Magnetic Field Strength Fluctuations in the Heliosheath: Voyager 1 Observations during 2009

We analyze the ''microscale fluctuations'' of the magnetic field strength B on a scale of several hours observed by Voyager1 (V1) in the heliosheath during 2009. The microscale fluctuations of B range from coherent to stochastic structures. The amplitude of microscale fluctuation...

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Bibliographic Details
Published in:The Astrophysical journal 2012-01, Vol.744 (1), p.51-jQuery1323898604676='46'
Main Authors: Burlaga, L. F, Ness, N. F
Format: Article
Language:English
Subjects:
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Computational fluid dynamics
Fluctuation
Fluid flow
GAUSS FUNCTION
HELIOSPHERE
MAGNETIC FIELDS
NOISE
SOLAR WIND
STOCHASTIC PROCESSES
Strength
SUN
TURBULENCE
Turbulent flow
VOYAGER SPACE PROBES
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Summary:We analyze the ''microscale fluctuations'' of the magnetic field strength B on a scale of several hours observed by Voyager1 (V1) in the heliosheath during 2009. The microscale fluctuations of B range from coherent to stochastic structures. The amplitude of microscale fluctuations of B during 1 day is measured by the standard deviation (SD) of 48 s averages of B. The distribution of the daily values of SD is lognormal. SD(t) from day of year (DOY) 1 to 331, 2009, is very intermittent. SD(t) has a 1/f or 'pink noise' spectrum on scales from 1 to 100 days, and it has a broad multifractal spectrum f( alpha ) with 0.57 less than or equal to alpha less than or equal to 1.39. The time series of increments SD(t + tau ) - SD(t) has a pink noise spectrum with alpha ' = 0.88 plus or minus 0.14 on scales from 1 to 100 days. The increments have a Tsallis (q-Gaussian) distribution on scales from 1 to 165 days, with an average q = 1.75 plus or minus 0.12. The skewness S and kurtosis K have Gaussian and lognormal distributions, respectively. The largest spikes in K(t) and S(t) are often associated with a change in B across a data gap and with identifiable physical structures. The 'turbulence' observed by V1 during 2009 was weakly compressible on average but still very intermittent, highly variable, and highly compressible at times. The turbulence observed just behind the termination shock by Voyager 2 was twice as strong. These observations place strong constraints on any model of 'turbulence' in the heliosheath.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/744/1/51