利用北斗观测数据实时监测中国区域电离层变化

北斗卫星导航信号采用三个频点工作,可以利用伪距双频组差方法解算电离层电子含量,为实时监视中国区域电离层变化提供新的技术手段.中国中低纬度处于电离层赤道异常变化区,在北纬20°±5°区域时常发生较大梯度的电离层变化.利用北斗实时多频伪距和相位观测数据,采用相位平滑伪距方法计算电离层穿刺点电子含量,分析通过北斗系统GEO卫星监测的电离层周日变化特性;采用多面函数方法拟合中国区域1°×1°分辨率的电离层延迟量,每5min绘制一幅中国区域电离层图,观测区域所有电离层穿刺点拟合残差RMS为2.778TECU;分析北斗系统实时监测中国区域电离层异常情况,当发生电离层异常变化时,相邻两天的VTEC（Vertical Total Electronic Content）峰值相差约60TECU.      

非相干雷达探测低电离层的结果分析

位于波多黎各的Arecibo非相干雷达可以获得低电离层电子和离子密度, 利用此非相干雷达数据对中纬度低电离层的运动特征进行研究. 得到了电子密度随时间和高度的变化 情况, 结果显著呈现出周日变化特征, 并分析了电子密度随高度的变化规律. 进一步对数据进行频谱分析, 深入研究低电离层电子密度的周日变化效应. 得到电子密度的高度剖面, 发现从F层底部到E层有明显的等离子体沉降. 低电离层的层结构特征及电子密度变化表明, 在该区域还存在不同程度的等离子体扰动, 由此对低电离层的作用因素 进行分析, 认为大气潮汐或声重波可能对低电离层产生扰动, 即低电离层与大气存在一定程度的耦合作用.      

电离层周日变化对解算GPS硬件延迟稳定性的影响

针对电离层周日变化特征分析了其可能对SCORE方法估算的硬件延迟稳定性的影响. 利用BJFS以及XIAM台站的GPS观测数据, 解算了位于太阳活动高年(2001年)和太阳活动低年(2009年)的卫星硬件延迟并分析了估算的硬件延迟的稳定性. 研究发现, 电离层周日变化对估算的硬件延迟稳定性具有一定影响, 但是利用不同台站所得到的卫星硬件延迟稳定性在昼夜不同时间上的解算结果存在一定差异. 电离层周日变化对利用 BJFS台站数据解算的硬件延迟稳定性日夜差异较为明显, 在太阳活动高年利用XIAM 台站数据解算的硬件延迟日夜稳定性差异不很明显, 由于XIAM台站处于电离层赤道异常峰附近, 夜间电离层变化很大, 因此对比中纬度地区, 电离层周日变化对赤道异常峰附近地区硬件延迟稳定性解算结果的影响相对较小, 但在太阳活动低年, 其影响仍较为显著.      

日照边缘区域电离层对耀斑的响应特点研究

利用MSIS模型和背景太阳辐射谱模型,在一定大耀斑辐射谱假设的前提下,计算了耀斑期间日照边缘区域的电子产生率,分析了这一区域电离层电子密度的变化特点.结果表明,大耀斑期间在日照边缘区域,甚至大于太阳天顶角90°的区域都有明显的电子产生率的增加.从不同太阳天顶角处的电子产生率剖面的形态来看,随着天顶角的增加最大电离率减少,但高度增加.计算还显示了在太阳天顶角小于90°的区域内电子产生率的垂直分布有明显的双峰结构,这种结构对应着电离层的E区和F区,但在天顶角大于90°区域,F区的电子产生率要大得多.考虑到离子和电子的复合过程,这一区域的总电子含量的增加主要产生在高F区.      

1984年4月24日大太阳耀斑爆发对电离层电子总含量的影响

本文给出1984年4月24日2356UT太阳耀斑爆发期间在新乡和重庆两地利用法拉第技术接收日本同步卫星ETS-Ⅱ的甚高频信号所得到的电离层电子总含量的异常变化。两站在耀斑爆发期间的三分半钟内同时观测到电离层电子总含量的突然急剧增加。它们的增量分别为9.4×1016和14.3×1016ele/m2.本文还将偏振仪所观测到的现象与电离层垂测记录及甚低频锁相接收机所观测到的记录作了比较。分析的结果表明,大太阳耀斑期间不仅D层的电子浓度大大增加,而且F层的电子浓度也显着增加,后者是这次总含量剧增的主要部分。      

通过GPS测量数据研究电离层电子总含量的逐日变化

提出了一种直接通过双频GPS伪距测量数据导出接收站附近垂直TEC的方法,这种方法不需要事先知道卫星和接收机电路时延的精确值,前者可在换算过程中自洽地加以修正,而接收机时钟误差则利用IRI模式的夜晚平均值作为参考来订正,这一订正存在一定的绝对误差,但不会影响逐日相对变化,却使数据处理过程大为简化.得到的垂直TEC为天顶周围60锥角内的平均值,能够相当好地反映电离层电子总含量的周日变化.一个计算实例显示了连续三天北京地区TEC的日变化情况,证实了这一方法的实用性.文中还提出一个新概念或问题,即GPS卫星仰角很小时,通常认为多径效应造成大的误差,本文的一些实例似乎表明,这种多径效应的概念应当包括电离层不规则结构的贡献.     

南极地区电离层总电子含量分布特征的初步探讨

通过对微分多普勒数据处理后得到的电离层总电子含量的分析, 探讨了南极地区总电子含量随纬度的分布变化特征及规律。      

利用GPS技术实时监测上海区域电离层变化

基于GPS技术实时监测电离层变化原理, 利用载波平滑伪距观测值建立区域电离层模型的方法, 计算了电离层延迟量和硬件延迟, 根据硬件延迟值相对稳定的特点, 采取一定时段求解出硬件延迟量, 对实时硬件延迟量进行预报, 进而实时分离GPS信号传播路径上的垂直总电子含量VTEC. 利用上海区域内的GPS网的观测数据, 建立实时上海区域电离层延迟模型, 监测上海区域的电离层变化. 数据分析结果表明, 这种方法的内符合精度优于3 TECU.      

新乡上空电离层总电子含量的经验模式

基于电离层总电子含量与太阳活动性之间的线性相关关系,利用在新乡长期测量所得的电离层总电子含量的资料,得出了总电子含量的一种经验模式。      

应用高频多普勒方法对耀斑期间电离层TEC变化的估算

通过分析前人对耀斑期间电离层各区域电子密度的变化情况,总结了一个应用耀斑期间的高频多普勒扰动记录估算出层总电子含量变化的方法,并应用这一方法计算了１９９０年３－６月几次耀斑引起的低电离层总电子含量的变化,同时还与各耀斑对应的最大流量密度进行了比较,并对两者之间的相关情况进行了分析。     

Diurnal and seasonal variations of F2 layer characteristics over Irkutsk during the decrease in solar activity in 2003–2006: Observations and IRI-2001 model predictions

The diurnal and seasonal variations of F2 layer characteristics (critical frequency, peak height and bottomside thickness) over Irkutsk, Russia (52.3 N and 104.3 E) are studied by the method of running medians. The comparison with the IRI-2001 model during the decrease in solar activity in 2003–2006 revealed cases of both close agreement and systematic differences between predictions and observations. The systematic difference is not the only reason for disagreement between IRI and observations; there are also intrayear variations which are not associated with seasonal behavior. The period of observation was too short to make conclusions about solar activity dependence of the noon bottomside thickness and the modification of its diurnal behavior with decreasing solar activity.     

第22与23周磁静日北京台银河宇宙线周日变化与半日变化特征

利用快速傅里叶变换及其计算功率谱的方法研究了第22和23周磁静日北京宇宙线台站记录的银河宇宙线强度的周日变化与半日变化，计算结果表明，在两个太阳活动周交替时，银河宇宙线的周日变化与半日变化特征消失，在太阳活动低年逐渐向高年过度时，首先出现的是周日变化。半日变化特征出现要滞后于周日变化，22周太阳活动高年看不出周日变化，而23周太阳活动的高年周日变化非常显著，22周太阳活动的下降期。只有周日变化而无半日变化。这是分析北京宇宙线台近2个太阳活动周数据得到的新结果。     

The structure of the solar cycle maximum phase in the galactic cosmic ray 11-year variation

Two phenomena connected with the maximum phase of the 11-year solar cycle in the galactic cosmic ray intensity – the change in the energy dependence of the intensity variations and the double-peak structure in the intensity modulation time profile – are considered for the last five solar cycles (Nos. 19–23). The distinct 22-year cycle in the magnitude of the so called energy hysteresis is observed.The periods of the solar cycle maximum phase in the galactic cosmic ray intensity, characterized by the specific energy dependence of the intensity, are estimated. It is found that the double-peak structures belonging to the solar cycle maximum phase and those around it are very similar both in the amplitude and in its energy dependence.     

Comparison of ionospheric F2 peak parameters foF2 and hmF2 with IRI2001 at Hainan

Monthly median values of foF2, hmF2 and M(3000)F2 parameters, with quarter-hourly time interval resolution for the diurnal variation, obtained with DPS4 digisonde at Hainan (19.5°N, 109.1°E; Geomagnetic coordinates: 178.95°E, 8.1°N) are used to investigate the low-latitude ionospheric variations and comparisons with the International Reference Ionosphere (IRI) model predictions. The data used for the present study covers the period from February 2002 to April 2007, which is characterized by a wide range of solar activity, ranging from high solar activity (2002) to low solar activity (2007). The results show that (1) Generally, IRI predictions follow well the diurnal and seasonal variation patterns of the experimental values of foF2, especially in the summer of 2002. However, there are systematic deviation between experimental values and IRI predictions with either CCIR or URSI coefficients. Generally IRI model greatly underestimate the values of foF2 from about noon to sunrise of next day, especially in the afternoon, and slightly overestimate them from sunrise to about noon. It seems that there are bigger deviations between IRI Model predictions and the experimental observations for the moderate solar activity. (2) Generally the IRI-predicted hmF2 values using CCIR M(3000)F2 option shows a poor agreement with the experimental results, but there is a relatively good agreement in summer at low solar activity. The deviation between the IRI-predicted hmF2 using CCIR M(3000)F2 and observed hmF2 is bigger from noon to sunset and around sunrise especially at high solar activity. The occurrence time of hmF2 peak (about 1200 LT) of the IRI model predictions is earlier than that of observations (around 1500 LT). The agreement between the IRI hmF2 obtained with the measured M(3000)F2 and the observed hmF2 is very good except that IRI overestimates slightly hmF2 in the daytime in summer at high solar activity and underestimates it in the nighttime with lower values near sunrise at low solar activity.     

半个太阳活动周期内我国中纬地区上空电离层等效板厚的变化特征

本文用新乡(电离层400km对下点是:32.4°N,115.6°E)、重庆(电离层400km对下点是:27.2°N,108.7°E)接收日本同步卫星ETS-Ⅱ的信标资料,研究了我国中纬地区上空半个太阳活动周期内(1981—1985)电离层等效板厚的变化特征,得到了等效板厚日变化、季变化的二维和三维等值图。由付里叶分析和回归方法得出等效板厚日变化各谐波分量与太阳黑子数12个月滑动平均值之间存在弱的线性关系。同时指出在等效板厚日变化中,于当地时0400—0700LT存在一明显的黎明峰。并对出现这种峰的原因作了讨论。      

Periodic variations of ionization rate in the low and middle atmosphere

The cosmic ray ionization source functions which were obtained using a simplified extensive air shower model are used to calculate the eleven year cycle, seasonal and diurnal variations of ionization rate in the low and middle atmosphere. The ionization source function, as a function of the penetrating depth and the energy of cosmic ray particles, is the ionization rate per unit depth for a unit flux of incoming cosmic ray particles with certain energy.The calculation of the eleven year cycle variation of ionization rate in the low and middle atmosphere due to the modulation of galactic cosmic ray intensity by solar activity shows that the amplitude is larger at a higher magnetic latitude and is generally larger at higher altitudes. The relative amplitude of fluctuation of the ionization peak value (at altitudes near 15 km) is up to 45% in the magnetic polar region. The ionization rate, due to the seasonal variation of the atmospheric density, varies from several per cent below the ionization peak to several tens per cent above the peak. This seasonal variation of ionization rate reaches 35% at 70 km. The diurnal variation of atmospheric densities caused by atmospheric tidal oscillation can produce a diurnal variation of the ionization rate to an amplitude of several per cent at altitudes above 40 km. The diurnal oscillation is less than 1% below 35 km.     

In situ results on the variation of neutral atmospheric hydrogen at venus

The concentrations of neutral hydrogen within the atmosphere of Venus are investigated for the period 1979–1980. During this period, the planet made nearly three orbits about the Sun, so that nearly three complete diurnal cycles were observed from the Pioneer Venus Orbiter (PVO). Values of n(H) are derived from in-situ ion and neutral composition measurements from the Orbiter Ion Mass Spectrometer (OIMS) and the Orbiter Neutral Mass Spectrometer (ONMS) using a charge exchange relationship involving O⁺, H⁺, O and CO₂. The dawn bulge in the diurnal distribution of n(H), reported from the first diurnal cycle by Brinton et al., is found to persist with n(H) peaking at levels near 2 - 5 × 10⁷/cm³ at altitudes below 165 km. At peak levels, the bulge exhibits a concentration ratio up to 400/1 relative to dayside values. Large day to day variations of up to a factor of five in n(H) are frequently encountered, and are attributed to perturbations induced by the solar wind interaction. These short term variations, plus a suggestion of some local time variation in the bulk location, make precise assessment of interannual variations in the n(H) difficult. Between the first diurnal cycle in early 1979 and the third in mid 1980, the decline in solar euv flux was of the order of 10% or less. Allowing for uncertainties due to short term variations, no clear evidence is found for an interannual variation in the hydrogen concentrations.     

Comparison of Diurnal,Seasonal and Solar Cycle Variations of High-latitude,Mid-latitude and Low-latitude Ionosphere

Comparison of regular (diurnal, seasonal and solar cycle) variations of high-latitude,mid-latitude and low-latitude ionospheric characteristics has been provided on basis of local empirical models of the peak electron density and the peak height. The local empirical models were derived from the hand-scaled ionogram data recorded by DPS-4 digisondes located at Norilsk (69°N, 88°E), Irkutsk (52°N, 104°E) and Hainan (19°N, 109°E) for a 6-year period from December, 2002 to December, 2008. The technique used to build the local empirical model is described. The primary focus is diurnal-seasonal behavior under low solar activity and its change with increasing solar activity. Both common and specific features of the high-latitude (Norilsk), mid-latitude (Irkutsk) and low-latitude (Hainan) regular variations were revealed using their local empirical models.      

Comparison of GPS TEC measurements with IRI-2007 TEC prediction over the Kenyan region during the descending phase of solar cycle 23

This paper presents an analysis of the Total Electron Content (TEC) derived from the International GNSS Service receiver (formerly IGS) at Malindi (2.9°S, 40.1°E), Kenya for the periods 2004–2006 during the declining phase of solar cycle 23. The diurnal, monthly and seasonal variations of the TEC are compared with TEC from the latest International Reference Ionosphere model (IRI-2007). The GPS–TEC exhibits features such as an equatorial noon time dip, semi-annual variations, Equatorial Ionization Anomaly and day-to-day variability. The lowest GPS–TEC values are observed near the June solstice and September equinox whereas largest values are observed near the March equinox and December solstice. The mean GPS–TEC values show a minimum at 03:00 UT and a peak value at about 10:00 UT. These results are compared with the TEC derived from IRI-2007 using the NeQuick option for the topside electron density (IRI–TEC). Seasonal mean hourly averages show that IRI-2007 model TEC values are too high for all the seasons. The high prediction primarily occur during daytime hours till around midnight hours local time for all the seasons, with the highest percentage deviation in TEC of more 90% seen in September equinox and lowest percentage deviation in TEC of less than 20% seen in March equinox. Unlike the GPS–TEC, the IRI–TEC does not respond to geomagnetic storms and does overestimate TEC during the recovery phase of the storm. While the modeled and observed data do correlate so well, we note that IRI-2007 model is strongly overestimating the equatorial ion fountain effect during the descending phase of solar cycle, and this could be the reason for the very high TEC estimations.     

Ionospheric variability at taiwan low latitude station: Comparison between observations and IRI-2001 model

This paper presents the observed ionospheric F-region critical frequency, foF2, and peak height, hmF2, at northern crest of equatorial ionization anomaly (EIA) area station, namely Chung-Li (24.9°N, 121.1°E, dip 35°), and to be compared with International Reference Ionosphere model (IRI-2001) predictions for the period from 1994 to 1999, corresponding to half of the 23rd solar cycle. The diurnal and seasonal variation of foF2 and hmF2 are analyzed for different solar phases, respectively. The result shows the largest discrepancies were observed during nighttime for foF2 and hmF2, respectively. The value of foF2 both CCIR and URSI selected in the IRI model produced a good agreement during the daytime and underestimated during the noon time for high solar activities. The underestimation at noon time is mainly caused by the fountain effect from equator. Further, the peak height hmF2 shows a larger variability around the midnight than daytime in the equinox and winter seasons and reserved in summer, respectively. The study shows that the monthly median values of observed hmF2 is somewhat lower than those predicated by the IRI model, at night time in all the seasons except the period of 04:00–06:00 LT and reverse at daytime in summer. In general the IRI model predictions with respect to the observed in hmF2 is much better than foF2. The percentage deviation of the observed foF2 (hmF2) values with respect to the IRI model varies from 5% to 80% (0–25%) during nighttime and 2–17% (0–20%) at daytime, respectively. In general, the model generates good results, although some improvements are still necessary to implement in order to obtain better simulations for ionospheric low-latitudes region.