Letters of Intent received in 2016

LoI 2018-1971
Solar Irradiance: Physics-Based Advances

Topics

Overview of solar-irradiance datasets, availability, and Commission E1 Solar-Irradiance WG recommendations
- Solar-magnetic-field observations and proxies on various timescales
- Physics-based improvements to solar-irradiance and stellar-variability models from:
----Radiative-transfer improvements
----MHD-simulation model improvements
----Surface-flux-transport model improvements
- Stellar analogs and implications on solar variability; and vice-versa

Rationale

Almost four decades of space-based monitoring reveal that solar irradiance varies on all timescales and in all wavelengths at which it has been measured. The need to understand and model solar variability has been primarily driven by two factors: a) There is strong evidence that solar-irradiance variability influences terrestrial climate, and b) the solar paradigm helps assess stellar-brightness variations and the resulting limitations imposed on the detectability and habitability of exoplanets.

Initial solar-brightness-variability models were purely empirical. These were primarily based on the observed correlations between measured solar-irradiance and solar-magnetic-activity proxies, such as sunspot and facular indices. Successive semi-empirical models based on the one-dimensional parametrization of the solar atmosphere provided further understandings of the physical causes of solar-irradiance variability. More recently, a new degree of realism via three-dimensional magneto-hydrodynamic simulations and surface-flux-transport models as well as new computationally-efficient radiative-transfer schemes enabled development of a third generation of irradiance models. These models, based on fundamental knowledge of the solar atmosphere, provide a new means of understanding solar variability and long-term reconstructions. The physics-based foundation of the latest models furthermore enables their extension to modeling brightness variations of other stars.

The fast pace of this third generation of irradiance-model development makes the discussion between the solar-irradiance community and solar/stellar physicists especially timely. IAU General Assemblies attract both categories of researchers and hence provide a unique venue to host such a meeting. The proposed IAU XXX General Assembly Focus Meeting will bring together solar-irradiance experts with those in solar and stellar MHD simulations, radiative transfer, and atmospheres to connect recent physics-based advances in those fields with corresponding improvements in understanding the solar irradiance.