Hydromagnetic waves and discontinuities in the solar wind

Burlaga, L. F.

doi:10.1007/bf00173345

Cited by 157 publications

(104 citation statements)

References 50 publications

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“…A decrease with increasing r occurs. This form of the distribution has been previously observed (Burlaga, 1971a;Mariani et al, 1973;Barnstorf, 1980). In Pioneer 6 data at 1 AU, Burlaga (1969Burlaga ( , 1971b determines ω s to be 75 • , which is in good agreement with our results for Wind and IMP 8.…”

Section: Directional Change Of the Magnetic Fieldsupporting

confidence: 82%

Radial and latitudinal dependencies of discontinuities in the solar wind between 0.3 and 19 AU and −80° and +10°

Söding¹,

Neubauer²,

Tsurutani

et al. 2001

Ann. Geophys.

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Abstract. Directional discontinuities (DD) from 5 missions at 7 different locations between 0.3 and 19 AU and −80 • and +10 • in the 3D heliosphere are investigated during minimum solar activity. The data are surveyed using the identification criteria of Burlaga (1969) (B) and Tsurutani and Smith (1979) (TS). The rate of occurrence depends linearly on the solar wind velocity caused by the geometric effect of investigating a larger plasma volume if the solar wind velocity v sw increases. The radial dependence is proportional to r −0.78 (TS criterion) and r −1.28 (B criterion), respectively. This dependence is not only due to an increasing miss rate with increasing distance. The DDs must be unstable or some other physical effect must exist. After normalization of the daily rates to 400 km/s and 1 AU, no dependence on heliographic latitude or on solar wind structures is observable. This means that the DDs are uniformly distributed on a spherical shell. Normalized 64 DD per day are identified with both criteria. But large variations of the daily rate still occur, indicating that other influences must exist. The ratio of the rates of rotational (RDs) and tangential discontinuities (TDs) depends on the solar wind structures. In high speed streams, relatively more RDs exist than in low speed streams. In the inner heliosphere (r < 10 AU), no radial or latitudinal dependence of the portions of the DD types occur. 55% clear RDs, 10% clear TDs and 33% EDs (either discontinuities) are observed, but the portions differ with regard to the criteria used. In the middle heliosphere (10 AU < r < 40 AU), the DD types are more uniformly distributed. The distribution of the directional change ω over the transition evolves to an increase of smaller ω with increasing distance from the sun. The evolution is yielded by the anisotropic RDs with small ω. The spatial thickness d km in kilometers increases with distance. The thickness d rg normalized to the proton gyro radius decreases by a factor of 50 between 0.3 and 19 AU, from 201.3 r g down to 4.3 r g . In the middle heliosphere, the orientation of the normals relative to the local magnetic field is essentially uniform except for the parallel direction where no DDs occur.Correspondence to: A. Söding (soeding@geo.uni-koeln.de) This indicates that RDs propagating parallel to B play a special role. In addition, in only a few cases is [v] parallel to [B/ρ], which is required by the MHD theory for RDs. The DDs have strongly enhanced values of proton gyro radius r g for ω ∼ 90 • . In contrast, in the inner heliosphere, only a small increase in r g with ω is observed.

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Section: Directional Change Of the Magnetic Fieldsupporting

confidence: 82%

Radial and latitudinal dependencies of discontinuities in the solar wind between 0.3 and 19 AU and −80° and +10°

Söding¹,

Neubauer²,

Tsurutani

et al. 2001

Ann. Geophys.

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“…(In general, 4 is observed to be quite close to unity (> 0.9) (e.g., see Table 1 in Burlaga, 1971) and it can be set equal to 1 for the purposes of this paper). Unlike the Alfv6n wave of incompressible MHD, the magnetic field intensity does vary for the wave we are considering, but it is subject to the condition that the total pressure given by (4) is constant.…”

Section: Observations Of 'Alfv6n Waves'mentioning

confidence: 85%

Microscale ‘Alfvén waves’ in the solar wind at 1 AU

Burlaga¹,

Turner²

1976

J. Geophys. Res.

134

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Analysis of Imp 1 (Explorer 43) interplanetary plasma and magnetic field fluctuations on a scale of 1 hour for the period March 18 to April 7, 1971, reveals that linearly and circularly polarized Alfvén waves were rarely present. Fluctuations having most of the characteristics of large amplitude ‘Alfvén waves’ were observed ≈40% of the time and moved away from the sun nearly along B. These were not pure transverse Alfvén waves, however, because they were accompanied by nonzero fluctuations in the magnetic field intensity . No simple relation between ‘Alfvén waves’ and streams was found.

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“…As it can be seen in Figure 2 this small change during this period cannot produce the observed hysteresis but it could be one of the -6-factors affecting the power spectrum of magnetic field fluctuation making Ko (Table I) smaller. Further, since the condition for hydromagnetic instabilities (which presumably generate magnetic field irregularities) to occur depends strongly on the ion plasma density (Burlaga, 1971, Drvidson, 1972, this plasma parameter was also examined. The smoothed average plasma ion density was available during the period 1967 -July 1970 from Vela 4, Pioneer VI and Vela 5 (Bame, Private communication).…”

Section: Examination Ofmentioning

confidence: 99%