Assessing the Constrained Harmonic Mean Method for Deriving the Kinematics of ICMEs with a Numerical Simulation

In this study we use a numerical simulation of an artificial coronal mass ejection (CME) to validate a method for calculating propagation directions and kinematical profiles of interplanetary CMEs (ICMEs). In this method observations from heliospheric images are constrained with in-situ plasma and field data at 1 AU. These data are used to convert measured ICME elongations into distance by applying the Harmonic Mean approach that assumes a spherical shape of the ICME front. We use synthetic white-light images, similar as observed by STEREO-A/HI, for three different separation angles between remote and in-situ spacecraft, of 30{\deg}, 60{\deg}, and 90{\deg}. To validate the results of the method they are compared to the apex speed profile of the modeled ICME, as obtained from a top view. This profile reflects the "true" apex kinematics since it is not affected by scattering or projection effects. In this way it is possible to determine the accuracy of the method for revealing ICME propagation directions and kinematics. We found that the direction obtained by the constrained Harmonic Mean method is not very sensitive to the separation angle (30{\deg} sep: \phi = W7; 60{\deg} sep: \phi = W12; 90{\deg} sep: \phi = W15; true dir.: E0/W0). For all three cases the derived kinematics are in a relatively good agreement with the real kinematics. The best consistency is obtained for the 30{\deg} case, while with growing separation angle the ICME speed at 1 AU is increasingly overestimated (30{\deg} sep: \Delta V_arr ~-50 km/s, 60{\deg} sep: \Delta V_arr ~+75 km/s, 90{\deg} sep: \Delta V_arr ~+125 km/s). Especially for future L4/L5 missions the 60{\deg} separation case is highly interesting in order to improve space weather forecasts.Comment: accepted for publication in Solar Physic

Influence of the ambient solar wind flow on the propagation behavior of interplanetary CMEs

We study three CME/ICME events (2008 June 1-6, 2009 February 13-18, 2010 April 3-5) tracked from Sun to 1 AU in remote-sensing observations of STEREO Heliospheric Imagers and in situ plasma and magnetic field measurements. We focus on the ICME propagation in IP space that is governed by two forces, the propelling Lorentz force and the drag force. We address the question at which heliospheric distance range the drag becomes dominant and the CME gets adjusted to the solar wind flow. To this aim we analyze speed differences between ICMEs and the ambient solar wind flow as function of distance. The evolution of the ambient solar wind flow is derived from ENLIL 3D MHD model runs using different solar wind models, namely Wang-Sheeley-Arge (WSA) and MHD-Around-A-Sphere (MAS). Comparing the measured CME kinematics with the solar wind models we find that the CME speed gets adjusted to the solar wind speed at very different heliospheric distances in the three events under study: from below 30 Rs, to beyond 1 AU, depending on the CME and ambient solar wind characteristics. ENLIL can be used to derive important information about the overall structure of the background solar wind, providing more reliable results during times of low solar activity than during times of high solar activity. The results from this study enable us to get a better insight into the forces acting on CMEs over the IP space distance range, which is an important prerequisite in order to predict their 1 AU transit times.Comment: accepted for publication in Ap

Characteristics of Kinematics of a Coronal Mass Ejection during the 2010 August 1 CME-CME Interaction Event

We study the interaction of two successive coronal mass ejections (CMEs) during the 2010 August 1 events using STEREO/SECCHI COR and HI data. We obtain the direction of motion for both CMEs by applying several independent reconstruction methods and find that the CMEs head in similar directions. This provides evidence that a full interaction takes place between the two CMEs that can be observed in the HI1 field-of-view. The full de-projected kinematics of the faster CME from Sun to Earth is derived by combining remote observations with in situ measurements of the CME at 1 AU. The speed profile of the faster CME (CME2; ~1200 km/s) shows a strong deceleration over the distance range at which it reaches the slower, preceding CME (CME1; ~700 km/s). By applying a drag-based model we are able to reproduce the kinematical profile of CME2 suggesting that CME1 represents a magnetohydrodynamic obstacle for CME2 and that, after the interaction, the merged entity propagates as a single structure in an ambient flow of speed and density typical for quiet solar wind conditions. Observational facts show that magnetic forces may contribute to the enhanced deceleration of CME2. We speculate that the increase in magnetic tension and pressure, when CME2 bends and compresses the magnetic field lines of CME1, increases the efficiency of drag.Comment: accepted for Ap

Propagation direction and kinematics of Coronal Mass Ejections in the Heliosphere

Das Ziel dieser Diplomarbeit ist die Untersuchung von Kinematik und Ausbreitungsrichtung von koronalen Massenausw\ufcrfen der Sonne (?coronal mass ejections - CMEs?) bis zu einer Entfernung von 1 AU (?astronomische Einheit?, mittlerer Abstand zwischen Erde und Sonne). Mit Hilfe der verwendeten Methoden sollen Modelle entwickelt werden, um die Ankunftszeit von m\uf6glichen geoeffektiven CMEs bei der Erde besser vorherzusagen. F\ufcr diese Analyse wurden Daten der NASA Mission Solar TERrestrial RElations Observatory (STEREO) herangezogen. Die STEREO Mission besteht aus zwei nahezu identischen Satelliten, durch deren Beobachtungen R\ufcckschl\ufcsse auf die dreidimensionale Struktur und die Kinematik von CMEs gezogen werden k\uf6nnen. Mit Hilfe der ?Heliospheric Imager (HI)?, welche Teil der SECCHI Instrumente von STEREO sind, ist es erstmals m\uf6glich, den gesamten Bereich von der Sonne bis zur Erde zu beobachten. Durch die neue Methode der Verkn\ufcpfung von Fernerkundungsdaten und in situ Daten von STEREO und Wind lassen sich durch die dadurch bekannte Ankunftszeit des interplanetaren CMEs (ICME) die Ausbreitungsrichtung sowie die Kinematik bestimmen. Das erste Kapitel dieser Diplomarbeit soll die Motivation der Arbeit beschreiben und im zweiten Kapitel werden einige grundlegende Begriffe erl\ue4utert. Die STEREO?Mission und ihre verschiedenen Instrumente ? vor allem die ?Heliospheric Imager? werden im 3. Kapitel vorgestellt. Das 4. Kapitel beschreibt die Reduktion der Daten, die Erzeugung von Jplots (?time?elongation plots?) und die weitere Auswertung der Messergebnisse. Die beiden verwendeten Methoden zur Umrechnung von der gemessenen Auslenkung von ICMEs in Grad in lineare Distanzen werden hergeleitet und erkl\ue4rt (Fixed?Phi, Harmonic Mean). Als letzter Punkt wird die ?Sheeley?elongation?fitting? Methode beschrieben, mit der die Resultate verglichen wurden. Die Ergebnisse der drei untersuchten ICMEs werden in Kapitel 5 gezeigt.The aim of this thesis is to investigate the kinematics and propagation directions of Coronal Mass Ejections (CMEs) up to a distance of 1 AU (?astronomical unit?, distance from Sun to Earth). This should lead to develop adequate methods to predict the arrival times of Earth directed CMEs. The STEREO mission consists of two similar satellites that offer the possibility to observe CMEs from two different vantage points. The ?Heliospheric Imager? onboard both STEREO satellites enable for the first time remote sensing in white light all over the way from Sun to Earth. It is a new approach to combine remote observations and in situ data of the NASA mission Solar TERrestrial RElations Observatory (STEREO) and Wind to constrain the arrival time of ICMEs and to derive their kinematics and propagation directions. Chapter 1 describes the motivation of investigating CMEs, in Chapter 2 the basic terms and definitions are illustrated. Data sources ? especially of STEREO HI data but also the in situ data sources are described in Chapter 3. Chapter 4 is about the data handling and describes the data reduction as well as the process to construct time?elongation plots (Jplots). The methods applied to convert the measured elongation angles into distances from Sun (Fixed?Phi and Harmonic Mean) are deduced from geometrical conditions. In addition we compare our results to the Sheeley?elongation?fitting method that is described in the end of this Chapter. The results of three investigated ICMEs are presented in Chapter 5.Tanja RollettAbweichender Titel laut cbersetzung der Verfasserin/des VerfassersZsfassung in dt. SpracheGraz, Univ., Dipl.-Arb., 201

Evolution of coronal mass ejections and their heliospheric imprints

Koronale Massenausw\ufcrfe (engl. coronal mass ejections, \u201eCMEs\u201c) sind die st\ue4rksten Ausbr\ufcche der Sonne, k\uf6nnen Geschwindigkeiten von mehr als 3000 km/s erreichen und geomagnetische St\ufcrme verursachen, wenn sie mit dem Erdmagnetfeld wechselwirken. Die Ausbreitung von CMEs ist noch nicht restlos gekl\ue4rt. Wechselwirkung mit dem Sonnenwind und anderen CMEs erschweren zuverl\ue4ssige Vorhersagen. Die \u201eConstrained Harmonic Mean (CHM)\u201c Methode kombiniert Wei flichtbeobachtungen von STEREO/HI mit in situ Messungen und erm\uf6glicht es, kinematische Profile von CMEs zu erstellen. Mit Hilfe dieser Profile wurde der Einfluss des Sonnenwindes auf die Ausbreitung von CMEs untersucht, indem die Geschwindigkeiten von CME und Sonnenwind verglichen wurden. Das Ergebnis zeigt eine hohe Abh\ue4ngigkeit der CME Geschwindigkeit von der des umgebenden Sonnenwindes. Ein Test \ufcber die Zuverl\ue4ssigkeit der CHM Methode wurde mithilfe von simulierten STEREO/HI Beobachtungen eines CMEs durchgef\ufchrt. Das Resultat zeigt, dass sich die Methode am besten f\ufcr Beobachtungen eignet, bei denen die Positionen der Satelliten nicht weit von einander entfernt liegen. Eine Studie \ufcber einen besonders schnellen CME, der von zwei Satelliten im Wei flicht und von vier Satelliten in situ beobachtet wurde, zeigt eine unterschiedlich schnelle Ausbreitung von verschiedenen Teilen des selben CMEs und eine daraus resultierende Verformung. Die pr\ue4sentierten Studien zeigen die starke Abh\ue4ngigkeit der CMEs vom umgebenden Sonnenwind. Auch die Wechselwirkung mit anderen CMEs beeinflusst ihre Ausbreitung massiv und f\ufchrt zu einer \uc4nderung ihrer Ankunftszeit bei der Erde und ihrer Geoeffektivit\ue4t.Coronal mass ejections (CMEs) are the most powerful eruptions on the Sun and can reach speeds up to more than 3000 km/s. CMEs are the most important drivers of space weather and can cause geomagnetic storms when interacting with the Earth magnetosphere.The evolution and propagation of CMEs in interplanetary space is still not well understood. Interactions with the solar wind as well as other CMEs make accurate forecasting of arrival times difficult. The Constrained Harmonic Mean (CHM) method combines remote sensing white light data of STEREO/HI with in situ data and offers the possibility to derive kinematical profiles for any segment along the CME front to study its evolution in interplanetary space. We studied the influence of the ambient solar wind flow on the propagation behavior for three CME events. The kinematics revealed by the CHM method were compared to the simulated background solar wind. We found that CMEs are highly dependent on speed variations of the ambient medium. The CHM method was tested by analyzing a simulated CME as observed by STEREO/HI. After applying the CHM method, the resulting CME kinematics were compared to the real kinematics of the simulated CME. We found that the CHM method works best for small separation angles between the spacecraft. A case study of a fast CME that has been remotely observed by both STEREO/HI and in situ measured by four spacecraft at different heliocentric distances is also presented. Using this high number of in situ detections and the two side views we derived different speed profiles for the two different segments of the same CME causing a deformation of the overall structure of the CME. The studies presented show the effects of different influences of the ambient solar wind on the CME evolution. Interaction of CMEs with the solar wind or other CMEs lead to disturbances of the speed as well as the shape of CMEs, affecting their arrival time and their geoeffectivity.Tanja RollettAbweichender Titel laut cbersetzung der Verfasserin/des VerfassersZsfassung in dt. und engl. SpracheGraz, Univ., Diss., 2014 2.165

Strong coronal channelling and interplanetary evolution of a solar storm up to Earth and Mars

The severe geomagnetic effects of solar storms or coronal mass ejections (CMEs) are to a large degree determined by their propagation direction with respect to Earth. There is a lack of understanding of the processes that determine their non-radial propagation. Here we present a synthesis of data from seven different space missions of a fast CME, which originated in an active region near the disk centre and, hence, a significant geomagnetic impact was forecasted. However, the CME is demonstrated to be channelled during eruption into a direction + 37+/-10 degree (longitude) away from its source region, leading only to minimal geomagnetic effects. In situ observations near Earth and Mars confirm the channelled CME motion, and are consistent with an ellipse shape of the CME-driven shock provided by the new Ellipse Evolution model, presented here. The results enhance our understanding of CME propagation and shape, which can help to improve space weather forecasts.Comment: 6 figures, published in Nature Communications as open acces