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LWS TR&T Focus Teams:

Solar Origins of Irradiance Variations

Team Chair: James Klimchuk
Next Team Meeting: July 22 & 23, 2008 at HAO
Team-Maintained Web Site:
Team Publications:
Team Members:

  • Fontenla, John
  • Lionello, Roberto
  • Nandi, Dibyendu
  • Pap, Judit

May 29, 2008 Press Release - "Warm Coronal Loops Offer Clue to Mysteriously Hot Solar Atmosphere"

Target Description: Solar irradiance is the dominant driver of Earth climate. The variations in this fundamental parameter which are best known are the cyclic changes in total solar irradiance (TSI). In recent years continuous records of fluctuations in spectral irradiance have also been acquired. These data are now being incorporated in Earth-atmosphere models that include the absorption of different wavelengths of solar irradiation in different atmospheric layers and their coupling to fundamental modes of atmospheric oscillation. The variable solar soft X-ray, EUV, and coronal X-ray emissions play a dominant role in controlling the thermodynamics, chemistry, and ionization state of the terrestrial upper atmosphere, and are largely responsible for the most severe space weather impacts affecting telecommunications and satellite drag.

Progress in nowcasting and forecasting the solar spectrum depends critically on the availability of realistic, physics-based models of the solar activity affecting irradiance. Both total and spectral irradiance variations have been associated with manifestations of solar activity since the availability of the first space-borne measurements of these parameters, but less has been done to understand the physical processes by which solar activity causes these variations. Improved understanding of the detailed properties of solar active regions and solar impulsive events will allow the construction of models that describe the spectrum of the radiation emitted from the Sun under different conditions, and thus indicate where in the terrestrial atmosphere the radiant energies will be deposited.

Goals and measures of success: The goals of this Focused Science Topic are to understand how spectral irradiance variations from the Sun are produced and, in particular, to understand the physical processes causing variations in the solar spectral emissions. The prime measure of success for this work would be a substantial improvement in our ability to reproduce multi-spectral observations of active regions using physics-based models.

Types of solicited investigations: It is expected that the focus team will include investigations to model active regions based on first principles; predict the dependence of solar spectral irradiance on key physical parameters such as magnetic topology, field strength, loop length, and velocity patterns; and give a relationship between active region evolution and changes in the solar radiation spectrum.

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