共查询到20条相似文献，搜索用时 78 毫秒
1.
G. A. Mansilla 《Studia Geophysica et Geodaetica》2007,51(4):563-574
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 相似文献
2.
Geomagnetism and Aeronomy - The behaviour of the ionospheric F2-layer during geomagnetic storm is studied using the critical frequency parameter foF2. The magnetic storms of 2nd October 2013 and... 相似文献
3.
《Journal of Atmospheric and Solar》2003,65(9):987-995
Neutral gas composition and ionospheric measurements taken by the Dynamic Explorer 2 satellite at F2-region heights during two geomagnetic storms are used to analyze the role of some possible physical mechanisms responsible for the changes of electron density at equatorial and low geomagnetic latitudes. The storms considered occurred on October 2, 1981 (storm 1) and July 13, 1982 (storm 2). During storm 1 (weak), vertical plasma drifts and equatorward storm-time winds operated increasing of the electron density at the trough of equatorial anomaly and the decreases at the crest region. During storm 2 (intense) changes of composition (increase of molecular nitrogen and atomic oxygen) played a fundamental role for the changes of electron density observed at low latitudes in summer hemisphere. It is concluded that different physical processes seem to have varying degrees of importance depending on the intensity of the storm. 相似文献
4.
Victor U. Chukwuma 《Acta Geophysica》2007,55(4):469-489
A study of the geomagnetic storm of July 13–14, 1982, and its ionospheric response is presented using the low-latitude magnetic
index, Dst, and interpreted using solar wind interplanetary data: proton number density, solar wind flow speed, interplanetary magnetic
field southward component B
Z
, and solar wind dynamic pressure. The F2 region structure response to the geomagnetic storm was studied using foF2 data obtained during the storm from a network of various ionosonde stations. Our results appear to show simultaneous abrupt
depletion of foF2 that occurred at all latitudes in both the East Asian and African/European longitudinal zone during the period: 18:00–19:00
UT on July 13 and is as result of an abrupt increase in the dynamic pressure between 16:00 and 17:00 UT. The dynamic pressure
increased from 3.21 to 28.07 nPa within an hour. The aforementioned abrupt depletion of foF2 simultaneously resulted in an intense negative storm with peak depletion of foF2 at about 19:00 at all the stations in the East Asian longitudinal zone. In the African/European longitudinal zone, this simultaneous
abrupt depletion of foF2 resulted in intense negative storm that occurred simultaneously at the low latitude stations with peak depletion at about
20:00 UT on July 13, while the resulting negative storm at the mid latitude stations recorded peak depletion of foF2 simultaneously at about 2:00 UT on July 14. The present results indicate that most of the stations in the three longitudinal
zones showed some level of simultaneity in the depletion of foF2 between 18:00 UT on July 13 and 2:00 UT on July 14. The depletion of foF2 during the main phase of the storm was especially strongly dependent on the solar wind dynamic pressure. 相似文献
5.
O.M. Pirog N.M. Polekh E.B. Romanova G.A. Zherebtsov Jiankui Shi Xiao Wang 《Journal of Atmospheric and Solar》2010,72(2-3):164-175
In this paper, we present analyses of the great geomagnetic storms observed during last two cycles of solar activity. This study is based on data from a network of ionosondes located within the longitudinal sector of 80–150°Е. it was found that the superstorms were observed predominantly in equinox. Long-lasting severe decreases of ionization at high and middle latitudes were the most impressive storm effect. A short-time positive phase occurred in response to the onset of both ssc and recovery phases of the magnetic storm in the daytime at high and middle latitudes. Large time-varying rates of foF2 were observed at low latitudes. Modeling results of the ionospheric response to two superstorms are also presented. It is established that the storm effect at middle latitudes was controlled predominantly by disturbed thermospheric composition. At high latitudes, the impact of magnetospheric processes and thermospheric composition on the ionosphere was the same. 相似文献
6.
N. M. Polekh O. M. Pirog S. V. Voeikov P. V. Tatarinov A. E. Stepanov V. V. Bychkov Z. F. Dumbrava 《Geomagnetism and Aeronomy》2006,46(5):593-602
Results of the studies of ionospheric parameter variations during the intense geomagnetic storm on November 7–11, 2004, in the 20°–80° N, 60°–180° E sector are presented. The data of ionospheric stations and the results of total electron content (TEC) measurements at the network of the GPS ground-based receivers and of the GPS receiver onboard the CHAMP satellite were used. Periods of total absorption and blanketing sporadic E layers were observed at high latitudes, whereas durable negative disturbances typical of geomagnetic storms of high intensity were detected at midlatitudes. In the afternoon hours of local time on November 8, 2004, a large-scale ionospheric disturbance of a frontal type was detected on the basis of foF2 and TEC measurements. The disturbance propagated southwestward at a mean velocity of about 200 m/s. The comparison of the relative amplitude of this large-scale disturbance according to the total electron content (～70%) and foF2 (～80%) measurements made it possible to assume a large vertical scale of the disturbance. 相似文献
7.
An investigation is made in order to analyse the role of neutral gas composition in the equatorial and low latitude ionosphere during intense geomagnetic storms. To this end data taken by the Dynamic Explorer 2 satellite at 280–300 km (molecular nitrogen N2 and atomic oxygen O concentrations, electron density and vertical plasma drifts) are used. The sudden commencements of the events considered occurred at 11:38 UT on March 1, 1982, 18:41 UT on November 20, 1982 and 16:14 UT on February 4, 1983. Vertical plasma drifts are the most important contributor to the initial storm time response of the equatorial F region. Neutral composition changes (expressed as an increase in the molecular species, mainly N2) possibly play a predominant role in the equatorial and low latitude (10–20°) decreases of electron density at heights near F2-region maximum during the main and recovery phases of intense geomagnetic storms. Delayed increases of electron density observed at daytime during the recovery phase may be also attributed to increases in atomic oxygen. At low latitudes possibly a combined effect of O increase and upward plasma drift due to enhanced equatorward winds is the responsible mechanism for the maintenance of enhanced electron density values. 相似文献
8.
基于CHAMP卫星加速度计数据,对2002年4月和2004年11月两个连续磁暴事件期间400 km高度热层大气密度时空变化特征进行了分析,结果表明,地磁扰动相近的连续磁暴发生时,热层密度对第一个磁暴的响应幅度明显大于后续磁暴;磁暴间歇期有时会出现密度低值;磁暴恢复相,热层密度先于ap指数快速恢复至暴前水平,甚至更低;热层大气经验模式NRLMSISE00的预测结果中没有包含这些现象.利用TIMED卫星SABER辐射计数据进一步分析同时段100~155 km高度NO冷却率的变化特点,NO冷却率在暴时的增大滞后热层密度2~6 h;磁暴恢复相,NO冷却率保持在较高水平,弛豫时间远大于热层密度.暴时增强的NO冷却率及其缓慢的恢复是导致热层密度响应幅度变小的原因,间歇期是否出现热层密度异常低值也与NO冷却率的增幅有关. 相似文献
9.
10.
Geomagnetism and Aeronomy - The behavior of the critical frequency of the F2 layer, foF 2, during the 3 days preceding a magnetic storm is analyzed. A total of 254 storms in 1976–2010... 相似文献
11.
《Journal of Atmospheric and Solar》2002,64(5-6):593-599
The relativistic electron fluxes of the Earth's outer radiation belt are subjected to strong temporal variations. The most prominent changes are initiated by fast solar wind streams impinging upon the magnetosphere, which often also cause enhanced substorm activity and magnetic storms. Using 4 years of data from the particle detector REM aboard the UK satellite Strv-1b in a GTO, we investigated the relation between these different appearances of geomagnetic activity. A typical sequence is that there is a drop in the relativistic electron intensity during the main phase of the magnetic storm and a successive enhancement during the recovery phase which sometimes leads to much higher than pre-storm fluxes. Whereas the flux drop is well correlated with the magnetic storm intensity and is mainly due to the deceleration and loss of particles caused by the ring-current-induced magnetic field changes, there is only a bad correlation between the post-storm electron flux and Dst. As we show here, it is much more the level of substorm activity during the whole event which determines the size of the flux enhancements. 相似文献
12.
Victor U. Chukwuma 《Acta Geophysica》2010,58(6):1164-1192
An investigation to elucidate the mechanisms responsible for the pre-storm and main phase ionospheric phenomena during November
20–21, 2003, is presented using heliophysical, interplanetary, geomagnetic, and global ionospheric data. The results show
that the ionospheric responses in the main phase do not indicate prompt penetration electric fields as the main ionospheric
driver. The results also show that the pre-storm phenomena do not originate from a local time effect. The simultaneous occurrence
of ƒoF2 enhancements at two widely separated longitudinal zones appeared to suggest a role played by the magnetospheric electric
field. However, the analysis of hmF2 at the stations could not confirm the notion that these fields are the main drivers of pre-storm phenomena. An investigation
of flare effects on the pre-storm phenomena also revealed that solar flares are not the main drivers. The present results
appear to suggest that the pre-storm ionospheric phenomena could be a result of some underlying mechanisms that are working
together with varying degree of importance. 相似文献
13.
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. 相似文献
14.
本文利用DMSP F13和F15卫星观测数据,对2001—2005年58个磁暴(-472 nT≤Min.Dst≤-71 nT)期间高纬顶部电离层离子整体上行特征进行了统计研究.观测表明,磁暴期间,顶部电离层离子上行主要发生在极尖区和夜间极光椭圆区.在北半球,磁正午前,高速的离子上行(≥500 m·s-1)多集中在65° MLat以上;午后,高速离子上行区向低纬度扩展,上行速度要略高于午前;在南半球,磁午夜前,DMSP卫星在考察区域内几乎所有的纬度上都观测到了高速上行的离子;午夜后,各纬度上观测到上行离子的速度明显降低.离子上行期间,DMSP卫星在极区顶部电离层高度上也频繁地观测到电子/离子增温,且电子增温发生的频率要远高于离子增温.O+密度变化分析显示,DMSP卫星磁暴期间观测到的上行离子更多地源于顶部电离层高度.这些结果表明电子增温在驱动暴时电离层离子整体上行过程中起着重要作用. 相似文献
15.
Studia Geophysica et Geodaetica - The ionospheric response to geomagnetic storms is usually investigated by considering the variability of the critical frequency of the F2-layer (foF2) or the total... 相似文献
16.
The relation of the fluxes of relativistic electrons in geostationary orbit during magnetic storms to the state of the magnetosphere and variations in the solar wind parameters is studied based on the GOES satellite data (1996–2000). It has been established that, in ～52–65% of all storms, the fluxes of electrons with energies higher than 0.6 and 2 MeV during the storm recovery phase are more than twice as high as the electron fluxes before a storm. It has been indicated that the probability of such cases is closely related to the prestorm level of fluxes and to a decrease in fluxes during the storm main phase. It has been found that the solar wind velocity on the day of the storm main phase and the geomagnetic activity indices at the beginning of the storm recovery phase are also among the best indicators of occurrence of storms with increased fluxes at the storm recovery phase. 相似文献
17.
《Journal of Atmospheric and Solar》1999,61(3-4):309-327
GPS satellite transmissions have been used to study the development of moderateionospheric phase irregularities. The use of the multi-station, multi-path observations of the GPSbeacons has allowed the study of the time development of irregularities as a function of latitudeand longitude of individual storms. The basic storms studied were those of January 10, April10–11, and May 15, 1997. The results from studying these storms showed the unique nature ofeach storm. For the three storms, data were available from four stations near 65° CorrectedGeomagnetic Latitude (CGL); the stations ranged from Fairbanks to Tromso. In addition, datafrom higher latitude stations are analysed. For the January storm, irregularity development startedat Fairbanks. Then as magnetic midnight approached longitudes to the west, the storm effectsreached the Tromso–Kiruna longitudes. For the April magnetic storm, at 65° CGL, irregularitydevelopment maximized at approximately the same UT at stations ranging in longitude fromFairbanks to Kiruna. For this storm, the development of irregularities was dominated by stormtime. The May storm irregularities were dominated by magnetic local time once the stormcommenced.With both total electron content and rate of change of total electron content (phasefluctuations) available, it was noted that over periods of minutes, clumps of irregularities wereaccompanied by increases in TEC. In addition total electron content increased over large areasduring maximum magnetic activity in the auroral oval. During the storms, ionograms showed thatthe altitude of maximum electron density fluctuated; at times the dominant maximum frequencywas noted in the E layer and at other times in the F layer. This fluctuation of electron density ineach layer during storms led to the conclusion that the turbulent activity within the auroral regiondominated the development of irregularities. The irregularities that are noted on trans-ionosphericpaths are therefore thought to be in both the E and the F layers with a combination of structuredhard and soft electron precipitation and coupling initiating the turbulent activity. The generalpositive correlation of one periods phase scintillation data with the Ultra Violet Imagerobservations as shown on POLAR indicates the importance of 100–200 km precipitation.However the very high occurrence of spread F at high latitudes as shown by both ground andsatellite ionosondes indicates the considerable contributions of F layer irregularities. 相似文献
18.
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. 相似文献
19.
本文利用低纬地磁台站的Pi1、Pi2地磁脉动（Pi1-2）资料和地球同步轨道的Pc5地磁脉动资料,对2004年1月到2006年12月38个磁暴事件的地磁脉动参数进行了统计分析.在此基础上,考虑相对论电子的局部加速机制,并加入损失机制,建立了一个初步的磁暴期间地球同步轨道相对论电子通量对数值的预报模型.利用该模型,我们对上述38个磁暴事件进行预报试验,最优化结果是：相对论电子通量对数值的预测值和观测值之间的线性相关系数为0.82,预报效率为0.67.这说明该模式具有较好的预报效果,也表明利用地磁脉动参数进行相对论电子通量预报是可行的. 相似文献
20.
Ionospheric effects of a large number (51) of severe geomagnetic storms are studied using total electron content (TEC) and VHF/UHF scintillation data from Calcutta, situated near the northern crest of equatorial ionization anomaly and equatorial spread-F (ESF) data from Kodaikanal. The susceptibility of the equatorial ionosphere to develop storm time plasma density irregularities responsible for ESF and scintillation is found to be largely modulated by the local times of occurrences of main and recovery phases as seen in the Dst index. While inhibition of premidnight scintillation for lower TEC values compared to the quiet day averages is omnipresent, occurrence of scintillation for enhancements of TEC is largely dependent on initiation time and amplitude of the said deviations. An overall reduction in threshold values of h′F for observing storm induced ESF and scintillation compared to reported quiet time values is noted. The results are discussed in terms of storm time variabilities in electric fields, neutral wind system and composition changes. 相似文献