Interplanetary Scintillation Power Spectra

Milne, RG

doi:10.1071/ph760201

Cited by 7 publications

(4 citation statements)

References 4 publications

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“…Very compact radio sources are extremely rare and it has been established at a number of frequencies, using both IPS (Bourgois 1969;Bourgois & Creynet 1972;Milne 1976) and long baseline interferometry (Clark et al 1968;Clarke et al 1969), that the radio source 1148-001 has an angular diameter of ≈10 milliarcsecond (mas) at meter wavelengths. Thus, the source 1148-001 can be treated as a nearly ideal point source at 327 MHz, with almost all of its flux contained in a compact scintillating component with very little flux outside this compact component (Swarup 1977;Venugopal et al 1985).…”

Section: Discussionmentioning

confidence: 99%

A study of density modulation index in the inner heliospheric solar wind during solar cycle 23

Janardhan

Ingale

Subramanian

et al. 2014

2014 XXXIth URSI General Assembly and Scientific Symposium (URSI GASS)

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An understanding of variations of density modulation index = ΔN/N, the ratio of the electron density fluctuation (ΔN) to the absolute solar wind density ( ), in the inner heliosphere is of vital importance for understanding turbulent dissipation and consequent local heating of solar wind. In addition, the density modulation index plays crucial role in understanding the propagation of energetic electrons, through the heliosphere, produced by solar flares and other explosive solar surface phenomena. We have made a detailed study of in the inner heliosphere spanning the distance range from 0.2 to 0.8 AU, for the period 1998 -2008, covering solar cycle 23. The rms electron density fluctuations (ΔN) have been deduced using ground-based interplanetary scintillation (IPS) observations at 327 MHz from the multi-station IPS observatory, at STEL, Japan. Before deriving ΔN, we have appropriately normalized scintillation measurements to remove the effect of finite source size. The absolute solar wind density ( ), on the other hand, has been obtained from the space-borne Advanced Composition Explorer (ACE) mission. However, ACE density measurements are effectively at a distance of 1 AU at the Largangian point L1. Thus, for estimation of density at the location of the relevant scintillating sources, spreading over distances of 0.2 -0.8 AU, the measured ACE densities at 1 AU are extrapolated in the sunward direction using an electron density model. Our analysis shows that does not vary with heliocentric distances and the typical value of ranges from 1% to 10% which is is consistent with the earlier findings. A systematic decline in the solar wind electron density turbulence levels has been reported earlier for the period 1995 to 2008. Our investigation of the long-term temporal variations of over the distance range 0.2 -0.8 AU have also shown a similar decline during the period 1998 -2008. It therefore appears reasonable, from the linear relationship between the density fluctuations and magnetic field fluctuations, to conclude that the decrease in is connected to the unusual solar magnetic activity during the long and deep solar minimum at the end of the solar cycle 23.

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Section: Discussionmentioning

confidence: 99%

A study of density modulation index in the inner heliospheric solar wind during solar cycle 23

Janardhan

Ingale

Subramanian

et al. 2014

2014 XXXIth URSI General Assembly and Scientific Symposium (URSI GASS)

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Section: Discussionmentioning

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 extend the isotropic electron density power spectrum to include an elongation (axial ratio) parameter, R > 1, and angle, θ, over elongation to the x axis (direction of motion of solar wind) (Rickett et al 2002;Macquart and de Bruyn 2007). In line with observations, we take θ = 0, and define the anisotropic power spectrum (Cronyn 1970;Milne 1976;Coles 1978):…”

Section: Interplanetary Scintillation Formalismmentioning

confidence: 99%

“…Direct measurements of the density and speed by spacecraft (Unti et al 1973;Neugebauer 1975Neugebauer , 1976, and indirect measurements by probing the temporal and spectral fluctuation in the flux density of astronomical radio 1 ARC Centre of Excellence for All Sky Astrophysics (CAASTRO) 2 ARC DECRA Fellow arXiv:1510.02283v1 [astro-ph.CO] 8 Oct 2015 sources (e.g., Ekers and Little 1971;Bourgois 1972;Armstrong and Coles 1978), yield a comprehensive understanding of the structure of the medium. Foundation work by Salpeter (1967); Cronyn (1970); Milne (1976); Coles (1978); Readhead et al (1978) laid the theoretical groundwork for connecting the power spectrum of density fluctuations to that of phase and intensity fluctuations.…”

Section: Introductionmentioning

confidence: 99%

The Effect of Interplanetary Scintillation on Epoch of Reionization Power Spectra

Trott¹,

Tingay

2015

ApJ

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Interplanetary Scintillation (IPS) induces intensity fluctuations in small angular size astronomical radio sources via the distortive effects of spatially and temporally varying electron density associated with outflows from the Sun. These radio sources are a potential foreground contaminant signal for redshifted HI emission from the Epoch of Reionisation (EoR) because they yield time-dependent flux density variations in bright extragalactic point sources. Contamination from foreground continuum sources complicates efforts to discriminate the cosmological signal from other sources in the sky. In IPS, at large angles from the Sun applicable to EoR observations, weak scattering induces spatially and temporally correlated fluctuations in the measured flux density of sources in the field, potentially affecting the detectability of the EoR signal by inducing non-static variations in the signal strength. In this work, we explore the impact of interplanetary weak scintillation on EoR power spectrum measurements, accounting for the instrumental spatial and temporal sampling. We use published power spectra of electron density fluctuations and parameters of EoR experiments to derive the IPS power spectrum in the wavenumber phase space of EoR power spectrum measurements. The contrast of IPS power to expected cosmological power is used as a metric to assess the impact of IPS. We show that IPS has a different spectral structure to power from foregrounds alone, but the additional leakage into the EoR observation parameter space is negligible under typical IPS conditions, unless data are used from deep within the foreground contamination region.

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Interplanetary Scintillation Power Spectra

Cited by 7 publications

References 4 publications

A study of density modulation index in the inner heliospheric solar wind during solar cycle 23

A study of density modulation index in the inner heliospheric solar wind during solar cycle 23

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

The Effect of Interplanetary Scintillation on Epoch of Reionization Power Spectra

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