Photoelectrons as a Tool to Evaluate Spectral and Temporal Variations of Solar EUV Irradiance Models

W.K. Peterson1, J.M. Fontenla1, T.N. Woods1,

P.G. Richards2, S.C. Solomon3, H.P. Warren4,

W.K. Tobiska5, and P.C. Chamberlin6

1LASP/CU, 2George Mason, 3NCAR/HAO,

4NRL, 5Utah State, 6NASA/GSFC

Peterson, MURI, October 2003

Outline• Our method to compare photoelectron energy

observations and irradiance models • Comparisons of photoelectron energy spectra with those

predicted with two photoelectron production codes driven by the SPRM predictive model, and the FISM, HEUVAC, S2000, and NRL irradiance models

• Conclusions: – Surprisingly the empirical HEUVAC (EUVAC extended to 1 nm)

model produces photoelectron spectra that match the observations on daily and solar rotation period time scales.

– The SRPM prediction model matches the data as well or better than any of the data or index driven models.

– The physics based NRLEUV model does the poorest job of capturing the variation of energetic photoelectrons on a solar rotation time scale.

Peterson, MURI, October 2003

Uncertainties in solar Irradiances create uncertainties in thermospheric models

Altitude-wavelength dependence of energy deposition from solar irradiance in units of Log10(Wm-4)

From Solomon and Qian 2005

Solar minimum conditions

Color Bar: Log10(Wm-4)Peterson, MURI, October 2003

Photoelectron Observations

FAST observations available from January 1, 1997 to April 30, 2009

ePOP observations available in late 2011

Peterson, MURI, October 2003

Model Data Comparison

Average of 56 one-minute average spectra obtained for SZA < 90o

Two PE production codes

Seven Solar irradiance models

Peterson, MURI, October 2003

Transformation to Equivalent Wavelength

Use a constant15 eV ionization potentialPeterson, MURI, October 2003

Relative DifferenceObservation - Model / Model

as a Function of the Wavelength Equivalent of the Photoelectron Energy

S/N inadequate below ~3 nm (> 385 eV)

Above ~16 nm differences are less than +/- 50%

Above ~30 nm slight differences in PE’s predicted from the GLOW and FLIP models.

Both the GLOW and FLIP codes showTIMDED/SEE irradiances systematicallylow below about 15 nm

Peterson, MURI, October 2003

* GLOW/HEUVAC best agrees with observations

FAST Observations from August 31 to September 30 2005

Observed Photoelectron flux vs. Energy (eV)

Vs. Equivalent Wavelength (nm)

F10.7

KP

DST

Each line in the color spectrogram panels shows a daily average photoelectron energy spectra with the flux given by the color bars on the right.

Peterson, MURI, October 2003

F10.7

AP

Differences between Observations and Model PE Energy Spectra over a Solar Rotation

HEUVAC

SPRM-Rome

FISM

S2000

NRLEUV

Photoelectron energy spectra produced using the empirical HEUVAC model agree best with Observations.

The SPRM predictive model does as well as the TIMED/SEE based FISM model

Peterson, MURI, October 2003

SPRM-MLSO

Observation-Model Differences -2

FISM produces good agreement except for underestimating the PE fluxes between 5 and 15 nm

S2000 produces low fluxes below 15 nm and relatively good agreement above 15 nm.

NRLEUV systematically underestimates the photoelectron flux below 15 nm

RED: Model >200% LowGREEN: Model = ObservationsBLACK: No data

Peterson, MURI, October 2003

HEUVAC

SPRM-Rome

FISM

S2000

NRLEUV

SPRM-MLSO

Solar Irradiance Models Differ at Many Wavelengths

HEUVAC Model Color Bar is Irradiance in w/m2

Relative Differences are(Model - HEUVAC) / HEUVAC

HEUVAC

FISM

S2000

NRLEUV

RED: Model >400% than HEUVACGreen: Model = HEUVAC

Irradiance models are qualitatively

different above and below

~27 nm Peterson, MURI, October 2003

SPRM-Rome

SPRM-MLSO

F10.7

Irradiance Power above and below 27 nm

HEUVAC

FISM

S2000

NRLEUV

Lowest: NRLEUVHighest: HEUVAC/S2000

Lowest: HEUVAC/NRLHighest: SPRM

SPRM-Rome

SPRM-MLSO

Peterson, MURI, October 2003

Photoelectron spectra produced using HEUVAC agree best with data

Irradiance Spectral Models

• HEUVAC model has by design has broad spectral structure (~1eV) above 27 nm

• To first order all models agree about the spectral shape below 27 nm

• The most significant differences between irradiance models are in the relative power above and below 27 nm.

HEUVAC

FISM

S2000

NRLEUV

SPRM-Rome

SPRM-MLSO

Peterson, MURI, October 2003

Conclusions• Surprisingly the empirical HEUVAC (EUVAC extended

to 1 nm) model produces photoelectron spectra that best match the observations on daily and solar rotation period time scales.

• Fontenla’s SRPM prediction model matches the photoelectron data as well or better than any of the other data or index driven models investigated.

• The physics based NRLEUV model does the poorest job of capturing the variation of energetic photoelectrons on a solar rotation time scale.

• We need SDO/EVE observations to fully understand We need SDO/EVE observations to fully understand the temporal and spectral variations of solar the temporal and spectral variations of solar irradiance.irradiance.

Peterson, COSPAR, 2010, C12-0018