ARRIVAL TIME CALCULATION FOR INTERPLANETARY CORONAL MASS EJECTIONS WITH CIRCULAR FRONTS AND APPLICATION TOSTEREOOBSERVATIONS OF THE 2009 FEBRUARY 13 ERUPTION

Abstract

One of the goals of the NASA Solar TErestrial RElations Observatory (STEREO) mission is to study the feasibility of forecasting the direction, arrival time, and internal structure of solar coronal mass ejections (CMEs) from a vantage point outside the Sun-Earth line. Through a case study, we discuss the arrival time calculation of interplanetary CMEs (ICMEs) in the ecliptic plane using data from STEREO/SECCHI at large elongations from the Sun in combination with different geometric assumptions about the ICME front shape [fixed-Φ (FP): a point and harmonic mean (HM): a circle]. These forecasting techniques use single-spacecraft imaging data and are based on the assumption of constant velocity and direction. We show that for the slow (350 km s −1 ) ICME on 2009 February 13-18, observed at quadrature by the two STEREO spacecraft, the results for the arrival time given by the HM approximation are more accurate by 12 hr than those for FP in comparison to in situ observations of solar wind plasma and magnetic field parameters by STEREO/IMPACT/PLASTIC, and by 6 hr for the arrival time at Venus Express (MAG). We propose that the improvement is directly related to the ICME front shape being more accurately described by HM for an ICME with a low inclination of its symmetry axis to the ecliptic. In this case, the ICME has to be tracked to >30 • elongation to obtain arrival time errors <± 5 hr. A newly derived formula for calculating arrival times with the HM method is also useful for a triangulation technique assuming the same geometry.

Assessing the Effect of Spacecraft Motion on Single-Spacecraft Solar Wind Tracking Techniques

“…This diagram follows the notation used by Davies et al (2012) and Möstl et al (2011) and uses d 0 instead of r sc .…”

A probabilistic approach to the drag-based model

“…Such an approach leads to analytical models or empirical models which require modest computational power. Those models assume a morphology (either simple as in Möstl et al (2011) or more complex as in Isavnin (2016)), a fixed direction and a velocity evolution for the CME and can predict an arrival time and speed from relatively limited initial information on the CME onset conditions. Such initial conditions can be obtained from several sources, such as LASCO C2 and C3 coronal imagers on-board the SOlar and Heliospheric Observatory ( SOHO Domingo et al, 1995) and, more recently, from COR1 and COR2 and the Heliospheric imager (HI) on-board the Solar Terrestrial Relation Observatory ( STEREO Kaiser et al, 2008) spacecraft either separately or using appropriate tools to merge the measures taken from the different instruments and the different points of view (Lugaz et al, 2009;Davies et al, 2012;Möstl and Davies, 2013;Möstl et al, 2014).…”

A Self-Similar Expansion Model for Use in Solar Wind Transient Propagation Studies

“…Initially, we compare results of analyses based on two such techniques, which are often used to derive the propagation characteristics of solar wind transients from their time-elongation profiles in single-spacecraft heliospheric imaging observations from the STEREO/HI and Coriolis/SMEI instruments. Both of these methods, namely fixed φ fitting (FPF; Rouillard et al 2008;Sheeley et al 2008) and harmonic mean fitting (HMF; Lugaz 2010;Möstl et al 2011), are based on the exploitation of a simple geometrical concept, originally recognized by Sheeley et al (1999): an observer viewing a solar wind transient propagating radially away from the Sun out to large elongations at a constant speed will perceive a nonlinear time-elongation profile, the shape of which will depend on the radial speed and the propagation direction relative to the Sun-observer line. In light of this geometrical effect, the time-elongation profile of a solar wind transient viewed from a single vantage point can be analyzed to retrieve best-fit estimates of the propagation direction and radial speed.…”

“…of interest (often corresponding to the ecliptic plane) can be described by a propagating point source (the fixed φ, FP, model; e.g., Kahler & Webb 2007;Rouillard et al 2008;Sheeley et al 2008). In the HMF technique, however, the transient cross section in that plane is assumed to take the form of an expanding circle anchored to Sun center by a point on its circumference (the harmonic mean, HM, model; e.g., Lugaz et al 2009; Lugaz For a much more detailed discussion of the FPF and HMF techniques and their application, the reader is directed to Möstl et al (2011) and references therein (note that the nomenclature used by Möstl et al 2011 is also adopted here), although the basic principles are noted below. The radial distance from the center of the Sun, R FP , of a pointlike transient propagating radially outward from the Sun at an angle φ relative to an observer situated at a distance d 0 from the Sun, which is observed at a time t and along an elongation (see Figure 1 …”