Science case (25): Energy transport and dynamics in/above the solar network and coronal heating mechanisms

Upper parts of the solar atmosphere (i.e. chromosphere, transition region and corona) are planned to be investigated in order to identify the most probable physical mechanism responsible for the heating of the solar corona localized particularly in/above chromospheric network. At present, two main groups of the physical mechanisms are proposed to understand coronal heating problem: dissipation of magneto-acoustic waves excited in the photosphere and small-scale magnetic reconnection in the corona. Although these two groups of mechanisms are based on different physics, both suggest presence of the propagating waves in the upper solar atmosphere (e.g. Hansteen et al., 1996, ASP Conf.Ser. 111,116). Difference is situated in the opposite direction of the wave propagation (e.g. Wikstol et al., 1997, ApJ 483, 972). Determination of the dominant mechanism can be therefore based on analysis of the wave modulation of the spectral lines emissions.

Our latest results indicate presence of the downward propagating waves in/above chromospheric network and thus preferring magnetic reconnection as the dominant heating mechanism (Gomory et al., 2006, A&A 448, 1169). On the other hand, findings of other authors (e.g. Curdt et al., 1999, ESA SP-448, 177; Marsh et al., 2003, A&A 404, L37) show evidence of propagating intensity oscillations spreading out from the photosphere to the corona and therefore preferring the alternative heating mechanism.

To clarify these findings we propose the following simultaneous measurements of the SOHO/SUMER and HINODE/EIS spectrometers:

- SUMER: time series of the line profiles of the 'cooler' spectral lines (i.e. C II 1037.018 A and O VI 1037.613 A), fixed 1D slit position, the disk center, slit 1x120 arcsec, no rotation compensation. Provided information: line intensities and Doppler shifts - chromosphere and transition region - 1D

- EIS: images of the limited field-of-view, slot 40", FOV 40x200", centred at the SUMER slit position, lines: He II 256.32 A, Si VII 275.35 A, Fe XII 195.12 A, Ca XVII 192.82 A, cadence 12 sec. Provided information: line emission - chromosphere, transition region, corona - 2D.

- Total duration of the common observational run: 3.5 hours. Measurements repeated for several days in order to acquire sufficiently large material also for a statistical analysis of more network areas.

The acquired SUMER and EIS data are planned to be used for study of possible waves in the upper solar atmosphere and for determination of direction of their propagation. We will employ improved cross-correlation algorithm (e.g. Gomory et al., 2004, ESA SP-575, 400), wavelet analysis (Torrence & Compo, 1998, Bull. Amer. Meteor. Soc. 79, 61) and phase difference analysis (e.g. Bloomfield et al., 2004, ApJ 617, 623) of the SUMER 1D and EIS 2D line intensities (and 1D SUMER Doppler shifts) of all selected spectral lines. This approach has been used already by our group for CDS data
(Gomory et al., 2006, A&A 448, 1169).

We expect that merging of the 1D SOHO/SUMER data with the 2D HINODE/EIS images will provide a perfect temperature coverage of the line emissions from chromosphere up to the corona and thus allow us to reach our main goal. Combination of the SUMER 1D and EIS 2D FOVs seems to be optimal for our purpose.

Possible supporting observations: HINODE/SOT BFI: G-band, Ca II H, Blue_cont

EIS Exposure duration: 10 seconds

Ion Species Wavelength Total counts for exposure (A) (per pixel)

Ca XVII      192.82          0.0
Fe XII          195.12       138.2
He II            256.32        47.4
Si VII           275.35        12.3

last modified:   15 Mar 2007