Modeling of Propagation of Coronal Mass Ejections Using Interplanetary Scintillation Data

We present a summary of results from ten years of interplanetary scintillation (IPS) observations of stream interaction regions (SIRs) in the solar wind. Previous studies had shown that SIRs were characterized by intermediate-velocity solar wind and – in the case of compressive interactions – higher levels of scintillation. In this study we considered all cases of intermediate velocities in IPS observations from the European Incoherent SCATter (EISCAT) radar facility made at low- and mid-heliographic latitudes between 1994 and 2003. After dismissing intermediate-velocity observations which were associated with solar-wind transients (such as coronal mass ejections) we found that the remaining cases of intermediate velocities lay above coronal structures where stream interaction would be expected. An improved ballistic mapping method (compared to that used in earlier EISCAT studies of interaction regions) was used to identify the regions of raypath in IPS observations which might be expected to include interaction regions and to project these regions out to the distances of in-situ observations. The early stages of developing compression regions, consistent with their development on the leading edges of compressive stream interaction regions, were clearly detected as close to the Sun as 30 R ⊙, and further ballistic projection out to the distances of in-situ observations clearly associated these developing structures with density and velocity features characteristic of developed interaction regions in in-situ data in the cases when such data were available. The same approach was applied to study non-compressive interaction regions (shear layers) between solar-wind streams of different velocities where the stream interface lay at near-constant latitude and the results compared with those from compressive interaction regions. The results confirm that intermediate velocities seen in IPS observations above stream boundaries may arise from either detection of intermediate-velocity flow in compression regions, or from non-compressive shear layers. The variation in velocity about the mean determined from IPS measurements (representing the spread in velocity across that part of the raypath associated with the interaction region in the analysis) was comparable in compressive and non-compressive regions – a potentially interesting result which may contain important information on the geometry of developing SIRs. It is clear from these results that compressive and non-compressive interaction regions belong to the same class of stream – stream interaction, with the dominant mode determined by the latitudinal gradient of the stream interface. Finally, we discuss the results from this survey in the light of new data from the Heliospheric Imagers (HI) on the Solar TErrestrial RElations Observatory (STEREO) spacecraft and other instruments, and suggest possible directions for further work.

We report radial speed evolution of interplanetary coronal mass ejections (ICMEs) detected by the SOHO/LASCO coronagraph, interplanetary scintillation (IPS) at 327 MHz, and in-situ observations. In this study, we analyze solar wind disturbance factor (g-value) data derived from IPS observations during 1997-2009 covering nearly the whole period of Solar Cycle 23. By comparing observations from the SOHO/LASCO, IPS, and in situ, we then identify 39 ICMEs that could be analyzed carefully. Here, we define two speeds V_SOHO and V_bg, which are initial speed of ICME and the speed of the background solar wind, respectively. Examinations of these speeds yield the following results; i) Fast ICMEs (with V_SOHO - V_bg > 500 km/s) rapidly decelerate, moderate ICMEs (with 0 km/s < V_SOHO - V_bg < 500 km/s) show either gradually decelerating or uniform motion, and slow ICMEs (with V_SOHO - V_bg < 0 km/s) accelerate. The radial speeds converge on the speed of background solar wind during their outward propagation. We subsequently find; ii) both the acceleration and deceleration are nearly complete by 0.79 (+/- 0.04) AU, and those are ended when the ICME speed reaches a given speed. We find the value of that to be 480 (+/- 21) km/s. iii) For the fast and moderate ICMEs, a linear equation with a constant coefficient is more appropriate than a quadratic equation to describe their kinematics, because the chi-square for the linear equation satisfies the statistical significance level of 0.05, while the quadratic one is not. These results support the hypothesis that the radial motion of ICMEs is governed by a drag force due to interaction with the background solar wind. These findings also suggest that ICMEs propagating faster than background solar wind are controlled mainly by the hydrodynamic Stokes drag.

Interplanetary scintillation (IPS) measurements made with the Solar‐Terrestrial Environment Laboratory, Nagoya University, multi‐station system at 327 MHz are used to study the global structure of the interplanetary counterpart of coronal mass ejections (so‐called interplanetary CMEs or ICMEs). We have analyzed our IPS data of four ICME events which occurred successively in July 2000; those are 2000 July 10, 11, 12 and 14 events (the last one corresponds to “Bastille day event”). We have employed the model fitting method to obtain unbiased three‐dimensional properties of ICME from IPS observations. The parameters determined here include the location of the ICME center, the e‐folding radial thickness and angular span, anisotropy of the angular extent, the local enhancement factor, the (average) expansion speed, and its angular dependence. The results suggest that the global shape of July 12 and 14 events were loop‐like; the latitude angular span of these events was much smaller than the longitude one. The July 10 and 11 events are found to be explained excellently by a shell‐shape ICME model. The mass contained by the ICME has been estimated using information on the global structure obtained here.Interplanetary scintillation (IPS) measurements made with the Solar‐Terrestrial Environment Laboratory, Nagoya University, multi‐station system at 327 MHz are used to study the global structure of the interplanetary counterpart of coronal mass ejections (so‐called interplanetary CMEs or ICMEs). We have analyzed our IPS data of four ICME events which occurred successively in July 2000; those are 2000 July 10, 11, 12 and 14 events (the last one corresponds to “Bastille day event”). We have employed the model fitting method to obtain unbiased three‐dimensional properties of ICME from IPS observations. The parameters determined here include the location of the ICME center, the e‐folding radial thickness and angular span, anisotropy of the angular extent, the local enhancement factor, the (average) expansion speed, and its angular dependence. The results suggest that the global shape of July 12 and 14 events were loop‐like; the latitude angular span of these events was much smaller than the longitude one. The ...

The evolving ambient solar wind is one of the key links between the Sun and planetary bodies in our solar system. Here we present a comprehensive catalogue of solar wind properties, stream interaction regions, and coronal mass ejections at different locations in the inner heliosphere. Our database incorporates observational data products and also solar wind modelling results. The solar wind modelling is based on two different approaches for modelling the conditions in the ambient solar wind. While the WSA/THUX model combination solves the viscous form of the underlying Burgers equation to compute the two-dimensional solar wind conditions in our solar system, the second approach is a computationally fast machine learning method for predicting the ambient solar wind flows at Earth. Statistics of the ambient solar wind model results for more than 15 years in combination with a catalogue of coronal mass ejections observed at the Earth, Mars and STEREO satellites along with stream interaction regions provide a comprehensive overview of the past and present solar wind behaviour for shaping planetary space weather.

We present an analytical model that describes the evolution of two consecutive interplanetary coronal mass ejections (ICMEs), their interaction, and the evolution of the merged region. In this model, the coronal mass ejections (CMEs) are seen as velocity and density (mass loss rate) fluctuations of the solar wind that result in the formation of shocks traveling into the ambient solar wind (ASW). The dynamical evolution of these structures depends on both the CME parameters such as the initial velocity, density, and the duration of the eruption as well as the solar wind conditions (ejection velocity and mass loss rate). The probability of an interaction of two consecutive CMEs launched in the same direction is high, basically depending on their speeds and the interval of time between the CMEs. As a result of the interaction, a merged region is formed. Its dynamical evolution is also addressed by the present model. Given a set of initial CMEs and ASW conditions, our model is able to predict the time and distance of the interaction between the ICMEs and the velocity of the merged region as a function of the heliospheric distance. These are fundamental parameters of space weather predictions. Also, the model is able to predict the arrival time and velocity of the merged region at 1 AU. In this work, we validate the model through its application to well documented interaction events observed on 2007 January 24, 2010 May 23, 2010 August 01, and 2012 November 09.

This paper reports on the first combination of results from in-situ plasma measurements at Venus, using data from Venus Express, and remote sensing data from observations of interplanetary scintillation (IPS). In so doing, we demonstrate the value of combining remote sensing and in-situ techniques for the purpose of investigating interaction between solar wind, under several different conditions, and the Venusian magnetosphere. The ion mass analyser instrument (IMA) is used to investigate solar wind interaction with the Venusian magnetosphere in the presence of two different solar wind phenomena; a co-rotating interaction region (CIR) and a coronal mass ejection (CME). The CIR, detected with IPS and sampled in-situ at Venus is found to dramatically affect upstream solar wind conditions. These case studies demonstrate how combining results from these different data sources can be of considerable value when investigating such phenomena.

Observations of interplanetary scintillation (IPS) provide a set of data that is used in estimating the solar wind parameters with reasonably good accuracy. Various tomography techniques have been developed to deconvolve the line‐of‐sight integration effects ingrained in observations of IPS to improve the accuracy of solar wind reconstructions. Among those, the time‐dependent tomography developed at the University of California, San Diego (UCSD) is well known for its remarkable accuracy in reproducing the solar wind speed and density at Earth by iteratively fitting a kinematic solar wind model to observations of IPS and near‐Earth spacecraft measurements. However, the kinematic model gradually breaks down as the distance from the Sun increases beyond the orbit of Earth. Therefore, it would be appropriate to use a more sophisticated model, such as a magnetohydrodynamics (MHD) model, to extend the kinematic solar wind reconstruction beyond the Earth's orbit and to the outer heliosphere. To test the suitability of this approach, we use boundary conditions provided by the UCSD time‐dependent tomography to propagate the solar wind outward in a MHD model and compare the simulation results with in situ measurements and also with the corresponding kinematic solution. Interestingly, we find notable differences in proton radial velocity and number density at Earth and various locations in the inner heliosphere between the MHD results and both the in situ data and the kinematic solution. For example, at 1 AU, the MHD velocities are generally larger than the spacecraft data by up to 150 km s−1, and the amplitude of density fluctuations is also markedly larger in the MHD solution. We show that the MHD model can deliver more reasonable results at Earth with an ad hoc adjustment of the inner boundary values. However, we conclude that the MHD model using the inner boundary conditions derived from kinematic simulations has little chance to match IPS and in situ data as well as the kinematic model does unless it too is iteratively fit to the observational data and measurements.

Composition and magnetic structure of interplanetary coronal mass ejections at 1 AU

We report extensive interplanetary scintillation (IPS) observations of the solar wind during the period centered around 11 May 1999, when the Earth was engulfed by a region of solar wind with unusually low densities (&lt;1 cm−3) and velocities (&lt;350 km s−1). IPS observations with the Ooty Radio Telescope (ORT), operating at 327 MHz, probe the inner heliosphere along a large number of closely spaced lines of sight over the heliocentric distance range of 0.2 to 1.0 AU, daily, at the rate of about 150 sources in the course of 10 hours. Using these observations, the southern half of the inner heliosphere was monitored everyday between 3 and 16 May 1999. The data show that the solar wind densities were globally subdued, having started subsiding from 3 May 1999, itself at different parts of the heliosphere. This was accompanied by a noticeable decrease in the velocity of the general solar wind also. The IPS data also reveal a small subset of closely spaced sources lying to the west of the Sun that show a steep drop in inferred densities to immeasurably low amounts on and around the 11th May. The actual morphology of the subsidence event, from our observations, is shown to be that of a “void‐within‐a‐void”. The role of the polar magnetic field reversal that was taking place between Carrington rotations 1947–1954, which may have played a key role in generating the subsidence event, is also examined. To the best of our knowledge this is the first time that sustained levels of low densities and velocities have been recorded for such a long period over a large part of the inner heliosphere. Some possible signatures of high energy “strahl” electrons were also recorded in this period.

The propagation properties of coronal mass ejections (CMEs) are crucial to predict its geomagnetic effect. A newly developed three dimensional (3D) mask fitting reconstruction method using coronagraph images from three viewpoints has been described and applied to the CME ejected on August 7, 2010. The CME's 3D localisation, real shape and morphological evolution are presented. Due to its interaction with the ambient solar wind, the morphology of this CME changed significantly in the early phase of evolution. Two hours after its initiation, it was expanding almost self-similarly. CME's 3D localisation is quite helpful to link remote sensing observations to in situ measurements. The investigated CME was propagating to Venus with its flank just touching STEREO B. Its corresponding ICME in the interplanetary space shows a possible signature of a magnetic cloud with a preceding shock in VEX observations, while from STEREO B only a shock is observed. We have calculated three principle axes for the reconstructed 3D CME cloud. The orientation of the major axis is in general consistent with the orientation of a filament (polarity inversion line) observed by SDO/AIA and SDO/HMI. The flux rope axis derived by the MVA analysis from VEX indicates a radial-directed axis orientation. It might be that locally only the leg of the flux rope passed through VEX. The height and speed profiles from the Sun to Venus are obtained. We find that the CME speed possibly had been adjusted to the speed of the ambient solar wind flow after leaving COR2 field of view and before arriving Venus. A southward deflection of the CME from the source region is found from the trajectory of the CME geometric center. We attribute it to the influence of the coronal hole where the fast solar wind emanated from.

[1] We analyze the dynamics of interplanetary coronal mass ejections (ICMEs) through the interplanetary medium from the lower solar corona to ∼5.3 AU. Our analysis uses a one-dimensional hydrodynamical model derived from the fluid equation of motion that considers an effective drag force under both the laminar and turbulent hypotheses (low and high Reynolds number, respectively). The model has three sets of input parameters. The first set is related to the ICME itself, i. e., initial speed and mass; the second set of parameters is related to the ambient solar wind: density and velocity; and the final set corresponds to the ambient solar wind–ICME interaction: an ICME expansion factor and a viscosity or drag parameter. We use this model to explain the radial dynamics of a particular ICME detected at three different locations: close to the Sun, where the ICME was ejected on 20 January 2004, and detected by the SOHO/LASCO coronagraphs; two days later, at Earth's L1 by the ACE spacecraft (∼1.0 AU), and finally, ∼14 days later, at ∼5.3 AU by the Ulysses spacecraft near Jupiter's orbit. The model is then compared to a general set of ICMEs data from Ulysses that cover distances from ∼1.3 AU to ∼5.3 AU. Our model successfully reproduces the dynamical behavior of ICMEs at distances near Earth's orbit and works reasonably well at larger distances ≈5.3 AU. Therefore, our analysis shows that the ICME - solar wind interaction may be treated as a drag interaction with the appropriate drag factors, not only at distances ≤1 AU, but at larger distances. Finally, we show that our model is useful in identifying ICMEs at different heliocentric distances.

This paper discusses small solar wind transients (STs) from 1995 to 2014. Using STEREO data, we have more sites from which to study STs near 1 AU. STEREO measurements are compared with wind observations near the Sun‐Earth line. We examined statistically the dependence of ST occurrence frequency on (i) solar cycle phase, as monitored by the sunspot number (SSN), and (ii) solar wind speed. We find dependencies on both: an anticorrelation with SSN, an opposite trend to that of interplanetary coronal mass ejections (ICMEs), and correlation with slow solar wind (over 80% in the slow wind). We compare ST distributions during solar maximum year 2003, which had the lowest percentage of slow wind, and minimum year 2009, which had the highest percentage thereof, and show evidence of both dependencies. We give a statistical overview of ST parameters: field strength, B, Alfvén Mach number, MA, and proton beta, βp. They show the same temporal trends as the ambient solar wind but have twice (B) or one half (MA, βp) of its average values. In STs, the proton temperature is not below the temperature expected from corotating solar wind expansion. Non‐force free models should be used in solar minimum years where βplasma≈ 1, while the force free models could be used in solar maximum when βplasma&lt;&lt;1. We find that only ∼5% of STs show enhanced values of iron charge states. Our work further supports the two‐source origin of STs, i.e., the solar corona and the interplanetary medium.

In this study, we evaluate a coronal mass ejection (CME) arrival prediction tool that utilizes the wide‐angle observations made by STEREO's heliospheric imagers (HI). The unsurpassable advantage of these imagers is the possibility to observe the evolution and propagation of a CME from close to the Sun out to 1 AU and beyond. We believe that by exploiting this capability, instead of relying on coronagraph observations only, it is possible to improve today's CME arrival time predictions. The ELlipse Evolution model based on HI observations (ELEvoHI) assumes that the CME frontal shape within the ecliptic plane is an ellipse and allows the CME to adjust to the ambient solar wind speed; that is, it is drag based. ELEvoHI is used to perform ensemble simulations by varying the CME frontal shape within given boundary conditions that are consistent with the observations made by HI. In this work, we evaluate different setups of the model by performing hindcasts for 15 well‐defined isolated CMEs that occurred when STEREO was near L4/5, between the end of 2008 and the beginning of 2011. In this way, we find a mean absolute error of between and hr depending on the model setup used. ELEvoHI is specified for using data from future space weather missions carrying HIs located at L5 or L1. It can also be used with near‐real‐time STEREO‐A HI beacon data to provide CME arrival predictions during the next 7 years when STEREO‐A is observing the Sun‐Earth space.

During its passage through the high‐latitude heliosphere, Ulysses observed interplanetary coronal mass ejections (ICMEs) bounded by shocks. These forward‐reverse shock pairs have only been observed at high latitude in the fast solar wind. It has been suggested (e.g., Gosling et al., 1995) that these shock pairs are the result of expansion of coronal mass ejections into the ambient solar wind, so‐called “overexpansion”. Here we demonstrate an alternative explanation for forward‐reverse shock pairs by means of a three‐dimensional numerical magnetohydrodynamics (MHD) model of a CME interacting with the solar wind. Our global steady state coronal model possesses fast and slow speed solar wind at high and low latitudes, respectively, reminiscent of near solar minimum conditions. Within this model system, a CME erupts from the coronal streamer belt with an initial speed in excess of 1000 km/s, which naturally drives a forward shock into the ambient solar wind. When the CME is greater than 40 R⊙ from the Sun, we find that a reverse shock forms poleward of the CME as a result of the interaction of the CME with the solar wind. In front of the CME, the slow wind is deflected to higher latitude while behind the CME, fast wind is deflected to low latitude. These deflected streams collide to form a reverse shock. The shock pair formed in this way naturally occurs at high latitude in the fast wind as observed. We will discuss these model results in the context of in situ solar wind data.

We present the first observational evidence of the near-Sun distortion of the leading edge of a coronal mass ejection (CME) by the ambient solar wind into a concave structure. On 2007 November 14, a CME was observed by coronagraphs onboard the STEREO-B spacecraft, possessing a circular cross section. Subsequently the CME passed through the field of view of the STEREO-B Heliospheric Imagers where the leading edge was observed to distort into an increasingly concave structure. The CME observations are compared to an analytical flux rope model constrained by a magnetohydrodynamic solar wind solution. The resultant bimodal speed profile is used to kinematically distort a circular structure that replicates the initial shape of the CME. The CME morphology is found to change rapidly over a relatively short distance. This indicates an approximate radial distance in the heliosphere where the solar wind forces begin to dominate over the magnetic forces of the CME influencing the shape of the CME.