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Using "ghost front" to predict the arrival time and speed of CMEs at Venus and Earth
Using in-situ measurements and remote-sensing observations, we study two Coronal Mass Ejections
(CMEs) that left the Sun on 13-14 June 2012 and impacted both Venus and Earth while the planets
were in close radial alignment. The two CMEs generate multiple fronts in STEREO/HI images,
which can also be observed in ‘J-map’ as bifurcated features. We present the ‘ghost front’ model to
combine remote observations from STEREO/SECCHI and in-situ observations from the Wind and
VEX spacecraft, and to derive the kinematics and propagation directions of the CMEs. By fitting the
observations of multiple fronts to a kinematically evolving flux rope (KEFR) model and assuming the
CMEs undergo deceleration through frictional drag with a steady-state solar wind, we confirm that
the outer and inner fronts of the CMEs as detected in HI images are consistent with peaks in Thomson
scattered light returned from the flank and nose of a single front for each CME. An interaction takes
place between the CME-1 and CME-2 that can be observed in the HI-1 field of view before CME-1
encounters Venus. The multi-point in-situ observations of the shock-CME interaction event serve as
further evidence of the interaction between CMEs. The arrival times calculated from the ghost-front
model are within 2.5 hours of those observed at VEX and Wind. Our analysis indicates that ghost
fronts could provide information about the longitudinally-extended shape of the CME in the field of
view of HI-1, which can be used to improve the forecast of ICME arrival time at Earth