Power spectra and discontinuities of the interplanetary magnetic field: Mariner 4

Abstract

Power spectra from 3 × 10−4 to 0.5 cps based on Mariner 4 interplanetary magnetic field data show a dependence on frequency ƒ that is roughly of the form ƒ−γ with γ typically near 3/2 and essentially always between 1 and 2 for each of the three components and for the absolute value of the field. This is based on the analysis of data for days of widely ranging degrees of activity near solar minimum. Power levels were typically a factor of 10 higher for disturbed than for quiet days and, except on quiet days, were a factor of 2 higher for the various components than for the absolute value. Data relating to frequently occurring field discontinuities show few shocks and many contact surfaces. The associated current sheets are found to be unusually thin, roughly 50% of those analyzed had thicknesses less than 3500 km and 10% less than 500 km. The structure of the current sheets that produced the cleanest discontinuities was analyzed and shown to be consistent with that of a tangential discontinuity characterized by zero normal field and normal velocity components. The directional distribution of current sheet normals strongly suggests a local latitudinal solar wind shear that prevails over one sector and can change from sector to sector. The cross sections of magnetic filaments are found to be in some cases highly elliptical rather than more‐or‐less circular, again suggesting a latitudinal solar wind shear.

Heliosheath Magnetic Field and Plasma Observed by Voyager 2 During 2012 in the Rising Phase of Solar Cycle 24

“…The current sheets associated with tangential discontinuities were first observed in the solar wind at 1 au by Siscoe et al (1968) and Burlaga (1969), who found that they have thicknesses 10 proton Larmor radii, R L . Current sheets associated with tangential discontinuities observed at 1 au were modeled by Lemaire & Burlaga (1976), who modeled them as boundary layers across which the sum of the gas pressure, magnetic pressure, and electric field pressure is constant and whose internal structure is described by the Vlasov equation and Maxwellʼs equations.…”

Modulation of low-energy cosmic rays

“…Thus, the results of Siscoe et al (1968) and Ness (1969, 1970), although attractive, cannot be considered as testing the validity of the diffusion coefficientpower spectrum relation at low energies.…”

“…Power spectra obtained for interplanetary conditions in 1965 by Siscoe et al (1968) and in 1966 by Ness (1969, 1970) indicated a frequency dependence of close to f-2 at high frequencies, (f > 2.8 x 10-4Hz), corresponding to rigidities R A .5 BV, and a dependence of f-3/2 to f-5 / 3…”

“…The results were consistent with theory at high energies (>500 MeV/nucleon) where the diffusionconvection model holds. However, this method has produced no conclusive results at low energies, where the appropriate power spectra have been shown to vary on a day to day basis (Coleman, 1966;Siscoe et al, 1968;Sari and Ness, 1969) and where the simple diffusion-convection model must be modified by the effects of adiabatic deceleration (Parker, 1965).…”

Waves in the Vicinity of the Magnetopause

“…The first (hereafter called Method 1), the technique usually used in magnetopause studies (Sornerup and Cahill, 1968), selects the direction n that minimizes the quantity E i (B i-B 'n where Bi are the vector measurements r,-aade throughout the magnetopause region and B is the average over the interval. The second method (Method 2) has been used on interplanetary discontinuities, and in a similar manner it minimizes the quantity B i • n. (Siscoe et al , 1968). Clearly, for an idealized tangential discontinuity, there will be a direction of zero field and zero variation and b-th methods will yield this direction.…”