Photoelectrons as a tool to evaluate
Solar EUV and XUV model irradiance
spectra.
W.K. Peterson1, T.N. Woods1, J.M. Fontenla1,
P.G. Richards2, W.K. Tobiska3, S.C. Solomon4,
and H.P. Warren5
1LASP/CU, 2George
Mason, 3Utah State,
4HAO/NCAR, 5NRL
Peterson, SORCE, Sedona, 2011
Outline
• How do we compare photoelectrons and irradiance
models?
• Some details of the comparisons:
• Conclusions:
– Solar irradiance models and photoelectron codes agree
reasonably well with observations except during some periods
of Solar activity.
– No code/model pair captures the full variability of observed
photoelectron fluxes within the ± 20% observational
uncertainties
– During modest Solar activity in December 2006, we estimate
that Solar irradiance models underestimated the ~3 x10-4 W/m2
irradiance below 10 nm by 30%.
– Surprisingly the empirical HEUVAC and EUVAC models
produce photoelectron spectra that generally agree with the
observations on daily and solar rotation period time scales.
Peterson, SORCE, Sedona, 2011
Uncertainties in solar Irradiances create
uncertainties in thermospheric models
Altitude-wavelength
dependence of
energy deposition
from solar irradiance
in units of Log10(Wm4)
From Solomon and
Qian 2005
Solar minimum
conditions
Lyman Alpha = Fundopause
Color Bar: Log10(Wm-4)
Peterson, SORCE, Sedona, 2011
Photoelectron Observations
FAST observations
available from
January 1, 1997 to
April 30, 2009
ePOP observations
available in 2012?
Peterson, SORCE, Sedona, 2011
Photoelectron Observations
Energetic
photoelectrons
are produced
primarily by
irradiance
below ~ 45 nm
so we display
energy in units
of equivalent
wavelength
September 14 to December 31, 2006
Peterson, SORCE, Sedona, 2011
Solar irradiance models
TIMED/SEE observations (Right panel, black line)
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Peterson, SORCE, Sedona, 2011
Comparison of observed and modeled
photoelectron
spectra
We estimate that escaping photoelectrons have ~1.7 % of the
power incident ionizing solar irradiance below ~45 nm.
Peterson, SORCE, Sedona, 2011
Comparisons of power
density (right) and
relative number flux
differences (below)
2 – 45 nm
Number Flux
Power Density
2 – 45 nm
4 – 8 nm
Peterson, SORCE, Sedona, 2011
Average Power Density from
September 14 – December 31
for 6 Energy bands
FLIP CODE
GLOW CODE
Power Density in W/m2
Grey indicates value is outside +/- 20% observational uncertainty
FLIP/HEUVAC 6 bands within +/- 20%
GLOW/HEUVAC, GLOW/FISM, GLOW/S2000, and SRPM driven
by Rome observations with a coronal filling factor of 0.5 have 5
bands within +/-20%
Peterson, SORCE, Sedona, 2011
Comparisons of Photoelectron
Production Models and Observations
• Best Agreement depends on method used
•Relative Differences of photoelectron number
flux spectra are minimized by the FLIP/HEUVAC
and the FLIP/ and GLOW/ SRPM Rome pairs
•Average power density in selected bands best
matched by FLIP/HEUVAC, GLOW/HEUVAC
FISM, S2000, SRPM Rome model pairs
Peterson, SORCE, Sedona, 2011
Conclusions
• Solar irradiance models and photoelectron codes agree
reasonably well with observations except during some
periods of Solar activity.
• During modest Solar activity in December 2006, we
estimate that Solar irradiance models underestimated the
~3 x10-4 W/m2 irradiance below 10 nm by 30%.
• No code/model pair captures the variability of observed
photoelectron fluxes within the ± 20% observational
uncertainties
• Surprisingly the empirical HEUVAC and EUVAC models
produce photoelectron spectra that generally agree with
the observations on daily and solar rotation period time
scales.
• We need SDO/EVE observations to fully understand the
temporal and spectral variations of solar irradiance.
Peterson, SORCE, Sedona, 2011
Extra Slides