1978—1988年间磁扰的分析与日地耦合

用1978-1988年间行星际磁场(IMF)的B_z分量、极光区AL指数和赤道附近地磁台Z分量等资料探讨了日地耦合中的主要物理过程。B_z的11年变化大致与太阳活动程度相当,但AL和赤道附近ΔZ更多地受磁层和电离层内部过程所控制。分析中强调了对国际磁抗日按物理过程进行分类的必要性。      

从地磁扰动分析太阳共转周期结构

本文运用相关、功率谱等数字信号处理方法对20周太阳风速度和地磁扰动进行比较,得出两者反映的太阳共转周期结构十分相似.且用1900—1979年的地磁C₉指数进行了自相关分析,发现在相当长的时间中,地磁扰动存在13天、27天的周期成份,说明日冕上可能具有某种固有的分布结构,通过不同的太阳活动周的比较,说明太阳活动水平及黑子面积南北半球不对称都对地磁C₉指数能否明显反映日冕上固有分布结构的活动和发展有影响.      

极端太阳风条件下的磁层顶位形

基于极端太阳风条件下的三维MHD数值模拟数据, 构建了一种极端太阳风条件下的三维非对称磁层顶位形模型. 所提出的模型考虑了行星际南向磁场(IMF) B_z日下点距离侵蚀的饱和效应, 太阳风动压B_d对磁层顶张角影响的饱和效应, 赤道面、昼夜子午面磁层顶的不对称性以及极尖区的内凹结构和内凹中心的移动, 并利用Levenberg-Marquart多参量非线性拟合方法拟合了模型参数. 数值模拟研究表明, 在极端太阳风条件下, 随B_d增大, 磁层顶日下点距离减小, 磁层顶磁尾张角几乎不变; 随南向(IMF)B_z增大, 磁层顶日下点距离略有减小, 磁层顶磁尾张角减小, 极尖区内凹中心向低纬移动. 通过对2010年8月1日太阳风暴事件验证发现, 本文所建立的模型能够描述极端太阳风条件下的三维磁层顶位形.      

利用转移熵研究引起磁暴扰动的太阳风参数重要性排序

磁暴是重要空间天气灾害性事件，能够影响卫星的安全在轨运行和地面电网系统等。目前，对于太阳风–磁层相互作用的研究多集中在分析相关系数的线性关系，而基于信息论的转移熵可以提供强大的无模型有向统计量，可用来分析传统相关性分析和模型假设检测不到的非线性关系。本文利用转移熵的方法，研究了磁暴期间的太阳风驱动参数。利用第23和24太阳活动周的小时精度数据进行长时间尺度分析，发现太阳风向地磁的信息传递呈双峰分布，表现出与太阳活动水平的一致性。利用2010-2018年93个地磁暴期间的分钟精度数据进行短时间尺度分析，结果表明：行星际电场(E)和行星际磁场南向分量(B z)对地磁指数Sym-H在时间延迟为60 min时信息传递较强，而太阳风速度v_{s w}、温度T _sw、数密度D_sw、磁场B和动压P_sw对Sym-H指数的信息传递较弱。上述研究结果能够为太阳风–磁层相互作用的建模提供参数选择及确定预测范围的依据。     

具有阻尼耗散的DNLS方程的孤立子解析解

用变换和数值积分的方法找到了考虑欧姆阻尼效应时DNLS方程的一类含激波层结构的解析解,讨论了耗散对其振幅及磁场B_yB_z的影响.结果表明,耗散时激波厚度有很强的控制作用,耗散越小,激波厚度越大,B_y和B_z衰减越慢.耗散项很小时振幅基本不变,B_y和B_z过渡成孤立子解.      

2009年1月平流层爆发性增温期间全球电离层响应的研究

2009年1月平流层爆发性增温(Stratospheric Sudden Warming, SSW)事件是有记录以来最强、持续时间最长的一次主增温事件(Major Warming Event, MWE), 期间太阳活动和地磁活动均处于较低的水平, 因此非常有利于研究电离层对平流层增温事件的响应情况. 本文利用COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate)系统提供的掩星数据, 使用Kriging方法分别构建了此次SSW期间及平静期的电离层N_mF₂, h_mF₂和110～750km高度范围的垂直积分TEC (简称VTEC)地图, 同时从全球定位导航卫星系统服务组织(International GNSS Service, IGS)发布的全球电离层TEC地图(Global Ionospheric Maps, GIMs)中提取了日固坐标系(Sun-fixed, 地磁纬度和地方时)下全球TEC地图. 通过对比发现, SSW期间与平静期相比, 地磁纬度中低纬电离层参数存在早晨上升, 下午和夜间下降的现象. 利用OSTM/JASON-2卫星高度计观测值进行验证后的结果显示, 此前研究均未有提及的夜间时段电离层参数N_mF₂, h_mF₂和TEC (VTEC和IGS TEC)的下降现象的确存在.      

行星际磁场北向分量触发磁层扰动的可能性

本文用典型事件和统计分析论证了行星际磁场北向分量触发地磁扰动的可能性.给出了行星际电场E_y分量对磁层大尺度对流电场E_M的耦合系数.从耦合方程出发讨论了磁层对太阳风作用的响应,证明磁层不是起半波整流器作用,从而表明经典的重联理论应有所修改.      

太阳活动与地磁扰动的变化

以每年中地磁指数C9≥L事件的次数表示地磁扰动程度.研究下列六种情况:L=3、4和5,其中每一种又再分成重现的和一般的两类.用曲线分段拟合法求出地磁扰动年次数C_k与黑子相对数R_k之间的经验的平均关系f(R);计算出△_k=C_k-f_k,其中f_k≡f(R_k).计算结果表明:1.用黑子相对数极小年之前四年作太阳活动周的起算点.对这种“活动周”求△_k=C_k-f_k的平均,得到各个△.各“活动周”的△的符号依次正负交替.2.由90年地磁扰动观测资料得来的符号交替规律出现在C9≥3、4和5时的各种情况.这很可能是由于太阳极区磁场符号依次交替变化造成的.进一步地划分时段后,各个“活动周”中△_k对于△的弥散程度σ不同.σ序列显现出约70年的长周期.      

低纬100—200km间电子数密度的变化

利用光化平衡模式计算了低纬100—200km间白天电子数密度的变化。求得E-F₁谷区的谷深,谷宽、谷高的变化特征。获得如下结果:a.太阳活动明显影响电子数密度随高度及太阳天顶角的变化,发现太阳活动指数与电子数密度间不仅存在正相关,而且存在负相关;b.太阳活动明显影响E-F₁谷区的形态。在一定太阳活动条件下,对同一太阳赤纬和地理纬度,谷深、谷宽与太阳天顶角的关系难以用一简单函数来表示;c.太阳耀斑、地磁活动对该区电子密度有明显影响;d.在讨论100—200km间电子密度时不能忽略O+（2P）和NO的光电离率。      

冕洞特征参数与重现型地磁暴关系的统计研究

在提取冕洞特征参数的基础上,利用1996年到2005年8月近十年来对地磁扰动有影响的356个冕洞事例,定量分析了冕洞特征参数(包括冕洞的面积比、经纬度跨度等)与冕洞高速流特征、重现型地磁扰动特征(包括扰动大小和持续时间等)之间的相关性,研究发现,从引起地磁扰动的冕洞在整个太阳活动周的分布来看,在地磁扰动峰年中冕洞影响同样具有重要的贡献;冕洞高速流太阳风速度与地磁扰动强度之间存在较强的相关性,而高速流中太阳风速度与冕洞面积比关系不大,与冕洞亮度存在一定相关性;冕洞的经度跨度与地磁扰动持续时间存在很强的正相关性.      

地球磁场对太阳风扰动响应的研究

分别对行星际激波、太阳风动压增大事件和减小事件的地球磁场响应进行了比较. 分析结果表明, 同步轨道磁场对太阳风扰动在向阳面产生较强的正响应, 在背阳面 响应较弱且有时会出现负响应, 地磁指数SYM-H对太阳风扰动的响应为正响应. 同时还得出, 向阳侧同步轨道磁场响应幅度d Bz与地磁指数响应幅度d SYM-H、上下游动压均方差均具有较好的相关性. 地磁指数响应幅度与同步轨道磁场响应幅度相关关系在激波和动压增大事件中具有一致性, 动压减小事件出 现明显差异, 这说明激波和动压增大事件在影响地球磁场方面具有某种共性.      

冕洞特征参数与地磁暴强度及发生时间统计

地磁暴是空间天气预报的重要对象.在太阳活动周下降年和低年，冕洞发出的高速流经过三天左右行星际传输到达地球并引发的地磁暴占主导地位.目前地磁暴的预报通常依赖于1AU处卫星就位监测的太阳风参数，预报提前量只有1h左右.为了增加地磁暴预报提前量，需要从高速流和地磁暴的源头即太阳出发，建立冕洞特征参数与地磁暴的定量关系.分析了2010年5月到2016年12月的152个冕洞-地磁暴事件，利用SDO/AIA太阳极紫外图像提取了两类冕洞特征参数，分析了其与地磁暴期间ap，Dst和AE三种地磁指数的统计关系，给出冕洞特征参数与地磁暴强度以及发生时间的统计特征，为基于冕洞成像观测提前1～3天预报地磁暴提供了依据.      

2000年7月空间天气大事件对地磁场的影响

2000年7月空间大事件对地磁场产生了巨大影响，7月15日至18日发生大磁暴(K=9)．磁暴为急始型，在我国地区初相期变幅有200—300nT，主相最大幅度有500—600nT，为多年来所罕见．在行星际磁场Bz由北向转向南向时，磁暴主相开始；南向分量达到最大值后大约2h，地磁H分量达到最小值，恢复相开始．并且，这次磁暴与太阳风也存在一定的对应关系。     

On the long-term variability of the heliosphere–magnetosphere environment

Annual means of measured and reconstructed solar, heliospheric, and magnetospheric parameters are used to infer solar activity signatures at the Hale and Gleissberg cycles timescales. Available open solar flux, modulation strength, cosmic ray flux, total solar irradiance data, reconstructed back to 1700, solar wind parameters (speed and density) and the magnitude of the heliospheric magnetic field at 1 AU, reconstructed back to 1870, as well as the time series of geomagnetic activity indices (aa, IDV, IHV), going back to 1870, have been considered. Simple filtering procedures (successive 11-, 22-, and 88-year running averages and differences between them) and scaling by the standard deviation from the average value for the common interval covered by the data show that the long-discussed variation in the 20th century (a pronounced increase since ∼1900, followed by a depression in the ‘60s and a new, slower, increase) seen in the 11-year averages of parameters such as geomagnetic activity indices and reconstructed heliospheric magnetic field strength, solar wind speed, open solar flux, is a result of the superposition in data of solar activity signatures at Hale and Gleissberg cycles timescales. The Hale and Gleissberg signals were characterized and similarities and differences in the temporal behavior of the analyzed parameters at these timescales are discussed. The similarities in the studied parameters point to a common pacing source, the solar dynamo.     

Advances in space research nonlinear dependence of Dst and AE indices on the electric field of magnetic clouds

Using the Dst and AE geomagnetic index values and parameters of interplanetary magnetic field and solar wind we have examined the geoeffectiveness of transient ejections in the solar wind, namely, magnetic clouds and high-speed streams. It is found that for magnetic clouds the dependences of indices on the solar wind electric field are nonlinear of different kind. In contrast to magnetic clouds, the dependence of Dst and AE geomagnetic index values on the solar wind electric field agrees closely with the linear one for high-speed streams. We suggest approximating formulas to describe dependences obtained taking into account the relation of the electric field transpolar potential to the electric field and dynamic pressure of the solar wind. We suppose that the interplanetary magnetic field fluctuations also contribute to these dependences.     

Interplanetary shocks and geomagnetic activity during solar maximum (2000) and solar minimum (1995–1996)

Plasma and magnetic field parameter variations through fast forward interplanetary shocks were correlated with the peak geomagnetic activity index Dst in a period from 0 to 3 days after the shock, during solar maximum (2000) and solar minimum (1995–1996). Solar wind speed (V) and total magnetic field (B_t) were the parameters with higher correlations with peak Dst index. The correlation coefficients were higher during solar minimum (r² = 56% for V and 39% for B_t) than during solar maximum (r² = 15% for V and 12% for B_t). A statistical distribution of geomagnetic activity levels following interplanetary shocks was obtained. It was observed that during solar maximum, 36% and 28% of interplanetary shocks were followed by intense (Dst  −100 nT) and moderate (−50  Dst < −100 nT) geomagnetic activity, whereas during solar minimum 13% and 33% of the shocks were followed by intense and moderate geomagnetic activity. It can be concluded that the upstream/downstream variations of V and B_t through the shocks were the parameters better correlated with geomagnetic activity level, and during solar maximum a higher relative number of interplanetary shocks can be followed by intense geomagnetic activity than during solar minimum. One can extrapolate, for forecasting goals, that during a whole solar cycle a shock has a probability of around 50% to be followed by intense/moderate geomagnetic activity.     

27-day variation in solar-terrestrial parameters: Global characteristics and an origin based approach of the signals

The Earth and the near interplanetary medium are affected by the Sun in different ways. Those processes generated in the Sun that induce perturbations into the Magnetosphere-Ionosphere system are called geoeffective processes and show a wide range of temporal variations, like the 11-year solar cycle (long term variations), the variation of ～27?days (recurrent variations), solar storms enduring for some days, particle acceleration events lasting for some hours, etc.In this article, the periodicity of ～27?days associated with the solar synodic rotation period is investigated. The work is mainly focused on studying the resulting 27-day periodic signal in the magnetic activity, by the analysis of the horizontal component of the magnetic field registered on a set of 103 magnetic observatories distributed around the world. For this a new method to isolate the periodicity of interest has been developed consisting of two main steps: the first one consists of removing the linear trend corresponding to every calendar year from the data series, and the second one of removing from the resulting series a smoothed version of it obtained by applying a 30-day moving average. The result at the end of this process is a data series in which all the signal with periods larger than 30?days are canceled.The most important characteristics observed in the resulting signals are two main amplitude modulations: the first and most prominent related to the 11-year solar cycle and the second one with a semiannual pattern. In addition, the amplitude of the signal shows a dependence on the geomagnetic latitude of the observatory with a significant discontinuity at approx. ±60°.The processing scheme was also applied to other parameters that are widely used to characterize the energy transfer from the Sun to the Earth: F10.7 and Mg II indices and the ionospheric vertical total electron content (vTEC) were considered for radiative interactions; and the solar wind velocity for the non-radiative interactions between the solar wind and the magnetosphere. The 27-day signal obtained in the magnetic activity was compared with the signals found in the other parameters resulting in a series of cross-correlations curves with maximum correlation between 3 and 5?days of delays for the radiative and between 0 and 1?days of delay for the non-radiative parameters. This result supports the idea that the physical process responsible for the 27-day signal in the magnetic activity is related to the solar wind and not to the solar electromagnetic radiation.     

On the time lag between solar wind dynamic parameters and solar activity UV proxies

The solar activity displays variability and periodic behaviours over a wide range of timescales, with the presence of a most prominent cycle with a mean length of 11 years. Such variability is transported within the heliosphere by solar wind, radiation and other processes, affecting the properties of the interplanetary medium. The presence of solar activity–related periodicities is well visible in different solar wind and geomagnetic indices, although their time lags with respect to the solar cycle lead to hysteresis cycles. Here, we investigate the time lag behaviour between a physical proxy of the solar activity, the Ca II K index, and two solar wind parameters (speed and dynamic pressure), studying how their pairwise relative lags vary over almost five solar cycles. We find that the lag between Ca II K index and solar wind speed is not constant over the whole time interval investigated, with values ranging from 6 years to $～$1 year (average 3.2 years). A similar behaviour is found also for the solar wind dynamic pressure. Then, by using a Lomb-Scargle periodogram analysis we obtain a 10.21-year mean periodicity for the speed and 10.30-year for the dynamic pressure. We speculate that the different periodicities of the solar wind parameters with respect to the solar 11-year cycle may be related to the overall observed temporal evolution of the time lags. Finally, by accounting for them, we obtain empirical relations that link the amplitude of the Ca II K index to the two solar wind parameters.     

Relationship between substorm activity and the interplanetary medium parameters during the main phase of strong magnetic storms

In the present paper dependences of substorm activity on the solar wind velocity and southward component (Bz) of interplanetary magnetic field (IMF) during the main phase of magnetic storms, induced by the CIR and ICME events, is studied. Strong magnetic storms with close values of Dst_min?≈??100?±?10?nT are considered. For the period of 1979–2017 there are selected 26 magnetic storms induced by the CIR and ICME (MC?+?Ejecta) events. It is shown that for the CIR and ICME events the average value of the AE index (AE_aver) at the main phase of magnetic storm correlates with the solar wind electric field. The highest correlation coefficient (r?=?0.73) is observed for the magnetic storms induced by the CIR events. It is found that the AE_aver for magnetic storms induced by ICME events, unlike CIR events, increases with the growth of average value of the southward IMF Bz module. The analysis of dependence between the AE_aver and average value of the solar wind velocity (Vsw_aver) during the main phase of magnetic storm shows that in the CIR events, unlike ICME, the AE_aver correlates on the Vsw_aver.