A study of density fluctuations in the solar wind acceleration region

Yamauchi, Y.; Tokumaru, M.; Kojima, M.; Manoharan, P. K.; Esser, Ruth

doi:10.1029/97ja03598

Cited by 39 publications

(36 citation statements)

References 39 publications

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“…The polarization properties of the MHD Alfv6n the power spectra of density fluctuations in coronal holes exhibit an inner scale (at which it is presumed that dissipation sets in) which is close to the inertial length for the protons [Coles and Harmon, 1989;Harmon, 1989;Yamauchi et al, 1998], as well as a flattening at spatial scales which are somewhat greater than the inner scale [e.g., Coles and Harmon, 1989]. We shall see that the ion inertial length plays a role in the compressive aspects of the kinetic Alfv6n wave and the observed characteristics of the coronal density fluctuations may indeed reflect the compressive nature of the Alfv6n mode at high k., as suggested by Harmon [1989].…”

Section: Eymentioning

confidence: 99%

Kinetic Alfvén wave revisited

Hollweg¹

1999

J. Geophys. Res.

251

252

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Abstract. We develop a series of new analytical expressions describing the physical properties of the kinetic Alfv6n wave. The wave becomes strongly compressive when k_7_ • is of the order of the ion inertial length. Thus, in a low-/3 plasma, the kinetic Alfv6n wave can be compressive at values of k ñ for which the dispersion relation departs only slightly from that of the usual MHD Alfvfin wave. The compression is accompanied by a magnetic field fluctuation •Bll such that the total pressure perturbation •Ptot m 0. Thus the wave undergoes transit-time damping as well as Landau damping; the two effects are comparable if the ion thermal speed is of the order of the Alfv6n speed. We find that the transverse electric field is elliptically polarized but rotating in the electron sense; this surprising behavior of the polarization of the Alfv6n branch was discovered numerically by Gary [1986]. We derive a new dispersion relation which explicitly shows how the kinetic Alfvfin wave takes on some properties of the large-k ñ limit of the slow mode. We also derive approximate dispersion relations valid for a multi-ion plasma with differential streaming. We suggest that the kinetic Alfvfin wave may be responsible for the flattening of density fluctuation spectra observed at large wavenumbers in the corona and in the solar wind. We also find that our derived properties of the kinetic Alternatively, large values of kñ could be the consequence of a turbulent cascade. In any case, at large values of k z, the Alfvfin mode, which is normally noncompressive, will become the kinetic Alfv6n wave, which is compressive. Harmon [1989] has suggested that the compressibility may be recognizable in the power spectra of coronal density fluctuations, which are derived from a variety of radio sounding techniques. Indeed, 14,811

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Section: Eymentioning

confidence: 99%

Kinetic Alfvén wave revisited

Hollweg¹

1999

J. Geophys. Res.

251

252

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“…It must be noted that the scintillations observed on Earth are modulated by the Fresnel filter function Sin 2 (q 2 λz/4π ), where q is the wave number of the irregularities, z is the distance from E to P, and λ is the observing wavelength. Due to the action of the Fresnel filter, IPS observations at 327 MHz enable one to probe solar wind electron density fluctuations of scale sizes 1000 km both in and out of the ecliptic (Pramesh Rao et al 1974;Coles & Filice 1985;Yamauchi et al 1998;Fallows et al 2008) and over a wide range of heliocentric distances in the inner heliosphere (Janardhan et al 1996).…”

Section: Interplanetary Scintillationmentioning

confidence: 99%

A Study of Density Modulation Index in the Inner Heliospheric Solar Wind During Solar Cycle 23

Janardhan

Ingale

Subramanian

et al. 2014

ApJ

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The ratio of the rms electron density fluctuations to the background density in the solar wind (density modulation index, N ≡ ΔN/N) is of vital importance for understanding several problems in heliospheric physics related to solar wind turbulence. In this paper, we have investigated the behavior of N in the inner heliosphere from 0.26 to 0.82 AU. The density fluctuations ΔN have been deduced using extensive ground-based observations of interplanetary scintillation at 327 MHz, which probe spatial scales of a few hundred kilometers. The background densities (N) have been derived using near-Earth observations from the Advanced Composition Explorer. Our analysis reveals that 0.001 N 0.02 and does not vary appreciably with heliocentric distance. We also find that N declines by 8% from 1998 to 2008. We discuss the impact of these findings on problems ranging from our understanding of Forbush decreases to the behavior of the solar wind dynamic pressure over the recent peculiar solar minimum at the end of cycle 23.

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“…We note that our definition differs slightly from that of Coles & Harmon (1989); Harmon (1989); Yamauchi et al (1998) who use…”

Section: Background Electron Density and The Inner Scalementioning

confidence: 91%

Turbulent Density Fluctuations and Proton Heating Rate in the Solar Wind from 9–20 R_⊙

Raja

Subramanian

Ramesh

et al. 2017

ApJ

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We obtain scatter-broadened images of the Crab nebula at 80 MHz as it transits through the inner solar wind in June 2016 and 2017. These images are anisotropic, with the major axis oriented perpendicular to the radially outward coronal magnetic field. Using these data, we deduce that the density modulation index (δN e /N e ) caused by turbulent density fluctuations in the solar wind ranges from 1.9 ×10 −3 to 7.7 ×10 −3 between 9 -20 R ⊙ . We also find that the heating rate of solar wind protons at these distances ranges from 2.2 × 10 −13 to 1.0 × 10 −11 erg cm −3 s −1 . On two occasions, the line of sight intercepted a coronal streamer. We find that the presence of the streamer approximately doubles the thickness of the scattering screen.

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A study of density fluctuations in the solar wind acceleration region

Cited by 39 publications

References 39 publications

Kinetic Alfvén wave revisited

Kinetic Alfvén wave revisited

A Study of Density Modulation Index in the Inner Heliospheric Solar Wind During Solar Cycle 23

Turbulent Density Fluctuations and Proton Heating Rate in the Solar Wind from 9–20 R_⊙

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A study of density fluctuations in the solar wind acceleration region

Cited by 39 publications

References 39 publications

Kinetic Alfvén wave revisited

Kinetic Alfvén wave revisited

A Study of Density Modulation Index in the Inner Heliospheric Solar Wind During Solar Cycle 23

Turbulent Density Fluctuations and Proton Heating Rate in the Solar Wind from 9–20 R⊙

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Turbulent Density Fluctuations and Proton Heating Rate in the Solar Wind from 9–20 R_⊙