Scientific Rationale

Science Question

High Temperature in the Sun's atmosphere

Heating of the solar atmosphere (i.e., the chromosphere, transition region, and corona) has been a central topic in solar physics for several decades. Magnetohydrodynamic (MHD) waves are often considered a principal mechanism for transferring energy and momentum between the solar interior and these elevated layers.

Current-generation solar telescopes, including the Swedish 1-m Solar Telescope (SST) and the Dunn Solar Telescope (DST), are producing a wealth of high-quality imaging and spectro-polarimetric datasets. These multi-wavelength optical and infrared observations contain rich information on MHD wave processes operating in the Sun's dynamic lower atmosphere. Such oscillations, including slow and fast magneto-acoustic waves as well as Alfvén waves, have the potential to transfer substantial energy flux into the solar chromosphere and corona, where strong radiative losses must be balanced. Furthermore, the differing rates of energy and plasma transmission through the various layers of the solar atmosphere have important implications for relating the Sun's energetics to those of the heliosphere.

Observations

Observing waves and oscillations
in the lower solar atmosphere

The WaLSA Team is fortunate to have direct access to a wide range of high-quality imaging and spectro-polarimetric datasets produced by most current-generation solar telescopes.

Swedish 1-m Solar Telescope (SST)

Dunn Solar Telescope (DST)

Sunrise Balloon-Borne Solar Observatory

Solar Dynamics Observatory (SDO)

Atacama Large Millimeter/submillimeter Array (ALMA)

Interface Region Imaging Spectrograph (IRIS)

GREGOR Solar Observatory

Hinode Space Telescope

...

Recent investigations have focused on the detection and identification of mixed-property wave modes across different magnetic solar features (e.g., sunspots, pores, magnetic bright points, spicules, and filaments). To quantify wave properties as accurately as possible, theoretical aspects of spectro-polarimetry, partial ionisation, and radiative-transfer processes must be incorporated, especially since the lower solar atmosphere is governed by optically thick plasma conditions. Many recent groundbreaking studies have begun to include Stokes inversions in order to better understand the spectro-polarimetric signatures produced by energetic wave fronts propagating through the highly stratified solar atmosphere. However, these types of processes are not without significant challenges. Often, the captured spectro-polarimetric Stokes profiles are significantly asymmetric and evolve on timescales shorter than typical camera integration times.

It is therefore imperative to bring together leading experts in observations, instrument design, wave theory, numerical simulations, spectro-polarimetric inversions, and radiative-transfer processes in order to drive forward cutting-edge research that will benefit the wider astrophysical community for decades to come. Importantly, this team brings together international experts from several leading countries to concentrate research efforts on obtaining reliable estimates of the energy transported by MHD waves into the upper solar atmosphere, and on providing new insight into the dissipation mechanisms of these waves and hence their contribution to heating the outer solar atmosphere.

The WaLSA team members hold a wealth of experience in the handling, preparation and exploitation of high-resolution data sequences from modern ground-based instruments, including CRISP, CHROMIS, IBIS, ROSA, HARDcam, and ALMA, which can be used in conjunction with numerous space-borne facilities, such as Hinode, SDO, and IRIS. The goal of the assembled team is to collaborate intensively in order to investigate different aspects of wave activity in the solar atmosphere. Importantly, members of the team are international experts in spectro-polarimetric signatures and radiative transfer processes, both of which need to be harnessed in order to reliably characterise the origins of detected wave signatures.

Simulations and Models

Complementary to
wave observations

The WaLSA Team contributes to the development of, or has direct access to, advanced state-of-the-art numerical simulations and theoretical models relevant to wave studies in the lower solar atmosphere.

Bifrost

MURaM

LARExD

CO5BOLD

Mancha

...

Furthermore, we complement our wave studies based on high-resolution observations with state-of-the-art numerical simulations and theoretical models, such as those provided by the Bifrost, MURaM, CO5BOLD, Mancha, and LARExD codes. Combining theory and simulations of wave propagation through the lower solar atmosphere with novel high-resolution observations will greatly improve our understanding of the physics of MHD waves and their role in governing the dynamics and energetics of the solar atmosphere. This combined approach should also help resolve earlier discrepancies in the interpretation of the various wave modes and their contributions to the net energy flux.

Timeliness

The importance of timing for the team's activities

The timing of these investigations is particularly important, especially in light of the recent observations from the 4-m Daniel K. Inouye Solar Telescope (DKIST) and the Sunrise iii balloon-borne solar observatory, which are already transforming our view of oscillatory phenomena in the Sun's atmosphere through their exceptionally high spatial resolution and novel spectropolarimetric capabilities. In-depth discussions and analyses related to spectropolarimetric inversions and modelled radiative-transfer signatures are expected to have important implications for DKIST and Sunrise iii observations, as well as for those from other ongoing and upcoming advanced facilities, including the Atacama Large Millimeter/submillimeter Array (ALMA), Solar Orbiter, and the European Solar Telescope (EST).

By harnessing expertise in instrumentation, observations, wave theory, numerical simulations, spectropolarimetric inversions, and radiative-transfer processes, the team is well placed to lead cutting-edge projects based on observations from these revolutionary facilities.