Multi-scale Energy Dissipation on the Sun

The outer atmosphere of the Sun is powered by the release of energy over a broad range of spatial and temporal scales. Coronal holes with scales typically on the order of a solar radius (6.95 x 10^5 km) are the sources of high speed solar wind streams, and coronal active region magnetic loops, with typical scales of 10,000 km, exhibit somewhat steady heating. Direct heating of the coronal plasma, unresolved in current instruments, takes place at a typical ohmic dissipation scale in the corona, which is likely to be as small as 100 km. The Sun also exhibits a broad range of temporal scales. The largest features are observed to last for months. Coronal holes and coronal streamers can persist for several 27-day solar rotations with little change. Solar flares release a vast amount of energy essentially doubling the solar luminosity for a brief period of a few minutes. Within these events time variability is observed down to a few milli-seconds. It is widely believed that the ultimate power source for all energy release processes in the upper solar atmosphere is convection at the solar surface. Convective flows (1) generate the magnetic field in the convection zone of the Sun, and (2) stress the field generating electrical currents allowing the buildup of energy in localized regions over time. How is the broad range of scales observed on the Sun coupled together? How is energy converted from local dissipation sites into the diffuse corona observed? How are the upper atmospheric layers, the corona and chromospheres, coupled to convective motions in the photosphere, the presumed energy source? How do these processes drive hazardous space weather events which exhibit power-law statistics characteristic of dynamical systems at criticality, and how good are our chances to predict such events considering their inherent multiscale origin? These are significant open questions that remain to be answered.