LWS research: Understanding the sources of the solar spectral and total irradiance variability and forecasting tools 2007/12/11 PI: J. Fontenla LASP – Univ. of Colorado

SRPM Project Goals Diagnosis of physical conditions through the solar atmosphere; energy balance of radiative losses and mechanical heating. Evaluating proposed physical processes to determine the solar atmosphere structure and spectrum at all spatial and temporal scales. Synthesizing solar irradiance spectrum and its variations to improve the above and produce complete and quantitative physical models. Forecasting spectral irradiance at any time and position in the Heliosphere. Weekly and monthly forecast is now becoming possible.

SRPM Flow Scheme I(λ,μ,φ,t) T,ne,nh,U,...(x,y,z,t) n lev,n ion,…(x,y,z,t) I(λ,μ,φ,t)

SRPM Technology Full non-LTE radiative transfer for all relavant species (including optically thick and thin) Multi-dimensional radiative transfer, 1D and 3D Modular, client-server, distributed structure Extensive relational SQL database storage for: –Atomic and molecular data –Physical models and simulations –Intermediate data (e.g., level populations) Object Oriented C++ reusable production code I/O interfaces to text, binary, FITS, NETCDF Parallel computing using available libraries

Modeling for various plasma regimes Photosphere (using average 1D models and external 3D simulations) –Slow motions (few km/s) dominated by convection overshoot –Weak ionization –All particles are unmagnetized –Plasma beta > 1 –At or near LTE Chromosphere (using average 1D models and 3D MHD simulations) –Motions and inhomogeneities change from weak to strong –Weak ionization (n p << e n~10 -4 n H ) –Ions unmagnetized, electrons magnetized (implies tensor conductivity) –Plasma beta crosses 1 somewhere within the chromosphere –Needs to consider full non-LTE radiative transfer radiative losses Corona (will use results from groups carrying coronal loops modeling) –Motions and ihomogeneities are very strong –Highly ionized –All species are magnetized –Plasma beta << 1 –Non-LTE effects are extreme and but optically thin applies –Particle transport is large and probably important departures from Maxwellian

Boundary conditions between layers Between photosphere and upper chromosphere: –The low chromosphere is near radiative equilibrium –Driven by convective overshoot and also by Lorentz forces (i.e. magnetic fields) in some locations –NLTE effects driven by illumination from above and below. Between corona and chromosphere: –The transition-region behaves like a boundary layer at the footpoints of coronal loops or solar wind open field lines –Energy balance between energy carried by conduction and diffusion from the corona is dissipated by radiation in the transition-region, optically thick and thin depending on species –Mass also flows through the transition-region and supplies the solar wind (Cool loops exist embedded in the corona and are dynamic, e.g. spicules, but are not too important for the solar irradiance) (Warm loops exist embedded in the chromosphere and are dynamic, but are not too important for the solar irradiance)

Photosphere (radiation/convection) 500 nm800 nm1200 nm1600 nm Stein & Nordlund 2000 convection simulations snapshots SRPM absolute radiance, wavelength and CLV dependence Slit spectrum Comparison of spatial averages with semi-empirical models points to improvements in average models and in simulations Mg I 4572C I 5381CN band

Solar Chromosphere (radiation/plasma heating?) New intranetwork model (B) matches the observations at most λ with no bifurcation. Allows a simple average model for computing all wavelengths.

Comparison of semi-empirical quiet-Sun model spectrum with observations, shows a good match but also some details to improve H alphaNa I D linesH betaMg I 4572 & Ti II 4573 CN Band head CH Band (G-band)CO BandsOH Lines Model 305 spectrum is ~3% too bright compared with the current observations of spectral irradiance. but the observations error is comparable.

Upper chromospheric network intensity structure shows distribution with relationship to magnetic fields UV (1540 A) continuumMDI magnetogram

The network intensity distribution is log-normal, an additional tail appears in active regions, we model a discretized distribution UV continuum Lyα Ca II K 3 Red cont.

Chromospheric heating & “microturbulence” appear to be closely related Model gives: Lower chromosphere: decreasing T - radiative equilibrium – subsonic motions - Vturb 1-3 km/s Upper chromosphere: relatively high T plateau - strong UV losses and heating – near-sonic motions - Vturb > 9 km/s Heavy ions dominate the positive charge making the ion-acoustic velocity very small

The FB instability can “continuously” heat the chromosphere Magnetic field Velocity The electrons Hall drift produce the “electrostatic” Farley-Buneman instability that probably dissipates energy in the chromosphere Convective motions should produce weak electric fields (~5 V/m) and drive the FB instability. Similar to the Earth ionosphere but in the Sun the instability is stronger and most everywhere because convective overshoot motions above granulation are above threshold most times. Hall drift

Particle magnetization and FB instability threshold

New vs. old Model Set New semi-empirical chromospheric model set is being developed to match the CO lines and many others that the old models did not match. The old set of models needs update to match several lines, including CO.

Revision to transition region (radiation/conduction+diffusion+flows) Energy balance transition region structure computed as in FAL. Optically thick and optically thin losses are included. Shown are the 306 model scaled with the usual (ne*nh) -1. Particle energy flux includes conduction and diffusion. TR is major energy sink for the corona and contributor to the UV radiation flux. Atomic data is being revised using CHIANTI

Corona (radiation/conduction+wind+heating) Several magnetic field extrapolation methods produce more or less the field structure inferred from observed loops. Magnetic field extrapolations tend to fill the corona, but the emissions do not. Partial filling is necessary. Solar wind needs to be included for coronal holes. Emission can be computed directly from loops and wind models, but needs 3D and full Sun. Coronal emission incident on the chromosphere has some effects, especially on He spectrum. For this task we intend to collaborate with groups working on coronal loops and solar wind modeling.

Evaluating irradiance using disk masks Using daily images of the solar disk various components are identified and a “mask” is produced. Daily spectra are computed using the semi-empirical models for the components (currently 7 components, will need 10). Comparison with SORCE data is shown for a few wavelengths (Lyα, 430 nm, and 656 nm).

SSI issues by SRPM Current research issues: –Discretization of continuous intensity distribution –UV & EUV surface features spectra distribution –Update plage & network chromospheric models –Inclusion of coronal holes and coronal loops –Status of magneto-convection simulations –3D effects especially near the limb –Contributions to TSI variation by various bands –Spectral changes effects on Earth’s atmosphere

Tools for forecasting solar irradiance