The contribution of jets and sporadic events to the coronal heating puzzle

The Sun is the only star whose interior, surface, and outer atmosphere can be resolved in detail, hence providing an important and unique base for the study of fundamental physics, astrophysics, fluid mechanics, plasma physics, and magnetohydrodynamics. The interplay of these aspects of physics creates an essential range of phenomena visible not only on the Sun, but also elsewhere in the Universe. The physical and temporal scales observable on the Sun are large enough to properly represent cosmic-scale phenomena, while the Sun is close enough that measurements can be made in great detail.


SUMER/SoHO O VI 1037 Å slit data showing both blue and red shifts events (commonly termed explosive events) over a two minute interval.

Higher resolution observations over the past decade have led to the increasing recognition that all layers of the solar atmosphere (the chromosphere, transition region and corona) are threaded with an incredible amount of highly dynamic small-scale structures. It is strongly believed that these may have a profound effect on the mass, momentum and energy transfer in the solar atmosphere. However, little is known about how these phenomena are produced and what their impact is on coronal heating and solar wind generation.

The Sun's magnetic field plays a key role in these small scale events with respect to guiding magnetohydrodynamic waves that couple into mass and energy outflows, as well as dissipating stored energy into plasma kinetic processes through magnetic reconnection. But exactly how these two separate powering mechanisms – propagating waves and reconnection – are triggered and interact in order to generate coronal heating and to accelerate the solar wind, is not precisely understood yet.

With the recent launch of Hinode and the Solar Dynamics Observatory, and the development of new ground-based instruments, we can now make highly detailed observations about the Sun, which should lead to a critical understanding of the basic physical processes which govern the solar atmosphere. We need to make fundamental measurements of the solar magnetic field on spatial and temporal scales on which the field interacts with the dynamic solar atmosphere and on which it evolves over the poorly understood solar cycle.

This project couples the academic boundaries of atomic physics and solar physics, plus chromospheric and coronal physics. There are major implications for a range of topics.  For example, can the current sheet model explain the apparent high velocity of some spicules, their short duration and fast disappearance?  This work will open a new avenue of research on linkage between the chromosphere and corona, for example, the confirmation of transient ionization in short duration dynamic features would open up the potential of using transition region lines as diagnostics of the plasma's electron density and temperatures, whether in spicules, larger jet structures or flares.

Professor John Gerard Doyle
Armagh Observatory

Professor Doyle was awarded a Leverhulme Trust Research Project Grant in March 2013.