Investigating our dynamic solar corona from near Sun to 1 AU

Abstract

In this thesis, we study two areas of high interest in solar physics: the propagation of coronal mass ejections (CMEs); and the heating and thermal evolution of coronal loops.
In our study of CMEs, two separate techniques are employed to derive the three-dimensional (3-D) position angles and kinematic profiles of three separate CME events as they propagate through the heliosphere and into interplanetary space.
By analysing observations from two vantage points of Sun-centred, and coronagraph stereoscopic data, provided by the NASA STEREO spacecraft, a triangulation technique is used to pin-point the location of the CME’s leading edge in 3-D space. The resulting direction of the CME is compared with that derived from a method which employs the construction of “j-maps”; continuous running-difference height-time maps of coronal ejecta displaying solar transients along a selected radial path as they propagate from the Sun. This technique uses the assumption that a CME will experience no change in velocity or direction once it has reached the field of view of STEREO’s Heliospheric Imager (HI). It is found that the two methods agree well for fast CMEs (propagating faster than the ambient solar wind speed), but there is a large discrepancy in the slow CME (propagating slower than the ambient solar wind speed), which is due to the longitudinal deflection of the CME by the interplanetary magnetic field. Also, the analyses show that the CME experiences both a latitudinal and longitudinal deflection early in its acceleration / propagation phase.

The study of coronal loops consists of two parts; hydrodynamics and hydrostatics.

Firstly, a 1-D hydrodynamic Lagrange re-map code is employed to numerically model a 10 Mm coronal loop which is split into many sub-resolution strands. Each strand is heated impulsively, by localised discrete energy bursts, and the strands are then amalgamated to form a global loop system. The effects of changing the parameters of the simulation upon the temperature and velocity profiles of the loop are examined and compared to observations. It is found that the multi-strand model can accurately match synthetic velocity observations to those from spectroscopic satellite observations from Hinode EIS, say.
Finally, a phase plane analysis is introduced to study the temperature structure along 1-D hydrostatic coronal loops. Using a new four-range optically thin radiative loss function, it is possible to analytically solve the thermal equilibrium equation and investigate the resulting solution space. It is found that the new radiative function produces many new solutions to the phase plane with a subsequent impact on coronal loop thermal equilibria.