Solar Cycle Electron Radiation Environment at GNSS Like Orbit A. Sicard-Piet (1), S. Bourdarie (1), D. Boscher (1 ), R. Friedel (2), T. Cayton (2), E. N. Sosnovets (3), V. Kalegaev (3), R. Ecoffet (4), G. Rolland (4) (3) MSU, Russian Federation (1) ONERA/DESP, Toulouse, France (2) Los Alamos National Laboratory, USA Third European Space Weather Week: November 2006, Brussels, Belgium (3) CNES, Toulouse, France

Data Analysis  Data Analysis - Data set (GPS Navstar, Glonass-94) - Contamination, Saturation Conclusions and Perspectives  Conclusions and Perspectives Outline Construction of the model  Construction of the model - Method used - Comparison with POLE model - Comparison with AE8 model

Data Analysis : Data Set GLONASS-94/DIERA2 2) A Russian spacecraft, with nearly the same orbit than GPS Navstar : GLONASS-94, equipped with DIERA2 particles detector measured MeV electrons between 1994/06/04 and 1996/09/ janv-88janv-92janv-96janv-00janv-04 date F10.7 (W.m - 2.Hz - 1 ) 1) Over the period from 1990 to present, 4 GPS Navstar satellites, equipped with BDD-II particles detectors which measure energetic electrons, were flown:  GPS-NS18  GPS-NS24 Only the five first energy channels have been used - Energy channels are different for each GPS satellite - For two satellites, energy channels change during the period of the satellite (NS-24 and NS -28)  GPS-NS28  GPS-NS33 Difficulty in GPS/BDD-II data analysis: GPS-NS18 / BDD2 GPS-NS24 / BDD2 GPS-NS28 / BDD2 GPS-NS33 / BDD2

Data Analysis : Data Set GPS-NS24 Ele > 0.8 MeV (cm -2.s -1.sr -1 ) GPS-NS28 Ele > 0.8 MeV (cm -2.s -1.sr -1 ) GLONASS-94 Ele MeV (MeV -1.cm -2.s -1.sr -1 )

Saturation of the data NS24/BDD2 1992/04/ /04/ L Ele. > 0.28 MeV (cm -2.s -1.sr -1 ) Saturation  Saturation: Electron flux is limited to certain value which cannot be exceeded (~ 10 7 cm -2.s -1.sr -1 ) while the percentage of points increases. Data Analysis : Saturation, contamination The method used to analyze GPS/BDD-II and GLONASS-94/DIERA2 data in term of saturation and contamination is compliant with the guidelines of COSPAR PRBEM: data analysis procedure.

Data contamination  The contamination of GPS/BDD-II electron channels by protons from solar flares is characterized by a correlation between measurements of GPS electron channels and protons from GOES data. Contamination GOES-08 Protons MeV GPS-NS-33 Electrons > 1.32 MeV Contamination Data Analysis : Saturation, contamination

Interpolation in energy Problems: - Energy channels of GPS Navstar satellites are different from one satellite to another. - Drift in energy Solutions:  Definition of a grid in energy and interpolation in this grid Construction of the model : Method used Calculation of yearly averaged electrons fluxes along GNSS orbit (Only the years with more than 70 % of data of good quality are kept) Year  Being given the quality and the quantity of the data, only the first five energy channels will be used in the MEO model: 0.28 MeV, 0.40 MeV, 0.56 MeV, 0.80 MeV and 1.12 MeV. Year of the solar cycle

MEO model Limitation: - only one solar cycle, not full - small statistic  Development of a mean model over a solar cycle and not dependant of the year of the solar cycle. Definition of an error bar (representing the uncertainties of the measurements and the fluctuations of flux levels from one solar cycle to another) : *E(keV) Mean flux Min flux ( / error bar) Max flux ( * error bar) Construction of the model : Method used

Construction of the model : Comparison with POLE model Comparison between MEO model at 5.5 < L < 6.5 and POLE model at geostationary orbit (yearly averaged electrons fluxes in function of the year of the solar cycle)  There is a good agreement between electron flux levels deduced from MEO model near geostationary orbit (5.5 < L< 6.5) and the one deduced from POLE model. MEO L~6 POLE MEO L~6 POLE

 Mean electrons flux over a solar cycle deduced from MEO model is similar to electrons flux deduced from NASA AE8 model. Construction of the model : Comparison NASA AE8 model Comparison between MEO model and NASA AE8 model along GNSS orbit Electrons flux over one solar cycle (11 years) Energy (MeV) MEO : mean case MEO : best case MEO : worst case AE8 (7 years MAX, 4 years MIN)

Conclusions MEO model (GNSS like orbit) : - from 0.28 MeV to 1.12 MeV - based on 14 years of GPS Navstar data (NS-18, NS-24, NS-28 and NS-33) and on GLONASS-94 data - electron fluxes deduced from the model are not dependent of the year of the solar cycle (mean model over 11 years).  Comparison between MEO model and NASA AE8 model: - Mean electrons flux deduced from MEO model is equivalent to the one deduced from AE8 model. Perspectives  Improvement of MEO model in order to evaluate electrons fluxes in function of the year of solar cycle (better statistics is essential: more data is needed)

Data Analysis : Background Ratio Flux with bg / Flux without bg Energy (MeV) Background of the instrument Background has been removed Definition of the background  In order to analyze the importance of the background in yearly averaged electron fluxes (used to construct the model), two averages have been calculated: one by taking into account the background and one without background.  Ratio is less than a factor 2  Background plays a minor role in yearly averaged fluxes. Importance of the background In the model we use yearly averaged flux with background: a small overestimation of electrons fluxes in the model is more secure than a underestimation