parker Solar Probe.

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On heating of solar wind protons by the breaking of large amplitude Alfvén waves

10.5194/angeo-2018-14 ◽

2018 ◽

Author(s):

Horia Comişel ◽

Yasuhiro Nariyuki ◽

Yasuhito Narita ◽

Uwe Motschmann

Keyword(s):

Solar Wind ◽

Pitch Angle ◽

Plasma Heating ◽

Alfven Waves ◽

Distribution Functions ◽

Alfven Wave ◽

Alfvén Waves ◽

Parametric Decay ◽

Angle Scattering ◽

Velocity Distribution Functions

Abstract. By means of hybrid simulations, we present a study on plasma heating by the field-aligned parametric decay of a monochromatic left-handed polarized Alfven wave. Simultaneous multidimensional comparisons of the wave modes and proton kinetics suggest that parametric decay of Alfven waves and pitch angle scattering of solar wind protons are interrelated. Parametric decay mechanism yields counter-propagating Alfven waves that can shape and broaden via pitch angle scattering mechanism both the sunward and antisunward sides of the proton velocity distribution functions in agreement with in situ measurements of fast stream solar wind plasmas.

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