Project Description
This research studies the physical origins of the solar spectral irradiance variations, with emphasis on the UV, and their contribution to the total irradiance. We use and extend the Solar Radiation Physical Modeling (SRPM) system, that was developed for studying the relationship between visible and infrared solar spectral irradiance variations with the physical structure and heating in active regions and network observed on the solar disk. The SRPM system is now extended to compute UV and EUV wavelengths by comprehensive calculations of non-Local Thermodynamic Equilibrium radiative transfer (full-NLTE) in all relevant optically thick lines and continua and uses a simpler NLTE approach for optically thin lines. The SRPM system uses observational diagnostics of physical parameters characterizing the solar chromosphere and corona and solar disk images at a few wavelengths to produce a semi-empirical physical structure of the solar features from which the entire spectrum at all wavelengths is then computed. The data for all features on the solar surface is assembled into "synoptic masks" based on the detailed distribution and radiative characteristics of the active regions and network over the entire solar surface, including the far-side from the previous images. Using these data we are able to compute the solar radiation detailed spectra in any direction.
Forecasting will use the SRPM methods in combination with far-side helioseismic imaging and images of Lyman alpha backscattering from the interplanetary medium observed by the SOHO/SWAN instrument. These data allow us to "refine" the synoptic masks with the inclusion of sunspot and plage changes observed on the far-side. Our approach can produce very high spectral resolution and greatly improved predictions of UV spectral irradiance that can be used for modeling the Earth's atmosphere since the EUV-UV wavelength range displays important variability and is critical for photochemical reactions and heating of the Earth's upper atmosphere and those of other planets. Also, this research enables us to compute the entire solar spectral irradiance at other planets or locations within the heliosphere and will produce forecasting tools better than the proxy methods currently available.
This research has important applications for understanding long-term spectral and total irradiance trends, for connecting solar dynamo and magnetic field studies with the Sun's radiative output, and for short-term (~<2 weeks) forecasting of the Earth's radiative environment which is critical for predicting satellite drag, communications, and GPS propagation.
Progress (First Year)
1- Studies
of theoretical modeling and data analysis using observations from
2- Modeling
efforts aided by observations from HINODE,
3- Important advances were made on the ability to synthesize the solar UV spectrum from physical models of the solar atmosphere components through the “Solar Radiation Physical Model” (SRPM) system. The full non-LTE radiative transfer equations are now solved for the 20 most abundant neutral and singly ionized species in the 7 component atmospheric models. Other species are partially included and the higher ionization states are currently being worked out using the CHIANTI atomic data and complementary sources. The data from SDO/EVE will provide essential validation and development for this modeling.
4- Progress
was made on the image decomposition that has been extended from including only
the Mauna Loa PSPT to also include Rome PSPT images, and studies are underway
to also use San Fernando Observatory data. These complementary data makes the
decomposition much more reliable and also helps in avoiding gaps in single
instrument coverage. These data, as well as SOHO data (EIT and
5- Forecast of solar UV radiation progressed through the various interactions and meetings with our collaborators at NSO (helioseismology) and CNRS (Lyα backscattering from SWAN/SOHO). Calibrated helioseismic maps of the far side are now available that allow for refining the SRPM synoptic maps. The Ly radiation shining over the interplanetary medium is now routinely computed from our data and permits interpretation of the backscattering images in terms of solar features. Thereby this allows for further refinement of the synoptic masks used for the irradiance forecast. STEREO will be used for validating the method and for testing improvements on the synoptic mask refinement that can also be used after this mission ends.
References
Fontenla, J.M., Peterson,
W.K., and Harder, J., “Chromospheric heating by the Farley-Buneman instability”, A&A, 480, 839-846
(2008).
Platnick, S., and Fontenla, J.M., “Model Calculations of Solar
Spectral Irradiance in the 3.7 µm Band for Earth Remote Sensing Applications”,
Journal
of Applied Meteorology & Climatology, 47, 124-134 (2008).
Fontenla, J., Balasubramaniam, K.S., Harder, J., “Semi-empirical
models of the solar atmosphere. II. The quiet-Sun low-chromosphere at moderate
resolution”,
ApJ, 667, 1243-1257 (2007).
Fontenla, J., Curdt, W., Avrett, E.H., and
Harder, J., “Log-normal intensity distribution of the quiet-Sun FUV continuum
observed by
Additional Resources
http://lasp.colorado.edu/science/solar_influence/
http://ccar.colorado.edu/muri/