Interaction of Alfven waves with a turbulent layer (original) (raw)
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Some properties of Alfvén waves: Observations in the tail lobes and the plasma sheet boundary layer
Journal of Geophysical Research, 2005
1] We report properties of substorm-related, globally excited Alfvén waves on a temporal scale of 6 to 300 s (3.3 to 167 mHz) at geocentric distances between 5 and 6 R E . The waves were observed in the tail lobes and the plasma sheet boundary layer (PSBL) by the Polar satellite. In each region we made the following observations: (1) The tail lobe Alfvén waves started at substorm onset as determined from ground magnetometer data. Hence these ULF lobe waves can possibly be used as a new substorm indicator. Although on open field lines, they often showed local standing wave signatures with a large perpendicular scale size and a near-zero net Poynting flux. We do not classify those waves as FLR but interpret them as the superposition of incident and reflected waves. The same oscillations were simultaneously recorded in ground magnetometer data. Immediately poleward of the PSBL, the lobe Alfvén waves traveled earthward (no reflection), suggesting their dissipation in the ionosphere. The lobe waves were superimposed on the signature of a field-aligned current (FAC). The onset of this FAC was simultaneous to the onset of the magnetic substorm bay. (2) The substorm-related PSBL Alfvén waves carried two to three orders of magnitude larger Poynting flux ($1 erg cm À2 s À1 ) than the lobe Alfvén waves. These PSBL waves were a mixture of standing and traveling Alfvén waves for different frequency ranges. Most Poynting flux was carried in large-scale earthward traveling waves (40-300 s). For one event, we also measured large standing wave components (>0.5 erg cm À2 s À1 ), but such events are rare. In the intermediate range (40-67 s), which overlaps with the Pi2 range, some waves showed clear standing wave signatures. At smaller periods (6-24 s), noninterfering earthward and tailward traveling waves were present with small Poynting fluxes (<0.05 erg cm À2 s À1 ). A trend for increasing E to B ratios with increasing wave frequency was observed. The PSBL waves were left-hand elliptically polarized. The wave vector was within 35°of the background magnetic field direction, suggesting that the waves were phase-mixed. The largeamplitude, substorm-related PSBL Alfvén wave events ($1 erg cm À2 s À1 ) were found in regions of upward currents. (2005), Some properties of Alfvén waves: Observations in the tail lobes and the plasma sheet boundary layer,
Interplay between Alfvén and magnetosonic waves in compressible magnetohydrodynamics turbulence
Physics of Plasmas, 2017
Using spatio-temporal spectra, we show direct evidence of excitation of magnetosonic and Alfvén waves in three-dimensional compressible magnetohydrodynamic turbulence at small Mach numbers. For the plasma pressure dominated regime, or the high β regime (with β the ratio between fluid and magnetic pressure), and for the magnetic pressure dominated regime, or the low β regime, we study magnetic field fluctuations parallel and perpendicular to a guide magnetic field B0. In the low β case, we find excitation of compressible and incompressible fluctuations, with a transfer of energy towards Alfvénic modes and to a lesser extent towards magnetosonic modes. In particular, we find signatures of the presence of fast magnetosonic waves in a scenario compatible with that of weak turbulence. In the high β case, fast and slow magnetosonic waves are present, with no clear trace of Alfvén waves, and a significant part of the energy is carried by two-dimensional turbulent eddies.
Journal of Geophysical Research: Space Physics, 2015
The mutual nonlinear interplay of kinetic Alfvén wave (KAW) and ion acoustic wave, for the high-β plasma (i.e., m e /m i ≪ β ≪ 1, where β is thermal to magnetic pressure ratio) in the magnetopause, has been considered in the present study. A set of dimensionless nonlinear Schrödinger equations has been derived taking into account the finite frequency as well as ion temperature corrections. The dynamical equation of the ion acoustic wave (propagating at an angle with respect to the background magnetic field) in the presence of ponderomotive nonlinearity due to KAW is also derived. Numerical simulation has been carried out to study the effect of nonlinear interaction between these waves which results in the formation of localized structures and turbulent spectrum, applicable to the high-β plasmas like magnetopause regions. Results reveal that due to the nonlinear interplay between these waves, natures of the formation of localized structures are complex and intense in nature in quasi steady state. From the results, we have found that spectral index follows the scaling ∼k À 3=2 ⊥ at large scale and spectral index follows ∼k À 2:80 ⊥ À Á at small scale. We also found the steepening in the turbulent spectrum. Steepening in the turbulence spectrum has been reported by the Time History of Events and Macroscale Interactions during Substorms spacecraft across the magnetopause, and results are found to be consistent with spacecraft observation. RINAWA ET AL.
Alfvén waves in the magnetosphere generated by shock wave / plasmapause interaction
Solnechno-Zemnaya Fizika, 2019
We study Alfvén waves generated in the magnetosphere during the passage of an interplanetary shock wave. After shock wave passage, the oscillations with typical Alfvén wave dispersion have been detected in spacecraft observations inside the magnetosphere. The most frequently observed oscillations are those with toroidal polarization; their spatial structure is described well by the field line resonance (FLR) theory. The oscillations with poloidal polarization are observed after shock wave passage as well. They cannot be generated by FLR and cannot result from instability of high-energy particle fluxes because no such fluxes were detected at that time. We discuss an alternative hypothesis suggesting that resonant Alfvén waves are excited by a secondary source: a highly localized pulse of fast magnetosonic waves, which is generated in the shock wave/plasmapause contact region. The spectrum of such a source contains oscillation harmonics capable of exciting both the toroidal and poloid...
Concurrent effect of Alfvén waves and planar magnetic structure on geomagnetic storms
Monthly Notices of the Royal Astronomical Society, 2019
Generally, interplanetary coronal mass ejection (ICME) triggers intense and strong geomagnetic storms. It has been established that the ICME sheath-moulded planar magnetic structure enhances the amplitude of the storms. Alfvén waves embedded in ICME magnetic clouds or high solar streams including corotating interacting regions (CIRs) in turn extend the recovery phase of the storm. Here, we investigate a geomagnetic storm with a very complex temporal profile with multiple decreasing and recovery phases. We examine the role of planar magnetic structure (PMS) and Alfvén waves in the various phases of the storm. We find that fast decrease and fast recovery phases are evident during transit of PMS regions, whereas a slight decrease or recovery is found during the transit of regions embedded with Alfvénic fluctuations.
Annales Geophysicae, 2008
The generation of a high-m Alfvén wave by substorm injected energetic particles in the magnetosphere is studied. The wave is supposed to be emitted by an alternating current created by the drifting particle cloud or ring current inhomogeneity. It is shown that the wave appears in some azimuthal location simultaneously with the particle cloud arrival at the same spot. The value of the azimuthal wave number is determined as m∼ω/ω d , where ω is the eigenfrequency of the standing Alfvén wave and ω d is the particle drift frequency. The wave propagates westward, in the direction of the proton drift. Under the reasonable assumption about the density of the energetic particles, the amplitude of the generated wave is close to the observed amplitudes of poloidal ULF pulsations.
Inertial Alfvén wave induced turbulent spectra in aurora
Astrophysics and Space Science, 2014
In the present paper, we investigate the localization of weak inertial Alfvén wave (IAW) in the presence of finite amplitude magnetosonic fluctuations in low β plasmas (β m e /m i ). When IAW is perturbed by these fluctuations, localized structures of IAW magnetic field intensity are formed. We have developed a semi analytical model based on paraxial approximation to study this interaction. Numerical method has also been used to analyse the localized structures and magnetic fluctuation spectrum of IAW. From the obtained results, we find that the magnetic turbulent spectrum upto k x λ e ≈ 3 fits power law spectrum with an index consistent with the Kolmogorov k −5/3 x law, here λ e is the electron inertial length. Furthermore, at shorter wavelengths the spectrum steepens to about k −3.8
arXiv (Cornell University), 2022
The dynamic evolution of coronal mass ejection (CME) in interplanetary space generates highly turbulent, compressed, and heated shock-sheath. This region furnishes a unique environment to study the turbulent fluctuations at the small scales and serve an opportunity for unfolding the physical mechanisms by which the turbulence is dissipated and plasma is heated. How does the turbulence in the magnetized plasma control the energy transport process in space and astrophysical plasmas is an attractive and challenging open problem of the 21st century. For this, the literature discusses three types of magnetohydrodynamics (MHD) waves/ fluctuations in magnetized plasma as the magnetosonic (fast), Alfvénic (intermediate), and sonic (slow). The magnetosonic type is most common in the interplanetary medium. However, Alfvénic waves/fluctuations have not been identified to date in the ICME sheath. The steepening of the Alfvén wave can form a rotational discontinuity that leads to an Alfvénic shock. But, the questions were raised on their existence based on the theoretical ground. Here, we demonstrate the observable in-situ evidence of Alfvén waves inside turbulent shock-sheath at 1 AU using three different methods desciribed in the literature. We also estimate Elsässer variables, normalized cross helicity, normalized residual energy and which indicate outward flow of Alfvén waves. Power spectrum analysis of IMF indicates the existence of Alfvénic turbulence in ICME shock-sheath. The study has strong implications in the domain of interplanetary space plasma, its interaction with planetary plasma, and astrophysical plasma.
Journal of Geophysical Research, 2008
During the early phase of the intense magnetic storm of 7-11 November 2004, the DEMETER satellite encountered large-scale equatorial plasma density depletions with density decreases of two or three orders of magnitude. Wave measurements carried out inside these depletions show the occurrence of broadband and localized lower-hybrid turbulence triggered by whistlers propagating from thunderstorm lightning occurring below the orbit path. High-sample-rate waveforms reveal that this lower-hybrid turbulence can evolve into localized large-amplitude quasi-monochromatic wave packets similar to lower-hybrid structures that were, up to now, only observed in the auroral regions, usually on high-latitude magnetic field lines associated with discrete aurora. These equatorial structures have typical amplitudes of up to 20 mV/m and durations of $20-30 ms. Simultaneous thermal ion measurements show that these bursts are often correlated with small-scale density depletions of 5-10%. Although the lower-hybrid structures are less intense than those observed in the auroral zone and although their energy source is different, our observations lend support to the idea that the formation of lower-hybrid structures is an universal mechanism operating in inhomogeneous magnetized space plasmas in the presence of VLF whistler mode turbulence. Besides the lower-hybrid turbulence, another interesting feature is the occurrence of strong narrowband electromagnetic ELF emissions with amplitudes of a few millivolts per meter at frequencies below the proton gyrofrequency. They are continuously observed throughout the entire depletion. These emissions occur not only within the depletions but also, although less intense, outside of them over a large latitudinal range. They are tentatively identified as magnetospheric line radiations (MLRs) commonly observed during magnetically disturbed periods. Similar events were observed on 15 May 2005 and on 24 August 2005 during two other intense magnetic storms.
Does the Alfvén wave disrupt the large-scale magnetic cloud structure?
Monthly Notices of the Royal Astronomical Society: Letters, 2018
Alfvén waves are primal and pervasive in space plasmas and significantly contribute to microscale fluctuations in the solar wind and some heliospheric processes. Here, we demonstrate the first observable distinct feature of Alfvén wave while propagating from magnetic cloud to trailing solar wind. The Walén test is used to confirm their presence in selected regions. The amplitude ratio of inward to outward Alfvén waves is employed to establish their flow direction. The dominant inward flow is observed in magnetic cloud whereas trailing solar wind shows the dominant outward flow of Alfvén waves. The observed reduction in Walén slope and correlation coefficient within magnetic cloud suggest (i) the simultaneous presence of an inward and outward Alfvén waves and/or (ii) a possibility of magnetic reconnection and/or (iii) development of thermal anisotropy, and/or (iv) dissipation of Alfvénic fluctuations. The study implies that either the Alfvén waves dissipate in the magnetic cloud or their presence can lead to a disruption of the magnetic cloud structure.