Objective: to determine the evolution and structure of thermal instability in loops and perform MHD seismology with coronal rain
Scientific Background: Coronal rain corresponds to emission in both chromospheric and transition region lines from neutral or partially ionised material occurring in a time scale of minutes along coronal loops. The blobs composing the rain act as tracers of the magnetic field, and have provided insight into the elementary length-scales, field topology and thermal structuring in the solar corona (Schrijver 2001, Antolin & Rouppe van der Voort 2012). It has been difficult however to quantify a coherent length scale over which neighbouring loops will share a common thermodynamic evolution due to the lack of instrument coverage in the chromosphere to transition region temperature range. It is also unclear whether significant braiding or twisting exists, and how thermal instability evolves and produces fine thermal structuring. The difficulty lies in the very fast timescale of the instability and the subsequent fast dynamics of the rain, which requires high temporal, spatial and spectral resolutions for its detection.
The high spatial resolution windows offered by the rain further allows to detect small amplitude transverse MHD waves in the corona. Both, observations and numerical simulations indicate a relatively high optical thickness and plasma-beta parameter for the coronal rain blobs, implying an interaction with the magnetic field through MHD wave generation/damping. This scenario constitutes a wealth of application for coronal seismology, which has yet to be exploited (Antolin & Verwichte, 2011).
Coordinated observations between IRIS and Hinode allows an excellent temperature coverage of the chromosphere and transition region at high spatial, temporal and spectral resolutions. Such combination represents a unique opportunity to study the evolution of thermal instability in loops and perform MHD seismology with unprecedented detail. |
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