Statistical Study of the Geoeffectivity of Halo Coronal Mass Ejections Associated with X-Class Flares during Solar Cycles 23 and 24

By analysing a long series of data (1996-2019), we show that solar cycle 23 was more marked by violent solar flares and coronal mass ejections (CMEs) compared to solar cycle 24. In particular, the halo coronal mass ejections associated with X-class flares appear to be among the most energetic events in solar activity given the size of the flares, the speed of the CMEs and the intense geomagnetic storms they produce. Out of eighty-six (86) X-class halo CMEs, thirty-seven (37) or 43% are highly geoeffective;twenty-four (24) or approximately 28% are moderately geoeffective and twenty-five (25) or 29% are not geoeffective. Over the two solar cycles (1996 to 2019), 71% of storms were geoeffective and 29% were not. For solar cycle 23, about 78% of storms were geoeffective, while for solar cycle 24, about 56% were geoeffective. For the statistical study based on speed, 85 halo CMEs associated with X-class flares were selected because the CME of 6 December 2006 has no recorded speed value. For both solar cycles, 75.29% of the halo CMEs associated with X-class flares have a speed greater than 1000 km/s. The study showed that 42.18% of halo (X) CMEs with speeds above 1000 km/s could cause intense geomagnetic disturbances. These results show the contribution (in terms of speed) of each class of halo (X) CMEs to the perturbation of the Earth’s magnetic field. Coronal mass ejections then become one of the key indicators of solar activity, especially as they affect the Earth.

Numerical study on the response of the Earth's magnetosphere-ionosphere system to a super solar storm

With the approaching of the 24th solar cycle peak year (2012-2014), the impacts of super solar storms on the geospace environment have drawn attentions. Based on the geomagnetic field observations during Carrington event in 1859, we estimate the interplanetary solar wind conditions at that time, and investigate the response of the magnetosphere-ionosphere system to this extreme solar wind conditions using global 3D MHD simulations. The main findings include: 1) The day-side magnetopause and bow shock are compressed to 4.3 and 6.0 Re (Earth radius), and their flanks are also strongly compressed. The magnetopause shifts inside the geosynchronous orbit, exposing geosynchronous satellites in the solar wind in the magnetosheath. 2) During the storm, the region-1 current increases by about 60 times, and the cross polar potential drop increases by about 80 times; the reconnection voltage is about 5 to 6 times larger than the average storms, which means a larger amount of the solar wind energy enters the magnetosphere, resulting in strong space weather phenomena.

Prediction method for October 2003 solar storm

Aiming at two intense shock events on October 28 and 29, 2003, this paper presents a two-step method, which combines synoptic analysis of space weather ——“observing” and quantitative prediction ——“palpating”, and then uses it to test predictions. In the first step of “observing”, on the basis of observations of the solar source surface magnetic field, interplanetary scintillation (IPS) and ACE spacecraft, we find that the propagation of the shocks is asymmetric relative to the normal direction of their solar sources, and the Earth is located near the direction of the fastest speed and the greatest energy of the shocks. As the two fast ejection shock events, the fast explosion of coronal mass of the extremely high temperature, the strong magnetic field, and the high speed background solar wind are also helpful to their rapid propagation. In the second step of “palpating”, we adopt a new membership function of the fast shock events for the ISF method. The predicted results show that for the onset time of the geomagnetic disturbance, the relative errors between the observational and the predicted results are 1.8% and 6.7%; and for the magnetic disturbance magnitude, the relative errors are 4.1% and 3.1%, re- spectively. Furthermore, the comparison among the predicted results of our two-step method with those of five other prevailing methods shows that the two-step method is advantageous. The results tell us that understanding the physical features of shock propagation thoroughly is of great importance in improving the prediction precision.

Relation between Solar Wind Parameter and Geomagnetic Storm Condition during Cycle-23

In the present paper dependence of geomagnetic activity on the solar-wind plasma and interplanetary magnetic field (IMF) parameters has been studied. We have taken interplanetary solar wind data at the instant of Dst minimum. Our study consists of 200 geomagnetic storms weighed by disturbance storm time (Dst) -50 nT, observed during solar cycle 23. The study suggests that the strength of the geomagnetic storm is strongly dependent on the total magnetic field Btotal. The correlation (-0.72) has been found reasonable. In perspective of previous studies, the strength of the geomagnetic storm is strongly dependent on the southward component (Bz) whereas in present study exposes that the correlation (0.22) is weak. This result indicates that solar wind southward magnetic field component Bz has significant growth particularly before the main phase of geomagnetic storm (not during the main phase). The present result implies that neither density nor temperature is significantly related to the variation of geomagnetic disturbance;rather the effects of the pressure and speed. However, a low plasma beta during highly geoeffective event seems to be an important criterion.

A statistical study of the likelihood of a super geomagnetic storm occurring in a mild solar cycle

The activities of geomagnetic storms are generally controlled by solar activities. The current solar cycle(SC) 24 is found to be mild; compared to SCs 19–23, the storm occurrence and size derived by averaging the occurrence number and D_(st) around the solar maximum are reduced by about 50–82% and 36–61%, respectively. We estimate separately, for SC 19 to 24, the repeat intervals between geomagnetic storms of specific D_(st), based on fits of power-law and log-normal distributions to the storm data for each SC. Repeat intervals between super geomagnetic storms with D_(st)≤–250 nT are found to be 0.36–2.95 year(s) for SCs 19–23, but about 20 years based on the data for SC 24. We also estimate the repeat intervals between coronal mass ejections(CMEs) of specific speed(V_(CME)) since CMEs are known to be the main drivers of intense storms and the related statistics may provide information about the potential occurrence of super geomagnetic storms from the location of the Sun. Our analysis finds that a CME with V_(CME)≥1860 km/s may occur once per 3 and 5 months in SC 23 and 24, respectively. Based on a V_(CME)-D_(st) relationship, such a fast CME may cause a storm with D_(st)=–250 nT if arriving at the Earth. By comparing the observed geomagnetic storms to storms expected to be caused by CMEs, we derive the probability of CME caused storms, which is dependent on V_(CME). For a CME faster than 1860 km/s, the probability of a CME caused storm with D_(st)≤–250 nT is about 1/5 for SC 23 or 1/25 for SC 24. All of the above results suggest that the likelihood of the occurrence of super geomagnetic storms is significantly reduced in a mild SC.

Statistical study on great geomagnetic storms during solar cycle 23

Characteristics of great geomagnetic storms during solar cycle 23 were statistically investigated. Firstly, we focused on the uniqueness of solar cycle 23 by analyzing both the great storm number and sunspot number from 1957 to 2008. It was found that the relationship between the sunspot number and great storm number weakened as the activity of the storms strengthened. There was no obvious relationship between the annual sunspot number and great storm number with Dst≤-300 nT. Secondly, we studied the relationship between the peak Dst and peak Bz in detail. It was found that the condition Bz〈-10 nT is not necessary for storms with Dst≤-100 nT, but seems necessary for storms with Dst≤-150 nT. The duration for Bz≤-10 nT has no direct relationship with the giant storm. The correlation coefficient between the Dst peak and Bz peak for the 89 storms studied is 0.81. After removing the effect of solar wind dynamic pressure on the Dst peak, we obtained a better correlation coefficient of 0.86. We also found the difference between the Dst peak and the corrected Dst peak was proportional to the Dst peak.

A Nonlinear Autoregressive Approach to Statistical Prediction of Disturbance Storm Time Geomagnetic Fluctuations Using Solar Data

A nonlinear autoregressive approach with exogenous input is used as a novel method for statistical forecasting of the disturbance storm time index, a measure of space weather related to the ring current which surrounds the Earth, and fluctuations in disturbance storm time field strength as a result of incoming solar particles. This ring current produces a magnetic field which opposes the planetary geomagnetic field. Given the occurrence of solar activity hours or days before subsequent geomagnetic fluctuations and the potential effects that geomagnetic storms have on terrestrial systems, it would be useful to be able to predict geophysical parameters in advance using both historical disturbance storm time indices and external input of solar winds and the interplanetary magnetic field. By assessing various statistical techniques it is determined that artificial neural networks may be ideal for the prediction of disturbance storm time index values which may in turn be used to forecast geomagnetic storms. Furthermore, it is found that a Bayesian regularization neural network algorithm may be the most accurate model compared to both other forms of artificial neural network used and the linear models employing regression analyses.

The Effects of the Recurrent Storms on Fof2 at Ouagadougou Station during Solar Cycles 21-22

The present paper deals with the effect of recurrent activity on the foF2 diurnal variation at Ouagadougou station for solar cycles 21 and 22. The recurrent activity produces at daytime positive storm for all solar cycle phases. For all seasons, the recurrent activity causes positive storm during nighttime and has no effect during daytime. From this study, it emerges that a positive effect of the storm at this station may be explained by the thermospheric composition changes. Recurrent activity more occurs during the solar decreasing phase and during spring month. The storm strength shows solar cycle phase and seasonal dependence. The storm strength is the highest during the solar increasing phase and during summer months.

Effect of solar wind plasma parameters on space weather

Today’s challenge for space weather research is to quantitatively predict the dynamics of the magnetosphere from measured solar wind and interplanetary magnetic field（IMF） conditions. Correlative studies between geomagnetic storms（GMSs）and the various interplanetary（IP） field/plasma parameters have been performed to search for the causes of geomagnetic activity and develop models for predicting the occurrence of GMSs, which are important for space weather predictions. We find a possible relation between GMSs and solar wind and IMF parameters in three different situations and also derived the linear relation for all parameters in three situations.On the basis of the present statistical study, we develop an empirical model. With the help of this model, we can predict all categories of GMSs. This model is based on the following fact： the total IMF Btotalcan be used to trigger an alarm for GMSs, when sudden changes in total magnetic field Btotaloccur. This is the first alarm condition for a storm’s arrival. It is observed in the present study that the southward Bzcomponent of the IMF is an important factor for describing GMSs. A result of the paper is that the magnitude of Bzis maximum neither during the initial phase（at the instant of the IP shock） nor during the main phase（at the instant of Disturbance storm time（Dst） minimum）. It is seen in this study that there is a time delay between the maximum value of southward Bzand the Dst minimum, and this time delay can be used in the prediction of the intensity of a magnetic storm two-three hours before the main phase of a GMS. A linear relation has been derived between the maximum value of the southward component of Bzand the Dst, which is Dst =（-0.06） ＋（7.65）Bz＋ t.Some auxiliary conditions should be fulfilled with this, for example the speed of the solar wind should, on average, be 350 km s-1 to 750 km s-1, plasma β should be low and, most importantly, plasma temperature should be low for intense storms. If the plasma temperature is less than 0.5 × 106 K then the Dst value will be greater than the predicted value of Dst or if temperature is greater than 0.5 × 106 K then the Dst value will be less（some nT）.

Effects of cloud,atmospheric water vapor,and dust on photosynthetically active radiation and total solar radiation in a Mongolian grassland

Photosynthetically active radiation （PAR） is an important input parameter for estimating plant produc- tivity due to its key role in the growth and development of plants. However, a worldwide routine network for sys- tematic PAR measurements is not yet established, and PAR is often calculated as a constant fraction of total solar radiation （SR）. Although the ratio of PAR to SR （PAR/SR） has been reported from many places, few studies have been performed for dry regions. The present study was therefore carried out in an arid region of Mongolia to obtain PAP-JSR and examine its dependency on sky clearness （the clearness index）, water vapor in the atmosphere and aeolian dust. Continuous measurements of PAR and SR were taken every one second using quantum and pyranometer sensors, respectively, and the readings were averaged and recorded at intervals of 30 minutes for a period of 12 months. The lowest monthly mean daily PAR/SR occurred in April （0.420）, while the highest ratio was observed in July （0.459）. Mean daily PAR/SR during plant growing season （May-August） was estimated to be 0.442, which could be useful for modeling plant productivity in the study area. The annual mean daily PAR/SR （0.435） was lower than the values reported in many previous studies. This difference could be explained with the regional variation in climate： i.e. drier climatic condition in the study area. PAR/SR was negatively correlated with the clearness index （r= -0.36, P〈0.001）, but positively with atmospheric water vapor pressure （r=0.47, P〈0.001）. The average PAR/SR was significantly lower （P=0.02） on the dusty days compared to the non-dust days. Water vapor in the atmosphere was shown to be the strongest factor in the variation of PAR/SR. This is the first study examining PAR/SR under a semi-arid condition in Mongolia.

Mid-Latitude Pc1, 2 Pulsations Induced by Magnetospheric Compression in the Maximum and Early Recovery Phase of Geomagnetic Storms

We investigate the properties of interplanetary inhomogeneities generating long-lasting mid-latitude Pc1, 2 geomagnetic pulsations. The data from the Wind and IMP 8 spacecrafts, and from the Mondy and Borok midlatitude magnetic observatories are used in this study. The pulsations under investigation develop in the maximum and early recovery phase of magnetic storms. The pulsations have amplitudes from a few tens to several hundred pT and last more than seven hours. A close association of the increase (decrease) in solar wind dynamic pressure (Psw) with the onset or enhancement (attenuation or decay) of these pulsations has been established. Contrary to high-latitude phenomena, there is a distinctive feature of the interplanetary inhomogeneities that are responsible for generation of long-lasting mid-latitude Pc1,2. It is essential that the effect of the quasi-stationary negative Bz-component of the interplanetary magnetic field on the magnetosphere extends over 4 hours. Only then are the Psw pulses able to excite the above-mentioned type of mid-latitude geomagnetic pulsations. Model calculations show that in the cases under study the plasmapause can form in the vicinity of the magnetic observatory. This implies that the existence of an intense ring current resulting from the enhanced magnetospheric convection is necessary for the Pc1, 2 excitation. Further, the existence of the plasmapause above the observation point (as a waveguide) is necessary for long-lasting Pc1 waves to arrive at the ground.

Variation of Total Ozone during 24 August 2005 Magnetic Storm: A Case Study

This paper presents the longitudinal distribution of total ozone along several latitudinal circles from both hemispheres during a strong geomagnetic storm that occurred on 24 August 2005 after a solar proton event (the maximum flux of protons with energy > 10 MeV was 1.70 × 107 protons cm-2.day-1.sr-1 on 23 August). For that, we use average daily values of total ozone observations (=column ozone amount) in Dobson units for the period 18-25 August 2005 (obtained from the Total Ozone Mapping Spectrometer, TOMS). The considered storm occurred after a relatively quiet geomagnetic period and it is not superposed by another perturbation, which permit us to identify clearly the effects of the geomagnetic storm on total ozone. The results show statistically significant decreases in ozone along the latitudinal circles 70°N and 70°S (summer and winter), no statistically significant effects at middle latitudes (40°S) and sparse statistically significant increases at low latitudes (20°S). The role of some mechanisms to explain the features observed is considered.

TEC Variability during Fluctuating Events at Koudougou Station during Solar Cycle 24

This paper deals with TEC variability during fluctuating geomagnetic events (FE) during solar cycle 24 at Koudougou station (lat: 12o15'N;Geo long: -2o20'E). The study was done by comparing TEC variations during FE days with those of quiet days (QA). Comparison was made taking into account solar phases’ and seasons’ influences. FE’s and QA’s TEC curves are characterized by dome profiles. All graphs show two troughs, one in the morning (0500 LT) and the second in the evening (around 2000 LT) and a peak around 1400 LT during all solar phases and winter months and around 1500 LT for the remaining seasons. Both troughs are caused by the decrease of the photo ionization and an increase of the recombination phenomena, as well for FE as for QA periods. FE cause positive storms during all solar phases as well as during seasons and some negative storms during spring and summer months and minimum and maximum solar phases.

Global distributions of storm-time ionospheric currents as seen in geomagnetic field variations

To investigate temporal and spatial evolution of global geomagnetic field variations from high-latitude to the equator during geomagnetic storms, we analyzed ground geomagnetic field disturbances from high latitudes to the magnetic equator. The daytime ionospheric equivalent current during the storm main phase showed that twin-vortex ionospheric currents driven by the Region 1 field-aligned currents （R1 FACs） are intensified significantly and expand to the low-latitude region of-30~ magnetic latitude. Centers of the currents were located around 70~ and 65~ in the morning and afternoon, respectively. Corresponding to intensification of the R1 FACs, an enhancement of the eastward/westward equatorial electrojet occurred at the daytime/nighttime dip equator. This signature suggests that the enhanced convection electric field penetrates to both the daytime and nighttime equa- tor. During the recovery phase, the daytime equivalent current showed that two new pairs of twin vortices, which are different from two-cell ionospheric currents driven by the R1 FACs, appear in the polar cap and mid latitude. The former led to enhanced north- ward Bz （NBZ） FACs driven by lobe reconnection tailward of the cusps, owing to the northward interplanetary magnetic field （IMF）. The latter was generated by enhanced Region 2 field-aligned currents （R2 FACs）. Associated with these magnetic field variations in the mid-latitudes and polar cap, the equatorial magnetic field variation showed a strongly negative signature, produced by the westward equatorial electrojet current caused by the dusk-to-dawn electric field.

Local Anomalies of the Load-Unload Response of the Geomagnetic Field to Solar Wind and Earthquakes in Southwest China

Many earthquakes occurred during the period 1994 -1996 in Sichuan and Yunnan Provinces, Southwest China. Taking the process of the initial main phase recovery phase of the magnetic storm as the process of load-unload response of the geomagnetic field to the solar wind, we have estimated and analyzed the distribution in time and space of the load-unload response ratio P(z) of the storm time disturbance daily variation of the vertical component Z of the geomagnetic field at ten stations in Southwest China. We found that the area with high ratio P(z) was just the area where moderately strong earthquakes would occur from 44 days to 15 months later. The relationship between the high ratio P(z) and weather disasters in both seismic and non-seismic areas is discussed briefly.

琳达·霍根《太阳风暴》中地方感的缺失与重建

地方感是印第安文化中的重要组成部分。琳达·霍根作为美国印第安族的作家,在其作品《太阳风暴》中生动展现了印第安文化中的地方感,强调了地方感对印第安人自我认同的重要性。提出了从地方依恋和地方认同两个维度实现地方感重建,对人们重新思考当下社会存在的生态危机具有现实意义。

2003年10月底太阳风暴期间中山站电离层吸收效应的观测与分析

本文介绍了成像式宇宙噪声接收机技术和数据分析方法,通过对南极中山站成像式宇宙噪声接收机在2003年10月底太阳风暴期间的观测数据进行分析,得到了相应的极区电离层的吸收效应,它们主要是强度为2. 7dB的宇宙噪声突然吸收和强度高达31dB持续4d的极盖吸收。

太阳风暴对电网干扰的日面参数与条件

由太阳磁场变化引起的太阳风暴对电网的影响是物理过程与模式极其复杂的电磁兼容问题。根据日冕物质抛射(CME)是驱动非重现性地磁暴和电网地磁感应电流(GIC)的太阳事件主因这一事实,提出研究电网GIC大小与CME的哪些参数关系密切,具备哪些条件的CME对GIC的贡献大,以便为预测对电网的影响提供依据。利用23太阳周广东岭澳核电站几次磁暴的GIC监测数据,以及太阳日球天文台/大视角分光日冕仪(SOHO/LASCO)的CME观测资料,研究了电网GIC大小与CME角宽度、初始速度、日面位置、加速度参数的关系,以及突发很大GIC的CME太阳源条件与原因。结果表明,电网GIC事件及大小与CME日面参数密切相关,但并不是单个参数能独立驱动的,CME的初始速度是对地CME能引起较大电网GIC的关键参数。

太阳风暴对四川500kV电网影响的评估

太阳活动引起的地磁场剧烈变化称为磁暴。近年来随着中国西电东送长距离输电的发展,江苏、广东等地发现磁暴在电网中产生了较大幅度的地磁感应电流(GIC),有可能对电网的安全运行造成一系列的危害。中国幅员广阔,地理跨越高、中纬度区域,电网规模越来越大,电网结构与运行方式也日益呈现多样化,高压、大电网的安全与稳定问题日益突出。因此,有必要对磁暴对我国电网产生的影响进行研究。结合四川电网部分超高压电网结构,建立了电网等效模型,选取典型磁暴感应出的地面电场数值,利用MATlAB仿真软件估算了四川电网中部分500 kV变电站的GIC水平。计算结果表明,在电网的终点和拐角处容易诱发较大的GIC,其数值可达数十A。因此在强磁暴发生时,四川超高压电网的GIC水平较高,可能影响电网的安全稳定运行,须引起足够的重视。

北京2004年一次强沙尘暴过程的辐射特征研究

利用2004年3月27～29日北京沙尘暴期间观测的辐射、气象以及气溶胶质量浓度的资料,分析了该过程的地面辐射、气象要素以及气溶胶与辐射相互作用的变化特征。结果表明,沙尘暴期间紫外辐射的衰减与可见光辐射强度衰减规律不一致。紫外衰减主要受到细粒子浓度影响,同时紫外辐射占总辐射的比重与气溶胶中细粒子含量成负相关;而可见光辐射强度衰减与总辐射衰减同步。辐射变化和气溶胶质量浓度观测结果均表明,此次沙尘暴过程分为3个阶段,即,细粒子累积期、外地沙尘输入期和清除期。在沙尘暴期间地面一直维持一个低压、干冷的状态;当过程结束后,气压急剧增高,并在一段时间内处于高压控制之下。