A catalogue of high-speed plasma streams in the solar wind

A catalogue of 346 well defined high-speed plasma streams detected in solar wind observations 1964–75 is presented. The data base for the study is the compilation of interplanetary plasma/magnetic field data prepared by J. King. It is believed that the catalogue may be found useful for studies of various solar-interplanetary and solar-terrestrial phenomena.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

Relationship between the coronal holes and high-speed streams of solar wind

The relationship between two classes of coronal holes and high-speed quasi-stationary streams of solar wind at the Earth’s orbit is investigated. “Open” coronal holes, whose area is invariable or increases with the height over the solar surface, are rated in the first class, and “closed” coronal holes with areas decreasing with the height are referred to as second-class holes. The parameters of the coronal holes are determined from IR and EUV images and spectroheliograms. It is shown that most open coronal holes can be associated with high-speed solar-wind streams, while most closed coronal holes exhibit a much lower correlation with such streams.     

Preferred bartels days of high-speed plasma streams in the solar wind

An analysis of 346 high-speed solar wind streams observed at 1 AU during 1964–75 is presented. The analysis shows that a two-sector structure was the dominant feature of the interplanetary magnetic field associated with the high-speed solar wind plasma. The high-speed streams occurred at preferred Bartels days: Positive polarity streams were most frequent near Bartels day 4, negative polarity streams were most frequent near Bartels day 17. Since the solar wind carries with it the photospheric magnetic polarity of the solar source region, the observed distribution of Bartels days must indicate a fundamental property of the distribution of the solar sources of high-speed plasma streams. The observations are explained in terms of a tilted dipole model of the solar-interplanetary field.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.     

Energy balance of the corona and the origin of quasi-stationary high-speed solar wind streams

The energy balance of open-field regions of the corona and solar wind and the influence of the flow geometry in the corona upon the density and temperature, are analyzed. It is found that the energy flux arriving at the corona is constant for the corona's open regions with different flow geometries. For the waves heating the corona and solar wind, the dependence of the absorption coefficient on the corona's plasma density is found to be within the range of distances r=1.05–1.5R . It is shown that the wave absorption is more dependent on electron density than the coronal emission. It is this difference that causes lower-density coronal holes to be colder than quiet regions. It is found that the additional energy flux necessary for providing energy balance of the corona and for producing solar wind is a flux of Alfvén waves, which can provide the energy needed for producing quasi-stationary high-speed solar wind streams. Theoretical models of coronal holes and the question of why the high-speed solar wind streams are precisely flowing out of coronal holes, are discussed.     

Interplanetary magnetic field enhancements in the solar wind: Statistical properties at 1 AU

A new class of magnetic field signatures in the solar wind has been studied using interplanetary data obtained in the vicinity of Earth. Typical behavior of these signatures is a slow rise of the total magnetic field to a sharp peak and then a gradual and almost symmetric decrease to the background interplanetary magnetic field. These events last from a minimum of 30 min to a maximum of more than 11 hr. The background magnetic field is enhanced from 13 to up to 168%. However, there is no correlation between the amplification of the background field and the duration of each event. A total of 45 events have thus been found in a survey of the magnetometer data of two spacecraft (ISEE-3 and IMP-8), corresponding to a total of more than 6 years of available survey data. The peak magnetic pressure of these events is always less than the solar wind dynamic pressure by a factor of 10 or more. These signatures are similar to those observed at Venus by the Pioneer Venus Orbiter. Based on these observations and the previously discovered signatures at Venus, the cause of these events is postulated to be small outgassing bodies which have passed by the spacecraft. These bodies must outgas enough to produce the field distortion observed and yet they must be small enough to be generally undetected by observers on Earth.     

The effect of solar wind high-speed streams on the galactic cosmic rays intensity

The effect of high-speed recurrent solar wind streams from coronal holes on the galactic cosmic rays intensity is investigated. The distribution of galactic cosmic rays for different solar cycles is considered based on the data of the world network of neutron monitors. Within the inhomogeneous model, which includes a homogeneous background and regions of high-speed streams (HSS’s), the transport equation has been solved and the effect of HSS’s on the spatial distribution of galactic cosmic rays is estimated. It is shown that theoretical calculations are agreed with the experimental results obtained for 2000–2014 under different assumptions about the mean free path of cosmic rays in the corresponding period of HSS’s.     

A catalogue of high-speed plasma streams in the solar wind 1975–78

Interplanetary magnetic field data compiled by King (1977, 1979) are used to obtain a list of high velocity solar wind streams for the period January 1975 through June 1978. The catalogue is a continuation of a previous list which covered 1964–75. The total number of high-speed solar wind streams listed in the catalogues is 455.     

Magnetic classification of solar wind streams

It is found that from the viewpoint of the magnetic field configuration there are only two types of solar wind: streams with closed field lines (flare-induced streams) and streams with open field lines (M-streams of various velocity and lifetime, and quiet solar wind). We emphasize that in the absence of flare-induced streams the Earth's magnetosphere is, as a rule, circum-flown not by a quiet but by a variably disturbed solar wind—M-streams. An important feature of M-streams is that within a given interplanetary magnetic field sector the sign (+ or −) of the stream magnetic field almost always coincides with that of the sector. These facts lead to the conclusion that M-streams are mainly responsible for the sector structure.     

Coronal sources of high-speed plasma streams in the solar wind during the declining phase of solar cycle 20

A correlative study is made between inferred solar sources of high-speed solar wind streams and extended white-light coronal features. The solar wind data used in the study consists of 110 co-rotating high-speed plasma streams observed from spacecraft at 1 AU in the period February 1971-December 1974; the coronal data consists of 144 equatorward extensions of polar coronal holes and 15 equatorial coronal holes, derived fromK-coronometer maps of the white-light corona during the same period. Of 110 observed solar wind streams 88 could directly be associated with an equatorward extension of a polar-cap coronal hole and 14 could be associated with a low-latitude equatorial coronal hole. In 8 cases no visible coronal feature was identified. Of 144 identified polar-cap extensions 102 were associated with a high-speed stream observed at 1 AU; 19 coronal features were related in time to data gaps in the solar wind measurements, while 38 features did not give rise to solar wind streams observed at Earth orbit. The probability of an association depended on the heliographic co-latitude of a polar hole extension, being 50% for a polar lobe extending down to 45° co-latitude and 100% for a polar coronal hole extending to 80° co-latitude or more.Paper presented at the 11th European Regional Astronomical Meeting of the IAU on New Windows to the Univese, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Interplanetary field enhancements in the solar wind: Statistical properties at 0.72 AU

A new class of disturbance in the interplanetary magnetic field has been discovered. This disturbance consists of an enhancement in the magnetic field strength lasting tens of minutes to hours. The strength of the enhancement is variable ranging up to over double the background field strength. The peak field pressure can be as high as 10% of the solar wind dynamic pressure. These events occur randomly with respect to the position of the spacecraft relative to Venus but not randomly with respect to Venus solar ecliptic longitude. There is a significant tendency for these events to cluster near certain ecliptic longitudes. The field distortion is often greater in the direction perpendicular to the solar wind flow rather than along it. These characteristics suggest that the source of the disturbances are weakly outgassing objects, possibly dispersed along their orbits such as in meteor streams.     

A third catalogue of high-speed plasma streams in the solar wind - data for 1978–1982

Interplanetary magnetic field data obtained from near-Earth spacecraft are used to compile a catalogue of high-velocity solar wind streams for the period June 1978 through October 1982 (Bartels rotations 1980–2039). The compilation of high-velocity streams is a continuation of two previous lists which covered the periods 1964–1975 and 1975–1978, respectively. The total number of high-speed solar wind streams listed in the catalogues is 637 of which 520 are corotating streams and 117 are classified as flare-associated streams.     

Solar wind flow associated with stream-free sector boundaries at 1 AU

The correlations between the plasma characteristics of the solar wind flow in the vicinity (± 12 hr) of stream-free sector boundaries near Earth are examined using the composite data base of interplanetary plasma for the period 1965–1980. We confirm the result of Lopez et al. (1986) of an inverse relationship of the proton temperature (T _p) with the momentum flux density (NV ²) in the low speed wind at 1 AU. The coefficients of lines of best fit to the T _pvs NV ²(as well as T _pvs V) distribution in our sample are, however, significantly different from those of the undifferentiated sample of low speed wind considered by Lopez et al. such that T _pis, in general, lower than expected. We find further that the proton number density (N) varies as the inverse cube of the flow speed (V) indicating an invariance of the kinetic energy flux density (NV ³) relative to velocity structure in the plasma flow around stream-free boundaries. These average relationships, which are unaffected by interplanetary dynamical processes, are suggested to be due to sub-sonic addition of momentum and energy to the solar wind flow from the source structures, namely coronal streamers.     

Magnetohydrodynamic tube waves and high speed solar wind streams

It has been widely conjectured that magnetohydrodynamic (MHD) waves may provide the extra momentum or energy required to explain the high speed solar wind streams that originate in coronal holes. Although the magnetic structuring inherent in this problem has been incorporated into models of the bulk flow, this is not generally true of the associated treatments of wave propagation. In particular, as pointed out by Davila (1985), we might generally expect the magnetic geometry to substantially modify those waves whose wavelength is comparable to the hole width. Using both a geometrical optics and an eigenmode approach, Davila addressed the question of wave propagation in a simple uniform width flux slab model of a coronal hole and concluded

1. the hole may act as a ‘leaky wave guide’, i.e., waves travelling along it may leak into the surrounding corona, but
2. the group velocity of waves with periods in a physically relevant range (around 100 s) is downward, indicating that such waves cannot carry energy into the solar wind and therefore cannot be driving it.

We agree with (i) but argue that (ii) results from a mistaken interpretation of a dispersion relation, and is incorrect. Furthermore, we apply the cylindrical tube leaky wave approach of Cally (1986) to a simple coronal hole model, and find two wavetypes with substantial upward energy fluxes. However, of these, we argue that the so-called ‘trig modes’ (geometry modified fast waves) leak so profusely that they are unable to transport energy over the distance required; the non-axisymmetric ‘thin tube’ modes, though, do not suffer from this disability.     

A hydromagnetic model of corotating conductive solar wind streams

Under the assumption of quasi-azimuthal symmetry the governing equations of a steady hydromagnetic flow in a thermally conductive flux tube possess six invariants. Four of them represent constancy of mass efflux, energy efflux, angular momentum efflux and magnetic flux. Based on the entropy equation we obtain useful approximation in explicit expressions for the two remaining invariants. One of them provides the constraint which determines the compatible heat flux to ensure a vanishing pressure at infinity. Thus, the admissible solution that represents a corotating solar wind stream in terms of specified interplanetary condition can be calculated by an algebraic method, without the necessity of numerical integration. A two-point relationship is then derived, which correlates the solar wind properties at two separated interplanetary sites measured at two properly separated instants. This relationship may be applied to observational data from space crafts and earth-bound satellites to discern the corotation feature in the solar wind.     

On the occurrence rate of high-speed solar wind events

We have investigated the rate of occurrence of solar wind phenomena observed between 1972–1984 using power-spectrum analysis. The data have been taken from the high-speed solar wind (HSSW) stream catalogue published by Mavromichalaki, Vassilaki, and Marmatsouri (1988). The power-spectrum analysis of HSSW events indicates that HSSW stream events have a periodicity of 9 days. This periodicity of HSSW events is of the 27-day period of coronal holes, which are major sources of solar wind events. In our opinion, the 9-day period may be the energy build-up time for coronal hole regions to produce the HSSW stream events.     

The interaction effect of fast and slow solar wind streams in interplanetary space on wind characteristics at the Earth's orbit

By analyzing observational data, it has been possible to determine quantitative relationships that represent the role of the interaction of fast and slow solar wind (SW) streams in the formation of characteristic SW properties at the Earth's orbit.It is shown that maximum values of magnetic field B _M and density n _M peaks in the neighbourhood of the sector boundary (SB) at the base of the high-speed stream front are associated with solar wind characteristics such as the SW minimum velocity near the SB, V _m, the maximum velocity in the central part of the fast stream, V _M, and the slope of the magnetic field neutral line to the solar equatorial plane at R = 2.5 R (R is the solar radius).It is concluded that enhancements of absolute values of the z-component of the magnetic field, ¦B _z¦, recorded at the Earth's orbit, are largely attributable, at sufficiently large values of , to the interaction of different-velocity SW streams.     

Cosmic ray modulation: Effects of high speed solar wind streams

Based on their source of origin, high speed streams detected in the solar wind plasma have been classified into two classes, coronal hole and solar flare associated streams. Observed heliospheric plasma and field parameters of these streams such as speed, field strength and its variance have been utilized in a systematic manner in order to see their effects in cosmic ray modulation. It is found that flare associated streams are much more effective in modulation than streams from coronal holes. Inspite of the possibility that solar wind structures during two types of streams might be different, the field variance appears to be the most cricial parameter responsible for this difference in their effectiveness in modulation.     

Interplanetary disturbances in the solar wind produced by density,temperature, or velocity pulses at 0.08 AU

Time-dependent solutions of a one-fluid model of the interplanetary medium are investigated. This set of unsteady hydrodynamic equations has been written in conservation form in order to apply the Lax-Wendroff method for the solution of this problem. The initial disturbance is specified by a pulse at 0.08 AU (astronomical units). Physically, this pulse can be interpreted as having been caused by a solar flare, surge, or any other solar disturbance. The equilibrium condition is determined to be the steady solution of the governing equations and represents the quiet solar wind. The results are presented in terms of density, temperature, and velocity profiles of the interplanetary gas flow at heliocentric distances up to 6 AU at several times. Also, the trajectories of disturbances for various initial pulses are shown. Finally, we have used some June 1972 interplanetary observational data to compare with these theoretical calculations. On the basis of these results, the effects of solar disturbances on the interplanetary environment (such as the generation of large non-linear wave trains in the shocks' wakes) can be inferred.     

Coronal ⋌5303 intensity,geomagnetic activity and solar sources of high-speed plasma streams

Investigations during the last 30 yr of the relationship between the green emission line corona and geomagnetism have yielded contradictory results. The papers on this subject can be separated into 2 groups; (a) papers reporting a negative correlation between green line intensity and geomagnetic activity, and (b) papers reporting a positive correlation. The negative correlation seems to be the one better supported by solar wind theory and observations. It implies that solar active regions are the base of low expansion speeds, whereas quasistationary high-speed solar plasma streams originate from regions of low density and open magnetic field structuresIn the present paper we have re-examined some of the analyses described in the group (b) papers. It is found that instead of indicating a positive correlation, these analyses in fact favour the negative correlation. Thus there does not appear to be any conflict at all between the different papers. The interpretation in favour of the positive correlation seems to be due to some accident of perspective having obscured the true connection     

Preferred Bartels days of high speed solar wind streams: An update

Comparison of distribution of solar wind streams as a function of Bartels rotation days for two successive epochs indicates several significant differences. These are likely to be due to the differing nature of IMF and solar wind in the two solar cycles 20 and 21.