Modelling solar irradiance variations: the influence of faculae and small-scale magnetic flux elements
Lead Research Organisation:
Imperial College London
Department Name: Physics
Abstract
The Sun is the main driver of the Earth's climate. The effect of its variability on the climate, however, remains poorly understood. This is due to a number of reasons, including the lack of a universally accepted mechanism for such an influence, the difficulties in attributing signals in the complex climate system unambiguously to the Sun as well as large uncertainties regarding the level of total and spectral solar variability over climate-relevant time scales. This proposal aims to provide state-of-the art solar irradiance reconstructions spanning all wavelengths from the UV to the IR. These will represent a major improvement compared to current reconstructions in two main respects: 1) We propose to combine non-LTE spectral synthesis calculations in parts of the UV spectrum with standard LTE calculations in the visible and IR. LTE calculations are sufficiently accurate over most of the visible and IR region and are computationally straightforward. We will complement these with non-LTE calculations where they are most needed, i.e., where our current LTE calculations are known to fail. The variability in the UV wavelength region is of particular interest as it currently the most promising mechanism to provide the Sun-climate coupling. 2) We will derive the intensities of the bright magnetic elements from magneto-convection simulations. This will allow us for the first time to obtain the spectral response for the small-scale magnetic elements that are thought to be the main cause for long-term irradiance variability. To our knowledge, this is currently the only way to estimate the long-term spectral variability. In addition, the magneto-convection simulations can be used to derive synthetic magnetograms that can then used to translate the observed magnetogram signals into intensities, thus dispensing with any free parameters in the irradiance reconstructions. As a by-product, we will test the simulations by deriving solar surface images that can be directly compared to observations, such as those taken by, e.g., Hinode or Sunrise.
People |
ORCID iD |
Yvonne Unruh (Principal Investigator) |
Publications
Ball W
(2014)
A New SATIRE-S Spectral Solar Irradiance Reconstruction for Solar Cycles 21-23 and Its Implications for Stratospheric Ozone*
in Journal of the Atmospheric Sciences
Ball W
(2014)
Assessing the relationship between spectral solar irradiance and stratospheric ozone using Bayesian inference
in Journal of Space Weather and Space Climate
Afram N
(2011)
Intensity contrast from MHD simulations and HINODE observations
in Astronomy & Astrophysics
Haywood R
(2014)
Planets and stellar activity: hide and seek in the CoRoT-7 system?
in Monthly Notices of the Royal Astronomical Society
Ermolli I
(2013)
Recent variability of the solar spectral irradiance and its impact on climate modelling
in Atmospheric Chemistry and Physics
Ball W
(2012)
Reconstruction of total solar irradiance 1974-2009
Ball W
(2012)
Reconstruction of total solar irradiance 1974-2009
in Astronomy & Astrophysics
Ball, W. T.
(2012)
Reconstruction of total solar irradiance 1974-2009
Unruh Y
(2011)
Solar Irradiance Models and Measurements: A Comparison in the 220-240 nm wavelength band
in Surveys in Geophysics
Solanki S
(2013)
Solar irradiance variability
in Astronomische Nachrichten
Yeo KL
(2017)
Solar Irradiance Variability is Caused by the Magnetic Activity on the Solar Surface.
in Physical review letters
Ball W
(2011)
Solar irradiance variability: a six-year comparison between SORCE observations and the SATIRE model
in Astronomy & Astrophysics
Norris C
(2017)
Spectral variability of photospheric radiation due to faculae I. The Sun and Sun-like stars
in Astronomy & Astrophysics
Haywood R
(2016)
The Sun as a planet-host star: proxies from SDO images for HARPS radial-velocity variations
in Monthly Notices of the Royal Astronomical Society
Krivova N
(2011)
Towards a long-term record of solar total and spectral irradiance
in Journal of Atmospheric and Solar-Terrestrial Physics
Yeo K
(2015)
UV solar irradiance in observations and the NRLSSI and SATIRE-S models
in Journal of Geophysical Research: Space Physics
Shapiro A
(2014)
Variability of Sun-like stars: reproducing observed photometric trends
in Astronomy & Astrophysics
Description | Please note that this grant was subsumed (after 18 months) into the consolidated grant for the astrophysics group at Imperial College London. The main outcomes are listed there. The key finding as part of this grant was a new (collaborative) reconstruction of the changing solar emission at ultra-violet wavelengths. |
Exploitation Route | Our findings have been taken forward to evaluate the solar influence on climate change (see recent work by W Ball) and to achieve parameter-free estimates of solar variability (Yeo et al 2017, PRL119, 1102). |
Sectors | Digital/Communication/Information Technologies (including Software),Environment |
Description | MPS |
Organisation | Max Planck Society |
Department | Max Planck Institute for Solar System Research |
Country | Germany |
Sector | Academic/University |
PI Contribution | provision of facular and spot contrasts as a function of limb angle; merged solar irradiance reconstructions using different instruments |
Collaborator Contribution | MPS provide - magnetoconvection simulations of solar and stellar granulation - expertise in solar irradiance reconstructions and solar imaging |
Impact | All papers pertinent to this grant have been in collaboration with at least one of our collaborators at the Max Planck Institute for Solar Systems Research. |