利用支持向量机预测大磁暴期间Dst指数的变化

利用支持向量机（SVM）模型对大磁暴期间Dst指数进行预报研究.以1995-2014年期间的80次大磁暴（Dst≤-100nT）事件共2662组观测数据为研究对象,以对应时间的太阳风参数为模型输入参数,同时建立了神经网络模型和线性机模型进行对比,并利用交叉验证提高预测结果的可靠性.为比较不同模型的预测效果,选用相关系数（CC）、均方根误差（RMS）、磁暴期间Dst指数最小值预测结果的平均绝对误差以及Dst指数最小值出现时间预测结果的平均绝对误差等统计量作为对比参数.结果显示SVM模型的预测效果最好,其中相关系数为0.89,均方根误差为24.27nT,所有磁暴事件的最小Dst值预测平均绝对误差为17.35nT,最小Dst值出现时间的预测平均绝对误差为3.2h.为进一步检验模型对不同活动水平磁暴预报效果的可能差异,将所有磁暴事件分为大磁暴（-200 相似文献   

全球电离层对2000年4月6-7日磁暴事件的响应

利用分布于全球的电离层台站的测高仪观测数据,对扰动期间,foF2值与其宁静期间参考值进行比较,研究了2000年4月6—7日磁暴期间全球不同区域电离层的响应形态,并通过对比磁扰期间NmF2的变化与由MSISR90经验模式估算的中性大气浓度比(no／nN2)的变化,探讨了本次事件期间的电离层暴扰动机制．结果表明,在磁暴主相和恢复相早期,出现了全球性的电离层F2层负相暴效应．最大负相暴效应出现在磁暴恢复相早期,即电离层暴恢复相开始时间滞后于磁暴恢复相开始时间．在磁暴恢复相后期,一些台站出现正相扰动．研究结果表明,本次事件期间的电离层暴主要是由磁暴活动而诱发的热层暴环流引起的．     

磁暴对赤道地区L波段电离层闪烁的影响研究

利用赤道地区Vamimo站闪烁数据, 选取两次典型大磁暴时段重点分析, 对比磁暴发生前、发生时以及发生后连续几天电离层幅度闪烁强度和发生率的变化, 引入瑞利elax-elax泰勒不稳定性(Rayleigh-Taylor, R-T不稳定性)线性增长率γ₀, 对磁暴影响闪烁的机制进行初步探讨. 结果表明, 磁暴可能触发闪烁发生, 也可能抑制闪烁发生, 这既与观测季节有关, 也与磁暴不同发展阶段的地方时有关. 触发发生于闪烁少发季节磁暴主相所在的午夜至黎明时段, 可能是磁层穿透电离层的东向电场所致; 抑制发生于闪烁多发季节磁暴恢复相所在的午夜前时段, 可能是西向电场作用的结果. 磁暴发生时的电场变化可能是抑制或触发闪烁的主导因素, 但仍需进一步分析研究.      

2004年11月一次磁暴期间全球电离层TEC扰动分析

利用全球分布的GPS原始观测数据提取的电离层总电子含量(TEC)分析了2004年11月6日至12日期间全球电离层暴的形态特点与发展过程.结果表明,11月8日磁暴主相期间电离层暴以大范围的强烈正暴为主,在11月10日的恢复相,Dst又一次降到最低值前后期间,电离层再次受到很强的扰动,大范围的正暴和负暴交替出现.这次磁暴期间夏季半球的负暴更加强烈,反映出负暴偏向于在夏季半球发生的季节变化特点.另外,磁暴期间,夜晚TEC值普遍比磁暴前的平静期要低,具体是什么机制导致还需要进一步收集数据和分析.      

2000年4月磁暴期间武汉地区F电离层突然抬升现象

2000年4月6-7日的大磁暴(Dst最小值达到-317nT),急始(SSC)在6日1640UT左右出现,随后磁暴主相开始,约在7日0013UT进入恢复相.磁暴主相前期武汉地区F区电离层出现突然抬高现象,在2h内h′F和h_mF₂分别较暴前日增加约200km.此期间台湾中沥也几乎同时出现了F区电离层突增现象.磁暴主相前期f₀F₂较暴前日下降1.6MHz,其变化幅度在f₀F₂逐日变化起伏范围内,但7日f₀F₂最大值明显低于4-6日暴前水平,并伴随着波动特征.认为此次磁暴主相前期武汉地区F区电离层突增现象,可能和夜间磁暴常出现的扰动东向电场有关.      

第23和24太阳活动周高纬地磁感应电流分布特性

基于高纬度芬兰Mäntsälä地区近两个太阳活动周期（1999—2017年）天然气传输管道的地磁感应电流（GIC,I_GIC）观测数据,统计研究了GIC扰动的分布特征以及强GIC扰动与磁暴和地磁亚暴的相关性.研究发现:95.83%时间段的GIC强度分布在0～1A之间.定义:若某个时间段|I_GIC|_max> 1A,则认为发生GIC扰动;|I_GIC|_max>10A,则认为发生强GIC扰动事件.GIC扰动在磁地方时夜侧附近发生的概率最高,这主要与地磁亚暴发生期间电离层电流最剧烈的变化发生在磁地方时夜侧附近有关;强GIC扰动经常爆发式出现,且都发生在磁暴期间,但大多数磁暴并不伴随强GIC扰动事件发生.磁暴急始驱动的强GIC扰动事件较少,由磁层压缩引起地磁场突然增强驱动的强GIC扰动事件持续时间较短;强GIC扰动事件主要发生在磁暴主相和恢复相,由环电流变化驱动的强GIC扰动事件一般持续时间较长且强度较大.      

磁暴期间电离层电磁离子回旋波的地方时分布差异

利用Swarm卫星的高精度（50 Hz）磁场观测数据,对2015年3月16—25日磁暴期间中纬度电离层电磁离子回旋（EMIC）波时空分布特征进行了研究.结果表明:晨侧EMIC波事件数与昏侧大致相当,午前时段明显多于子夜前时段.昏侧EMIC波高发生率与等离子体羽状结构有关,晨侧EMIC波高发生率与太阳风动压增强及稠密冷等离子体有关.晨侧-正午前EMIC波频率高于昏侧-子夜前,表明源区位置以及离子成分占比存在地方时差异.昏侧事件大多发生在早期恢复相,晨侧事件大多发生在晚期恢复相,晨-昏两侧的时间差异源于磁暴期间高能离子西向漂移所需时间及等离子体层顶位置的地方时差异.磁暴期间,EMIC波以H+波和He+为主,其中H+波主要分布在06:00 MLT—10:00 MLT（磁地方时）扇区,He+波主要分布在18:00 MLT—22:00 MLT扇区.在磁暴主相期间没有出现H+带波,但是出现He+-O+双波段EMIC波,表明磁暴主相期间环电流高浓度氧离子对H+带EMIC波具有抑制作用.      

2005年8月24日强磁暴事件对高层大气密度的扰动

对2005年8月24日发生的突发型强磁暴(Kp峰值达到9)事件,利用星载大气密度探测器在轨实时的连续探测数据进行了处理和分析.结果表明,此次强磁暴事件期间,引起560 km高度附近大气密度剧烈扰动,并存在着两种响应过程.一种是跟随地磁扰动程度变化的全球性大气密度涨落变化,响应时间滞后6h左右, 最大涨落变化比为2.5;另一种为磁暴峰期出现在高纬地区的大气密度突发性跃增,增变比高达5.5.后者存在着区域上的不对称性及时间上的突发性和增幅的差异.此次强磁暴峰期还同时出现了南北半球高纬地区的大气密度跃增双峰.同时还表明这种增变峰可能存在着由高纬向低纬地区迅速推移的现象,在中纬地区推移速度可达15°/h(纬度)左右.      

行星际扰动与不同级别磁暴强度关系的研究

利用1997-2004年间ACE卫星太阳风观测的时均值数据和相应的Dst指数,针对Dstmin≤-50 nT的磁暴,分析了行星际参数(Bz,Ey,v,Pk,|B|,ε'=vxB2zsin4(θ/2))与Dst指数的相关关系.验证了Ey,Bz与Dst指数的良好相关性;按磁暴强度的不同,发现磁暴强度越大,行星际参数与磁暴强度(Dstmin)的相关性就越好.对于中等磁暴(-100 nT＜Dstmin≤-50 nT),行星际参数与磁暴强度的相关系数不高.如果把磁暴分为两个档次,即-150 nT＜Dstmin≤-50 nT的磁暴和Dstmin≤-150 nT的磁暴,计算结果表明,ε'与Dst指数的相关性是最好的.在诸多行星际参数中,就单一因素来说,Ey对磁暴强度影响最大,Bz对磁暴强度影响次之.      

1998年5月磁暴事件期间全球电离层响应形态与机制的研究

利用全球40余个电离层台站的f0F2观测数据，采取对经度进行分区处理的方法，通过计算各台站f0F2参数对其月中的偏离百分比，对1998年5月大磁爆期间的电离层扰动形态进行了分析，并对可能的扰动机制进行了探讨，结果表明本次磁暴事件中，在磁暴主要活动相期间的电离层扰动与暴环流理论所描述的电脑层扰动特征相符，但在恢复相后期欧洲扇区台站出现的正相扰动似不能用暴环流理论来解释，它可能对应期间的行星行条件（太阳风与行星际磁场）的变化有关。     

Investigation of ionospheric response to two moderate geomagnetic storms using GPS–TEC measurements in the South American and African sectors during the ascending phase of solar cycle 24

The responses of the ionospheric F region using GPS–TEC measurements during two moderate geomagnetic storms at equatorial, low-, and mid-latitude regions over the South American and African sectors in May 2010, during the ascending phase of solar cycle 24, are investigated. The first moderate geomagnetic storm studied reached a minimum Dst value of −64 nT at 1500 UT on 02 May 2010 and the second moderate geomagnetic storm reached a minimum Dst value of −85 nT at 1400 UT on 29 May 2010. In this paper, we present vertical total electron content (VTEC) and phase fluctuations (in TECU/min) from Global Positioning System (GPS) observations from the equatorial to mid-latitude regions in the South American and African sectors. Our results obtained during these two moderate geomagnetic storms from both sectors show significant positive ionospheric storms during daytime hours at the equatorial, low-, and mid-latitude regions during the main and recovery phases of the storms. The thermospheric wind circulation change towards the equator is a strong indicator that suggests an important mechanism is responsible for these positive phases at these regions. A pre-storm event that was observed in the African sector from low- to the mid-latitude regions on 01 May 2010 was absent in the South American sector. This study also showed that there was no generation or suppression of ionospheric irregularities by storm events. Therefore, knowledge about the suppression and generation of ionospheric irregularities during moderate geomagnetic storms is still unclear.     

The solar wind control of the equatorial ionosphere dynamics during geomagnetic storms

The interplanetary magnetic field, geomagnetic variations, virtual ionosphere height h′F, and the critical frequency foF2 data during the geomagnetic storms are studied to demonstrate relationships between these phenomena. We study 5-min ionospheric variations using the first Western Pacific Ionosphere Campaign (1998–1999) observations, 5-min interplanetary magnetic field (IMF) and 5-min auroral electrojets data during a moderate geomagnetic storm. These data allowed us to demonstrate that the auroral and the equatorial ionospheric phenomena are developed practically simultaneously. Hourly average of the ionospheric foF2 and h′F variations at near equatorial stations during a similar storm show the same behavior. We suppose this is due to interaction between electric fields of the auroral and the equatorial ionosphere during geomagnetic storms. It is shown that the low-latitude ionosphere dynamics during these moderate storms was defined by the southward direction of the B_z-component of the interplanetary magnetic field. A southward IMF produces the Region I and Region II field-aligned currents (FAC) and polar electrojet current systems. We assume that the short-term ionospheric variations during geomagnetic storms can be explained mainly by the electric field of the FAC. The electric fields of the field-aligned currents can penetrate throughout the mid-latitude ionosphere to the equator and may serve as a coupling agent between the auroral and the equatorial ionosphere.     

The response of the ionosphere over Ilorin to some geomagnetic storms

The effects of some geomagnetic storms on the F2 layer peak parameters over Ilorin, Nigeria (Lat. 8:53°N, Long. 4.5°E, dip angle, −2.96°) have been investigated. Our results showed that the highest intensity of the noon bite-out occurred during the March equinox and lowest during the June Solstice on quiet days. Quiet day NmF2 disturbances which appeared as a pre-storm enhancement, but not related to the magnetic storm event that followed were observed at this station. These enhancements were attributed to the modification of the equatorial electric field as a result of injection of the Auroral electric field to the low and equatorial ionosphere. For disturbed conditions, the morphology of the NmF2 on quiet days is altered. Daytime and nighttime NmF2 and hmF2 enhancements were recorded at this station. Decreases in NmF2 were also observed during the recovery periods, most of which appeared during the post-noon period, except the storm event of May 28–29. On the average, enhancements in NmF2 (i.e. Positive phases) are the prominent features of this station. Observations from this study also indicate that Dst, Ap and Kp which have been the most widely used indices in academic research in describing the behavior of geomagnetic storms, are not sufficient for storm time analysis in the equatorial and low latitude ionosphere.     

Geomagnetic storm effects on the occurrences of ionospheric irregularities over the African equatorial/low-latitude region

The study investigated the effects of intense geomagnetic storms of 2015 on the occurrences of large scale ionospheric irregularities over the African equatorial/low-latitude region. Four major/intense geomagnetic storms of 2015 were analyzed for this study. These storms occurred on 17th March 2015 (?229?nT), 22nd June 2015 (?204?nT), 7th October 2015 (?124?nT), and 20th December 2015 (?170?nT). Total Electron Content (TEC) data obtained from five African Global Navigation Satellite Systems (GNSS) stations, grouped into eastern and western sectors were used to derive the ionospheric irregularities proxy indices, e.g., rate of change of TEC (ROT), ROT index (ROTI) and ROTI daily average (ROTI_AVE). These indices were characterized alongside with the disturbance storm time (Dst), the Y component of the Interplanetary Electric Field (IEFy), polar cap (PC) index and the H component of the Earth’s magnetic field from ground-based magnetometers. Irregularities manifested in the form of fluctuations in TEC. Prompt penetration of electric field (PPEF) and disturbance dynamo electric field (DDEF) modulated the behaviour of irregularities during the main and recovery phases of the geomagnetic storms. The effect of electric field over both sectors depends on the local time of southward turning of IMF Bz. Consequently, westward electric field inhibited irregularities during the main phase of March and October 2015 geomagnetic storms, while for the June 2015 storm, eastward electric field triggered weak irregularities over the eastern sector. The effect of electric field on irregularities during December 2015 storm was insignificant. During the recovery phase of the storms, westward DDEF suppressed irregularities.     

比斯开湾上空电子总量对磁暴的响应

本文论述过去十年中,在英国Aberystwyth城观测同步卫星Intelsat IIF2和SIRIO信标时获得的大西洋比斯开湾上空电子总量对磁暴的响应。所选择的地磁-电离层暴分属前后两个太阳活动较高周期,主要集中在春秋分阶段和冬夏至阶段。文中指出,春分期间连续型磁暴使TEC在正相效应之后出现加长的凋落周期,集中型磁暴导致TEC在正相之后产生凋落周期缩短;春秋分和冬夏至时磁暴伴生的电子总量形态受制于急始时刻与次数、磁暴主相、磁暴指数(即暴时位置和暴情指数)等因素。      

An investigation of ionospheric F region response in the Brazilian sector to the super geomagnetic storm of May 2005

In this paper, we have investigated the responses of the ionospheric F region at equatorial and low latitude regions in the Brazilian sector during the super geomagnetic storm on 15–16 May 2005. The geomagnetic storm reached a minimum Dst of −263 nT at 0900 UT on 15 May. In this paper, we present vertical total electron content (vTEC) and phase fluctuations (in TECU/min) from Global Positioning System (GPS) observations obtained at Belém, Brasília, Presidente Prudente, and Porto Alegre, Brazil, during the period 14–17 May 2005. Also, we present ionospheric parameters h’F, hpF2, and foF2, using the Canadian Advanced Digital Ionosonde (CADI) obtained at Palmas and São José dos Campos, Brazil, for the same period. The super geomagnetic storm has fast decrease in the Dst index soon after SSC at 0239 UT on 15 May. It is a good possibility of prompt penetration of electric field of magnetospheric origin resulting in uplifting of the F region. The vTEC observations show a trough at BELE and a crest above UEPP, soon after SSC, indicating strengthening of nighttime equatorial anomaly. During the daytime on 15 and 16 May, in the recovery phase, the variations in foF2 at SJC and the vTEC observations, particularly at BRAZ, UEPP, and POAL, show large positive ionospheric storm. There is ESF on the all nights at PAL, in the post-midnight (UT) sector, and phase fluctuations only on the night of 14–15 May at BRAZ, after the SSC. No phase fluctuations are observed at the equatorial station BELE and low latitude stations (BRAZ, UEPP, and POAL) at all other times. This indicates that the plasma bubbles are generated and confined on this magnetically disturbed night only up to the low magnetic latitude and drifted possibly to west.     

Moderate geomagnetic storms and their ionospheric effects at middle and low latitudes

This paper reports the global response of the mid high and low latitude ionosphere in four longitudinal sectors to two moderate geomagnetic storms that occurred during 2007 (the more intense storms occurred that year). The results obtained during these storms show that the ionospheric effects in general are not moderate in magnitude, showing an important degree of complexity as during intense storms. The outstanding features produced during the storms are significant positive storm effects at mid-high latitudes during the main phase/first part of the recovery, positive effects after the onset of the storm followed by negatives effects at middle latitudes and delayed positive effects during the night-time hours in the trough of the equatorial anomaly (“dusk” effect). Possible physical mechanisms for controlling the morphology of the ionosphere during these events are considered.     

Study of TEC changes during geomagnetic storms occurred near the crest of the equatorial ionospheric ionization anomaly in the Indian sector

GPS satellites data obtained at Bhopal (23.16° N, 77.36° E, geomagnetic latitude 14.23° N) India were analyzed to study the TEC changes during several geomagnetic storms (−300 nT < Dst < −50 nT) occurred in 2005–2007. We had segregated the storms according to the Dst value, i.e. moderate storms (−100 nT < Dst ? −50 nT), strong storms (−150 nT < Dst < −100 nT), and severe storms (Dst less than −150 nT). Total of 21 geomagnetic storms (10 moderate, 9 strong, 2 severe) are considered for the present study. Deviation in vertical total electron content (VTEC) during the main phase of the storm was found to be associated with the prompt penetration of electric field originated due to the under-shielding and over-shielding conditions for almost all geomagnetic storms discussed in this paper. For most of the storms VTEC shows the positive percentage deviation during the main phase while it shows positive as well as the negative deviation during the recovery phase of the storms. The −80% deviation in VTEC was found for geomagnetic storm occurred on July 17, 2005 and the negative trend continued for recovery phase of the storm. This was mainly due to the thermospheric composition changes by Joule heating effect at auroral latitudes that generate electric field disturbance at low latitudes. Traveling ionospheric disturbances (TIDs) were responsible for the formation of wave like nature in VTEC for the storms occurred on May 15, 2005, whereas it was not observed for storm occurred on August 24, 2005.     

Some ionospheric storm effects at equatorial and low latitudes

In this paper, the response of the equatorial and low latitude ionosphere to three intense geomagnetic storms occurred in 2002 and 2003 is reported. For that, critical frequency of F2-layer foF2 and the peak height hmF2 hmF2 for the stations Jicamarca (11.9°S), Ascension Is (7.92°S) and Tucuman (26.9°S) are used. The results show a “smoothing” of the Equatorial Anomaly structure during the development of the storms. Noticeable features are the increases in foF2 before the storm sudden commencement (SC) at equatorial latitudes and the southern crest of the Equatorial Anomaly. In some cases nearly simultaneous increases in foF2 are observed in response to the storm, which are attributed to the prompt electric field. Also, positive effects observed at equatorial and low latitudes during the development of the storm seem to be caused by the disturbance dynamo electric field due to the storm-time circulation. Increases in foF2 above the equator and simultaneous decreases in foF2 at the south crest near to the end of a long-duration main phase are attributed to equatorward-directed meridional winds. Decreases in foF2 observed during the recovery phase of storms are believed to be caused by composition changes. The results indicate that the prompt penetration electric field on the EA is important but their effect is of short lived. More significant ionospheric effects are the produced by the disturbance dynamo electric field. The role of storm-time winds is important because they modify the “fountain effect” and transport the composition changes toward low latitudes.