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Science objectives for helioseismology Understanding the interaction of the p-mode oscillations and the solar magnetic field + Resolving the discrepancies between local helioseismic methods = Accurate determination of structure below sunspots + Probing of solar atmospheric structure and magnetic fields Cally 2007
Science objectives for helioseismology • Cross-spectral analysis should provide more accurate frequencies • E.g. simultaneous four-spectra fitting (PI, Pv, CIV, φIV) • Can use AIA, HMI, MDI, GONG for development and explorations Barban, Hill & Kras, 2004
Additional wave-related objectives • Slowness (=1/speed) surfaces to study mode conversion properties • 4-dimensional power spectra: P(, kx, ky, kz)
Full-disk nonlinear force-free field extrapolation of SDO/HMI and SOLIS/VSM magnetograms NLFFF magnetic field lines agree well between HMI and VSM. Some connectivity in the corona is better represented by VSM data. Reconstructed magnetic field based on SDO/HMI data have more contents of total magnetic energy, free magnetic energy (about 14.4% difference), the longitudinal distribution of the magnetic pressure and surface electric current density compared to SOLIS/VSM data. The disagreement in free energy can be attributed to presence of weaker transverse fields in SDO/HMI measurements.
Coronal Holes & Chromospheric Synoptic Maps Two pairs of maps for selected Carrington rotations. The left column shows coronal hole locations (green and red colored areas) and a neutral line at 2.5 solar radii (smooth line near the equator) based on extrapolations of SOLIS chromospheric measurements. The right column is that same for extrapolated photospheric (GONG) measurements. The grey-scale image shows streamer locations from STEREO/SECCHI observations at 2.2 solar radii. The irregular line indicates coronal hole boundaries estimated from STEREO/SECCHI observations using 171 and 304 /AA wavelengths.
Additional magnetic field objectives • Better field extrapolations • Vector azimuthal ambiguity resolution
Broader science objectives • Understand the physical origins of the solar activity cycle • Understand the formation, growth, decay and disappearance of active regions • Understand the connections of the solar magnetic field from the interior to the corona • Understand the mechanisms of coronal mass ejections (CMEs), erupting filaments, flares, and other phenomena that can affect terrestrial technology and society • Understand the variations in solar irradiance that may affect terrestrial climate • Understand the origins of space weather and improve forecasts
Science requirements • Full-disk Doppler velocity, vector magnetic field images, and intensity images -> Stokes • Variety of wavelengths • Cadence of no longer than 60 seconds • Spatial resolution of 1” (0.5” pixels) (?) • 90% duty cycle • 25 year lifetime • Velocity sensitivity: 10 m/s /pixel /image (?) • Magnetic field sensitivity: 20 G /pixel /image (?)
Technical requirements • Observations in the following candidate spectral lines: • Ni I 6768 – GONG line • Fe I 6301/2 – SOLIS photospheric lines • H- -- space weather nowcasting • Ca K -- irradiance • He 10830 – coronal x-rays • CA 8542 – SOLIS chromospheric line • Fe I 6173 – HMI line • Fe I 1.5 μm (?) – good magnetic field sensitivity • Images of 4k 4k pixels – or 2k 2k pixels (?) • Entrance aperture of at least 0.2 m (?) • Adaptive optics or other image enhancement technology (?) • High-speed image post-processing • Instruments located at least six sites • High-speed real-time data return via the internet
Political requirements • Cost (< $50M ???) • Community support • Multi-agency support • Balance between research & operations • International participation • Long-term operational funding
Key technical challenges • Simultaneous wavelength and 2-D spatial sampling • Enough spectral points across a spectral line for additional height resolution • Polarization sensitivity • Simulations of wave mode conversion, how best to extract helioseismic information • Data center resources • Radio?
Possible instrument concepts • Filtergraph • Single optical beam through a set of filters moved mechanically by wheel or stage, single detector • Multiple optical beams, each through a single filter, onto multiple detectors • Spectrograph • Single optical beam, grating, prefilters, detector • Single beam, image slicer, lenslet array or fibers to create multiple spectral regions on detector • Interferometer • Multiple beams, one for each wavelength, prefilter, one interferometer and detector for each wavelength • Single beam, “stepped” interferometer with multiple optical path differences for multiple wavelengths, multiple detectors • Other solutions • Volume Phase Holographic Gratings • ????