Solar Wind Origin Research Articles

Nonlinear evolution of modified two‐stream instability above ionosphere of Titan: Comparison with the data of the Cassini Plasma Spectrometer

The ionosphere of Titan, moon of Saturn, is directly exposed to the streaming plasma either of magnetospheric or solar wind origin. A turbulent interaction region is formed, called here flowside plasma mantle, where both cold ionospheric and hot streaming plasma are present at comparable densities. Within the framework of a one‐dimensional electromagnetic hybrid simulation using realistic electron mass we have shown that significant wave activity may be generated because of a modified two‐stream instability (MTSI). Having its free energy in the relative drift between the streaming ion flow and the ionospheric ions MTSI is very effective in generating “anomalous viscosity” type interaction leading to significant bulk velocity loss of the proton component of the external plasma flow and turbulent heating of the ionospheric ions. The stochastic energy transfer from the streaming plasma to the ionospheric ions may also increase the tailward planetary ion escape by collective pickup mechanism enhancing the rate of erosion of the atmosphere of Titan. We predict significant wave activity within the characteristic frequency range of about 1–10 Hz and at saturated wave electric field levels of about 5–25 mV/m. Similarly, according to our model calculations superthermal charged particles of ionospheric origin with kinetic energies of about few tens of eV are expected to be detectable by the charged particle analyzers onboard of Cassini spacecraft close to the upper edge of Titan's ionosphere.

Space storm as a phase transition

Fluctuations of the SYM-H index were analyzed for several space storms preceded by more than a week of extremely quiet conditions to establish that there was a rapid and unidirectional change in the Hurst scaling exponent at the time of storm onset. That is, the transition was accompanied by the specific signature of a rapid unidirectional change in the temporal fractal scaling of fluctuations in SYM-H, signaling the formation of a new dynamical phase (or mode) which was considerably more organized than the background state. We compare these results to a model of multifractional Brownian motion and suggest that the relatively sudden change from a less correlated to a more correlated pattern of multiscale fluctuations at storm onset can be characterized in terms of nonequilibrium dynamical phase transitions. The results show that a dynamical transition in solar wind VB s is correlated with the storm onset for intense storms, suggesting that the dynamical transition observed in SYM-H is of external solar wind origin, rather than internal magnetospheric origin. However, some results showed a dynamical transition in solar wind scaling exponents not matched by similar transitions in SYM-H. In other instances, we observed some small storms where there was a strong dynamical transition in SYM-H without similar changes in the VB s scaling statistics, suggesting that changes were due to internal magnetospheric processes. In summary, the results for intense storms points to the solar wind as being responsible for providing the scale free properties in the SYM-H fluctuations but the evidence for small storms clearly limit the importance of the solar wind fluctuations; their interaction is more complex than simple causality.

Observation of two distinct cold, dense ion populations at geosynchronous orbit: local time asymmetry, solar wind dependence and origin

Abstract. We report on the observation of two distinct cold (Ti<5 keV), dense (Ni>2 cm−3) ion populations at geosynchronous orbit. A statistical study was performed on measurements from the geosynchronous Los Alamos plasma instruments, for the period 1990–2004, and complemented by corresponding large-scale plasma sheet data obtained by mapping DMSP observations in the tail. The first population, which has previously been reported in several studies, is observed in the midnight region of geosynchronous orbit. The second population, which has drawn less attention, is detected on the dawn side of geosynchronous orbit. No such cold, dense population is observed on the dusk side of geosynchronous orbit on a frequent basis. The temporal evolution of various plasma parameters as a function of local time shows that the two populations appear at geosynchronous orbit as distinct populations, since the appearance of a midnight population is not usually associated with that of a dawn population, and vice versa. The midnight ion population is typically observed after the IMF has been northward for some time and is convected inward toward geosynchronous orbit after an observed mild southward turning of the average IMF. It is interpreted that the source of the midnight population is the cold, dense plasma sheet (CDPS). The dawn-side cold and dense ion population is associated with previously strong southward IMF and consequently occurs during substantial geomagnetic activity. These events are typically observed around the end of the main phase of the corresponding Dst decrease, down to −50 nT on average. It is unlikely that this dawn population is simply the low-latitude boundary layer (LLBL) moving closer to Earth because (1) no symmetric dusk population is observed and (2) on average a small sunward flow (~15 km/s) is observed for those events. The cold, dense population at dawn is thus observed during active times (based on Dst, Kp and AE indices) in comparison with the midnight case. However, since the dawn population is observed only around the end of the main Dst decrease, it is concluded that this population does not typically contribute to the Dst decrease during the main phase. This population may rather be transported to geosynchronous orbit by means of a compression and convection enhancement in the magnetosphere, with a preferential access from the dawn flank with no apparent counterpart at dusk. DMSP data suggest that a cold and dense plasma source is mainly present at dawn.

Ring Current Dynamics

This chapter reviews the current understanding of ring current dynamics. The terrestrial ring current is an electric current flowing toroidally around the Earth, centered at the equatorial plane and at altitudes of ∼10,000 to 60,000 km. Enhancements in this current are responsible for global decreases in the Earth’s surface magnetic field, which have been used to define geomagnetic storms. Intense geospace magnetic storms have severe effects on technological systems, such as disturbances or even permanent damage of telecommunication and navigation satellites, telecommunication cables, and power grids. The main carriers of the ring current are positive ions, with energies from ∼1 keV to a few hundred keV, which are trapped by the geomagnetic field and undergo an azimuthal drift. The ring current is formed by the injection of ions originating in the solar wind and the terrestrial ionosphere into the inner magnetosphere. The injection process involves electric fields, associated with enhanced magnetospheric convection and/or magnetospheric substorms. The quiescent ring current is carried mainly by protons of predominantly solar wind origin, while active processes in geospace tend to increase the abundance (both absolute and relative) of O+ ions, which are of ionospheric origin. During intense geospace magnetic storms, the O+ abundance increases dramatically. This increase has been observed to occur concurrently with the rapid intensification of the ring current in the storm main phase and to result in O+ dominance around storm maximum. This compositional change can affect several dynamic processes, such as species-and energy-dependent charge-exchange and wave-particle scattering loss.

Local time distribution of reconnected field lines under northward interplanetary magnetic field conditions

[1] Plasma observations in the northern cusp region are used to study the reconnection process and the inflow of plasma into the magnetosphere during intervals of northward interplanetary magnetic field. Several intervals are examined for which He ++ of solar wind origin appears simultaneously with downgoing or counterstreaming O + ions of ionospheric origin. The presence of both He ++ and O + suggests that magnetic reconnection on the magnetopause has occurred. The cases of downgoing or counterstreaming O + observed in conjunction with He ++ suggests that reconnection has occurred tailward of both cusps. The local time distribution of the occurrence of these events is investigated as a function of the state of the solar wind.

Plasma Morphology at Mars. Aspera-3 Observations

A total of about of 400 orbits during the first year of the ASPERA-3 operation onboard the Mars Express spacecraft were analyzed to obtain a statistical pattern of the main plasma domains in the Martian space environment. The environment is controlled by the direct interaction between the solar wind and the planetary exosphere/ionosphere which results in the formation of the magnetospheric cavity. Ionospheric plasma was traced by the characteristic “spectral lines” of photoelectrons that make it possible to detect an ionospheric component even far from the planet. Plasma of solar wind and planetary origin was distinguished by the ion mass spectrometry. Several different regions, namely, boundary layer/mantle, plasma sheet, region with ionospheric photoelectrons, ray-like structures near the wake boundary were identified. Upstream parameters like solar wind ram pressure and the direction of the interplanetary electric field were inferred as proxy from the Mars Global Surveyor magnetic field data at a reference point of the magnetic pile up region in the northern dayside hemisphere. It is shown that morphology and dynamics of the main plasma domains and their boundaries are governed by these factors as well as by local crustal magnetizations which add complexity and variability to the plasma and magnetic field environment.

Abundance Variation at the Vicinity of an Active Region and the Coronal Origin of the Slow Solar Wind

The solar wind ion composition is generally frozen-in within 5 R☉ of the Sun. Many characteristics in the elemental abundances measured in the solar wind are believed to be set at the chromospheric and low coronal levels. By connecting plasma parameters in the coronal and in situ solar wind data, valuable insights can be obtained as to how and where the solar wind is produced. Elemental abundance is found to vary across solar structures and heliocentric heights, as well as in the solar wind. Therefore, solar wind elemental composition data (such as those from SWICS on board ACE), combined with spectroscopic observations of the inner corona (such as those from UVCS on board SOHO), are ideal for investigating the coronal origin of the solar wind. We present such joint analysis using data from SOHO UVCS and ACE SWICS. In 1999 October, UVCS observed the west limb corona at 1.64 R☉ for 7 days with the passing of an equatorial coronal hole followed by an active region complex. This corresponds to a rarefaction transition from fast to slow wind as measured by ACE. This presents an unprecedented opportunity for comparing the variations in the coronal plasma properties with those in the solar wind. We present the analysis for the electron temperature, density, and elemental abundances during this period. We compare these properties between the two data sets and discuss the implications on the formation region of the slow solar wind. Treatment of the line-of-sight effect in the UVCS data, along with 3D MHD coronal field models, are employed to connect the coronal and solar wind data.

Direct Measurements of Energetic Neutral Hydrogen in the Interplanetary Medium

We present an analysis of hydrogen energetic neutral atoms (ENAs) measured by the ASPERA-3 instrument on boardMars Express. We focus on ENAs that have no Martian origin. The energy spectra of these ENAs are all very similar and can be fitted well by a two-component power law. The fluxes, integrated from 0.2 to 10 keV, vary between 5 ; 10 3 and10 5 cm � 2 sr � 1 s � 1 .Wecheckedfor possiblesourcesfor theseENAs,but wecanruleoutaplanetaryorigin, a solar wind origin, contamination by UV from UV bright stars, and contamination by high-energy protons. With our present knowledge we conclude that the heliospheric termination shock is the most plausible source region. Subject headingg acceleration of particles — instrumentation: detectors — interplanetary medium — methods: data analysis — plasmas — solar wind

“Matreshka” model of multilayered current sheet

Current sheets are one of the key elements of the Earth's magnetosphere, determining the magnetic energy storage and release. An analytical self‐consistent model of multicomponent thin current sheets, where the plasma consists of ions of both solar wind and ionospheric origin, is presented. The influence of the electron population is taken into account assuming Boltzman‐like quasi‐equilibrium distribution in the electrostatic field, which can lead to a sharp peak in the electron current density in the center of the current sheet. We include the contribution of non‐adiabatic O+ ions in our model as one of the terms in the Grad–Shafranov‐like system of equations describing the quasi‐equilibrium configuration. The contribution of the oxygen ions to the total cross‐tail current usually does not exceed 30% for realistic conditions, but current “wings” carried by O+ ions produce significant broadening of the current profile.

Mapping of the heavy ion outflows as seen by IMAGE and multifluid global modeling for the 17 April 2002 storm

Multifluid global modeling that includes both light and heavy ion dynamics is used to investigate changes in magnetospheric dynamics produced by enhanced ionospheric outflows for the 17 April 2002 storm. The predicted outflow rates and their effects on the magnetosphere are compared with AMIE and IMAGE/HENA data as a function of relative O+ concentration in the ionosphere. It is shown that O+ can be the dominant species on the dusk side in the inner magnetosphere during the periods of high activity even for ionospheric concentrations as low as 5% as a result of differential heavy ion convection patterns. However, for these low outflow conditions, the cross‐polar cap potential is much larger than that calculated by AMIE. As the O+ ionospheric concentration increases, the heavy outflow rate approaches canonical values, and the effective ionospheric resistivity falls in association with a decrease in cross‐polar cap potential and an increase in the auroral field aligned currents. Within the magnetosphere, the region where the O+ concentration exceeds 50% expands toward the duskside and down the tail. Pressures in excess of 1 nPa can be supported by the enhanced O+ outflows. The presence of these enhanced outflows appears at about the same time and over a similar region to enhancements seen in the HENA 51–180 keV oxygen data. These results provide a direct tie between heavy ionospheric outflows and their energization in the tail and suggest that during this period the heavy ions provide a substantial amount of the plasma required to support the magnetotail current sheet. The model results also show that the enhanced O+ outflow leads to the enhanced exclusion of light ions of both solar wind and ionospheric origin in the plasma sheet, albeit with the light ions experiencing enhanced heating in an O+ dominated current sheet. These results indicate that observed heavy ionospheric outflows and their energetization in the tail have global consequences for the magnetosphere including supporting the dynamics of the tail current sheet during active times and in global circulation including the cross‐polar cap potential and the region 1 and 2 currents.

Multiple spacecraft observations of energetic ions during a high solar wind pressure event

On 28 June 1999 the Wind spacecraft (near the forward libration point) observed a large solar wind pressure spike from 0445 UT to 0600 UT. The Polar satellite at 7 hours magnetic local time detected an energetic particle event in the high‐altitude region associated with turbulent diamagnetic cavities from 0512 UT to 0627 UT. The particles and cavities are very similar to those that were previously found in the high‐altitude dayside cusp region. They are independent of both the solar wind velocity and the interplanetary magnetic field (IMF) vectors. The enhancements of the magnetic field fluctuations in the ultra‐low frequency range measured by the Wind were also observed by the Polar. Most of the time, during the event period, the IMF had a duskward component, suggesting that cusp diamagnetic cavities also existed in the postnoon sector in the Northern Hemisphere. Energetic ions of both ionospheric origin and solar wind origin were observed by the Polar spacecraft during this event period. The He++/H+ ratio in the diamagnetic cavities was a factor of four higher than in the quasi‐trapping region before the event onset, while the He+/He++ ratio in the cavities was more than one order of the magnitude lower. In this event, the measured cusp ions had energies up to 4 MeV. No clear relationship between the cusp energetic ion flux and the IMF cone angle was found. The Interball 1 spacecraft located just upstream of the bow shock in the prenoon sector measured an upstream ion event from about 0516 UT to 0600 UT. The onset of the energetic ions observed by Interball 1 in the upstream event was the same for different energies; the ion energy spectra were independent of the solar wind velocity and their intensities were independent of the bow shock geometry and the solar wind density. The energetic ion event onset was first detected in the cusp by Polar at 0512 UT, then near the bow shock in the prenoon by Interball 1 at 0516 UT, and then in the far upstream by Wind at 0523 UT. The measured energetic ion intensity decreased with increasing distance from the cusp diamagnetic cavities. These observational facts together with the IMF directions suggest that (1) this large solar wind pressure event produced an extremely large diamagnetic cavity (>10 RE) within the magnetosphere, (2) the bow shock was not the main source of both the cusp and upstream energetic ions, and (3) the upstream energetic ions most likely came from the cusp.

Origin and Acceleration of the Slow Solar Wind

This Letter uses Doppler dimming measurements by SOHO UVCS to elucidate the origin and acceleration of the slow solar wind. By investigating plasma flow in the corona over an active region during 2000 May 14-16, we confirm what has been suggested by the presence of the imprint of active regions in the solar wind near Earth orbit, that active regions are a source of slow wind. The observed active region does not have an associated streamer in the outer corona. We explain how this implies that any related heliospheric current sheet must be transverse to the line of sight. It is this favorable geometry of a transverse heliospheric current sheet that allows the plasma flow over the active region to be isolated in path-integrated Doppler dimming measurements. The results also show that acceleration of the slow wind associated with active regions toward its terminal speed is faster than that along the heliospheric current sheet. These differences in acceleration explain why the signatures of the heliospheric current sheet are dissimilar in velocity, but not in density, between the corona and solar wind measured near Earth orbit.

Radial distribution of production rates, loss rates and densities corresponding to ion masses ⩽40 amu in the inner coma of Comet Halley: Composition and chemistry

In this paper we have studied the chemistry of C, H, N, O, and S compounds corresponding to ions of masses ⩽40 amu in the inner coma of the Comet 1P/Halley. The production rates, loss rates, and ion mass densities are calculated using the Analytical Yield Spectrum approach and solving coupled continuity equation controlled by the steady state photochemical equilibrium condition. The primary ionization sources in the model are solar EUV photons, photoelectrons, and auroral electrons of the solar wind origin. The chemical model couples ion–neutral, electron–neutral, photon–neutral and electron–ion reactions among ions, neutrals, electrons, and photons through over 600 chemical reactions. Of the 46 ions considered in the model the chemistry of 24 important ions (viz., CH 3OH + 2, H 3CO +, NH + 4, H 3S +, H 2CN +, H 2O +, NH + 3, CO +, C 3H + 3, OH +, H 3O +, CH 3OH +, C 3H + 4, C 2H + 2, C 2H +, HCO +, S +, CH + 3, H 2S +, O +, C +, CH + 4, C + 2, and O + 2) are discussed in this paper. At radial distances <1000 km, the electron density is mainly controlled by 6 ions, viz., NH + 4, H 3O +, CH 3OH + 2, H 3S +, H 2CN +, and H 2O +, in the decreasing order of their relative contribution. However, at distances >1000 km, the 6 major ions are H 3O +, CH 3OH + 2, H 2O +, H 3CO +, C 2H + 2, and NH + 4; along with ions CO +, OH +, and HCO +, whose importance increases with further increase in the radial distance. It is found that at radial distances greater than ∼1000 km (±500 km) the major chemical processes that govern the production and loss of several of the important ions in the inner coma are different from those that dominate at distances below this value. The importance of photoelectron impact ionization, and the relative contributions of solar EUV, and auroral and photoelectron ionization sources in the inner coma are clearly revealed by the present study. The calculated ion mass densities are compared with the Giotto Ion Mass Spectrometer (IMS) and Neutral Mass Spectrometer (NMS) data at radial distances 1500, 3500, and 6000 km. There is a reasonable agreement between the model calculation and the Giotto measurements. The nine major peaks in the IMS spectra between masses 10 and 40 amu are reproduced fairly well by the model within a factor of two inside the ionopause. We have presented simple formulae for calculating densities of the nine major ions, which contribute to the nine major peaks in the IMS spectra, throughout the inner coma that will be useful in estimating their densities without running the complex chemical models.

The Effects of Differential Rotation on the Magnetic Structure of the Solar Corona: Magnetohydrodynamic Simulations

Coronal holes are magnetically open regions from which the solar wind streams. Magnetic reconnection has been invoked to reconcile the apparently rigid rotation of coronal holes with the differential rotation of magnetic flux in the photosphere. This mechanism might also be relevant to the formation of the slow solar wind, the properties of which seem to indicate an origin from the opening of closed magnetic field lines. We have developed a global MHD model to study the effect of differential rotation on the coronal magnetic field. Starting from a magnetic flux distribution similar to that of Wang and coworkers, which consists of a bipolar magnetic region added to a background dipole field, we applied differential rotation over a period of 5 solar rotations. The evolution of the magnetic field and of the boundaries of coronal holes are in substantial agreement with the findings of Wang and coworkers. We identified examples of interchange reconnection and other changes of topology of the magnetic field. Possible consequences for the origin of the slow solar wind are also discussed.

Solar Wind Origin in Coronal Funnels

The origin of the solar wind in solar coronal holes has long been unclear. We establish that the solar wind starts flowing out of the corona at heights above the photosphere between 5 megameters and 20 megameters in magnetic funnels. This result is obtained by a correlation of the Doppler-velocity and radiance maps of spectral lines emitted by various ions with the force-free magnetic field as extrapolated from photospheric magnetograms to different altitudes. Specifically, we find that Ne7+ ions mostly radiate around 20 megameters, where they have outflow speeds of about 10 kilometers per second, whereas C3+ ions with no average flow speed mainly radiate around 5 megameters. Based on these results, a model for understanding the solar wind origin is suggested.

Wave activity above the ionosphere of Titan: Predictions for the Cassini mission

In this paper we present a study of the beam‐driven wave generation mechanisms in linear approximation which are viable in the flowside plasma mantle of Saturn's moon, Titan. The flowside plasma mantle is defined, by analogy with the dayside plasma mantle of the planet Venus and Mars, as being the interaction region between the “cold” ionospheric plasma and “hot” streaming plasma of magnetospheric or solar wind origin, with both types of plasma being present in comparable densities. Since no in situ plasma and field measurements are currently available in Titan's flowside mantle, we performed our model calculations in a broad plasma parameter space encompassing the plasma characteristics determined by Voyager 1 in Titan's wake. Two types of beam instability modes were found to be dominant: a fluid‐like (nonresonant) modified two‐stream instability (MTSI) and the kinetic (beam resonant) ion‐ion acoustic instability (IIAI). The two instability modes are characterized by distinct frequency ranges (an order or below the lower hybrid frequency for the MTSI and a few times the lower hybrid frequency for the IIAI) and are found to be dominant in well‐separated spatial regions determined by the presence/absence of cold ionospheric electrons. Giving a global rather than a specific description of the instability types expected to be the most important growing modes within Titan's flowside mantle, we intend to make predictions concerning the wave characteristics of the dominant wave modes measurable by the plasma wave instrument on board the Cassini spacecraft.

A comparison between ion characteristics observed by the POLAR and DMSP spacecraft in the high-latitude magnetosphere

Abstract. We study here the injection and transport of ions in the convection-dominated region of the Earth's magnetosphere. The total ion counts from the CAMMICE MICS instrument aboard the POLAR spacecraft are used to generate occurrence probability distributions of magnetospheric ion populations. MICS ion spectra are characterised by both the peak in the differential energy flux, and the average energy of ions striking the detector. The former permits a comparison with the Stubbs et al. (2001) survey of He2+ ions of solar wind origin within the magnetosphere. The latter can address the occurrences of various classifications of precipitating particle fluxes observed in the topside ionosphere by DMSP satellites (Newell and Meng, 1992). The peak energy occurrences are consistent with our earlier work, including the dawn-dusk asymmetry with enhanced occurrences on the dawn flank at low energies, switching to the dusk flank at higher energies. The differences in the ion energies observed in these two studies can be explained by drift orbit effects and acceleration processes at the magnetopause, and in the tail current sheet. Near noon at average ion energies of ≈1keV, the cusp and open LLBL occur further poleward here than in the Newell and Meng survey, probably due to convection- related time-of-flight effects. An important new result is that the pre-noon bias previously observed in the LLBL is most likely due to the component of this population on closed field lines, formed largely by low energy ions drifting earthward from the tail. There is no evidence here of mass and momentum transfer from the solar wind to the LLBL by non-reconnection coupling. At higher energies ≈2–20keV), we observe ions mapping to the auroral oval and can distinguish between the boundary and central plasma sheets. We show that ions at these energies relate to a transition from dawnward to duskward dominated flow, this is evidence of how ion drift orbits in the tail influence the location and behaviour of the plasma populations in the magnetosphere. Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; magnetosphere-ionosphere interactions; magnetospheric configuration and dynamic)

Origin and Acceleration of Fast and Slow Solar Wind

Before the advent of the Solar and Heliospheric Observatory (SOHO, launched in 1995), we had little information on how coronal plasma gets accelerated to the high speed measured in situ. The Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO, acquiring UV data over the first few solar radii, a region unexplored in this spectral range, allowed us to build a profile of the outflow plasma speed vs. heliocentric distance, based on empirical constraints. Still, much has to be learnt about the behavior of solar wind in the extended corona. In the following, after briefly reviewing the general properties of the solar wind, I'll focus on controversial issues — like the identification of the sources of fast and slow wind, and the acceleration of fast vs. slow wind streams — and I'll illustrate recent contributions to the solution of these problems.

Origin of the slow solar wind

The origin and location of the slow wind are interesting subjects on their own and also they are important in the matter of the origin of the fast wind especially if the slow wind originates directly from a coronal hole. We have been studying the solar wind whose speed is comparative to or a little slower than that measured in the heliospheric plasma sheet. We derived solar wind velocity distribution maps on the source surface using an interplanetary scintillation tomography analysis, and low speed regions in them were investigated in relation to a coronal hole using potential field magnetic field lines. Slow solar wind was found to originate from an equatorial coronal hole located in the vicinity of active regions and also from a polar coronal hole which was about to disappear at solar activity maximum. The properties of the slow solar wind from an equatorial coronal hole were investigated using spacecraft in situ measurements. Magnetic polarity in this wind was uniform, as expected from a potential field analysis. The helium relative abundance was as large as the fast wind, and variances of density, velocity, and helium abundance were as small as the fast wind from a large coronal hole. In spite of the small equatorial coronal hole origin, the density and ion freeze-in temperature were as large as observed for the slow wind in the heliospheric plasma sheet.

The origin of the slow solar wind in coronal streamers

The highly variable slow solar wind has been associated with low-latitude regions of the heliosphere most clearly by the Ulysses spacecraft. Although, it is evident today that the slow solar wind originates in coronal helmet streamers, the mechanism of the slow solar wind acceleration, and the origin of the variability are still being debated. The combination of new observations and numerical modeling are beginning to address these questions. I will discuss how recent in-situ observations by Ulysses, white light and EUV observations by the LASCO and UVCS instruments on SOHO advanced our understanding of the streamer structure, dynamics, and stability. I will briefly review the current state of numerical MHD modeling of streamers, and the possible mechanisms that may produce the highly variable slow wind. I will present the results of recent heat-conductive MHD modeling of multiple streamer slow solar wind with heating function constrained by observations. I will show how multi-fluid numerical modeling of the slow solar wind in streamers helps to identify the regions of the slow solar wind outflow.