Presentation on theme: "Energy Release and Particle Acceleration in Flares Siming Liu University of Glasgow 9 th RHESSI Workshop, Genova, Italy, Sep. 2009."— Presentation transcript:
Energy Release and Particle Acceleration in Flares Siming Liu University of Glasgow 9 th RHESSI Workshop, Genova, Italy, Sep. 2009
The Zoo of Flare HXRs Aschwanden et al.1995
Flares are Multi- Scale Phenomena Bai 1993; Lee et al. 1995; Veronig et al. 2002
So Are the Energy Release and Particle Acceleration Processes Aschwandon et al. 1995
Elementary Flare Bursts Have Variable Timescale De Jager & De Jonge 1978; Liu et al. 2003, 2006
How Many Elementary Bursts Are There? Aschwanden et al. 1996, 1998
The Zoo of Flare HXRs Aschwanden et al.1998
High Degree of Freedom Initial and Boundary Conditions Grigis & Benz2005; Chernov 2008
Physics is Scale-Dependent Chernov 2008
Injection and Trapping Aschwanden et al.1996, 1998
Injection is an Artificial Process Aschwanden et al.1998; Chernov 2008 Release of Large Scale Magnetic Field Energy Wave Generation, Transport, and Dissipation Plasma Heating: Energy gain of the low-energy background particles Particle Acceleration: Energization of high- energy particles. Particle Transport: Beam Chromospheric Evaporation driven by energy deposition through particle beam, conduction, and wave flux. Radiative Processes.
Possible Justification for an Injection Aschwanden et al.1998; Chernov 2008 Particle acceleration timescale is short and nonthermal particles decouple from the background plasma. But solar flare studies are more concerned with the energetics and artificial injection is only appropriate for test particles or energetically unimportant component.
The Key: Energetics Aschwanden et al. 1996
Flares are multi-scale phenomena with high degree of freedom The physical processes are likely different on different scales Energetics is the key for the study of energy release of particle acceleration.
Generic Particle Distribution of Stochastic Particle Acceleration Liu et al Low DensityHigh Density High Temperature Low Temperature
Evolution of Elementary Events Appropriate for studies of the energetics Liu et al Low DensityHigh Density High Temperature Low Temperature
Weakness of Stochastic Acceleration No spatial structure and the relevant physical processes have to be treated approximately Kontar et al. 2005; Liu 2006
Extended Bursts Warren & Doschek 2004
Conclusions Energy release and particle acceleration in solar flares are multi-scale processes with high degree of freedom and different physical processes dominate on different scales. Their studies should follow the energetics, i.e. modeling the energetically dominant component first and treating other phenomena as “perturbations”. Stochastic particle acceleration provides an appropriate frame work, which can be combined with small scale plasma processes and large scale MHD processes.
Sub-second scale features are likely caused by transport and plasma physics processes Liu et al Multiple Loops
So Are the Energy Release and Particle Acceleration Processes Hoyng et al 1976; Liu et al. 2004, 2006; Lin et al Impulsive HXR Bursts Extended HXR Bursts
General Constraints on the Particle Acceleration: Fast De Jager & De Jonge 1978
General Constraints on the Particle Acceleration: Selective Energetically (Stochastic Acc., Sub Dreicer Field, Shock Injection) Kontar et al. 2005; Eichler 1979
General Constraints on the Particle Acceleration: Selective Spatially (Intermittency, Super-Dreicer) Dauphin et al. 2007
Which one looks more like an HXR flare? Aschwandon et al.1998
Stochastic Acceleration Liu et al. 2009
flare ribbons chromosphere UV loops (10 K) 5 H-alpha loops (10 K) 4 X-ray loops (10 K) 7 magnetic field lines conduction front reconnection inflow current sheet Superhot hard X-ray region (>10 K) 8 (standard flare configuration adapted from Forbes & Acton, 1996) Extended HXR Bursts
Impulsive Well-Observed Bursts Liu et al. 2003, 2006
Asymmetry Kontar et al. 2005
Extended Bursts Lin et al. 2003
Statistical Studies Battaglia & Benz
Statistical Studies Krucker et al. 2007
EUV at 171A (by TRACE) H-alpha 6563A (by BBSO) soft X-ray 1-8A (GOES) hard X-ray 20 keV (Yohkoh) hard X-ray 100 keV (Yohkoh) microwave 6.6 GHz (OVSA) Most flares have impulsive non-thermal and gradual thermal emission components
Measuring the electron acceleration efficiency?
Measuring the electron acceleration efficiency? Model the thermal X-ray emission and find the component correlated with the non-thermal X-ray emission. Challenging, if not impossible!
The particle transport, chromspheric evaporation, and radiative cooling processes are difficult to model for complex flares. If the particle acceleration process is universal for all flares, as we usually assume, we should study the particle acceleration efficiency with relatively simple flares.
Goals TheoryHow does the efficiency depend on properties of the background plasma: B, T, n, size of the flaring region, energy release rate, … ObservationsMeasure (constrain) the efficiency Explore its dependence on the emission characteristics: spectral features, flux density, size of the emission region, variation time scale, … Particle Acceleration Efficiency measures the energy partition between the emerging thermal and non-thermal particles.