Heynderickx sampex

SAMPEX/PET proton model : SAMPEX/PET proton model D. Heynderickx1, M.D. Looper2, J.B. Blake2 1BIRA, Belgium 2Aerospace Corp., U.S.A.


Overview : Overview Variability of the low altitude trapped proton environment Strengths and shortcomings of AP-8 SAMPEX mission and PET instrument New model development Coordinate system Data binning Solar cycle dependence and seasonal variations Sample model outputs and comparison to AP-8 Work to do Model software and distribution issues


Low altitude proton flux variations : Low altitude proton flux variations Geomagnetic secular variation Solar cycle activity Solar proton events Changes in atmospheric density


AP-8 strengths and shortcomings : AP-8 strengths and shortcomings Strengths Widely known and used, integrated in existing applications Provides (nearly) full energy range 100 keV – 400 MeV Provides complete spatial coverage Reasonably straightforward to use with TRARA Shortcomings No updates since 1970; would be very difficult to do No real solar cycle dependence No error bars ('probably a factor of two') TRARA doesn’t work well at low altitude


SAMPEX mission : SAMPEX mission SMEX mission Launched in 1992 Still operational? Orbit: 520 x 670 km, 82º, Sun pointing 3 month periodicity in orbit configuration Most of the time in non-spinning mode For this study: proton/electron telescope (PET)


Proton/Electron Telescope : Proton/Electron Telescope Array of Si solid state detectors Passive shielding + anti-coincidence through guard rings dE/dx – total energy technique + coincidence logic -andgt; 15 channels Opening angle: 58º -andgt; large geometric factor Counts and livetimes over 6s are stored because of telemetry limits


PET Channels : PET Channels


Coordinate system : Coordinate system (B,L) type coordinates not well suited for low altitudes Alternatives: Kaufmann K = I√B; minimum altitude on drift shell


Proton flux time series : Proton flux time series Monthly averages + F10.7 Averages + inverse F10.7 Averages + inverse F10.7 + inverse MSIS atmospheric density


Solar cycle dependence : Solar cycle dependence Monthly averages grouped by month Hysteresis effect Different behaviour for descending and ascending phases Two separate fits work better


Seasonal variations : Seasonal variations Annual variation of F10.7 fit parameters (coloured lines) Sine fit with fraction of year (black lines) MSIS total mass density Inverse density


Model fluxes : Model fluxes Fit was applied to all energy, K and hmin bins Model consists of tables of fit coefficients


Slide13 :


Work to do : Work to do Further validation of fitting procedure Smoothing in (hmin,K) plane Spectrum fits Elimination of data contaminated by SEP events Validation with AZUR, CRRES, … data


Final model format : Final model format Presently: tabel of sine fit coefficients for (E,hmin,K,F10.7,DOY) Sine fit parameters are extracted from (E,hmin,K) bin DOY is used with sine fit to generate coefficients for parabolic F10.7 function F10.7 function yields flux Energy dependence could also be fitted Low altitude proton model is probably not far away from standardization


Software and distribution issues : Software and distribution issues Software implementation Currently in IDL, will be ported to Fortran Stand-alone version for use with SPENVIS 'library' type version as a subroutine callable from IDL, Fortran, C, … Distribution Model source code and coefficients on web site, downloadable after user identification Regular updates when new data become available or fitting improves; notification of registered users Code for calculating magnetic coordinates must be available as well (UNILIB, …)