Research Highlights
Research Motivation
The Sun has been observed continuously shedding mass and magnetic flux from its outer atmosphere via the ubiquitous quasi-steady solar wind and episodic coronal mass ejections (CMEs). CMEs are large-scale plasma blobs expelled from the Sun that are understood as flux ropes that maintain their connection to the Sun while propagating in the ambient solar wind medium in the heliosphere. In addition to CMEs, corotating interaction regions (CIRs) and the supersonic solar wind govern the distribution of waves, turbulence, and dynamic pressure in the heliosphere. CMEs constitute the primary sources of variability in the space environment (i.e., space weather) around Earth and other planets in the heliosphere. Investigation of physical processes inside the Sun, CMEs, CIRs, solar activity cycle, heliosphere, and the space surrounding the Earth (i.e., magnetosphere, ionosphere, and thermosphere of the Earth) are key topics of research for solar-terrestrial physicists. Further, solar observations with a very high spatial resolution allow us to better understand phenomena in other solar-type stars and around the planets these stars host.
Research Highlights
Continuous tracking of CMEs using coronagraphic and heliospheric imaging (HI) observation from NASA's STEREO mission
Tracking of CMEs using wide-angle imaging observations helps to understand the CME acceleration and deceleration beyond the COR2 FOV and the role of the ambient solar wind in shaping CMEs kinematics.
J-maps constructed from STEREO/COR and heliospheric imager (HI) observations provide an opportunity to understand the heliospheric evolution of CMEs in general.
CME-CME interaction and its effect on plasma parameters of CMEs and their arrival time at Earth
To estimate the true kinematics of successive CMEs of 25 and 28 September 2012 (i.e., CME1 and CME2), 3D reconstruction of CMEs is done using the GCS model on the contemporaneous images from SECCHI/COR2-B, SOHO/LASCO and SECCHI/COR2-A.
CMEs are tracked in the HI-1 and HI-2 (beyond coronagraphic) field of view, and 3D reconstruction is done for estimating their true kinematics to understand the CME-CME interaction.
The 3-D kinematics of the interacting CMEs of 25 and 28 September 2012 using the Self-similar expansion (SSE) reconstruction method. The vertical lines show the error bars. The horizontal lines and filled circles in the speed panels, respectively, represent the in situ measured speed and arrival times of the CMEs.
Using the estimated kinematics and true masses of the CMEs, the coefficient of restitution for the collision is found to be close to super-elastic.
S1 and S2 mark the arrival of shocks associated with the CME1 and CME2, respectively. The in situ measurements at 1 AU show two distinct structures of interplanetary CMEs, heating of the following CME, and ongoing interaction between the preceding and the following CME. The interaction region formed close to 1 AU is responsible for enhanced geomagnetic activity.
Post-collision kinematics improves the CME arrival time estimation at the Earth.
Mass loss from the Sun via CMEs and solar wind over solar cycle 23 ad 24
CME occurrennce rate and associated mass loss rate can be better predicted by X-ray background luminosity than the sunspot number.
The solar wind mass loss rate which is an order of magnitude more than the CME mass loss rate shows no obvious dependency on cyclic variation in sunspot number and solar X-ray background luminosity.
The X-ray background luminosity, occurrence rate of CMEs and ICMEs, solar wind mass flux, and associated mass loss rates from the Sun do not decrease as strongly as the sunspot number from the maximum of solar cycle 23 to the next maximum.