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Christian Bethge

Publications and source records attributed to Christian Bethge.

9 records
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Space-based UV Spectropolarimetry for Chromospheric Magnetic Field Measurements

High-resolution observations with space-and ground-based telescopes, along with advanced numerical modeling, have highlighted the intricate coupling between the chromosphere, transition region, and corona, and the critical role the chromosphere plays in the mass and energy balance of the outer solar atmosphere. Despite these recent advances, a major impediment to better understanding the solar atmosphere is our lack of empirical knowledge regarding the direction and strength of the magnetic field in the upper chromosphere (Decadal Survey, 2012). Such measurements are crucial to address several major unresolved issues in solar physics: for example, to constrain the energy flux carried by the Alfvén waves propagating through the chromosphere, and to determine the height at which the plasma β = 1 transition occurs, which has important consequences for the braiding of magnetic fields, for propagation and mode conversion of waves and for non-linear force-free extrapolation methods that are key to determining what drives instabilities such as flares or coronal mass ejections. Probing the magnetic nature of the Sun’s atmosphere requires measurement of the Stokes I, Q, U and V profiles of relevant spectral lines (of which Q, U and V encode the magnetic field information). Many of the magnetically sensitive lines formed in the chromosphere and transition region are in the ultraviolet spectrum, necessitating observations above the absorbing terrestrial atmosphere. The Chromospheric Layer Spectro-Polarimeter (“CLASP2”) sounding rocket was flown successfully in April 2019, as a follow-on to the successful flight in September 2015 of the Chromospheric Lyman-Alpha Spectro-Polarimeter (“CLASP1”). In October of 2021, we re-flew the CLASP2 experiment with a modified observing program to further demonstrate the maturity of the UV spectropolarimetry techniques, and readiness for development into a satellite observatory. During the reflight, called “CLASP2.1”, the spectrograph slit was scanned across an active region plage to acquire a two-dimensional map of Stokes V/I, to demonstrate the ability of UV spectropolarimetry to yield chromospheric magnetic fields over a large area.

David E McKenzie↗
NASA NTRSDate not supplied

From the Solar Limb and Out: Results from the Wide-Field EUV Image Campaigns with GOES/SUVI

Traditional approaches to tracking solar outflows for space weather forecasting rely primarily on coronagraph images, which generally observe the solar corona above a minimum height of about 2.5 solar radii. EUV images have been widely used to characterize features on the solar disk, but the limited fields of view of most current EUV imagers have prevented their use for tracking outflows through the inner and middle coronae. A series of off-point campaigns with the GOES 16-18 Solar Ultraviolet Imager (SUVI) between 2018 and 2022 from three Flight Models have provided an opportunity to assess the value of extended EUV images for space weather forecasting applications. These new results demonstrate that wide field-of-view EUV images are useful for characterizing the early onset of eruptive events and tracking smaller outflow into the solar wind. They also reveal the origins of shocks that are known to accelerate particles and drive solar energetic particle (SEP) events. Because CMEs generally experience the bulk of their acceleration below the height of white light coronagraphic observations, these images provide information about the origins of these events that has not been available traditionally. Together with coronagraphic measurements, EUV images provide the continuous views needed to connect CMEs back to their source regions. Here, we present these new SUVI observations and discuss their potential use in space weather operations.

SUVI↗
NASA NTRSDate not supplied

Demonstration of Chromospheric Magnetic Mapping with CLASP2.1

Probing the magnetic nature of the Sun’s chromosphere requires measurement of the polarization profiles of relevant magnetically sensitive spectral lines, many of which are in the ultraviolet spectrum, necessitating observations above the absorbing terrestrial atmosphere. The CLASP series of sounding rocket missions were designed to develop and test a technique for observing the Sun in ultraviolet light, and for quantifying the polarization of that light. By demonstrating successful measurement and interpretation of the polarization in hydrogen Lyman-alpha and the Mg II h and k spectral lines, these missions are crucial steps towards routine quantitative characterization of the local thermal and magnetic conditions in the solar chromosphere. In the most recent observations, CLASP2.1, the spectrograph slit was scanned across an active region plage to acquire a two-dimensional map of Stokes V/I, to demonstrate the ability of UV spectropolarimetry to yield chromospheric magnetic fields over a large area. The technique yields a set of simultaneous line-of-sight magnetograms at multiple heights within the plage atmosphere. By combining the CLASP2.1 measurements with magnetograms from Hinode/SOT or SDO/HMI, a wide range of atmospheric heights are mapped, from the photosphere to the upper chromosphere.

David E McKenzie↗