White-Light Mass Determination and Geometrical Modelling of Coronal Mass Ejections [thesis]

Pluta Adam Martin
Coronal Mass Ejections (CMEs) are explosive large-scale outbursts of the Sun's coronal plasma and magnetic field. They can induce strong geomagnetic storms at Earth, which pose serious threats to space systems, communications and navigation. Hence, arrival predictions of CMEs are of special interest to the humane society. Such predictions require a meticulous analysis of CME properties in the earliest possible stage. Coronagraph observations can provide important insights into the CME
more » ... , morphology and mass at CME distances of only a few solar radii away from the Sun. However, the 3-dimensional structure of CMEs can only by analysed, based on their 2-dimensional projection in coronagraph images, which means that they are affected by projection effects. This thesis has the goal to present the state-of-the-art methods of CME parameterisation derived from coronagraph observations and to discuss arising issues resulting from projection effects. A focus is laid on the measurements of the CME mass and morphology as well as the question under which conditions they can be determined with highest accuracy. Further, the solar mass loss caused by CMEs is investigated. Also, CME mass determination is currently not feasible in real-time and therefore not applicable in actual terrestrial CME arrival predictions. Thus, it is discussed how the CME mass and the CME morphology can be empirically estimated from the CME speed. The thesis presents a new combined method which enables the measurement of relevant CME kinematics, morphology and mass in a consistent and comparable manner. The two vantage points of the COR2 coronagraphs onboard of the twin NASA STEREO spacecraft are used to apply the method to a set of 122 events with intense brightness. The modelling results are analysed to derive empirical correlations with the CME speed. Further, a CME propagation model -the Drag-Based Model (DBM) -is combined with the GCS model to predict the CME arrival of a sample event at Earth. It is shown that the largest CME parameterisation uncertainties arise for events emerging from close to the disk centre towards or away from the observer. For these events the term "disk events" is adopted. If an event is seen as disk event in both coronagraphs, the CME morphology can be overestimated by up to a factor of two from stereoscopical modelling. Equally the CME mass of disk events can be overestimated by a factor of 10 and more in the case of overlapping coronal streamers. Therefore, stereoscopical measurements of disk events are not always reliable, at least under a very active background corona. Though, the CME mass M can be estimated from the initial apex velocity v apex with the empirically derived equation This result is used to predict the terrestrial CME arrival of a CME with an Earth-directed initial speed of 1172 km/s with the GCS plus DBM model. The CME arrival time and the arrival speed are both strongly affected by the solar wind density and CME mass. For the presented case the arrival prediction limits spread to ∆T = 59 h and ∆v = 748 km/s for typical CME mass and solar wind values. It is demonstrated that the derived empirical equation can be very valuable to improve the arrival prediction accuracy. v "Modern society is becoming ever increasingly dependent on space technology for daily routine functions, such as communication, ship and satellite navigation, data transmission, global surveillance of resources, and atmospheric weather. However, if a Carrington-type storm (or a greater intensity one) were to occur now, it could cause much more damage to society than in 1859 when the telegraph (Boteler, 2006) was the latest technology of the time. Therefore, it is crucial to have knowledge about the occurrence of extreme events, and their causes in order to assess their possible impacts on society" -Lakhina & Tsurutani (2016)
doi:10.53846/goediss-7222 fatcat:djdpfjydp5dqnbxrhrb2wnvqfy