Evolution of the Global Temperature Structure of the Corona During the Minimum Between Solar Cycles 23 and 24

FRAZIN, RICHARD A.; NUEVO, FEDERICO A.; HUANG, ZHENGUANG; VÁSQUEZ, ALBERTO M.

La Roche-en-Ardenne

Workshop; Sixth Coronal Loops Workshop; 2013

The combination of Differential Emission Measure Tomography (DEMT, Frazin et al. 2009) with magnetic models allows determination of the electron density and electron temperature along individual magnetic field lines. The approach, named the Michigan Loop Diagnostic Tech- nique (MLDT), has been recently first applied to study the last absolute minimum during Carrington rotation (CR-)2077, between solar cycles (SC)-23 and 24 (Huang et al. 2012). In that work, two types of quiet Sun (QS) coronal loops were identified: "up" loops in which the temper- ature increases with height, and "down" loops in which the temperature decreases with height. While the first ones are expected, the latter ones were a surprise and, furthermore, found to be ubiquitous in the low- latitude corona. Here we extend the analysis to several CRs around the last solar minimum. We show that the population of down loops, which was always located at low latitudes, was maximum at solar minimum. The number of down loops systematically increased during the declin- ing phase of SC-23 and diminished during the rising phase of SC-24. We discuss the implications of this discovery for the investigation of the coronal heating problem.