Flare Dynamics in the Lower Solar Atmosphere
The lower solar atmosphere, in particular, the chromosphere, experiences during flares sudden changes in several basic physical parameters, such as opacity, collisionality, density, or plasma beta. Flares represent drastic impulsive perturbations of this complicated system, with interesting implications for particle acceleration, radiative transfer, and magnetic restructuring. The "impulsive phase" marks the epoch of most intense energy release and the main flare nonthermal effects, and coincides with the acceleration phase of the associated Coronal Mass Ejection (CME). The key process in the impulsive phase is the intense acceleration of non-thermal particles, recognized via the hard X-ray and gamma-ray bursts they produce. As a part of this Focused Science Topic, the apparently connected phenomena of the CME launch, the white-light flare (as observed also in the total solar irradiance), and the newly recognized "sunquake" seismic signature in the solar interior may be tied together. Success in understanding the energy transformations and momentum balance of the impulsive phase should help substantially in characterizing the initial development of a CME and the global coronal processes associated with it We now have major new observational and theoretical tools with the potential to make substantial progress in understanding this system. Previous studies have taken advantage of the stepwise changes in the photospheric line-of-sight magnetic field; which this FST will be able to extend to the full vector field from new observations (Hinode and SDO). The changes in the magnetic field at the time of the impulsive phase are expected to directly reflect the physical nature of the flare/CME instability, since they reveal the flow of energy from the field into particles, flows, and heating. The complexity of this Focused Science Topic requires a multidisciplinary approach, incorporating modeling efforts at several levels (MHD, radiation transfer, plasma) as well as a diverse set of observational material that will require analysis by different specialists. The key observations from space include those from RHESSI, Hinode, and SDO. Success in understanding the energy transformations and momentum balance of the impulsive phase should help substantially in characterizing the initial development of a CME and the global coronal processes associated with it.
Goals and Measures of Success:
The goal of this Focused Science Team is to advance our understanding of the dynamics of the Lower Solar Atmosphere during flares by making:
Progress in understanding the transport of energy and momentum into the interior from the solar atmosphere (sunquakes) during flares.
Progress in understanding high-energy phenomena in the impulsive phase of a flare.
Extensions of the photospheric field changes from the line-of-sight field to the full vector field.
Progress in revising the standard thick-target model of the flare impulsive phase.
Types of Investigations:
The characterization of sunquake signatures in terms of energy and momentum, and their relationship with the flare impulsive phase.
The application of plasma-physics tools to the chromosphere, in which (for example) ion-neutral coupling may dominate the electrodynamics and Hall currents during flares.
The analysis of footpoint emissions, relating hard X-rays and gamma rays with visible/UV continuum and EUV spectra, to understand energy transport.
The observation and characterization of flare seismic waves in order to distinguish among different mechanisms for corona/interior coupling.
The exploration of Alfven waves in the kinetic limit, in a dense, partially ionized medium, as a source of particle acceleration during flares.
Investigations using the anomalous 511-keV line widths observed by RHESSI, i.e., positron annihilation, as probes of the density structure of the chromosphere and transition region.