Dependence of Heating in Coronal Loops and Plumes on the Coalescence and Polarity Mixture of Magnetic Flux at their Feet
In this talk we will discuss some recent observational results bearing on the dependence of heating of coronal loops and plumes on the strength, polarity mixture, and convergence of magnetic flux at their feet. We recently demonstrated, using SDO/AIA and SDO/HMI data of solar active regions (ARs) and their non-linear force-free field modeling, that freedom of convection and strength of magnetic field in the photospheric feet of AR coronal loops, together, can engender or quench coronal heating in them. We did this by showing that the hottest and brightest coronal loops in ARs are ones connecting sunspot umbra/penumbra at one end to (a) penumbra, (b) unipolar plage, or (c) mixed-polarity plage at the other end. Loops rooted in dark sunspot umbra at both ends were not visible in any of the AIA EUV channels. Thus, these loops are the coolest, challenging the general validity of the rule that heating in coronal loops always increases with field strength. Further, the appearance/disappearance of coronal plumes, which are magnetic-funnel ends of open field or far-reaching closed field and are rooted predominantly in unipolar flux, directly correlates with convergence/divergence of their photospheric magnetic flux. Similarly, the brightness of coronal loops waxes/wanes with the convergence/divergence of magnetic flux at their feet. Additional heating in them apparently results from cancellation of mixed-polarity magnetic flux at their bases.
Dr. Sanjiv Tiwari completed his PhD from Physical Research Laboratory/Udaipur Solar Observatory, India, on "Helicity of the Solar Magnetic Field". He is the recipient of Justice Oak Best PhD Thesis Award of the year 2010, given by Astronomical Society of India. Dr. Tiwari worked as a Postdoctoral Fellow at MPS, Germany from 2011 to 2013. He then joined NASA/MSFC as an NPP Fellow, where he was also appointed as a Research Scientist at UAHuntsville. Dr. Tiwari is an Adjunct Graduate Faculty at CSPAR/UAH, and has mentored more than 15 students (including undergraduate, postgraduate, graduate students) on various research topics. Since June 2017 Dr. Tiwari has been appointed as a Senior Research Scientist at LMSAL/BAERI in Palo Alto, CA. He is currently a member of operations and/or science teams of solar missions Hinode/SOT, IRIS, Hi-C, and upcoming MUSE.