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LWS TR&T Strategic Capability:

Physical modeling of the radiative Sun-Earth connection

PI: John Fontenla/University of Colorado

Capability Description: A model of the solar spectral irradiance and its variability from 1 to 2500 nm based on solar imagery and/or wavelength proxies, to inform and provide inputs to climate studies

LWS Strategic Need: Many atmospheric/climate models employ inadequate solar irradiance inputs that do not take into account the most recent state-of-the art observations or models of the solar spectral variations. Typically, the spectrum is divided into rather broad bands and the terrestrial atmospheric transmission/reflection/radiation processes are only coarsely captured as a result. Improvements are needed, not only in the irradiance variability inputs (solar irradiance models), but also in the way that the climate/atmospheric models use those inputs. Progress requires that the solar and atmospheric/climate modeling communities collaborate on these efforts. The sensitivity of the Earth’s atmosphere to incident solar irradiance is highly wavelength dependent, allowing variations in solar radiation to affect differing heights in the Earth’s atmosphere differently. With the recent successes of the TIMED (2001) and the Solar Radiation and Climate Experiment (SORCE) (2003) missions, terrestrial atmosphere modelers now have access to daily solar spectral irradiance observations spanning 1 nm to 2700 nm. Developing a solar spectral irradiance model will:
• allow detailed climate sensitivity studies to spectral irradiance variability;
• quantify the relative magnitudes of variations at different wavelengths on time scales from one day to centuries;
• identify portions of irradiance fluctuations which are attributable to particular manifestations of solar magnetic activity; and
• allow solar spectral irradiance estimates to be made based on ground– or space– based solar images/wavelength proxies when direct measurements (either past or future) are missing.
Such estimates may be the only means of spanning expected upcoming gaps in spectral irradiance observations after the conclusion of the SORCE mission, when measured spectral irradiances will be limited to wavelengths shorter than 127 nm, which is the long-wavelength limit of the EVE experiment on SDO. Additionally, solar spectral irradiance models may facilitate simplification of future instrumentation, if measurements at select wavelengths can be identified which either allow accurate estimates of full spectral range or capture the most important variabilities.

Desirable Features:

  • Characterizes solar spectral properties and variation on time scales from months to centuries in ways most useful to atmospheric/climate models;
  • Correlates measurements of solar spectral irradiances with solar features and magnetic activity;
  • Uses existing spectrally continuous solar irradiance data from spacecraft measurements;
  • Spans the spectral range available from current spacecraft instruments (1 to 2500 nm);
  • Estimates solar spectral irradiances in absence of temporally nearby irradiance data (i.e., without relying on extrapolation over time);
  • Estimates irradiances through times of extreme solar activity, as well as during times of minimal activity;
  • Identifies select “proxy” wavelengths from which accurate, spectrally continuous solar irradiances can be estimated;
  • Identifies key solar spectral variability in solar terrestrial coupling; and
  • Involves collaborative efforts between space physics, aeronomy, and climate scientists.

 

 

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