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Solar Spectral Irradiance (SSI) changes, atmospheric effects?. J. Fontenla NorthWest Research Associates and LASP-University of Colorado. The topic: SSI changes, and does it matter?. Solar Physics issues: Solar atmosphere structure and SSI Non-LTE radiative transfer

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solar spectral irradiance ssi changes atmospheric effects

Solar Spectral Irradiance (SSI) changes, atmospheric effects?

J. Fontenla

NorthWest Research Associates


LASP-University of Colorado

the topic ssi changes and does it matter
The topic: SSI changes, and does it matter?
  • Solar Physics issues:
    • Solar atmosphere structure and SSI
    • Non-LTE radiative transfer
    • Solar magnetic (sunspot) cycle
    • Magnetic effects on the solar atmospheric layers
  • Atmospheric issues:
    • Photochemistry
    • Heating of various layers of the Earth atmosphere
    • Ocean currents and energy transport
    • Effects of all the above on circulation
the solar research on ssi modeling
The solar research on SSI modeling
  • Emitted intensity spectrum =>solar atmospheres
  • 1970s: HSRA, BCA, Gingerich, Peytremann, Holweger & Muller
  • Avrett et al. 1981 VAL non-LTE, Athay & Thomas non-LTE and chromosphere, Mihalas, Kurucz LTE stellar models, 1980s
  • Transition region and Lyα, Fontenla et al. 1993 FAL, 1990s
  • Solar atmospheres => SSI calculations
  • Solanki/Unruh 1998, 3 component, LTE
  • RISE models 1999, 6 components, full/approx NLTE
  • Shapiro/Krivova 2011, full NLTE in few species/levels
  • SRPM models 2011, 9 components, resolved over the disk, full NLTE in 50 species/over 13,000 levels/over 170,000 atomic/ionic lines and over 550,000 molecular lines (LTE).
ssi spectral features and atmospheric regions
SSI spectral features and atmospheric regions

Fontenla, Avrett, & Loeser 1991, FAL 2, The Astrophysical Journal, 377:712-725

Transition region: EUV/FUV emission lines

Upper chromosphere: deep absorption line cores and UV emission lines

Lower chromosphere: NUV, visible, IR absorption lines

Photosphere: visible,IR continuum and weak absorption lines

solar surface features
Solar Surface Features

A-weak internetwork (new)

B-internetwork (changed C)

D-network (new)

E-active network (changed F)

H-normal plage (new)

P-bright plage (changed P)

Q-very hot plage (new)

S-sunspot umbra (temp)

R-sunspot penumbra (new/temp)

models of solar atmospheric features
Models of solar atmospheric features

Fontenla et al. 2006,The Astrophysical Journal, 639:441–458,

Models cross at ~6500 K, in NLTE.

Fontenla et al. 2011, JGR, 116, full NLTE, Tmin very different

Solanki & Unruh 1998, Astron. Astrophys. 329, 747-753, LTE.

No crossing in these models, SSI computed in LTE from FAL P with modifications.

fontenla et al 2011 jgr 116 d20108
Fontenla et al. 2011, JGR, 116, D20108

Photospheric and chromospheric layers

Transition-region and Coronal layers

  • Contributions to Quiet-Sun TSI (1360 W m-2):
  • Photosphere: ~1351 W m-2
  • Chromosphere: ~8 W m-2 (power >> TSI observed changes)
  • Corona+Transition-region: ~70 mW m-2
some observations considered for srpm set of atmospheric models
Some observations considered for SRPM set of atmospheric models

Features continuum contrast varies with wavelength and heliocentric angle, corresponds to the slope of T vs p, SRPM model set used detailed radiance observations

Sanchez Cuberes et al. 2002, The Astrophysical Journal, 570:886–899

Topka et al. 1997, The Astrophysical Journal, 484:479-486

San Fernando ObservatoryGround-based radiance observations confirm that ARs are dim in the visible, over the solar cycle plage near the limb do not increase the visible SSI.Preminger et al. 2011, ApJ




controversy1 calculated ssi behavior
Controversy1: Calculated SSI behavior

Solanki & Unruh 1998,

Astron. Astrophys. 329, 747-753

According to this paper: «The dotted curve shows the observed relative irradiance variation for λ < 400 nm between solar activity minimum and maximum vs. wavelength, compiled by Lean et al. (1997) and extrapolated to longer wavelengths by Lean (1991). »

Relative changes between Solar Cycle 23 peak/min that I am using for WACCM4 simulation runs.

Nocorr – Fontenla et al 2011, SRPM + PSPT images

Corr - same as above with a correction to match TSI

NRLSSI – WACCM4 default.


Lower- and upper-chromospherebright/dark fine structure, 1-D models only a first approximation to the net medium-resolution

Lower chromosphere

Extension of the granulation structure. Some localized energy dissipation in the walls of downdrafts.


Loops and mechanical dissipation

3d radiation transport nlte
C I 5381

Mg I 4572

CN band

500 nm

800 nm

1200 nm

1600 nm




mostly radiative


Pressure (dyne cm^-2)

3D Radiation Transport & NLTE

Computed for photospheric convection simulation snapshot

with data from Stein & Nordlund 2005

network and its change over the cycle what is quiet sun








Network and its change over the cycle, what is “quiet-Sun”?

In the so-called “quiet-Sun”, i.e. locations where no obvious AR are present, the intensity distribution of the network is observed to change with the solar cycle (maybe not strictly in phase with the sunspot index).

This has implications for SSI and for TSI.

But available images lack reliable absolute calibration. Day to day matching was done with the median.

Feature, model, TSI

Intensity distribution at the disk center

controversy2 nuv observations
Controversy2: NUV Observations

Various instruments claiming reliable calibration for long term

Most instruments show variation of about ~50/1000~5% except for SUSIM.

Only SUSIM measured one peak, since UARS/SOLSTICE hardware failed in 2000

Both SORCE instruments show ~6% variations; their decreasing SSI turned around to increasing as SC 24 started in ~2010, but later data is not shown here.

nuv effects on o3
NUV effects on O3

Calculations were carried out by Merkel et al (see GRL38, L13802 2011), using SORCE data extrapolated in time. These are done with WACCM3 in static SSI runs.

Other authors also made simplified calculations showing important differences.

I am carrying out transient WACCM4 (NCAR Community Earth System Model 1.0.3 ) runs with coupled atmosphere, ocean, land, and ice. O3 is included but so are many other processes.

cesm waccm4 for ssi study
CESM (WACCM4) for SSI study
  • Transient runs 1955-2005 including all observed forcing. Imposing observed QBO.
  • SSI: wavelength < 120 nm uses F10.7 proxy
  • SSI: 120 nm < wavelength < 100 μm:
    • “const” uses time independent low activity SSI
    • “nocorr” from SRPM + PSPT & Meudon images, repeats SC23 (with stretching)
    • “corr” same as above but with a correction to match observed TSI, still under development
    • “nrlssi” using the default SSI in CESM, from Lean
ssi nocorr model of sc23 vs nrlssi










SSI “nocorr” model of SC23, vs NRLSSI

mW m-2 nm-1

W m-2

follow some preliminary results
Follow some preliminary results
  • Only from one complete run of each case, the 3 years near the minimum, over 4 solar cycles were averaged and compared.
  • The same was done for and 3 years near the maximum over 4 solar cycles.
  • Then, the averages of 12 years near min and 12 years near max were subtracted to show the effect of SSI change.
  • The maps shown below are for the DJF season, the JJA patterns are different.
  • The zonal means are annual.
  • More instances are running to form an ensemble. However, Earth behavior is only one instance.
preliminary waccm surface results
delta.CLOUDT const

delta.CLOUDT nocorr

delta.CLOUDT nrlssi

delta.TS const

delta.TS nocorr

delta.TS nrlssi

delta.PS const

delta.PS nocorr

delta.PS nrlssi

Preliminary WACCM surface results

Cloud fraction

Surfacte temperature

Surface pressure



enso and natural variability issues
ENSO and “natural” variability issues

Does the SSI choice affect these?

More “realizations” are needed

How to cancel volcanic effects?

Volcanic eruptions are a big issue:

Mt. St. Helens 1980

El Chichon 1982

Pinatubo 1991


zonal mean t and h2o changes



T (K)



Zonal mean T and H2O changes

“const” displays changes that are not due to the SSI choice, difference of difference can eliminate some but is affected by the “noise” in both “nocorr” and const”

Issues analyzing simulation results to separate SSI effects from other effectstropical (±25 deg) annual differences between peak and min years





Other WACCM Simulation Interesting Results


= DifDif.FSDS

Shows the downwelling solar shortwave flux at the surface increases of ~30 W m-2 at the Pacific Ocean Warm Pool region at solar max times. But was shown before that the surface temperature does not increase much there. Ocean effects, Kuroshio stream, moderate T?

The NRLSSI dif. of dif. have also some of this behavior on the Pacific Ocean Warm Pool but the details are quite different. Also, NRLSSI results show several differences in other regions, e.g. the patterns in Mexico Pacific area, Brasil Atlantic, and Madagascar Indian Ocean which are not shown by “nocorr” results


ocean gyres
Ocean gyres

Ocean currents couple to atmospheric winds and tropospheric energy transport. This is represented in CESM1.0.3/WACCM4 by the integration of the atmospheric model (CAM2) with the deep ocean model (POP).

The tropospheric and ocean phenomena are very tangled!

Analysis is very complex but these simulations contain a wealth of data which could nail down the physical processes induced by SSI changes.

That is, if one could also figure out other forcing and variability.

future work
Future work
  • All the maps shown above is for DJF season, similar ones for JJA season were done.
  • Still improving “corr” SSI case by reprocessing images into “corr2”, hope to have it by end of year 2012 .
  • Performing runs for more instances of all SRPM cases, necessary to separate natural variability and SSI effects 4 instances are the target.
  • Analysis of the data for ocean and other components of CESM model remains to be done.
  • Comparison between CESM 1.0.3 and [email protected] atmospheric radiative heating/cooling to be carried out to evaluate spectral model and resolution effects.
  • FUV/EUV SSI ongoing modeling for replacing F10.7 proxy and for forecast of thermospheric neutral density and ionization.
dark active regions
Dark active regions

A nice example on 2/3/2007 shows two large magnetic active regions sunspots side-by-side and one is associated with a lot of chromospheric and coronal heating but the other is not showing much heating.

The magnetic flux of the sunspots is not too different but the bright region is bipolar and more complex.