Research On Quantitative Assessment Of The Radiation Belt AP9 Model

The radiation belt is the main radiation environment of the satellite orbit.The radiation belts include inner radiation belt,outer radiation belt and slot region.The inner radiation belt is mainly composed of energetic protons,and the overall distribution is relatively stable.The main component of the outer radiation belt is high energy electron,and the high energy electron flux is greatly influenced by geomagnetic changes.All kinds of disturbances were caused to the detection equipment and precision equipment on the satellite in the low orbit radiation belt especially the South Atlantic Anomaly region.Therefore,the research and evaluation of the new model of space radiation environment and radiation belts are of great scientific significance and practical value.Aiming at the radiation belt AP9 model quantitative evaluation system is not enough,the observational data which represents the high,medium and the low solar activity was selected as reference data,and he South Atlantic Anomaly region which is of researching value was selected as comparison area,improved quantitative evaluation index was defined based on the existing evaluation index,and then based on the improved quantitative evaluation index the radiation belt AP9 model was compared with AP8 model and the reference data,finally,systemic quantitative evaluation of the AP9 model in the South Atlantic Anomaly region was finished.The main research contents are as follows:(1)Systemic quantitative evaluation of the AP9 model in SAA regionThe high,medium and low solar activity level is classified in view of the F107 index.The corresponding data of the proton flux between 140 and 500 MeV observed by NOAA-15 are chosen as the reference data.The objective region is the South Atlantic Anomaly region.The evaluation criterions conclude the goodness of boundary fitness and the magnitude difference between model and observation.By contrasting with the current applied AP8 model and reference data under high,medium and low solar activity level,the new radiation belts proton model-AP9 is systematically and quantitatively evaluated.The results show that:Both the AP8 and AP9 model can reconstruct the SAA region.However,the outline of SAA region reconstructed by AP8 is more consistent with the observation than that of AP9.On the whole,the AP8 and AP9 proton flux results are higher than the observations,and AP8 results are closer to the observations than AP9 results.The lower the solar activity level,the smaller the difference between AP9 model results and observations.(2)Study on the distribution law of radiation belt proton flux with pitch angleIt is necessary to point out that the conclusions of the assessment were based on the assumption that the radiation belt proton flux is isotropic distributed with the pitchangles,but this assumption does not apply to all situations,for this reason this paper will further studies the radiation belt proton flux distribution with the pitch angles,and the radiation belt AP9 model will be reevaluated based on this distribution law.Based on the study of proton flux distribution in the inner radiation belt from FY3 A observation,it is found that the 3-5MeV energy channel shows a second anomalous region besides the South Atlantic Anomaly region.Compared with the ‘main South Atlantic Anomaly region',the new anomaly region is weaker and smaller,so it is called ‘sub South Atlantic Anomaly region'.Based on this discovery,this paper attempts to explore the formation mechanism of ‘sub South Atlantic Anomaly region'.The results show that:In the process of studying,it was found that the radiation belt proton flux approximately normally distributed with pitch angle,and this law was further verified by the NOAA observation data,finally,the formation mechanism of ‘sub South Atlantic Anomaly region' was successfully explained by this law.(3)Improved quantitative evaluation of the AP9 model in SAA regionAiming at the defects of that the proton flux in radiation belt is isotropic with the pitch angle,the omnidirectional proton flux between 140 and 500 MeV observed by NOAA-15 under high,medium and low solar activity level is recalculated based on the fitted normal distribution law,and treated as the reference data.In addition,similarity degree which is a new comprehensive evaluation index is defined based on the analog deviation,and the AP8 model and AP9 model are reevaluated with the new evaluation index in the SAA region.The results show that:The similarity degree between AP9 model and observation is higher than that of AP8 model under high,medium and low solar activity level;As the level of solar activity decreases,the similarity degree between AP9 model and observation remained almost unchanged,however,the similarity degree between AP8 model and observation becomes lower and lower.