FIG. 8.— Top panels: CME morphology observed from COR2-A, C3, and COR2-B respectively at 10:54UT on April 11, 2013. Bottom panels: Overplot of the best fitted wireframe of MFR in GCS model. Note that in C3 the CME is halo directed toward Earth, whereas it directs away from COR-A on farside. Note the GCS parameters \( \gamma \) = −45o, \( _ \alpha \) = 50o, κ = 0.45 and \( h = 1 7 . 5 R _ { \odot } \) reproduce this CME morphology.

extremely difficult. However, to examine the effect of uncer-tainties in the estimated kinematics, we considered an error of 5 pixels in the measurements of elongation angle. Such an error corresponds to uncertainties of 0.02 degree, 0.1 degree and 0.35 degree in the derived elongation angles in COR2, HI1 and HI2 FOV, respectively. Corresponding to these elon-gation uncertainties, the calculated error for SSSE (with \( \lambda \) = 0) method maximally reaches up to \( 0 . 5 R _ { \odot } \) in distance, less than few degree in direction and few tens of km/s for speed. These errors certainly seem to be small but of course, they do not reflect the total error in derived kinematics. Further study is required to quantify the actual errors because of several in-valid idealistic assumptions in the methods.

Also, at higher elongation (greater than approx. \( 4 0 R _ { \odot } \)),larger variations in the estimated kinematics from SSSE method for different \( \lambda \) are noted. From Figure 11, it is clear that the estimated distance from GT method increased around 18:00 UT on April 11 at \( 9 0 R _ { \odot } \) from the Sun. Such an un-physically fast increase in distance and speed is meaningless due to the absence of forces capable of accounting for this acceleration at distances farther from the Sun (Cargill 2004;Vršnak et al. 2010). This is more likely because of improper use of SSSE with \( \lambda \) equal to 0 \( r \)(i.e. GT) method, especially for this CME which is propagating away from the observer. This late acceleration is significantly reduced (still unphysi-cal) if a higher value of \( \lambda \) is considered. SSSE with \( \lambda \) equal to \( 9 0 ^ { o } \)(i.e. TAS) method gives the lowest limit of the esti-mated distance and speed values. The kinematics from the TAS method is calculated up to \( 3 6 5 R _ { \odot } \) from the Sun.

The aforementioned facts highlight that the assumptions made in the GT method are not valid for a CME propagat-ing away from the observer. Also, the spherical front approx-imation in SSSE method with \( \lambda \) equal to nonzero value, be-comes worse due to flattening of the CME front on its inter-action with solar wind. These limitations start to play a cru-cial role much nearer to the Sun for a far-sided CME than for front sided CME (Liu et al. 2013). However, the distance be-yond which these effects are crucial depends on the direction of propagation of the CME and its size. We note that for a CME propagating at larger angle from the Sun-observer line, its kinematics depend more on the chosen value of \( \lambda \). This is because the flanks (not nose) for such CMEs are always ob-served from the observer and even a little change in its radius of curvature leads to huge difference in the estimated kine-matics from the SSSE method. It is noted that if direction of propagation of a CME from sun-observer line becomes more than 90 \( \gamma o \), an unphysical acceleration will be estimated from the SSSE methods irrespective of chosen \( \lambda \) value. However, such an acceleration is reduced with higher value of \( \lambda \) and gives more accurate kinematics.

To assess the relative performance, we also applied single spacecraft reconstruction methods on STEREO-A and B ob-servations. We employed the Fixed-Phi (FP: Kahler & Webb 2007), Harmonic Mean (HM: Lugaz et al. 2009), Self-Similar Expansion (SSE: Davies et al. 2012) methods on the derived time-elongation variations of the CME (Figure 10). These