Interplanetary Scintillation Measurements Research Articles

CME Propagation Characteristics from Radio Observations

We explore the relationship among three coronal mass ejections (CMEs), observed on 28 October 2003, 7 November 2004, and 20 January 2005, the type II burst-associated shock waves in the corona and solar wind, as well as the arrival of their related shock waves and magnetic clouds at 1 AU. Using six different coronal/interplanetary density models, we calculate the speeds of shocks from the frequency drifts observed in metric and decametric radio wave data. We compare these speeds with the velocity of the CMEs as observed in the plane-of-the-sky white-light observations and calculated with a cone model for the 7 November 2004 event. We then follow the propagation of the ejecta using Interplanetary Scintillation measurements, which were available for the 7 November 2004 and 20 January 2005 events. Finally, we calculate the travel time of the interplanetary shocks between the Sun and Earth and discuss the velocities obtained from the different data. This study highlights the difficulties in making velocity estimates that cover the full CME propagation time.

Interaction between coronal mass ejections and the solar wind

[1] Observations suggest that the interplanetary extensions of coronal mass ejections (iCMEs) may be accelerated or decelerated in their passage through the solar wind. Interplanetary scintillation measurements (IPS) can detect the passage of iCMEs beyond the field of view of the Large-Angle and Spectrometric Coronagraph coronagraphs and can provide information on their velocities. The European Incoherent Scatter Radar and the Multi Element Radio Linked Interferometer Network systems, with a field of view covering 10–120 solar radii, can provide information on iCMEs in the inner regions of the solar wind. IPS observations can also provide solar wind velocity measurements ahead of the iCME, and using this information, we consider the velocity profile of a number of clearly defined iCMEs and the relationship between iCME velocities and that of the background solar wind. The results provide additional confirmation that iCMEs converge toward the velocity of the solar wind ahead of the event and that most of the resulting acceleration or deceleration occurs in the innermost regions of the solar wind.

Propagation and interaction of interplanetary transient disturbances. Numerical simulations

We study the heliocentric evolution of ICME-like disturbances and their associated transient forward shocks (TFSs) propagating in the interplanetary (IP) medium comparing the solutions of a hydrodynamic (HD) and magnetohydrodynamic (MHD) models using the ZEUS-3D code [Stone, J.M., Norman, M.L., 1992. Zeus-2d: a radiation magnetohydrodynamics code for astrophysical flows in two space dimensions. i – the hydrodynamic algorithms and tests. Astrophysical Journal Supplement Series 80, 753–790]. The simulations show that when a fast ICME and its associated IP shock propagate in the inner heliosphere they have an initial phase of about quasi-constant propagation speed (small deceleration) followed, after a critical distance (deflection point), by an exponential deceleration. By combining white light coronograph and interplanetary scintillation (IPS) measurements of ICMEs propagating within 1 AU [Manoharan, P.K., 2005. Evolution of coronal mass ejections in the inner heliosphere: a study using white-light and scintillation images. Solar Physics 235 (1–2), 345–368], such a critical distance and deceleration has already been inferred observationally. In addition, we also address the interaction between two ICME-like disturbances: a fast ICME 2 overtaking a previously launched slower ICME 1. After interaction, the leading ICME 1 accelerates and the tracking ICME 2 decelerates and both ICMEs tend to arrive at 1 AU having similar speeds. The 2-D HD and MHD models show similar qualitative results for the evolution and interaction of these disturbances in the IP medium.

MHD simulation of two successive interplanetary disturbances driven by cone‐model parameters in IPS‐based solar wind

We present the measurement‐based MHD simulation model of the interplanetary disturbances; the quiet solar wind is obtained with the MHD‐based analysis method for the interplanetary radio scintillation (IPS) measurement data, and the interplanetary disturbance parameters, such as speed, direction and angular size of the expanding coronal mass ejection (CME), are determined from the SOHO LASCO/C3 data with the Cone‐model. We chose the two successive interplanetary disturbances resulting from two flare‐associated halo CMEs of April 2002. The simulated interplanetary shocks are compared with the nearby‐Earth measurement, and the well produced shock arrivals to the Earth implied the ability of the cooperation of the Cone‐model, the IPS‐analysis and MHD simulation. It is found that the second interplanetary disturbance propagated faster in the rarefaction region of the first event, implying that the multi‐event simulation is important to enhance the simulation model.

Evolving coronal holes and interplanetary erupting stream disturbances

Coronal holes and interplanetary disturbances are important aspects of the physics of the Sun and heliosphere. Interplanetary disturbances are identified as an increase in the density turbulence compared with the ambient solar wind. Erupting stream disturbances are transient large-scale structures of enhanced density turbulence in the interplanetary medium driven by the high-speed flows of low-density plasma trailing behind for several days. Here, an attempt has been made to investigate the solar cause of erupting stream disturbances, mapped by Hewish & Bravo (1986) from interplanetary scintillation (IPS) measurements made between August 1978 and August 1979 at 81.5 MHz. The position of the sources of 68 erupting stream disturbances on the solar disk has been compared with the locations of newborn coronal holes and/or the areas that have been coronal holes previously. It is found that the occurrence of erupting stream disturbances is linked to the emergence of new coronal holes at the eruption site on the solar disk.

Simulations of X-rays from solar wind charge exchange at Mars: Parameter dependence

A hybrid simulation of the solar wind–Mars interaction and a test particle simulation of heavy ion trajectories near Mars are used to compute the contribution from solar wind charge exchange processes to the X-ray emission from Mars. Here, we study how the simulated X-ray emissions depend on the parameters of the simulation model. Solar wind parameters are estimated using a ballistic model based on data from the WIND satellite and using an MHD model that uses inputs from interplanetary scintillation measurements. These two models produce X-ray images with significantly different structure. The intensity of the X-ray emissions and the size of the X-ray halo are also found to increase with an increasing exobase neutral temperature.

Interplanetary consequences caused by the extremely intense solar activity during October–November 2003

We report interplanetary scintillation (IPS) measurements made by the 327 MHz four‐station system of the Solar‐Terrestrial Environment Laboratory of Nagoya University, during 21 October to 8 November 2003. In this period, solar activity increased greatly owing to the appearance of huge eruptive sunspots on the solar disk. Interplanetary (IP) disturbance events traveling from the Sun beyond the Earth's orbit have been detected clearly from our IPS observations in association with most of the major eruptive events that occurred on the Sun during that period. A possible link between solar/IPS events and near‐Earth (IP shock) events in that same period was investigated in this study. As a result, an IP counterpart was identified by our IPS observations for all of the shock events which occurred during the period, and the link to solar events was established unambiguously for the majority of shock events on the basis of the identification of their IP counterparts. Among the IP disturbance events, the most prominent one occurred between 28 and 29 October 2003, and it is considered as an IP counterpart to the 28 October X17 flare event. Our IPS data revealed a complex feature of this IP disturbance and demonstrated that the global distribution of the solar wind density turbulence settled into a rather quiescent condition after the X17 event except between 2 and 4 November 2003, despite the occurrence of marked solar activities. This is in clear contrast to the fact that enhancements of the turbulence level had taken place frequently before the event. The lack of marked g‐value enhancements for those events is considered partly due to the intrinsic effect related to a change in the global distribution of the solar wind turbulence and partly due to artificial effects inherent in our IPS observations. The radial expansion of the IP disturbance was tracked successfully by consecutive IPS observations during the period between 2 and 4 November in association with the 2 November X8.3 flare event. The movement of this IP disturbance inferred from IPS data was found to be generally consistent with the average transit speed of the IP shock associated with the X8.3 event, although some deceleration of the IP disturbance may have taken place.

How did the solar wind structure change around the solar maximum? From interplanetary scintillation observation

Abstract. Observations from the second Ulysses fast latitude scan show that the global structure of solar wind near solar maximum is much more complex than at solar minimum. Soon after solar maximum, Ulysses observed a polar coronal hole (high speed) plasma with magnetic polarity of the new solar cycle in the Northern Hemisphere. We analyze the solar wind structure at and near solar maximum using interplanetary scintillation (IPS) measurements. To do this, we have developed a new tomographic technique, which improves our ability to examine the complex structure of the solar wind at solar maximum. Our IPS results show that in 1999 and 2000 the total area with speed greater than 700 km s-1 is significantly reduced first in the Northern Hemisphere and then in the Southern Hemisphere. For year 2001, we find that the formation of large areas of fast solar wind around the north pole precedes the formation of large polar coronal holes around the southern pole by several months. The IPS observations show a high level agreement to the Ulysses observation, particularly in coronal holes.Key words. Interplanetary physics (solar wind plasma) – Radio science (remote sensing)

Toroidal‐shaped interplanetary disturbance associated with the halo coronal mass ejection event on 14 July 2000

Interplanetary scintillation (IPS) measurements made with the 327 MHz radio telescopes of the Solar–Terrestrial Environment Laboratory, Nagoya University, have been used to study a three‐dimensional structure of the interplanetary (IP) disturbance associated with the halo coronal mass ejection (CME) event on 14 July 2000 (the so‐called “Bastille Day event”). The IPS observations indicated that the Bastille Day IP disturbance was between 0.3 and 0.7 AU at 17 ± 3 hours after the flare occurrence. A model fitting analysis has been applied here to the IPS observations to reconstruct a global structure of the Bastille Day IP disturbance. As a result, the IP disturbance is found to form a loop‐shaped structure that is significantly longer in the longitudinal (east–west) direction than in latitude. This toroidal‐shaped IP disturbance is found to cross the large‐scale magnetic neutral line almost perpendicularly at its center. Our IPS data also show a nonuniform expansion of the IP disturbance, and the fastest direction is found to lie near above the flare site. Using the best‐fit model determined here and information on the ambient solar wind density from in situ measurements, the mass contained by the IP disturbance has been estimated to be ∼ 5.3 × 1016 g. The result obtained from the present analysis is consistent with independent observations that suggest the Bastille Day interplanetary CME has decelerated significantly in the solar wind. The radial evolution of the apparent feature of the IP disturbance has been revealed from a model calculation using the best‐fit parameters, and this evolution is consistent with IPS measurements made at Ooty, India, slightly later in time. While an origin of the toroidal‐shaped disturbance is an open question, the compressed plasma between the coronal ejecta and the ambient solar wind or the ejecta itself are considered as a possible one.

Estimating random transverse velocities in the fast solar wind from EISCAT Interplanetary Scintillation measurements

Abstract. Interplanetary scintillation measurements can yield estimates of a large number of solar wind parameters, including bulk flow speed, variation in bulk velocity along the observing path through the solar wind and random variation in transverse velocity. This last parameter is of particular interest, as it can indicate the flux of low-frequency Alfvén waves, and the dissipation of these waves has been proposed as an acceleration mechanism for the fast solar wind. Analysis of IPS data is, however, a significantly unresolved problem and a variety of a priori assumptions must be made in interpreting the data. Furthermore, the results may be affected by the physical structure of the radio source and by variations in the solar wind along the scintillation ray path. We have used observations of simple point-like radio sources made with EISCAT between 1994 and 1998 to obtain estimates of random transverse velocity in the fast solar wind. The results obtained with various a priori assumptions made in the analysis are compared, and we hope thereby to be able to provide some indication of the reliability of our estimates of random transverse velocity and the variation of this parameter with distance from the Sun.Key words. Interplanetary physics (MHD waves and turbulence; solar wind plasma; instruments and techniques)

The solar wind at solar maximum: comparisons of EISCAT IPS and in situ observations

Abstract. The solar maximum solar wind is highly structured in latitude, longitude and in time. Coronal measurements show a very high degree of variability, with large variations that are less apparent within in situ spacecraft measurements. Interplanetary scintillation (IPS) observations from EISCAT, covering distances from 20 to 100 solar radii (RS), are an ideal source of information on the inner solar wind and can be used, therefore, to cast light on its evolution with distance from the Sun. Earlier comparisons of in situ and IPS measurements under solar minimum conditions showed good large-scale agreement, particularly in the fast wind. In this study we attempt a quantitative comparison of measurements made over solar maximum by EISCAT (20–100 RS) and the Wind and Ulysses spacecraft (at 215 RS and 300–1000 RS, respectively). The intervals studied were August–September 1999, May 2000, September 2000 and May 2001, the last-named being the period of the second Ulysses fast latitude scan. Both ballistic and – when possible – MHD/ballistic hybrid models were used to relate the data sets, and we compare the results obtained from these two mapping methods. The results of this study suggest that solar wind velocities measured in situ were less variable than those estimated from IPS measurements closer to the Sun, with the greatest divergence between IPS velocities and in situ measurements occurring in regions where steep longitudinal velocity gradients were seen in situ. We suggest that the interaction between streams of solar wind with different velocities leads to "smoothing" of solar wind velocities between 30–60 RS and 1 AU, and that this process continues at greater distances from the Sun.Key words. Interplanetary physics (solar wind plasma; sources of the solar wind; instruments and techniques)

Large-scale structure of the solar wind from interplanetary scintillation measurements during the rising phase of cycle 23

Multi-site measurements of interplanetary scintillation (IPS) can provide information on solar wind velocity at any heliolatitude or longitude and over a wide range of heliocentric distances, with the coverage limited only by the availability of suitable radio sources and the geometry of the observing system. The EISCAT facility has been used to make IPS measurements every summer from 1989 to the present day. In this paper we discuss results from solar minimum in 1996, through the rising phase of cycle 23 to the spring of 2000. We discuss the changes in the large-scale structure of the solar wind seen in the EISCAT IPS data and compare them with results from the Nagoya IPS system and with structures seen in coronal white-light intensity.

On the correlation between small scale density fluctuations and speed in the solar wind

The correlation between the level of small scale density fluctuations and the solar wind speed was recently found by Asai et al. (1998) from the tomography analysis of interplanetary scintillation measurements. The physical origin of this correlation is considered within an assumption that density fluctuations are generated locally by nonlinear interactions of Alfven waves. The radial evolution of density turbulence power spectrum is investigated as well as the speed dependence of the levels of Alfven waves and of density turbulence. It is shown that the combination of these two effects can result in sufficiently strong dependence of the fractional level of small scale density fluctuations on the solar wind speed. The fractional levels of density and of magnetic field fluctuations increase weakly with increasing of heliocentric distance due to the radial evolution of the turbulence power spectra. The results of the considered theoretical model are in a reasonably good agreement with the observational data of Asai et al. (1998) if invariance of the solar wind mass flux, but not the momentum flux, is assumed.

Interplanetary scintillation observations for the solar wind disappearance event of May 1999

In this article we present ground‐based interplanetary scintillation (IPS) measurements at 103 and 327 MHz for the period of the solar wind disappearance event of May 1999 as seen by various space probes. The solar wind velocity measurements at 327 MHz showed a variable solar wind velocity during this period at a distance of ∼0.5 AU from the Sun. The average solar wind velocity from three radio sources varied in the range of 200–300 km s−1. The scintillation index measurements at 103 MHz indicate that plasma density was very low in the interplanetary medium closer to the Earth and that the density was normal away from it during May 11–13. The scintillation index was enhanced significantly on May 14 after the disappearance event. The comparison with the in situ observations shows that the effect is dramatic in IPS observations. IPS and in situ measurements show that a large, tenuous, and slow plasma cloud engulfed our planet around this time, which could be because of a corotating low‐density narrow stream. From the source (Sun) point of view, this was mostly a normal plasma flow in most of the interplanetary medium.

Polar low‐speed solar wind at the solar activity maximum

The tomographic analysis of interplanetary scintillation (IPS) showed that low‐speed winds (≤ 370 km s−1) emanated out from the polar region at the last solar activity maximum. In order to investigate the origin of those low‐speed winds, we compared the velocity distribution derived from the IPS tomographic analysis to the magnetic field structure derived from the potential field analysis. We found that the polar low‐speed winds appeared for a short period just before and after the disappearance of polar open fields. When the polar coronal hole shrank very small before its disappearance, the coronal polar open field was encircled by large‐scale closed loops and became super radially diverging field into the interplanetary space. A low‐speed region appeared in this diverging polar magnetic field region. This situation is a condition very similar to the compact low‐speed streams associated with equatorial active regions, which were found by Kojima et al. [1999]. After the open field regions had disappeared from the pole, the polar regions were occupied with closed loops. These closed loops were overlapped by the magnetic field which fanned out from the midlatitudes. A low‐speed streamer located above these closed loops even after the polar open field had disappeared. The velocities of polar low‐speed streams before polar hole disappearance were much lower than those after disappearance. This result suggests that the physical conditions to generate much lower speed streams are closely associated with large expansion from small open field regions encircled by large‐scale closed loops. Finally, a reliability of the IPS measurement of polar low‐speed wind was examined by simulating synthetic IPS observations in hypothetical model polar streams.

Anisotropy of magnetosonic turbulence in the solar wind between 0.1 and 0.4 AU

The anisotropy of the density fluctuations in the solar wind is studied with the assumption that density fluctuations are connected to magnetosonic turbulence. It is shown that the anisotropy of density fluctuations does not coincide with that of the turbulence energy in the case of the fast magnetosonic waves while they are equal for the slow magnetosonic waves. The radial evolution of the two‐dimensional (2‐D) anisotropy ratio in the interplanetary scintillation (IPS) pattern plane due to the change of the ambient magnetic field direction is investigated. In the case of the Parker's spiral magnetic field the radial dependence of the 2‐D anisotropy ratio is shown to be considerably stronger for the fast magnetosonic waves than for the slow magnetosonic waves. The comparison between theoretical estimations and the results of the Kashima high‐frequency IPS measurements shows that the geometric effects are not sufficient to account for the observed radial dependence of the axial ratio, and that the angular distribution of turbulent energy evolves in the region of heliocentric distances between 0.1 and 0.4 AU toward the state enriched by the magnetosonic waves propagating at smaller angles relative to the ambient magnetic field. The nonlinear wave‐wave interactions seem to be responsible for this evolution of the density turbulence spatial power spectrum.

Simultaneous interplanetary scintillation and optical measurements of the acceleration of the slow solar wind

Abstract. Simultaneous observations of the slow solar wind off the southeast limb of the Sun were made in May 1999 using optical measurements from the C2 and C3 LASCO coronagraphs on board the SOHO spacecraft and radio-scattering measurements from the MERLIN and EISCAT facilities. The observations show the slow solar wind accelerating outwards from 4.5 solar radii (R), reaching a final velocity of 200-300 km s-1 by 25-30 R. The acceleration profile indicated by these results is more gentle than the average profile seen in earlier LASCO observations of larger scale features, but is within the variation seen in these studies.Key words: Interplanetary physics (solar wind plasma; sources of the solar wind; instruments and techniques)

Simultaneous interplanetary scintillation and optical measurements of the acceleration of the slow solar wind

Simultaneous observations of the slow solar wind off the southeast limb of the Sun were made in May 1999 using optical measurements from the C2 and C3 LASCO coronagraphs on board the SOHO spacecraft and radio-scattering measurements from the MERLIN and EISCAT facilities. The observations show the slow solar wind accelerating outwards from 4.5 solar radii (R), reaching a final velocity of 200-300 km s-1 by 25-30 R. The acceleration profile indicated by these results is more gentle than the average profile seen in earlier LASCO observations of larger scale features, but is within the variation seen in these studies.Key words: Interplanetary physics (solar wind plasma; sources of the solar wind; instruments and techniques)

Connecting the Sun and the solar wind: Source regions of the fast wind observed in interplanetary space

Highly sensitive radio occultation and white light measurements of path‐integrated density have shown that the solar corona comprises three distinct morphological regions, streamer, quiet Sun, and polar coronal hole, which except for the streamer region, extend radially into interplanetary space from 1.15 Rs to at least 30 Rs. In this paper we build on these results by comparing solar wind flow speeds observed at the same time as path‐integrated density. Flow speeds are inferred from the Doppler dimming of O VI lines with the ultraviolet coronagraph spectrometer on the Solar and Heliospheric Observatory, while the simultaneous polarized brightness measurements of path‐integrated density are from the High Altitude Observatory Mauna Loa Mk III K‐coronameter. The comparison of global flow speed and density observations in 1997 produces three new results. First, it shows, that the three distinct morphological regions, identified earlier in density measurements, are present in the latitudinal profile of the flow speed in the corona. In particular, the flow speed measurements provide evidence for the quiet Sun as an additional source of fast wind. Second, the comparison shows that flow speed and density are anticorrelated in the solar corona. Third, it demonstrates that the Mk III pB measurements can readily serve as a proxy for velocity distribution in the outer corona. The extensive Mk III data set that spans nearly two solar cycles therefore provides the framework of near‐Sun measurements with which connections with solar wind measurements in interplanetary space can be made. Specifically, we show that fast wind regions in the heliosphere, observed directly by Ulysses and Wind plasma measurements and remotely by Nagoya interplanetary scintillation measurements, map radially back to fast wind regions at the Sun identified by the Mk III data.

Three‐dimensional propagation of interplanetary disturbances detected with radio scintillation measurements at 327 MHz

Interplanetary scintillation (IPS) measurements at 327 MHz have been used to study the three‐dimensional propagation of interplanetary (IP) disturbances between 0.2 AU and near‐Earth distance (∼ 1 AU). IPS data of four events, September 23 and August 24, 1998, and November 4 and 6, 1997, events, in which marked IP disturbances were observed in association with energetic solar flares, have been analyzed in this study. From the analysis of these events it is found that the propagation speed of IP disturbances varies with longitude and latitude. We also found that the fast speed direction does not necessarily agree with the flare normal direction. Slow propagation speeds of IP disturbances appear to be closely associated with the slow speed region of ambient solar wind. This suggests that the large‐scale structure of the solar wind speed may play an important role in determining the propagation speed of IP disturbances, although further study is necessary.