CHAMOS

The APEEP electron precipitation models and ionization data sets were developed in a collaboration of institutes as a response to requests from the SOLARIS-HEPPA community. The datasets provide the solar forcing of medium-energy electrons (MEE; energies between about 30 keV and 1 MeV), which information serves as input into long-term simulations of atmosphere and climate. The models were developed using the electron flux observations of the MEPED instruments aboard the POES satellites.

Figure: Ionization rates at 80 km altitude due to energetic electron precipitation according to the model of van de Kamp et al. (2018), as a function of MLT (Magnetic Local Time) and McIlwain L-shell value (a measure of magnetic latitude), for three levels of magnetic disturbance.

The latest model APEEP v3 (van de Kamp et al., 2025) was based on the MEPED measurents from 1998-2023. The electron content of the bounce loss cone was derived from both the 0-degree and 90-degree channels of the SEM-2 MEPED package in combination with models of pitch angle diffusion, following the approach of Nesse et al. (2016). The data were corrected and calibrated for proton contamination and instrument sensitivity as described by Asikainen and Mursula (2013).

The electron fluxes were modelled from the measured data, separately in three separate energy ranges (30-100, 100-300 and 300-1000 keV), with a 1-day time resolution, as functions of magnetic latitude and value of the Ap index. As part of the model, the Ap index is integrated over a convolution function in time, to account for a latitude- and energy-dependent delay in response to magnetic disturbances. The energy spectrum between 30 and 1000 keV was constructed from these three modelled energy bins by fitting a power-law model with one gradient valid for 30-100 keV electrons and another gradient for 100-1000 keV. The resulting energy-flux spectra were used to calculate atmospheric ionization rates, using the NRLMSISE-00 atmosphere (Picone et al., 2002) and parameterized ionization rate calculation by Fang et al. (2010).

In older versions of the model and older data sets, the methods described above were in some respects different and less advanced. Details can be found in the respective references.

The following provides a brief description of the available data sets, links to more detailed information, and access to the data sets. These data sets are freely available for scientific use. We ask you to cite the references, as given below for each data set, in any publication using the data.

APEEP v3 PROXY MODEL, DATA SET

APEEP v3, MEE precipitation model and ionization rates: years 1850-2023, temporal resolution 1 day, part of the CMIP7 recommendation. Access the data set through the SOLARIS-HEPPA CMIP7 page.

EARLIER PROXY MODELS, DATA SETS

APEEP v1, MEE precipitation model and ionization rates: years 1850-2015, temporal resolution 1 day, part of the CMIP6 recommendation. This is a statistical model fitted on zonally averaged MEPED data, it is described in detail by van de Kamp et al. (2016). This is a proxy model depending solely on the geomagnetic Ap index, which allows to extend the data set back in time. This model is recommended for the Coupled Model Intercomparison Project Phase 6 (CMIP6), see Matthes et al. (2017) for details. Access the data set through the SOLARIS-HEPPA CMIP6 page.

APEEP v2, MEE precipitation model and ionization rates: years 1932-2017, temporal resolution 1 day. This model is an improved version of APEEP v1. Noise-affected data were more carefully removed, to provide more realistic representations of low fluxes during geomagnetically quiet times. For a detailed description, see van de Kamp et al. (2018). Data access: contact Pekka Verronen (FMI).

APEEP-MLT v2, MEE precipitation model and ionization rates: years 1932-2017, temporal resolution 1 day (with 8 MLT sectors). Distinct from the earlier versions, which were zonally averaged, this model is dependent also on the magnetic local time (MLT) which is an important factor affecting precipitation flux characteristics. For a detailed description, see van de Kamp et al. (2018). Data access: contact Pekka Verronen (FMI).

DSTEEP v1, MEE precipitation model and ionization rates: years 1957-2015, temporal resolution 1 day. This is otherwise as APEEP v1, except that the Dst index is used as the proxy instead of Ap. See a detailed description in van de Kamp et al. (2016). Data access: contact Pekka Verronen (FMI).

DATA SETS CALCULATED DIRECTLY FROM MEPED DATA

ISSI MEE ionization rates: years 2000-2012, temporal resolution 3 hours. These rates are calculated directly from the zonally averaged electron fluxes observed by MEPED after some major corrections to the data. Note that compared to the other data sets, the energy range is different (50-2000 keV) and a different method was used to calculate ionization rates from spectra (Rees, 1989). For a detailed description, see Orsolini et al. (2018). Data access: contact Pekka Verronen (FMI).

NOHO MEE ionization rates: years 2013-2015, temporal resolution 3 hours. These rates are also calculated from MEPED observations. However, the flux data correction is different. For more information, see Newnham et al. (2018) and Orsolini et al. (2018). Data access: contact Pekka Verronen (FMI). Note: we do not recommend this data set for general use due to issues found in the flux data correction method.

REFERENCES:

Asikainen, T., and Mursula, K. (2013). Correcting the NOAA/MEPED energetic electron fluxes for detector efficiency and proton contamination, J. Geophys. Res., 118 , 6500-6510. DOI:10.1002/jgra.50584

Nesse, H., Sandanger, M. I., Ødegaard, L.-K. G., Stadsnes, J., Aasnes, A., and Zawedde, A. E. (2016). Energetic electron precipitation into the middle atmosphere - constructing the loss cone fluxes from MEPED POES, Journal of Geophysical Research: Space Physics, 121 (6), 5693-5707. DOI:10.1002/2016JA022752

van de Kamp, M., Asikainen, T., Nesse, H., Seppälä, A., Funke, B., Sinnhuber, M., Verronen, P. T., and Marsh, D. R. (2025), An improved model of energetic electron precipitation providing a long-term ionization data set for CMIP7, to be submitted to J. Geophys. Res.

Fang, X., Randall, C. E., Lummerzheim, D., Wang, W., Lu, G., Solomon, S. C., and Frahm, R. A. (2010). Parameterization of monoenergetic electron impact ionization, Geophys. Res. Lett., 37, L22106. DOI:10.1029/2010GL045406

Picone, J. M., Hedin, A. E., Drob, D. P., and Aikin, A. C. (2002), NRLMSISE-00 empirical model of the atmosphere: Statistical comparisons and scientific issues, J. of Geophys. Res., 107(A12), 1468. DOI:10.1029/2002JA009430

van de Kamp, M., A. Seppälä, M.A. Clilverd, C.J. Rodger, P.T. Verronen, and I.C. Whittaker (2016), A model providing long-term datasets of energetic electron precipitation during geomagnetic storms, J. Geophys. Res. Atmos., 121, 12520-12540. DOI:10.1002/2015JD024212

Matthes, K., Funke, B., Andersson, M.E., Barnard, L., Beer, J., Charbonneau, P., Clilverd, M.A., Dudok de Wit, T., Haberreiter, M., Hendry, A., Jackman, C.H., Kretschmar, M., Kruschke, T., Kunze, M., Langematz, U., Marsh, D.R., Maycock, A., Misios, S., Rodger, C.J., Scaife, A., Seppälä, A., Shangguan, M., Sinnhuber, M., Tourpali, K., Usoskin, I., van de Kamp, M., Verronen, P.T. and Versick, S. (2017), Solar Forcing for CMIP6, Geosci. Model Dev., 10, 2247-2302. DOI:10.5194/gmd-10-2247-2017

van de Kamp, M., Rodger, C.J., Seppälä, A., Clilverd, M.A., and Verronen, P.T. (2018), An updated model providing long-term datasets of energetic electron precipitation, including zonal dependence, J. Geophys. Res. Atmos., 123, 9891-9915, DOI:10.1029/2017JD028253

Rees, M. H. (1989). Physics and chemistry of the upper atmosphere, Cambridge atmospheric and space science series. Cambridge, UK: Cambridge University Press. DOI:10.1017/CBO9780511573118

Orsolini, Y.J., C. Smith-Johnsen, D.R. Marsh, F. Stordal, C.J. Rodger, P.T. Verronen, and M.A. Clilverd (2018), Mesospheric nitric acid enhancements during energetic electron precipitation events simulated by WACCM-D, J. Geophys. Res. Atmos., 123, 6984-6998. DOI:10.1029/2017JD028211

Newnham, D.A., M.A. Clilverd, C.J. Rodger, K. Hendrickx, L. Megner, A.J. Kavanagh, A. Seppälä, P.T. Verronen, M.E. Andersson, D.R. Marsh, T. Kovacs, W. Feng, and J.M.C. Plane (2018), Observations and modelling of increased nitric oxide in the Antarctic polar middle atmosphere associated with geomagnetic storm driven energetic electron precipitation, J. Geophys. Res. Space, 123, 6009-6025. DOI:10.1029/2018JA025507