【作者】 陈光明；

【导师】 徐寄遥； 王文斌；

【作者基本信息】 中国科学院研究生院（空间科学与应用研究中心） ， 空间物理学， 2009， 博士

【摘要】 本文主要包括两部分的内容,第一部分为顶部电离层O+场向扩散通量研究,分别利用CHAMP卫星和COSMIC星座的资料研究了太阳活动高年和太阳活动低年中低磁纬扩散通量的统计特征,还利用非相干散射雷达数据分析了磁暴时中纬顶部电离层扩散通量的变化特征;第二部分分析了CHAMP卫星的就地观测资料,包括大气密度、电子密度、电子温度,介绍了大气密度的反演方法,并进行了密度模式方面的初步探索,这部分有较强的应用价值。第一部分:顶部电离层O+场向扩散通量研究。扩散通量的研究,对电离层和等离子体层/内磁层动力学和质量耦合的研究非常重要,对电离层和热层的动力学耦合研究也有重要的意义,而且还有助于人们分析清楚双极扩散作用和中性风、电场以及化学过程等各种物理过程对电离层结构的相对影响大小。扩散通量还是很多全球电离层-热层模式必需的上边界条件之一,如NCAR-TIEGCM和TING模式。(1)利用CHAMP卫星资料研究太阳活动高年顶部电离层O+场向扩散通量的统计特征。本文从等离子体运动方程出发,用CHAMP卫星的电子浓度剖面数据,结合经验模式IRI2007和NRLMSISE00,计算顶部电离层的O+场向扩散速度和扩散通量,并分析了2002年1月~2003年12月期间中低磁纬扩散速度和扩散通量的变化特征。结果表明,在中低磁纬地区,hmF2+100 km高度以下,平均扩散速度大约为-15 ms-1~25 ms-1;白天等离子体扩散速度的方向随高度增加由向下(极向)逐步变为向上(赤道向),方向转变的高度在hmF2+50 km左右。在中磁纬,向上的扩散通量和扩散速度在中午最大。白天,在磁纬±25°左右的区域存在着最大的向上等离子体扩散通量,而磁赤道区的等离子体通量很小。在分点O+扩散通量基本关于磁赤道对称,而冬季半球的等离子体扩散通量明显大于夏季半球的。(2)利用COSMIC卫星资料研究太阳活动低年顶部电离层O+场向扩散通量的统计特征。利用COSMIC掩星数据计算了2006年第300天至2007年第300天顶部电离层O+场向扩散速度和扩散通量,并分析其全球分布和日变化特征。在白天的较高高度(hmF2+80 km以上),各纬度等离子体扩散速度都向上;在夜间,扩散速度的方向向下。在白天的较高高度,在南北磁纬10°~20°左右存在着方向向上的最大扩散速度和扩散通量;而在夜间,在南北磁纬30°~40°左右,存在方向向下的最大扩散速度和扩散通量。在分点时,南北半球的扩散通量和扩散速度大致对称,而在至点,扩散通量存在着明显的南北半球不对称的现象,在白天的较高高度上(如hmF2+80 km以上),夏季半球中低纬度的扩散速度和扩散通量明显高于冬季半球的,而在至点的较低高度上(如hmF2+50 km),没有这样的特征,甚至冬季半球的扩散速度还高于夏季半球的。另外,不同纬度的扩散速度有着不同的日变化特征。通过对CHAMP资料和COSMIC资料研究结果的对比,发现太阳活动低年的最大扩散通量值要小于太阳活动高年的值。(3)利用非相干散射雷达资料研究磁暴时O+扩散通量的变化特征。本文利用Millstone Hill非相干散射雷达(288.5°E, 42.6°N)观测的电子密度、电子温度和离子温度剖面来计算扩散通量,并对2002年10月份两次磁暴期间的电离层扩散通量、扩散速度以及相关参数的变化特征进行了分析。发现在500 km高度上,两次磁暴的主相期间,白天向上的扩散通量有明显的减小,夜间向下的扩散通量明显增大;在两次磁暴的恢复相期间,夜间观测到比平静期更小的扩散速度,在某些时段其方向甚至转为向上。第二部分:利用CHAMP卫星的就地观测数据进行热层和电离层方面的研究。(1)大气密度研究。介绍了利用CHAMP卫星的加速度计数据和相关测量反演高层大气密度的方法,并尝试利用该数据建立大气密度的经验模式。随着越来越多载有加速度计的卫星开始运行,该研究结果有着广阔的应用前景。(2)电子温度和电子密度研究。利用CHAMP卫星朗缪尔探针的观测数据,分析了电子温度和电子密度年内变化特征以及它们与太阳活动的关系。更多还原

【Abstract】 This thesis includes two parts. One part is the study of O+ field-aligned diffusive fluxes in the topside ionosphere. In this part, the statistical characteristics of the diffusive fluxes in the mid- and low-latitude topside ionosphere are analyzed under low and high solar activity conditions from radio occultation measurements by CHAMP and COSMIC, respectively. The characteristics of diffusive fluxes during two geomagnetic storms are analyzed using the measurements by incoherent scatter radar. In the other part, the in-situ measurements, including atmospheric densities, electron densities and electron temperatures, are analyzed. A method of retrieving atmospheric density is introduced. The preliminary result of atmospheric density model is given. The study in this part has important applied values.1. The study of field-aligned O+ diffusive fluxes.The knowledge of plasma diffusive fluxes is not only important to the study of the dynamical and mass coupling between the ionosphere and plasmasphere/inner magnetosphere, but it is helpful to the research of the dynamical coupling between the ionosphere and thermosphere. It also helps to elucidate the relative contributions of each physical process, including neutral wind, electric field, chemistry and ambipolar diffusion, to variations of the global ionosphere during both storm and quite times. Topside diffusive fluxes are also one of the primary top boundary conditions for many global thermosphere/ionosphere models, such as the NCAR-TIEGCM and TING model.(1) The statistical characteristics of diffusive fluxes under high solar activity conditions are analyzed. O+ field-aligned diffusive velocities and fluxes in the topside ionosphere are calculated from electron density profiles retrieved from CHAMP radio occultation measurements and empirical predicts from IRI2007 and NRLMSISE00 models. The velocities and fluxes from January 2002 to December 2003 at low- and mid-latitudes have been statistically analyzed. The results show that the averaged velocities were between -15ms-1~25 ms-1. The diffusive fluxes during the daytime changed gradually from downwardto upward as altitude increases. The transition heights from downward flows to upward flows were about hmF2+50 km. The largest values of the upward diffusive fluxes and velocities occurred at around±25o geomagnetic latitude. The diffusive fluxes near the equator were small. During solstices the plasma fluxes in the winter hemisphere were larger than those in the summer hemisphere.(2) The statistical characteristics of diffusive fluxes under low solar activity conditions are analyzed. O+ field-aligned diffusive velocities and fluxes in the topside ionosphere have been calculated from electron density profiles retrieved from COSMIC radio occultation measurements. The diffusive velocities and fluxes from October 2006 to October 2007 at low- and mid-latitudes have been statistically analyzed. The results show that the directions of diffusive fluxes are upward in the daytime, but downward at night. The largest values of the upward diffusive fluxes and velocities during daytime occur at at geomagnetic latitudes from 10°to 20°above hmF2+80 km , whereas for the nighttime the maximum downward fluxes occur at geomagnetic latitudes from 30°to 40°. Diffusive fluxes are roughly symmetric around the magnetic equator during equanoxes. But they are asymmetric during solstices, the winter hemisphere has smaller fluxes than the summer hemisphere does above hmF2+80 km. In addition, the diurnal variations have latitudinal dependences. The values from CHAMP data are compared with those from COSMIC data, and the results show that during the daytime the maximum diffusive fluxes under low solar activity conditions are less than those under high solar activity conditions.(3) The variations of diffusive fluxes during geomagnetic storms are analyzed. A 30-day ISR experiment was conducted at Millstone Hill (288.5°E, 42.6°N) from 4 October to 4 November 2002. O+ field-aligned diffusive velocities and fluxes in the topside ionosphere have been calculated from the altitude profiles of electron density, ion and electron temperature during this experiment. The characteristics of Vd,Фd and some other ionospheric parameters are analyzed during two geomagnetic storms. Upward Vd andФd during the storm main phases were significantly less than the averaged values in quiet time at 500 km height. In the nighttime of the storm main phases, downward Vd was larger than the averaged value sometimes. During the recovery phases, the decrease of Vd andФd, and the changes of their directions in the nighttime are observed.2. The thermospheric and ionospheric parameters are analyzed using in-situ measurements by CHAMP.(1) A method of retrieving the upper-atmospheric densities using the measurements from the accelerometer is introduced. A test model is constructed. Since many satellites will carry accelerometers, this method can be widely used in the future.(2) The annual and semiannual variations of electron densities and electron temperatures from Langmuir probe and their dependences of the solar activity are analyzed.更多还原