日冕加热与太阳风加速初步

日冕加热与太阳风加速-a(very,very)brief introduction李波科学实验楼418BBBLSDU.EDU.CNPPT:http:/219.231.169.72/bblOutlinel太阳大气简介l日冕加热为什么重要？为什么困难？l太阳风加速一点历史,many ingredients of which still apply学术界目前的认识l小结2lthe innocuous Sun:need to go to the Space若干太阳的事实：半径70万公里，距离地球=215太阳半径=1.5亿公里=8光分，表面重力加速度=274m/s2是人类唯一可分辨唯一可分辨的恒星，理解太阳对理解cool stars极重要！SunsetSunrise over the Mediterranean sea3太阳的总体结构4Kirchhoffs lawslA hot solid,liquid or gas,under high pressure,gives off a continuous spectrum.lA hot gas under low pressure produces a bright-line or emission line spectrum.lA dark line or absorption line spectrum is seen when a source of a continuous spectrum is viewed behind a cool gas under pressure.56labsorption lines:loads of them7色球？Flash spectrum:emission line8l1859:Busen&Kirchoff devised spectroscopel1868:Helium identified by Sir Norman Lockyerl1879:Young&Harkness noticed this 5303 green line remains mysterious for 60 years until Edlin determined its nature:Fe XIV!How could the corona be so hot as reaching millions of Kelvin?9So far a sense of height dependence of temperature?1011More about photosphere12地面望远镜拍摄13corona in EUV&Soft X-raySOHO EITYOHKOH SXT141-D temperature distribution15Magnetic structuring of the solar atmospherelA digression to MHD(MagnetoHydroDynamics)Let us kick off with the motion of a charged particle考虑体积V内有Ns个s类带电粒子，那么单位体积s类粒子的“平均”运动粒子的热运动16磁流体力学动量方程Ampere定律17lPlasma beta,and how and when can we reduce the problem to Force-free and potential fields什么时候重力可忽略？什么时候热压可忽略？什么时候惯性项可忽略？当它们都可忽略时，就有这叫做force-free field势场是特例18lPFSS：potential field source surfacePink(green):open,outward(inward)pointingBlack:closedSchrijver&DeRosa,2003开放场、闭合场共存，开放场似乎总伴有闭合部分19Evolving picture of the solar atmosphere20Evolving picture of the solar atmosphere21Given the complexity,structuring,how do we define coronal heating?Trace 171,19990809,high loopsYohkoh SXTTrace 171,200912310703,AR1103922Magnetically closed vs.openlLoops are basic building blocks of the solar coronalHowever,there are unsung heroes:open structureslCoronal heating means heating of both closed and open structures23lHeating of magnetically closed structuresAC:wave heatingDC:Joule heating24AC heating:phase mixing as an examplel效率：敏感地依赖于粘性Erdelyi(2007)25DC heating:magnetic braidinglSteps involvedBraiding of mag field linesFormation of current sheetsStrong Joule heating26Magnetic braiding made more realistic 272.Coronal heating:interim summarylWhy important?Counterintuitivel为什么困难？Highly structured atmosphere293.Solar wind accelerationlthe“space”is not emptyComet Hale-BoppIon tail告诉我们，有来自太阳的连续粒子流，速度在几百km/s进一步的飞船测量表明太阳风=高速（达800km/s)+低速(约400km/s)303.Solar wind accelerationlThe original ideaThe electron thermal conductivity is high=a nearly isothermal solar coronaFor a multi-million corona,the gas can not stay at rest=it will be forever expanding.Coronal expansion=solar wind!The simplest case regards 1-dimensional,isothermal flow31lParkers windParker 19583233The solar wind scenarios:nowRLO,Fisk 1999Reconnection/Loop Opening34Wave Turbulence Driven modelMatthaeus et al.199935WTD modelltends to treat Coronal heating and Solar wind acceleration simultaneously Cranmer et al.200736Similarities and dissimilaritieslenergetics are similarGranular motion-Electromagnetic energy-wind(kinetic+potential)lmass supply is quite different37Solar Wind:intrinsically multicomponentMarsch:1982a,1982b38Solar Wind:intrinsically multicomponent39the need to go kineticproton&Helium VDFslVelocity Distribution Functions:at the heart of solar wind studies!40A simplified approach to kinetic treatment-Multifluid modelingLi&Li 200941Multifluid modeling:what it addresses Li et al.,200442lkinetic modellingVocks&Marsch,200243kinetic solar wind models:exospheric modellexospheric model-a completely different school of thinking44Exospheric solar wind modelMaksimovic et al.1997Maxwellian vs.Kappa45总结l太阳大气是高度复杂的Magnetically structuredSpectroscopic diagnosis play a key role in problem definition&solvingl日冕加热磁闭合区与磁开放区有本质的区别，需分别对待Loop heating:magnetic braiding is the most promising mechanism(as of now!)l太阳风加速有两类不同的源头观:WTD+RLO描述方式:fluid vs.kinetic高速流的加速是冕洞区域日冕加热的自然结果无需将高速流的加速作为单独问题来提出46建议的课程论文题目l光谱学发展史与Helium的发现l太阳可见光谱中的Fraunhofer线lCoronium与日冕高温证认的历史l太阳在UV及X-ray波段观测的历史l磁流体力学(MHD)发展史l磁流体力学(MHD)的工业应用lHans Alfven及Alfven波lAlfven波的空间物理及工业应用lEugene Parker及太阳风的预言l太阳风帆 solar sail47致谢l本次课程参考了Dr.Hardi Peter 2010年在Max-Planck的讲义Prof.Eckart Marsch 2010年在Max-Planck的讲义l引用了很多网络上可查到的图片，特别需要致谢的是TRACESOHOhttp:/solar-center.stanford.edu/teachers/48