The pulsation activity of a geomagnetic storm

um mam aau ¶rt; a¶rt;uaum nau mu m¶rt; a aum u a ¶rt;u uma.     

Ionospheric effetcs of an intense geomagnetic storm

An investigation of the response of the mid-high, mid and low latitude critical frequency foF2 to the geomagnetic storm of 15 July 2000 is made. Ground-based hourly foF2 values (proportional to square root of peak electron density of F2-layer) from four chains of ionospheric stations located in the geographic longitude ranges 10°W–35°E, 60°E–120°E, 130°E–170°E, 250°E–295°E are used. Relative deviations of foF2 are considered. The main ionospheric effects for the considered storm are: long-duration negative disturbances at mid-high latitudes in summer hemisphere in sectors where the storm onset occurred in the afternoon/night-time hours; short-duration positive disturbances in the summer hemisphere at mid-high latitudes in the pre-sunset hours during the end of main phase-first stage of the recovery; small and irregular negative disturbances in the low latitude winter hemisphere which predominate during the main phase and first part of the recovery, and positive disturbances in both hemispheres at mid-high and mid latitudes prior to the storm onset irrespective of the local time. In addition, the validity of some physical mechanisms proposed to explain the F2 region behaviour during disturbed conditions is considered. gus-mansilla@hotmail.com     

Planetary distribution of geomagnetic pulsations during a geomagnetic storm at solar minimum

We investigate the features of the planetary distribution of wave phenomena (geomagnetic pulsations) in the Earth’s magnetic shell (the magnetosphere) during a strong geomagnetic storm on December 14–15, 2006, which is untypical of the minimum phase of solar activity. The storm was caused by the approach of the interplanetary magnetic cloud towards the Earth’s magnetosphere. The study is based on the analysis of 1-min data of global digital geomagnetic observations at a few latitudinal profiles of the global network of ground-based magnetic stations. The analysis is focused on the Pc5 geomagnetic pulsations, whose frequencies fall in the band of 1.5–7 mHz (T ～ 2–10 min), on the fluctuations in the interplanetary magnetic field (IMF) and in the solar wind density in this frequency band. It is shown that during the initial phase of the storm with positive IMF Bz, most intense geomagnetic pulsations were recorded in the dayside polar regions. It was supposed that these pulsations could probably be caused by the injection of the fluctuating streams of solar wind into the Earth’s ionosphere in the dayside polar cusp region. The fluctuations arising in the ionospheric electric currents due to this process are recorded as the geomagnetic pulsations by the ground-based magnetometers. Under negative IMF Bz, substorms develop in the nightside magnetosphere, and the enhancement of geomagnetic pulsations was observed in this latitudinal region on the Earth’s surface. The generation of these pulsations is probably caused by the fluctuations in the field-aligned magnetospheric electric currents flowing along the geomagnetic field lines from the substorm source region. These geomagnetic pulsations are not related to the fluctuations in the interplanetary medium. During the main phase of the magnetic storm, when fluctuations in the interplanetary medium are almost absent, the most intense geomagnetic pulsations were observed in the dawn sector in the region corresponding to the closed magnetosphere. The generation of these pulsations is likely to be associated with the resonance of the geomagnetic field lines. Thus, it is shown that the Pc5 pulsations observed on the ground during the magnetic storm have a different origin and a different planetary distribution.     

Imaging a geomagnetic storm with energetic neutral atoms

The ring current during a geomagnetic storm on May 2, 1986 has been modeled using a bounce averaged kinetic equations for the phase space density of hydrogen ions, considering charge exchange and Coulomb losses along the drift path. The resulting equatorial pitch angle distribution is used to generate data simulating the medium and high energy neutral atom imagers to be flown on IMAGE. A method for deconvolving these images is described and applied to the simulated data. The results show that, when there are sufficient counts, the deconvolved distribution contains the main features of the original source and that the energy spectrum at a specific time as well as the total energy of the ring current as a function of time can be extracted from the energetic neutral atom images.     

2017年9月强磁暴及引发的电离层扰动

本文研究内容基于2017年9月7日20UT开始的一次强烈的地磁暴事件.这是一次"特殊"的磁暴,在持续两天的磁暴期间,出现了两次强度较大的主相,相隔约14 h.本文通过多项磁暴指数进行研究,发现各项指数均出现两个峰值,两次主相对应的磁暴环电流指数(Dst)最小值都低于100 nT.强磁暴引发了剧烈的电离层扰动,本文中采用...     

Relation of PC index to the geomagnetic storm Dst variation

Relationships between the polar cap magnetic activity index PC and the magnetic storm Dst index have been studied for the magnetic storms with duration more 12 h and peak value Dst<?30 nT and, observed in 1998–2002 and 2004–2005. Along with PC index the geoeffective interplanetary electric field Em was also examined. It has been found that all examined storms, lying in range from ?30 to ?373 nT, started when the PC index and, correspondingly, the Em field firmly exceeded the threshold >2 mV/m. In particular, the “anomalous” magnetic storm on January 21–22, 2005 occurring under conditions of northward IMF B_Z (Du et al., 2008) is usual phenomena fitted well with the threshold restriction owing to the large IMF By component input. The maximal storm depression (the peak value of Dst) is linearly related to the quantities Em and PC, averaged for the time interval from the storm beginning to the storm maximum. The correlation between Dst and PC is more steady and larger than correlation between Dst and Em, the latter being dependent on Em value (effect of “Dst saturation”). The moment of the firm descent of the Em and PC quantities below the threshold level ～2 mV/m is indicative of the depression damping and transition to the recovery phase. The results are consistent with the similar peculiarities revealed for substorms development (Troshichev and Janzhura, 2009) and support the conclusion that the PC index is a reliable proxy characterizing the solar wind energy having been entered into the magnetosphere.     

太原基准地震台地磁背景噪声分析

太原基准地震台数字化地磁观测项目建成运行后,背景噪声水平较大,影响观测资料的使用.采取多种技术措施,认为地电阻率观测对地供电是地磁稳频干扰的主要成分,是地磁背景噪声的一项重要干扰因素.     

基于经验正交分析法的暴时热层大气密度时空分布规律

本文选取2002—2006年期间的36个强磁暴为研究对象,对CHAMP卫星加速度仪反演的实测大气密度进行经验正交分解,研究暴时热层大气密度的纬度分布特征,以及大气密度与ap指数、Dst指数的关系.结果表明,大气密度的纬度分布与季节相关,夏季半球的密度大于冬季半球,春秋季节南北半球的大气密度几乎对称分布;春秋季节白天大气密度在低纬地区呈现出赤道密度异常结构,在中高纬地区密度随纬度增加而减小,夜间则呈现抛物线的形状,赤道附近密度值最小.大气密度的纬度分布特征在若干天内具有良好的稳定性,发生时间相近的磁暴事件,纬度分布曲线非常相似,并且暴前与暴时的纬度分布变化不大.相关性分析表明,大气密度滞后ap指数2~6 h,相对Dst指数平均提前0~1 h,对磁暴的响应速度在日照区比在阴影区快,大气密度与ap指数、Dst指数具有较好的相关性.     

基于离散Gabor变换的磁暴识别

以地磁秒数据为研究对象,通过离散Gabor变换将时域的地磁数据转换至二维时频面,提取Gabor变换谱图的均值和方差作为特征值,使用支持向量机实现地磁正常数据与磁暴干扰数据的自动分类识别。对5个地磁台的200组地磁秒数据进行计算分析,结果表明该方法对测试样本数据的识别率可达94%。     

Effects of geomagnetic storm on GPS ionospheric scintillations at Sanya

The effects of geomagnetic storm on GPS ionospheric scintillations are studied here using GPS scintillation data recorded at Sanya (18.3°N, 109.5°E; geomagnetic: 7.6°N, 180.8°E), the southmost station in the Chinese longitude region. GPS scintillation/TEC and DMSP data are utilized to show the development of irregularities during the period year 2005 (solar minimum). Statistical analysis of K planetary index (Kp) and amplitude scintillation index (S4) indicates that most storms of the year did not trigger the scintillation occurrence at Sanya. However, cases of scintillation occurring during moderate and strong storm (Dst<−100) periods show clearly that the development of irregularities producing scintillations can be triggered by geomagnetic storms during the low scintillation occurrence season. The effects (trigger or not trigger/inhibit) depend on the maximum dDst/dt determined local time sector, and can be explained by the response of the equatorial vertical drift velocities to magnetospheric and ionospheric disturbance electric fields. For station Sanya, the maximum dDst/dt determined local time is near the noon (or post-midnight) sector for most storms of the year 2005, which inhibited (or did not trigger) the post-sunset (or post-midnight) scintillation occurrence and then led to the phenomena that the statistical results presented.     

Interpretation and possibilities of applying LHR frequency determined from satellite VLF measurements in middle geomagnetic latitudes

un nmu a ¶rt;u ¶rt;am ¶rt; mm u a uuuu¶rt; a () a na. m nm, u , ¶rt;um a amm mmu nmua a m m na ¶rt; mum uaum um (2uamm m f_H u na amm m f_N. uam mm n au ¶rt; amm , ¶rt;mum amu¶rt; f _N ² f _H ² u f _H ² f _N ² . a m a n¶rt;um umnmau aamumu auauu amm n u nmu a¶rt;u.     

Peculiarities of electron precipitation in morning sector of auroral zone during geomagnetic storm

Summary The analysis of electron (E _e >30keV) and proton (E _p >150keV) precipitating fluxes measured on low altitude satellite Intercosmos-17 during the geomagnetic storm December 2, 1977 is presented. Particularly, the gap in electron precipitation on morning side at L=5÷6 is analyzed and discussed in terms of strong cyclotron diffusion.     

磁暴时磁场变化率与地电场相关性研究

对2003年10月29日、10月30日两个典型大磁暴进行了分析,研究了磁暴期间磁场变化率与地电场的关系,以及磁暴期间磁暴、磁场变化率及地电场的周期成分。结果表明,磁暴期间H分量变化率与地电场东向分量观测数据显著相关,并且周期成分相同。     

Evidence of geomagnetic storm effects in the lower atmosphere: A case study

Disturbances produced by geomagnetic storms in the higher regions of the Earth’s atmosphere, such as in the ionospheric F2 region and in the lower ionosphere, are relatively better known than those produced at lower altitudes, where the effects of geomagnetic storms have been little studied. During magnetically perturbed conditions, some changes in pressure and temperature at high latitudes have been observed, from the surface level to heights of around 30 km, but there are no morphological studies and/or patterns of behavior. Moreover, the physical mechanisms are still unknown and what exists is a matter of controversy. Thus, the aim of this paper is to contribute to the vertical profile of the effects of geomagnetic storms as observed in the lower sectors of the atmosphere. For that, we study the variations of two atmospheric parameters (temperature and wind speed) during an intense geomagnetic storm (minimum Dst = −300 nT), at heights between about 6 km and 20 km. The data used were obtained from weather balloon flights carried out at low, mid and mid-high latitudes in different longitudinal sectors of the northern hemisphere, which took place twice per day: 00:00 and 12:00 UT. Small, but statistically significant changes in temperature and in zonal component of the neutral winds are observed at mid-high latitudes, which can be linked to short-term geomagnetic forcing. However, the results show different atmospheric response to the geomagnetic storm in the different longitudinal sectors at tropospheric and stratospheric levels, which suggests a regional character of the geomagnetic storms effects at tropospheric levels.     

评"对地磁九倍法的思考"

“思考”一文对磁暴倍九法的否定没有说出任何道理，因之这个“否定”是没有道理的。     

Ionospheric effects of the December 16–18, 1971 geomagnetic storm

Summary The post-storm effect (PSE) of the December 16–18, 1971 geomagnetic storm is studied with the use of the ionospheric radio wave absorption measurements and f _min data from a network of the GDR, USSR and Czechoslovak observatories. Only a high latitude effect of the storm was found. We found more significant absorption effects associated with later weaker enhancements of geomagnetic activity. The part played by the interplanetary magnetic field is demonstrated. A magnetospheric explanation of the observed variability of PSE based on the time-development of filling up the slot region is suggested.     

Response of the topside ionosphere over Arecibo to a moderate geomagnetic storm

We analyze the data obtained using the Arecibo incoherent scatter radar to examine the response of the topside ionosphere to a moderate geomagnetic storm that occurred during the period March 7–11, 2008. During this time period a magnetic storm with a non-monotonic main phase decrease in the Dst index occurred. The recovery phase also exhibited a secondary Dst decrease. During the initial phase of the storm, Te and Ti increased coincident with the arrival of the solar wind. The main phase registered an increase in proton concentration proportional to Ne while temperatures reached the lowest values. Variations in O⁺ concentration were not significant but a reduction in helium fraction was observed. Soon after the peak of the storm, the transition height between the topside ionosphere and the protonosphere, where H⁺ ions dominate composition, was lower than would be expected during quiet conditions and this behavior lasted for approximately 12 h.     

高能质子能谱特征在日冕物质抛射影响预报中的应用

日冕物质抛射(CME)的规模和对地有效性是地磁暴预报中重点关注的特征.本项研究的目的是通过对行星际高能质子通量和能谱的特征与演化规律的分析,得到CME对粒子的加速能力,评估CME可能对地磁场造成的影响.在工作中,统计分析了ACE/EPAM的1998—2010年的质子数据,对质子能谱进行了拟合,得到了能谱指数,并对能谱指数及其变化特征所对应的CME和地磁暴进行了相关统计.通过研究发现:(1)能谱指数随着太阳活动水平而变化,高年最大,达到-2.6,而且涨落幅度也达到±0.4,而在太阳活动低年则稳定在-3.0左右;(2)CME对粒子的加速对应着能谱指数的升高,幅度达到20%时,CME引起地磁暴的可能性较大;(3)冕洞高速流到达地球时,高能质子通量也会升高,但能谱指数同时会有下降;(4)以2004年全年的能谱指数为例,对能谱指数在地磁暴预报中的应用进行了评估,结论认为,能谱指数的升高是CME引发地磁暴的必要条件,可以作为地磁暴预报的参数使用.