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Mariani, F.

Publications and source records attributed to Mariani, F..

53 records · Page 3
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NASA NTRS1978

Magnetic dips in the solar wind

Using magnetic data from the HELIOS 1 fluxgate magnetometer, with a 0.2 sec resolution, the structures of several interplanetary discontinuities involving magnetic dips and rotations of the magnetic field vector were investigated. A minimum variance analysis illustrates the behavior of the magnetic field through the transition in the plane of its maximum variation. Using this analysis, quite different structures have been individuated and, in particular, narrow transitions resembling almost one dimensional reconnected neutral sheets. For the thinner cases (scale lengths of the magnetic rotation of the order or smaller than 1,000 km), results show the observed structures could be the nonlinear effect of a resistive tearing mode instability having developed on an originally one dimensional neutral sheet at the solar corona.

Dobrowolny, M.↗
NASA NTRS1978

IMF structures between 0.3 and 1 A.U. - A comparison of two-spacecraft observations

Interplanetary-magnetic-field observations by Helios 1 and IMP 8 have been compared for a period of time (corresponding to four solar rotations) in which the radial and latitudinal separations between spacecraft, respectively, ranged between 0 and 0.69 AU and 0 and 14.5 degrees. The correspondence between macrostructural features is good even when the observing spacecraft are located at opposite sides of the solar equatorial plane. Unipolar regions of the interplanetary magnetic field are confirmed as steady-state, corotating structures and are also mostly consistent with a quite regular extension of the field polarities of the observed coronal holes. There are, however, interesting examples of recurrent unipolar regions which are not associated with the recurrent pattern of high-velocity streams. A comparison of two field enhancements suggests that these structures do not experience significant modifications with the heliocentric distance.

Villante, U.↗
NASA NTRS1978

Magnetic fields and flows between 1 AU and 0.3 AU during the primary mission of HELIOS 1

The recurrent flow and field patterns observed by HELIOS 1, and the relation between these patterns and coronal holes are discussed. Four types of recurrent patterns were observed: a large recurrent stream, a recurrent slow (quiet) flow, a rapidly evolving flow, and a recurrent compound stream. There recurrent streams were not stationary, for although the sources recurred at approximately the same longitudes on successive rotations, the shapes and latitudinal patterns changed from one rotation to the next. A type of magnetic field and plasma structure characterized by a low ion temperature and a high magnetic field intensity is described as well as the structures of stream boundaries between the sun at approximately 0.3 AU.

Burlaga, L. F.↗
NASA NTRS1976

Variations of the interplanetary magnetic field intensity between 1 and 0.3 AU

This is a preliminary report on the interplanetary magnetic field intensity B measured by the Rome/GSFC experiment carried on Helios 1 over the period 10 December 1974 to 3 April 1975 when the spacecraft moved from 1 AU to 0.3 AU (on 15 March 1975) and back to 0.47 AU. The large-scale radial variations between 1 and 0.3 AU are consistent with Parker's model for a spiral field. The distribution of B between 0.30 AU and 0.32 AU is comparable to that generally observed near 1 AU. Large changes are observed from day to day. Surprisingly large and abrupt changes in B (about 30 gammas in a few hours) are observed near perihelion.

Mariani, F.↗
NASA NTRS1975

The Rome-GSFC magnetic field experiment for Helios A and B /E 3/

The Rome-GSFC magnetic field experiment utilizes a triaxial fluxgate (saturable inductor) magnetometer. The sensor unit is mounted on the end of a boom approximately four meters from the spacecraft spin axis. The three analog outputs of the magnetometer are converted into three 9 bit digital words. The experiment utilizes an automatic inflight range switch to select the optimum dynamic range out of 4 ranges. A nonmagnetic thermally oscillating actuator is used to reorient the sensor unit by 90 deg to determine all three axes zero levels. The accuracy should be approximately plus or minus 0.1 gamma. The vector measurements are made at equal intervals in time ranging from 16 per second down to 1 per second depending on the telemetry bit rate.

Scearce, C.↗
NASA NTRS1973

Variations of the occurrence rate of discontinuities in the interplanetary magnetic field

A statistical study of magnetic field discontinuities for the interval from February to October 1968 using data from the NASA Goddard Space Flight Center/University of Rome experiment on Pioneer 8 has been conducted. High-resolution data (10-sec averages) have been employed, stringent criteria being utilized to select more than 16,000 events, about 50 per cent being identified as disturbances that are probably tangential discontinuities (TD). Near 1 AU the average occurrence rate of discontinuities is about 3.6/hr, whereas that of tangential-like discontinuities is about 1.6/hr. The rate of occurrence of discontinuities is found to be correlated with the directional change of the field across the discontinuity surface. The normal to the TD discontinuity plane is most often perpendicular to the Archimedean spiral field configuration. A decrease in the rate of occurrence of TD is found with increasing heliocentric distance and/or with decreasing heliocentric latitude. Possible interpretations of the effect are discussed.

Mariani, F.↗
NASA NTRS1973

Pioneer 8 observations and interpretations of sixteen interplanetary shock waves observed in 1968.

A study has been made of 16 interplanetary shock waves observed in 1968 by Pioneer 8 at large distances from earth. A comparison with the shapes of interplanetary shock fronts obtained by De Young and Hundhausen (1971) suggests that in general the ejection of flare gas occurs within a cone of half-angle between 30 and 60 deg. For near-earth events a deflection of the shock front has been observed, possibly owing to an interaction with the bow shock. The average duration of the postshock perturbation is about 20 hours. Strong magnetic fields and rapid fluctuations occur during the first 6 to 12 hours. Electric field perturbations in the VLF band are also noted during these periods. There is limited evidence for one corotating shock in these data.

Bavassano, B.↗
NASA NTRS1972

Reinterpretation of the Pioneer 6 bow shock crossing.

This paper re-examines and reinterprets the interesting bow shock crossing of Pioneer 6 on December 16, 1965, by combining the high-resolution data for the magnetic field measurements with all the available plasma data. It is shown that, although a small correction of the magnetic field data improves the validity test of the MHD Rankine-Hugoniot (R-H) conditions, it is the plasma density measurements that are the principal source of the remaining inconsistencies. With the exception of the densities, the best agreement between the measurements and the R-H relations is obtained when the specific heat ratio is slightly less than the classical value of 5/3 expected for a magnetized plasma in the magnetosheath. A more accurate shock normal determination has been made, and it is found that the shock itself is possibly in motion with respect to the earth and that locally it may be approximated as a normal shock.

Mariani, F.↗