大尺度电离层行扰的GPS观测

利用日本境内的高空间分辨率的双频GPS台站资料,观测研究了发生于2000年7月中旬太阳强活动期间的一次大尺度电离层行扰. 结果表明:在7月15日11:00UT-1:00UT期间观测区域的电离层中出现了大尺度电离层行扰. 在15:00UT之前,扰动周期为2h左右,在15:00UT以后,扰动周期为1h左右;总电子含量扰动幅度的变化范围约为1-2TECU;通过对15:00-17:00UT之间总电子含量扰动曲线同相位点的分析,发现这期间的电离层行扰的扰动速度约为600-700m/s,扰动波长在2200km左右,扰动传播的方向几乎沿着经线从高纬向低纬传播. 该行扰与此次强太阳活动有直接的关系,因其发生在7月15日的磁暴急始之前数小时,因此与磁暴本身没有因果关系,应与磁暴之前先期到达地球空间的高能质子流有关.     

A comparison of solar wind and ionospheric plasma contributions to the September 24–25, 1998 magnetic storm

We have used a global time-dependent magnetohydrodynamic (MHD) simulation of the magnetosphere and particle tracing calculations to determine the access of solar wind ions to the magnetosphere and the access of ionospheric O⁺ ions to the storm-time near-Earth plasma sheet and ring current during the September 24–25, 1998 magnetic storm. We found that both sources have access to the plasma sheet and ring current throughout the initial phase of the storm. Notably, the dawnside magnetosphere is magnetically open to the solar wind, allowing solar wind H⁺ ions direct access to the near-Earth plasma sheet and ring current. The supply of O⁺ ions from the dayside cusp to the plasma sheet varies because of changes in the solar wind dynamic pressure and in the interplanetary magnetic field (IMF). Most significantly, ionospheric O⁺ from the dayside cusp loses access to the plasma sheet and ring current soon after the southward turning of the IMF, but recovers after the reconfiguration of the magnetosphere following the passage of the magnetic cloud. On average, during the first 3 h after the sudden storm commencement (SSC), the number density of solar wind H⁺ ions is a factor of 2–5 larger than the number density of ionospheric O⁺ ions in the plasma sheet and ring current. However, by 04:00 UT, ∼4 h after the SSC, O⁺ becomes the dominant species in the ring current and carries more energy density than H⁺ ions in both the plasma sheet and ring current.     

Spatial correlation of foF2 and vTEC under quiet and disturbed ionospheric conditions: A case study

The spatial variations of the ionospheric F2-layer vertical incidence critical frequency (foF2) and GPS-derived vertical total electron content (vTEC) under geomagnetically quiet and disturbed days are examined using measurements from the latitudinal and longitudinal chains of ionospheric stations and GPS receivers over the European area. Plots produced for January 2005 are used to discuss temporal structures in terms of the prevailing solar-terrestrial conditions. Then the line trends procedure has been applied to simultaneous data collected from a limited number of measuring stations during quiet monthly median ionospheric conditions as well as during the storm period of 16–23 January 2005. The procedure is explained involving an application of the least squares method to define latitudinal and longitudinal dependence of foF2 and vTEC at different locations. Examples of coefficients of determination thereby produced show that the linear regression equations are very helpful in predicting longitudinal and latitudinal vTEC and foF2 variations during the quiet as well as disturbed ionospheric conditions.     

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     

Magnetic Pulsations: Their Sources and Relation to Solar Wind and Geomagnetic Activity

Ultra low frequency (ULF) waves incident on the Earth are produced by processes in the magnetosphere and solar wind. These processes produce a wide variety of ULF hydromagnetic wave types that are classified on the ground as either Pi or Pc pulsations (irregular or continuous). Waves of different frequencies and polarizations originate in different regions of the magnetosphere. The location of the projections of these regions onto the Earth depends on the solar wind dynamic pressure and magnetic field. The occurrence of various waves also depends on conditions in the solar wind and in the magnetosphere. Changes in orientation of the interplanetary magnetic field or an increase in solar wind velocity can have dramatic effects on the type of waves seen at a particular location on the Earth. Similarly, the occurrence of a magnetospheric substorm or magnetic storm will affect which waves are seen. The magnetosphere is a resonant cavity and waveguide for waves that either originate within or propagate through the system. These cavities respond to broadband sources by resonating at discrete frequencies. These cavity modes couple to field line resonances that drive currents in the ionosphere. These currents reradiate the energy as electromagnetic waves that propagate to the ground. Because these ionospheric currents are localized in latitude there are very rapid variations in wave phase at the Earth’s surface. Thus it is almost never correct to assume that plane ULF waves are incident on the Earth from outer space. The properties of ULF waves seen at the ground contain information about the processes that generate them and the regions through which they have propagated. The properties also depend on the conductivity of the Earth underneath the observer. Information about the state of the solar wind and the magnetosphere distributed by the NOAA Space Disturbance Forecast Center can be used to help predict when certain types and frequencies of waves will be observed. The study of ULF waves is a very active field of space research and much has yet to be learned about the processes that generate these waves.     

南向行星际磁场事件与磁暴关系的研究

利用172-182年IMP-8飞船的太阳风观测资料和相应地磁活动性指数Dst和AE,研究了43个南向行星际磁场事件期间太阳风和磁层的耦合问题. 与这43个事件对应的地磁暴是中等的和强的磁暴(Dst＜-50nT). 结果表明:(1) 在43个事件中有11个(约占25.6髎)紧随激波之后,18个处于激波下游流场中(占42髎),其余14个(占33髎)和激波没有关连. 绝大多数事件都伴有太阳风动压和总磁场强度的增加;(2) 当行星际晨昏向电场强度EI＞-4mV/m时,只引起磁亚暴,对Dst指数没有明显影响. 仅当EI＜-5mV/m时,磁亚暴和磁暴才会同时出现;(3) 太阳风动压的增加会增强能量向环电流的输入,但不是密度和速度单独起作用,而是以PK=ρV2的组合形式影响能量的输入;(4) 虽然行星际磁场(IMF)南向分量BZ对太阳风和磁层的耦合起着关键作用,但IMF的BX和BY分量相对于BZ的大小对太阳风向磁层的能量传输也有一定影响. 当BX、BY相对BZ较大时能量耦合加强.     

Long-period geomagnetic pulsations caused by the solar wind negative pressure impulse on 22 March 1979 (CDAW-6)

An analysis is made of the long-period geomagnetic pulsations as recorded at seven Norilsk meridian stations ( = 162°, latitudinal range: 61°–71°N) following abrupt magnetospheric expansion during the storm of 22 March 1979 caused by a rapid decrease in solar wind density. As with the time interval following an abrupt contraction at the time of sudden storm commencement, there exist two types of pulsations in the pulsation spectra: latitude-independent (T>400 s) and latitude-dependent (T<200 s) pulsations. The first pulsation type is interpreted in terms of forced pulsations associated with magnetopause oscillations. The oscillation period is determined by plasma density in the boundary layer and by the radius of the magnetosphere (T ^1/2R⁴). The latitudinal dependence of the period, amplitude and polarization of the second-type pulsations is in agreement with the resonance mechanism of their origin.     

Ionospheric response to the geomagnetic storm on 13–17 April 2006 in the West Pacific region

This paper presents an investigation of geomagnetic storm effects in the equatorial and middle-low latitude F-region in the West Pacific sector during the intense geomagnetic storm on 13–17 April, 2006. The event, preceded by a minor storm, started at 2130 UT on April 13 while interplanetary magnetic field (IMF) B_z component was ready to turn southward. From 14–17 the ionosphere was characterized by a large scale enhancement in critical frequency, foF2 (4～6 MHz) and total electron content (TEC) (～30TECU, 1TECU=1×10¹⁶el/m²) followed by a long-duration negative phase observed through the simultaneous ionospheric sounding measurements from 14 stations and GPS network along the meridian 120°E. A periodic wave structure, known as traveling ionospheric disturbances (TIDs) was observed in the morning sector during the initial phase of the storm which should be associated with the impulsive magnetospheric energy injection to the auroral. In the afternoon and nighttime, the positive phase should be caused by the combination of equatorward winds and disturbed electric fields verified through the equatorial F-layer peak height variation and modeled upward drift of Fejer and Scherliess [1997. Empirical models of storm time equatorial electric fields. Journal of Geophysical Research 102, 24,047–24,056]. It is shown that the large positive storm effect was more pronounced in the Southern Hemisphere during the morning-noon sector on April 15 and negative phase reached to lower magnetic latitudes in the Northern Hemisphere which may be related to the asymmetry of the thermospheric condition during the storm.     

Global Pi3 geomagnetic pulsations as a response of large variations in the solar wind and IMF during the magnetic storm of August 5, 2011

Spatial-temporal and spectral features of ground geomagnetic pulsations in the frequency range of 1–5 mHz at the initial phase of a strong magnetic storm of the 24th cycle of solar activity (August 5–6, 2011, with a Dst-variation in the storm maximum of ?110 nT) are analyzed. Large opposite in sign amplitudes of variations in IMF parameters (from ?20 to +20 nT) at a high velocity of the solar wind (～650 km/s) accompanied by intense bursts in solar-wind density (up to ～50 cm^?3) were distinctive feature of interplanetary medium conditions causing the storm. Geomagnetic Pi3 pulsations global in longitude and latitude and in-phase in the middle and equatorial latitudes were found. The onset of pulsation generation was caused by a pulse of dynamic pressure of the solar wind (～20 nPa), i.e., by a considerable compression of the magnetosphere. The maximum (2–3 mHz) in the amplitude spectrum of near-equatorial pulsations coincided with the maximum of pulsations in the daytime polar cap. After the next jump of the dynamic pressure of the solar wind (～35 nPa), an additional maximum appeared in the pulsation spectrum in the frequency band of ～3.5–4.5 mHz. Global pulsations suddenly stopped after a sharp decrease in the solar-wind dynamic pressure and corresponding extension of the magnetosphere. The obtained results are compared with the time dynamics of the position and shape of the plasmapause.     

Prediction of variations from Polar Cap indices using time-delay neural network

The hourly averaged Polar Cap (PC) index was used as the input parameter for the ring current index D_st variation forecasting. The PC index is known to describe well the principal features of the interplanetary magnetic field as well as the total energy input to the magnetosphere. This allowed us to design a neural network that was able to forecast the D_st variations 1 h ahead. 1995 PC and D_st data sets were used for training and testing and 1997 data sets were used for validation. From 15 moderate and strong geomagnetic storms observed during 1997, 10 were successfully forecasted. In 3 cases the observed minimum D_st value was less than the predicted value, and only in 3 cases the neural network was not able to reproduce the features of the geomagnetic storm.     

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.     

甘肃嘉峪关、瓜州地电场日变化与地电暴差异机理分析

通过甘肃省嘉峪关台地磁场观测资料,研究嘉峪关台、瓜州台磁静日地电场日变化的时频特征波;由地电场分钟值观测数据的时序叠加残差方法,研究嘉峪关、瓜州山的地电暴变化。结果表明:(1)两台地电场静日变化以两次起伏变化为主,无相位差,但两台之间日变幅差异较大;(2)地电场分量变化与地磁场正交分量变化显著相关;地电场与地磁场日变波形不同,极值时间有差异。2个台存在很明显的高频成分,在去除了高频变化后,其优势周期也相同,从大到小依次为12 h、8 h、24 h。地磁场H分量因存在磁暴影响,故高频变化较多,在去除了磁暴影响后,其优势周期从大到小依次为24 h、12 h、8 h;(3)当电磁暴扰动剧烈时,两台可以较清晰地记录到地电暴的完整变化。在发生电磁暴时,地电场与地磁场的相关性明显降低,且不同台、不同测向之间的变化幅度也不尽相同。两台东分量E_Y暴日的日变幅较静日明显增大,磁暴期间Y分量变化率与地电场东分量E_Y观测数据显著相关,由此说明:两台日变幅的不同与台站台址电导率有关,太阳风引起的电离层活动是引起了地电场日变化主因。引起电暴的原因可能不同于引起日变化的原因,主要是两台之间及不同测向之间的浅、深层电阻率和地质构造等诸多因素的结果。     

地电暴事件判别方法及特征分析

本文基于我国2015—2018年间地电暴事件,通过对筛选的数据曲线变化特征归纳分析,总结出以下快速准确判断地电暴事件的依据:(1)地电暴发生时,会压制地电场六道观测数据正常日变形态,且变幅是正常日变幅值2倍以上或更大;(2)地电暴事件具有广域同步性,可通过多台观测数据对比判断;(3)地电暴和地磁暴具有同源性,可通过地磁观测来判断;(4)经过上述初判后,还应排除观测系统、自然环境、人为干扰、场地环境事件影响,才能确认为单一地电暴事件。通过对地电暴波形特征的分析,发现一般情况下地电暴变幅与地磁磁情指数—K指数呈正比关系,但是同一台站地电暴变幅在同一K指数下差异较大。不同台站对同一地电暴事件幅度响应不同,仅从变幅来看纬度效应不明显,有局部区域性特点,可能与台站台址条件\,地电场布极方式方位等因素均有关。     

The impact of temporal ionospheric gradients in Northern Europe on relative GPS positioning

The effect of temporal ionospheric gradients on measured baselines was studied at mid and high latitudes. The experimental analysis was carried out from 14 to 17 July 2000 (day of year (DOY) from 196 to 199), which includes both quiet and stormy days for comparison purposes. Temporal ionospheric gradients caused by the geomagnetic storm affect the ambiguity resolution, resulting in unresolved ambiguities up to 61% for the time periods 21:00–24:00 UT on DOY 197 and 00:00–03:00 UT on DOY 198 for the Kiru-Soda and Kiru-Tro1 baselines (high-latitude, K_p>7). RMS of epoch by epoch coordinate residual change gradually increases from 1.45, 0.96 and 3.67 cm at 9:00–12:00 UT on DOY 197 to 1.79, 1.22 and 4.61 cm at 0:00–03:00 UT on DOY 198 (K_p>8) for the same baselines’ north, east and up coordinate components, respectively. There are no remarkable effects for the selected baselines in the mid-latitude region in both ambiguities and coordinate components.     

Non-linear predictions ofAp by activity class and numerical value

Two neural network algorithms are applied to the short-term,1 to 3 days, prediction of theAp geomagnetic index. A multi-layer, back-propagation (MBP) network is used to implement a self-prediction filter forAp and this provides a forecast of the numerical value of the index. A probabilistic neural network (PNN) is used to estimate the probability distribution of theAp index, in six activity classes, and to provide a forecast of the single most likely activity class for each day. BothAp and an index of solar activity, based on the daily reports issued by the Space Environment Services Centre (Boulder), are input to the probabilistic net. It is found that the numerical forecasts of the MBP filter are most accurate at low, non-storm, levels of activity. This non-linear method provides quantitatively better estimates of activity than are produced by an existing linear prediction filter, particularly with increasing forward forecasting lag. At high levels of the solar activity index the PNN is found to anticipate storm classAp with around 60% accuracy in 1992 and 1993. Some details of the algorithms and implementation issues are described. It is concluded that interplanetary field and solar wind data will be significant components of any of the possible future developments which are discussed.     

太阳风压力系数的研究

利用全球磁流体力学(MHD)的模拟结果,研究了太阳风压力系数与上游太阳风参数和日下点磁层顶张角的相关性.在识别出日下点附近磁层顶位置后,通过拟合得到日下点附近的磁层顶张角.在考虑上游太阳风中的磁压和热压以及磁层顶外侧的太阳风动压的情况下,计算了太阳风压力系数.通过分析行星际磁场不同方向时太阳风动压在日地连线上与磁压和热压的转化关系,详细研究了太阳风参数和日下点磁层顶张角对太阳风压力系数的影响,得到以下相关结论:(1) 在北向行星际磁场较大(B_z≥5 nT)时,磁层顶外侧磁压占主导,南向行星际磁场时磁层顶外侧热压占主导;(2) 太阳风压力系数随着行星际磁场的增大而增大,随着行星际磁场时钟角的增大而减小;并且在行星际磁场大小和其他太阳风条件相同时,北向行星际磁场时的太阳风压力系数要大于南向行星际磁场时的;北向行星际磁场时,太阳风压力系数随着太阳风动压的增大而减小,南向行星际磁场时,太阳风压力系数随着太阳风动压的增大而增大;以上结论是对观测结果的扩展;(3) 最后,我们还发现太阳风压力系数随着日下点磁层顶张角的增大而增大.     

High-latitude geomagnetic disturbances during the initial phase of a recurrent magnetic storm (from February 27 to March 2, 2008)

A complex of geophysical phenomena (geomagnetic pulsations in different frequency ranges, VLF emissions, riometer absorption, and auroras) during the initial phase of a small recurrent magnetic storm that occurred on February 27–March 2, 2008, at a solar activity minimum has been analyzed. The difference between this storm and other typical magnetic storms consisted in that its initial phase developed under a prolonged period of negative IMF B _z values, and the most intense wave-like disturbances during the storm initial phase were observed in the dusk and nighttime magnetospheric sectors rather than in the daytime sector as is observed in the majority of cases. The passage of a dense transient (with N _p reaching 30 cm⁻³) in the solar wind under the southward IMF in the sheath region of the high-speed solar wind stream responsible for the discussed storm caused a great (the AE index is ∼1250 nT) magnetospheric substorm. The appearance of VLF chorus, accompanied by riometer absorption bursts and Pc5 pulsations, in a very long longitudinal interval of auroral latitudes (L ∼ 5) from premidnight to dawn MLT hours has been detected. It has been concluded that a sharp increase in the solar wind dynamic pressure under prolonged negative values of IMF B _z resulted in the global (in longitude) development of electron cyclotron instability in the Earth’s magnetosphere.     

Polar regionSq

Geomagnetically quiet day variations in the polar region are reviewed with respect to geomagnetic field variation, ionospheric plasma convection, electric field and current. Persistently existing field-aligned currents are the main source of the polar regionSq. Consequently, the morphology and variability of the polar regionSq largely depend upon both field-aligned currents and ionospheric conductivity. Since field-aligned currents are the major linkage between the ionosphere and the magnetosphere, the latter is controlled by solar wind state, in particular, the interplanetary magnetic field, the polar regionSq exhibits remarkable IMF dependence.     

Coupling the Solar-Wind/IMF to the Ionosphere Through the High Latitude CUSPS

Magnetic merging is a primary means for coupling energy from the solar wind into the magnetosphere–ionosphere system. The location and nature of the process remain as open questions. By correlating measurements from diverse locations and using large-scale MHD models to put the measurements in context, it is possible to constrain our interpretations of the global and meso-scale dynamics of magnetic merging. Recent evidence demonstrates that merging often occurs at high latitudes in the vicinity of the cusps. The location is in part controlled by the clock angle in the interplanetary magnetic field (IMF) Y–Z plane. In fact, B_Y bifurcates the cusp relative to source regions. The newly opened field lines may couple to the ionosphere at MLT locations of as much as 3 hr away from local noon. On the other side of noon the cusp may be connected to merging sites in the opposite hemisphere. In fact, the small convection cell is generally driven by opposite hemisphere merging. B_X controls the timing of the interaction and merging sites in each hemisphere, which may respond to planar features in the IMF at different times. Correlation times are variable and are controlled by the dynamics of the tilt of the interplanetary electric field phase plane. The orientation of the phase plane may change significantly on time scales of tens of minutes. Merging is temporally variable and may be occurring at multiple sites simultaneously. Accelerated electrons from the merging process excite optical signatures at the foot of the newly opened field lines. All-sky photometer observations of 557.7 nm emissions in the cusp region provide a “television picture” of the merging process and may be used to infer the temporal and spatial variability of merging, tied to variations in the IMF.     

Ionospheric convection during the magnetic storm of 20–21 March 1990

We report on the response of high-latitude ionospheric convection during the magnetic storm of March 20–21 1990. IMP-8 measurements of solar wind plasma and interplanetary magnetic field (IMF), ionospheric convection flow measurements from the Wick and Goose Bay coherent radars, EISCAT, Millstone Hill and Sondrestrom incoherent radars and three digisondes at Millstone Hill, Goose Bay and Qaanaaq are presented. Two intervals of particular interest have been identified. The first starts with a storm sudden commencement at 2243 UT on March 20 and includes the ionospheric activity in the following 7 h. The response time of the ionospheric convection to the southward turning of the IMF in the dusk to midnight local times is found to be approximately half that measured in a similar study at comparable local times during more normal solar wind conditions. Furthermore, this response time is the same as those previously measured on the dayside. An investigation of the expansion of the polar cap during a substorm growth phase based on Faraday’s law suggests that the expansion of the polar cap was nonuniform. A subsequent reconfiguration of the nightside convection pattern was also observed, although it was not possible to distinguish between effects due to possible changes in B_y and effects due to substorm activity. The second interval, 1200–2100 UT 21 March 1990, included a southward turning of the IMF which resulted in the B_z component becoming -10 nT. The response time on the dayside to this change in the IMF at the magnetopause was approximately 15 min to 30 min which is a factor of \sim2 greater than those previously measured at higher latitudes. A movement of the nightside flow reversal, possibly driven by current systems associated with the substorm expansion phases, was observed, implying that the nightside convection pattern can be dominated by substorm activity.