地面放射性异常引起电离层扰动的计算研究

Calculation Study of Ionospheric Disturbance Caused by Ground Radioactive Anomaly

地面的放射性主要来源于空间辐射、地壳放射性元素衰变和人工核活动等,地面放射性可引起地表电场的变化,地表电场变化的区域和强度达到一定的条件后可引起电离层的扰动。基于LAIC电场机制假设,本文从地面放射性引起空气电离开始推导地表大气电导率变化、地面垂直电场至电离层底部传导过程,根据临界电场理论计算地面大气垂直电场、大气附加电流密度以及电离层准静态电场的电势分布,最后通过格林函数法求解得到电离层中水平电场的分布。建立了基于地面放射性活度的地表大气电导率公式,改进了地表异常电场传播到电离层的计算过程,给出了电离层电场扰动的计算公式。利用氡和地面电场仪的实例观测数据对地面放射性异常引起的电离层扰动的计算过程进行了验证,理论计算得到的地面电场和电离层扰动的结果与实际测量结果基本一致。

The ionosphere is composed of electrostatic equilibrium plasma,which can produce electromagnetic wave reflection,scattering,absorption and refraction,and is the key factor affecting the propagation of electromagnetic wave in the atmosphere.The delay of electromagnetic wave signal caused by the ionosphere anomaly has become the maximum error source of GPS.Ground radioactivity can cause the change of earth’s surface electric field,earth’s surface electric field change can cause the disturbance of ionosphere when the conditions of area and amplitude reach certain threshold.The main sources of ground radioactivity are cosmic rays,the decay of radioactive minerals in earth’s crust and artificial nuclear activities,among which the crustal radioactive minerals are considered as the chief source of earth’s surface atmospheric ionization.For the interpretation of the ionospheric disturbance before large earthquake,it is stated that caused by the process of earthquake preparation,the change of fault stress leads to radon gas in rock emitted from inner to surface,and then radon concentration above the fault appears abnormal.Radon progeny radioactive decay releases a lot of energy and high energy alpha particles,and then the air is ionized,which triggers a series of physical and chemical changes.A large number of ions and ion clusters are generated near the earth’s surface,forming low altitude current and local electric field,changing the atmospheric conductivity,disturbing the gradient of atmospheric electric field,causing abnormal changes of atmospheric electric field,especially in the vertical electric field,and then affecting the ionosphere.The ionosphere can be divided into D,E and F layers due to the obvious stratification of its electron density.In order to simplify the analysis model,the single-layer model was adopted as the structure model of the ionosphere for derivation and calculation.Ionospheric disturbances were mainly presented as disturbances of ionospheric electric field,magnetic field,total electron content(TEC),critical frequency,etc.The characteristic parameters of the ionosphere can be calculated by the analysis of electromagnetic pulse reflection,and the numerical values of ionospheric disturbances can be extracted.Based on LAIC electric field mechanism hypothesis,the change of atmospheric conductivity above the earth’s surface and the conduction process from ground vertical electric field to the bottom of ionosphere were deduced,starting from air ionization caused by surface radioactivity.According to the critical electric field theory,the atmospheric additional current density and the potential distribution of the ionosphere with the condition of quasi-static electric field were calculated.Finally,the distribution of the horizontal electric field in the ionosphere was obtained by Green’s function method.In this paper,earth’s surface atmospheric conductivity formula based on ground radioactive activity was established,the calculation process of earth’s surface abnormal electric field propagating to ionosphere was improved,and the calculation formula of ionospheric electric field disturbance was given.The calculation process of ionospheric disturbance caused by ground radioactivity anomaly was verified by the observation data of gas radon and earth’s surface electric field instrument.The theoretical calculation results of earth’s surface electric field and ionospheric disturbance are basically consistent with the actual measurement results.