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1.
The ionosphere often becomes turbulent and develops electron density irregularities. These irregularities scatter radio waves to cause amplitude and phase scintillation and affect satellite communication and GPS navigation systems. The effects are most intense in the equatorial region, moderate at high latitudes and minimum at middle latitudes. The thermosphere and the ionosphere seem to internally control the generation of irregularities in the equatorial region and its forcing by solar transients is an additional modulating factor. On the other hand, the irregularity generation mechanisms in the high-latitude ionosphere seem to be driven by magnetospheric processes and, therefore, high-latitude scintillations can be tracked by following the trail of energy from the sun in the form of solar flares and coronal mass ejections. The development of a global specification and forecast system for scintillation is needed in view of our increased reliance on space-based communication and navigation systems, which are vulnerable to ionospheric scintillation. Such scintillation specification systems are being developed for the equatorial region. An equatorial satellite equipped with an appropriate suite of sensors, capable of detecting ionospheric irregularities and tracking the drivers that control the formation of ionospheric irregularities, has also been planned for the purpose of specifying and forecasting equatorial scintillations. In the polar region, scintillation specification and forecast systems are yet to emerge although modeling and observations of polar cap plasma structures, their convection and associated irregularities have advanced greatly in recent years. Global scintillation observations made during the S-RAMP Space Weather Month in September 1999 are currently being analyzed to study the effects of magnetic storms on communication and navigation systems.  相似文献   

2.
太阳活动低年夏季,低纬电离层F区场向不规则体表现出与太阳活动高年和其他季节明显不同的特征.本文利用我国三亚站（18.4°N,109.6°E,地磁倾角纬度dip latitude 12.8°N）VHF雷达、电离层测高仪、GPS闪烁监测仪和美国C/NOFS卫星观测数据,研究了太阳活动低年夏季我国低纬电离层F区场向不规则体的基本特征.分析发现无论磁静日还是磁扰日,夏季电离层F区不规则体回波主要出现于地方时午夜以后,回波出现的时间较短,高度范围较小,伴随着扩展F出现,但没有同时段的L波段电离层闪烁.太阳活动低年夏季午夜后的低纬电离层F区不规则体回波,可能并不总是与赤道等离子体泡沿磁力线向低纬地区的延伸相关,而可能由本地Es等扰动过程引起.  相似文献   

3.
本文利用GPS-CHAMP高分辨率的掩星探测数据,考察了E_S层不规则结构随地理经度和随季节、倾角磁纬与太阳活动的变化特征.研究发现,E_S层不规则结构的经度变化以波数1~5分量为主,呈现出多重波数特征.在低纬度带存在显著的波数4分量,其幅度存在季节依赖,在夏季和秋季明显高于春季和冬季.E_S层不规则结构出现率随倾角磁纬的变化表现为赤道区和中纬度区较低,低纬区和极区较高.E_S层不规则结构出现率的季节变化和年均值的逐年变化表现为夏季出现最频繁,秋季次之,冬春季最弱,随太阳活动水平的减弱而降低.  相似文献   

4.
穿过电离层不规则体传播后的无线电波,其振幅和相位出现快速随机起伏,即电离层闪烁.为了量化电离层不规则体和相位闪烁的强度,本文提出用TEC起伏δTEC作为特征参量,并用δTEC的标准差构建一种新指数σtec.文中证明指数σtec与相位闪烁指数完全等效.在电离层强闪烁期间,经常出现信号短暂失锁和周跳,导致TEC值突跳和不连续.为此,本文设计了一种周跳检测与校正的批处理算法,用于消除TEC值突跳.在此基础上,利用位于我国中南部电离层闪烁监测台网2012—2015年的观测数据,考察了GPS信号相位闪烁和不规则体的统计特征.结果表明,我国低纬电离层不规则体和相位闪烁与振幅闪烁随地方时和月份变化的特征类似,一天之中主要出现在日落后至黎明前,一年之中,春季不规则体出现最频繁、秋季次之,呈现春秋不对称性,冬夏季出现很少.此外,我们还比较分析了指数S4与σtec的联系,两者之间显著正相关表明,小于第一菲涅尔带尺度的小尺度不规则体和大于第一菲涅尔带尺度的大尺度不规则体一般同时存在.  相似文献   

5.
暴时低纬电离层不规则体响应特征的多手段观测   总被引：4，自引：2，他引：2       下载免费PDF全文
2010年10月11日发生了一次中等强度的磁暴.本文利用三亚(18.4°N,109.6°E)数字测高仪、VHF雷达和GPS TEC/闪烁监测仪数据以及120°E子午线附近我国漠河(53.5°N,122.4°E)、北京(40.3°N,116.2°E)和武汉(30.6°N,114.4°E)的数字测高仪和GPS TEC/闪烁监测仪数据,分析了磁暴期间我国中低纬地区电离层不规则体的响应特征.结果表明:这次磁暴触发了10月11日午夜前后两个时段低纬(三亚)电离层不规则体事件,而在较高的纬度地区(武汉及以北),并没有观测到电离层不规则体与闪烁.在午夜前,电离层不规则体的发生受磁暴主相期间快速穿透电场激发;在午夜后,电离层不规则体受磁暴恢复相的扰动发电机电场触发,该时段伴随行星际磁场北向翻转的过屏蔽穿透电场也可能是扰动源之一.此外,磁暴期间不同尺度的电离层不规则体会伴随发生.  相似文献   

6.
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.  相似文献   

7.
This study investigated a long-term climatology of nocturnal equatorial F-region irregularities by using phase fluctuations of the global positioning system during the solar cycle of 1996–2006 at the west Pacific longitudes. The results showed that the distribution of the occurrence of irregularities is a two-peak pattern, which peaks in equinoxes with a shallow/deep dip in June/December solstice during high solar activity but with two about the same dips in magnitude in both June and December solstices during low solar activity. Moreover, the most interesting longitudinal effect in the area is in solstice occurrences of irregularities during high solar activity that the irregularities in December solstice months develop easier in the west area but those in June solstice months develop easier in the east area.  相似文献   

8.
Interplanetary scintillation (IPS) can be used to identify changes in solar wind parameters over a wide range in heliographic latitude and elongation and constrain models of its large-scale structure, velocity and density. This paper reviews the scintillation density mapping method specifically, and presents over three years of data taken between March 1990 and September 1993 with the 3.6 hectare array in Cambridge. A novel form of synoptic plot that is particularly sensitive to corotating structures is introduced, and low-density streams are identified by their unequivocal signatures within it. Stable corotating structures are evident throughout - even during the active phase of the solar cycle - and specific periods are examined. Density measurements inferred from scintillation are compared with IMP-8 data for the same period and are shown to be in good agreement, giving further support to the scintillation/density relationship determined by Tappin (1986).  相似文献   

9.
This paper reports differences in the occurrence statistics of global positioning system (GPS) L-band scintillations at observational sites located in the inner regions of the northern and southern crests of the equatorial ionization anomaly. Ground-based GPS data acquired at the closed magnetically aligned stations of Manaus (3.1°S; 59.9°W; dip lat. 6.2°N) and Cuiabá (15.5°S; 56.1°W; dip. lat. 6.2°S), Brazil, from December 2001 to February 2007 are used in the analysis. The drift dynamics of Fresnel-scale ionospheric irregularities at the southern station of Cuiabá are also investigated. Only geomagnetically quiet days with the sum of daily Kp < 24 were used in the analysis statistics and in the irregularity drift studies. The results reveal a clear dependence of the scintillation occurrence with the solar activity, but there exists an asymmetry in the percentage of scintillation occurrence between the two stations throughout the period analyzed. The nocturnal occurrence of the scintillations over Cuiabá is predominantly larger than over Manaus, but this scenario seems to change with the decline in the solar activity (mainly during local post-midnight hours). A broad minimum and maximum in the scintillation occurrence appears to occur over both the stations, respectively, during the June solstice (winter) and December solstice (summer) months. The dynamics of the Fresnel-scale irregularities, as investigated from the estimations of the mean zonal drift velocities, reveals that the amplitude of the eastward drifts tends to reduce with the decline in the solar activity. The magnitude of the zonal drift velocities during the December solstice months is larger than during the equinoxes, with the differences being more pronounced at solar maximum years. Other relevant aspects of the observations, with complementary data from a low-latitude ionospheric model, are highlighted and discussed.  相似文献   

10.
Ionospheric scintillations are fluctuations in the phase and/or amplitude of trans-ionospheric radio signals caused by electron density irregularities in the ionosphere. A better understanding of the scintillation pattern is important to make a better assessment of GPS receiver performance, for instance. Additionally, scintillation can be used as a tool for remote sensing of ionospheric irregularities. Therefore, the study of ionospheric scintillation has both scientific as well as technological implications. In the past few years, there has been a significant advance in the methods for analysis of scintillation and in our understanding of the impact of scintillation on GPS receiver performance. In this work, we revisit some of the existing methods of analysis of scintillation, propose an alternative approach, and apply these techniques in a comprehensive study of the characteristics of amplitude scintillation. This comprehensive study made use of 32?days of high-rate (50?Hz) measurements made by a GPS-based scintillation monitor located in S?o José dos Campos, Brazil (23.2°S, 45.9°W, ?17.5° dip latitude) near the Equatorial Anomaly during high solar flux conditions. The variability of the decorrelation time (τ0) of scintillation patterns is presented as a function of scintillation severity index (S 4). We found that the values of τ0 tend to decrease with the increase of S 4, confirming the results of previous studies. In addition, we found that, at least for the measurements made during this campaign, averaged values of τ0 (for fixed S 4 index values) did not vary much as a function of local time. Our results also indicate a significant impact of τ0 in the GPS carrier loop performance for S 4?≥?0.7. An alternative way to compute the probability of cycle slip that takes into account the fading duration time is also presented. The results of this approach show a 38% probability of cycle slips during strong scintillation scenarios (S 4 close to 1 and τ0 near 0.2?s). Finally, we present results of an analysis of the individual amplitude fades observed in our set of measurements. This analysis suggests that users operating GPS receivers with C/N 0 thresholds around 30?dB-Hz and above can be affected significantly by low-latitude scintillation.  相似文献   

11.
We have analyzed GPS data from 2007–2011 to determine the nature of variation of scintillation index with elevation of the direction of propagation at an observing point Warsaw, Poland, and Hornsund, Svalbard. To compare with the theory, the intensity scintillation index is simulated as a function of elevation angle, azimuth, magnetic field inclination, and shape of irregularities, using the phase screen model of scintillation as formulated by Rino (1979). Data analysis has been done for the seasonal as well as geomagnetic activity dependence of ionospheric scintillation. Scintillation index is a power-law function of the cosecant of the elevation angle. Results show that the power law strongly depends on the form of irregularities, being larger than in isotropic case for irregularities with dimension along the magnetic field direction smaller than those across the magnetic field. The present work also shows the need to use experimentally derived dependence on elevation.  相似文献   

12.
With increasing reliance on space-based platforms for global navigation and communication, concerns about the impact of ionospheric scintillation on these systems have become a high priority. Recently, the Air Force Research Laboratory (AFRL) performed amplitude scintillation measurements of L1 (1.575 MHz) signals from GPS satellites at Ascension Island (14.45° W, 7.95° S; magnetic latitude 16° S) during February–April, 1998, to compare amplitude scintillations with fluctuations of the total electron content (TEC). Ascension Island is located in the South Atlantic under the southern crest of the equatorial anomaly of F2 ionization where scintillations will be much enhanced during the upcoming solar maximum period. Ascension Island is included in the global network of the International GPS Service (IGS) and the GPS receivers in this network report the carrier to noise (C/N) ratio, the dual frequency carrier phase and pseudorange data at 30-s intervals. Such data with a sampling interval of 30 s were analyzed to determine TEC, the rate of change of TEC (ROT) and also ROTI, defined as the standard deviation of ROT. The spatial scale of ROTI, sampled at 30 s interval, will correspond to 6 km when the vector sum of the ionospheric projection of the satellite velocity and the irregularity drift orthogonal to the propagation path is of the order of 100 m/s. On the other hand, the scale-length of the amplitude scintillation index corresponds to the Fresnel dimension which is about 400 m for the GPS L1 frequency and an ionospheric height of 400 km. It is shown that, in view of the co-existence of large and small scale irregularities in equatorial irregularity structures, during the early evening hours, and small magnitude of irregularity drifts, ROTI measurements can be used to predict the presence of scintillation causing irregularities. The quantitative relationship between ROTI and S4, however, varies considerably due to variations of the ionospheric projection of the satellite velocity and the ionospheric irregularity drift. During the post-midnight period, due to the decay of small scale irregularities leading to a steepening of irregularity power spectrum, ROTI, on occasions, may not be associated with detectable levels of scintillation. In view of the power law type of irregularity power spectrum, ROTI will, in general, be larger than S4 and the ratio, ROTI/S4, in the present dataset is found to vary between 2 and 10. At high latitudes, where the ionospheric motion, driven by large electric fields of magnetospheric origin, is much enhanced during magnetically active periods, ROTI/S4 may be considerably larger than that in the equatorial region.  相似文献   

13.
In this work, the climatology of ionospheric scintillations at global positioning system (GPS) L-band frequency and the zonal drift velocities of scintillation-producing irregularities were depicted for the equatorial observatory of São Luis (2.33°S; 44.21°W; dip latitude 1.3°S), Brazil. This is the first time that the hourly, monthly, and seasonal variations of scintillations and irregularity zonal drifts at São Luis were characterized during periods of different solar activity levels (from December 1998 to February 2007). The percentage occurrence of scintillations at different sectors of the sky was also investigated, and the results revealed that the scintillations are more probable to be observed in the west sector of the sky above São Luis, whereas the north–south asymmetries are possibly related to asymmetries in the plasma density distribution at off-equatorial latitudes. The scintillations on GPS signals occurred more frequently around solar maximum years, but it is also clear from the results of a strong variability in the scintillation activity in the years with moderate solar flux during the descending phase of the solar cycle. The equatorial scintillations occur predominantly during pre-midnight hours with a broad maximum near the December solstice months. In general, weak level of scintillations (S 4 index between 0.2 and 0.4) dominated at all seasons; however, during the winter months around solar maximum years (although the scintillation occurrence is extremely low), stronger levels of scintillations (S 4 > 0.6) may occur at comparable rate with the weak scintillations. The irregularity zonal velocities, as estimated from the GPS spaced-receiver technique, presented a different scenario for the two seasons analyzed; during the equinoxes, the magnitude of the zonal velocities appeared not to change with the solar activity, whereas during the December solstice months, the larger magnitudes were observed around solar maximum years. Other relevant aspects of the observations are highlighted and discussed.  相似文献   

14.
黄智 《地球物理学报》2017,60(2):480-488
利用气象、电离层和气候卫.星联合观测系统COSMIC掩星2007-2013年探测资料,分析了120°E经线附近电离层E层区域(70~140km)闪烁指数的季节、地方时和空间变化.结果表明强电离层闪烁主要集中在磁纬度±30°内,夏季达到最大,冬季其次,春季最小.闪烁峰值大小与太阳辐射有关,但北半球夏冬季闪烁峰值大于南半球观测结果,秋半球闪烁峰值大于春半球观测结果.地磁高纬地区较强闪烁现象出现在地方时傍晚之后,午夜前后达到最大值.地磁中纬和低纬区域日出后即出现较为明显的闪烁现象,一直持续至夜间甚至凌晨,分别约在中午和傍晚前达到最大值.磁赤道区闪烁现象通常始于地方时日出后,最大值发生在傍晚1800LT左右.电离层E区的闪烁峰值大都集中110km高度,但高纬地区的峰值高度略有降低.此外,太阳和地磁活动的增强一定程度上会抑制E层闪烁现象.相关研究结果有利于分析E层不规则结构及物理形成机制,同时为电离层区域闪烁模型的建立提供有用的信息.  相似文献   

15.
为构建赤道-低纬电离层不规则结构和闪烁活动出现率的理论模型,本文根据分析赤道-低纬电离层的广义Rayleigh-Taylor(R-T)不稳定性得到的三维线性增长率的表达式,计算分析了线性增长率随地方时的变化特征.并选取计算得到的每日增长率的极大值表征每日的线性增长率,分析增长率随季节、太阳活动和地理经度的变化特征以及逐日变化特征,建立三维广义R-T不稳定性线性增长率的理论统计特征模型,发现增长率表现出显著的随地方时、季节、太阳活动和地理经度以及逐日变化特征.通过比较分析增长率的变化特征与不规则结构和闪烁活动的变化特征,发现三维广义R-T不稳定性的线性增长率能较好地反映不规则结构和闪烁活动随季节、太阳活动、地理经度以及逐日变化规律.本文建立的R-T不稳定性的三维线性增长率的统计特征模型可用于构建赤道-低纬电离层不规则结构和闪烁出现率的理论形态特征模型.  相似文献   

16.
《Journal of Atmospheric and Solar》2002,64(12-14):1531-1543
Jicamarca unattended long term investigations of the ionosphere and atmosphere radar observations of equatorial spread F (ESF) plasma irregularities made between August 1996 and April 2000 are analyzed statistically. Interpretation of the data is simplified by adopting a taxonomy of echo types which distinguishes between bottom-type, bottomside, topside, and post-midnight irregularities. The data reveal patterns in the occurrence of ESF in the Peruvian sector that are functions of season, solar flux, and geomagnetic activity. We confirm earlier work by Fejer et al. (J. Geophys. Res. 104 (1999) 19,859) showing that the quiet-time climatology of the irregularities is strongly influenced by the climatology of the zonal ionospheric electric field. Under magnetically quiet conditions, increasing solar flux implies greater pre-reversal enhancement amplitudes and, consequently, irregularity appearances at earlier times, higher initial altitudes, and higher peak altitudes. Since the post-reversal westward background electric field also grows stronger with increasing solar flux, spread F events also decay earlier in solar maximum than in solar minimum. Variation in ESF occurrence during geomagnetically active periods is consistent with systematic variations in the electric field associated with the disturbance dynamo and prompt penetration described by Fejer and Scherliess (J. Geophys. Res. 102 (1997) 24,047) and Scherliess and Fejer (J. Geophys. Res. 102 (1997) 24,037). Quiet-time variability in the zonal electric field contributes significantly to variability in ESF occurrence. However, no correlation is found between the occurrence of strong ESF and the time history of the zonal electric field prior to sunset.  相似文献   

17.
The characteristics of ionospheric scintillations at Rajkot in the equatorial anomaly crest region in India are described for the years 1987–1991 by monitoring the 244-MHz transmission from the satellite FLEETSAT. This period covers the ascending phase of solar cycle 22. Scintillations occur predominantly in the pre-midnight period during equinoxes and winter seasons and in the post-midnight period during summer season. During equinoxes and winter, scintillation occurrence increases with solar activity, whilst in summer it is found to decrease with solar activity. Statistically, scintillation occurrence is suppressed by magnetic activity. The characteristics observed during winter and equinoxes are similar to those seen at the equatorial station, Trivandrum. This, coupled with the nature of the post-sunset equatorial F-region drift and h‘F variations, supports the view that at the anomaly crest station, scintillations are of equatorial origin during equinox and winter, whilst in summer they may be of mid-latitude type. The variations in scintillation intensity (in dB) with season and solar activity are also reported.  相似文献   

18.
Observations from a network of specially equipped GPS scintillation receivers in Northern Europe are used to investigate the dynamics of ionospheric plasma during the storm events of 30 October and 20 November 2003. The total electron content (TEC) and scintillation data, combined with ionospheric tomography produced by the multi-instrument data analysis system (MIDAS), reveal strong enhancements and steep gradients in TEC during nighttime under a prevailing negative Bz component of the interplanetary magnetic field (IMF). Amplitude and phase scintillation maxima are often co-located with the TEC gradients at the edge of plasma patches, revealing the presence of small-scale irregularities and suggesting association with a tongue of ionization (TOI) convecting in an anti-sunward direction from the American sector across the polar cap. Similarities and differences between the ionospheric response to the two storms are investigated. The 30 October event reveals a quite complex scenario showing two phases of plasma dynamics: the former reflects the expected convection pattern for IMF Bz southward and the latter possibly indicates a sort of TEC plasma stagnation signature of the more complex convection patterns during several positive/negative excursions of IMF Bz.  相似文献   

19.
The possible role, on L-band scintillation activity, played by the nighttime magnetic meridional component of the thermospheric horizontal neutral winds, the post-sunset F-layer base height, the electrical field pre-reversal enhancement (PRE) and the latitudinal gradients of the F2-layer peak density is analyzed, considering different cases of scintillation occurrence (and their latitudinal extent) during August and September 2002. The meridional winds were derived over low-latitudes from a modified form of the nonlinear time-dependent servo-model. A chain of two scintillation monitors and three digital ionosondes was operational in Brazil and used to collect, respectively, global positioning system signal amplitude scintillation and ionospheric height (h′F; hpF2) and frequency (foF2) parameters. From the overall behavior in the 2 months analyzed, the results suggest that high near sunset upward vertical plasma drifts are conducive for the generation of spread-F irregularities, whereas large poleward meridional winds tend to suppress the development of plasma bubble irregularities and the occurrence of their associated scintillations. Even when generated, a reduced fountain effect, due to weak electric field PRE, acts for the bubbles to be expanded less effectively to higher latitudes. The results also reveal that high F-layer base and peak heights (at equatorial and off-equatorial latitudes), and intense gradients in the F2-peak density between the dip equator and the equatorial anomaly crests, are favorable conditions for the generation of F-region irregularities and increased scintillation activity. Other distinct features of the controlling factors in the cases of occurrence and non-occurrence of equatorial scintillations are presented and discussed.  相似文献   

20.
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   

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