TY - JOUR

T1 - Effects of Thomson-scattering geometry on white-light imaging of an interplanetary shock

T2 - synthetic observations from forward magnetohydrodynamic modelling

AU - Xiong, Ming

AU - Davies, J. A.

AU - Bisi, M. M.

AU - Owens, M. J.

AU - Fallows, R. A.

AU - Dorrian, G. D.

PY - 2013/7

Y1 - 2013/7

N2 - Stereoscopic white-light imaging of a large portion of the inner heliosphere has been used to track interplanetary coronal mass ejections. At large elongations from the Sun, the white-light brightness depends on both the local electron density and the efficiency of the Thomson-scattering process. To quantify the effects of the Thomson-scattering geometry, we study an interplanetary shock using forward magnetohydrodynamic simulation and synthetic white-light imaging. Identifiable as an inclined streak of enhanced brightness in a time-elongation map, the travelling shock can be readily imaged by an observer located within a wide range of longitudes in the ecliptic. Different parts of the shock front contribute to the imaged brightness pattern viewed by observers at different longitudes. Moreover, even for an observer located at a fixed longitude, a different part of the shock front will contribute to the imaged brightness at any given time. The observed brightness within each imaging pixel results from a weighted integral along its corresponding ray-path. It is possible to infer the longitudinal location of the shock from the brightness pattern in an optical sky map, based on the east-west asymmetry in its brightness and degree of polarisation. Therefore, measurement of the interplanetary polarised brightness could significantly reduce the ambiguity in performing three-dimensional reconstruction of local electron density from white-light imaging.

AB - Stereoscopic white-light imaging of a large portion of the inner heliosphere has been used to track interplanetary coronal mass ejections. At large elongations from the Sun, the white-light brightness depends on both the local electron density and the efficiency of the Thomson-scattering process. To quantify the effects of the Thomson-scattering geometry, we study an interplanetary shock using forward magnetohydrodynamic simulation and synthetic white-light imaging. Identifiable as an inclined streak of enhanced brightness in a time-elongation map, the travelling shock can be readily imaged by an observer located within a wide range of longitudes in the ecliptic. Different parts of the shock front contribute to the imaged brightness pattern viewed by observers at different longitudes. Moreover, even for an observer located at a fixed longitude, a different part of the shock front will contribute to the imaged brightness at any given time. The observed brightness within each imaging pixel results from a weighted integral along its corresponding ray-path. It is possible to infer the longitudinal location of the shock from the brightness pattern in an optical sky map, based on the east-west asymmetry in its brightness and degree of polarisation. Therefore, measurement of the interplanetary polarised brightness could significantly reduce the ambiguity in performing three-dimensional reconstruction of local electron density from white-light imaging.

KW - White-light imaging

KW - Thomson scattering

KW - Polarisation brightness

KW - Interplanetary shock

KW - CORONAL MASS EJECTIONS

KW - REMOTE-SENSING OBSERVATIONS

KW - MAGNETIC CLOUD

KW - SOLAR-WIND

KW - GEOMAGNETIC-ACTIVITY

KW - HELIOSPHERIC IMAGER

KW - STEREO MISSION

KW - ALFVEN WAVES

KW - 1 AU

KW - SCINTILLATION

U2 - 10.1007/s11207-012-0047-0

DO - 10.1007/s11207-012-0047-0

M3 - Journal article

VL - 285

SP - 369

EP - 389

JO - Solar Physics

JF - Solar Physics

SN - 0038-0938

IS - 1

ER -