Day-to-day variability of equatorial anomaly in GPS-TEC during low solar activity period

The ionospheric total electron content (TEC) in the northern hemispheric equatorial ionization anomaly (EIA) crest region is investigated by using dual-frequency signals of the Global Positioning System (GPS) acquired from Rajkot (Geog. Lat. 22.29°N, Geog. Long. 70.74°E; Geom. Lat. 14.21°N, Geom. Long. 144.90°E), India. The day-to-day variability of EIA characteristics is examined during low solar activity period (F10.7∼83 sfu). It is found that the daily maximum TEC at EIA crest exhibits a day-to-day and strong semi-annual variability. The seasonal anomaly and equinoctial asymmetry in TEC at EIA is found non-existent and weaker, respectively. We found a moderate and positive correlation of daily magnitude of crest, Ic with daily F10.7 and EUV fluxes with a correlation coefficient of 0.43 and 0.33, respectively indicating an existence of a short-term relation between TEC at EIA and the solar radiation even during low solar activity period. The correlation of daily Ic with Dst index is also moderate (r = −0.35), whereas no correlation is found with the daily Kp index (r = 0.14) respectively. We found that the magnitude of EIA crest is moderately correlated with solar flux in all seasons except winter where it is weakly related (0.27). The magnitude of EIA crest is also found highly related with EEJ strength in spring (r = 0.69) and summer (r = 0.65) than autumn (0.5) and winter (r = 0.47), though EEJ is stronger in autumn than spring.     

Ionospheric disturbances on 8 September, 2010: Was it connected with the incoming moderate Chongqing earthquake?

Earthquake prediction stimulates the searches for a correlation between seismic activity and ionospheric anomalies. Contrary to common focuses on strong earthquakes, we report the ionospheric disturbances, 2 days before a moderate Ms = 4.7 Chongqing earthquake (29.4°N, 105.5°E, depth = 7.0 km, occurred at 21:21 LT, 10 September, 2010) with the data of ground-based ionosondes and IGS receivers. The data covering the period under the quiet geomagnetic conditions and a geomagnetic storm was analyzed with upper and lower bounds. It is found that there were significant enhancements of foF2 and total electron content (TEC) on the afternoon of 8 September, 2010, with a limited area close to the epicentre, which was different from the feature of ionospheric perturbations triggered by the geomagnetic storm on 15 September. Taking into account the heliogeomagnetical condition, we conclude that the observed ionospheric enhancements were very likely associated with the forthcoming moderate Chongqing earthquake, which implies that the relationship between the amplitudes of ionospheric disturbances and earthquakes is very complicated.     

GNSS single frequency ionospheric range delay corrections: NeQuick data ingestion technique

A study of the performance of the NeQuick model and the Klobuchar model for GNSS single frequency range delay correction on a global scale was done using data for moderate solar activity. In this study NeQuick was used in the way intended for Galileo. This study is to assess the performance of the two models at each ionospheric geographic region during moderate solar activity as previously published studies were concentrated only on high solar activity. The results obtained showed that NeQuick outperformed Klobuchar for the whole year at the three geographical regions of the ionosphere. In terms of monthly root mean square of mismodeling, NeQuick outperformed Klobuchar by 15 TECU or more at low-latitudes, 5 TEC or more at mid-latitudes, and 1 TECU or more at high-latitudes.     

浆料固相含量对多孔氮化硅陶瓷结构和性能的影响

以琼脂糖作为凝胶物质,采用凝胶注模工艺制备了多孔氮化硅陶瓷,通过改变浆料的固相含量,制备了不同性能的多孔氮化硅陶瓷.结果表明,随着浆料的固相含量从35vol％增加到45vol％,材料的气孔率从57.6％减小至40.8％,弯曲强度从96 MPa增加到178 MPa;大量的长棒状β-Si3N4晶粒从孔壁上生长出来,将气孔填充,其生长方式为溶解-沉淀-析出与气-液-固两种生长机制协同作用的结果.长棒状的氮化硅晶须和恰当的界面结合强度是多孔氮化硅陶瓷具有较高强度的主要原因.     

Traveling ionospheric disturbances observed at South African midlatitudes during the 29–31 October 2003 geomagnetically disturbed period

This paper presents traveling ionospheric disturbances (TIDs) observations from GPS measurements over the South African region during the geomagnetically disturbed period of 29–31 October 2003. Two receiver arrays, which were along two distinct longitudinal sectors of about 18°-20° and 27°-28° were used in order to investigate the amplitude, periods and virtual propagation characteristics of the storm induced ionospheric disturbances. The study revealed a large sudden TEC increase on 28 October 2003, the day before the first of the two major storms studied here, that was recorded simultaneously by all the receivers used. This pre-storm enhancement was linked to an X-class solar flare, auroral/magnetospheric activities and vertical plasma drift, based on the behaviour of the geomagnetic storm and auroral indices as well as strong equatorial electrojet. Diurnal trends of the TEC and foF2 measurements revealed that the geomagnetic storm caused a negative ionospheric storm; these parameters were depleted between 29 and 31 October 2003. Large scale traveling ionospheric disturbances were observed on the days of the geomagnetic storms (29 and 31 October 2003), using line-of-sight vertical TEC (vTEC) measurements from individual satellites. Amplitude and dominant periods of these structures varied between 0.08–2.16 TECU, and 1.07–2.13 h respectively. The wave structures were observed to propagate towards the equator with velocities between 587.04 and 1635.09 m/s.     

Analysis of the ionosphere/plasmasphere electron content variability during strong geomagnetic storm

The ionosphere/plasmasphere electron content (PEC) variations during strong geomagnetic storms in November 2004 were estimated by combining of mid-latitude Kharkov incoherent scatter radar observations and GPS TEC data derived from global TEC maps. The comparison between two independent measurements was performed by analysis of the height-temporal distribution for specific location corresponding to the mid-latitudes of Europe. The percentage contribution of PEC to GPS TEC indicated the clear dependence from the time with maximal values (more than 70%) during night-time. During day-time the lesser values (30–45%) were observed for quiet geomagnetic conditions and rather high values of the PEC contribution to GPS TEC (up to 90%) were observed during strong negative storm. These changes can be explained by the competing effects of electric fields and winds, which tend to raise the layer to the region with lower loss rate and movement of the ionospheric plasma to the plasmasphere.     

不同回流位置液体火箭发动机循环预冷回路特性

液体火箭发动机的循环预冷是复杂的传热过程并且受到很多因素的影响,回流口位置则是影响管路预冷效果的重要因素。为了研究不同回流位置对液体火箭发动机预冷效果的影响,文中采用一维均相平衡态流体模型,通过离散化方法分析了不同回流位置时循环预冷过程中泵体温度的变化规律及预冷管路中流体各参数的分布趋势,得出回流上升管出口最佳位置。     

测量围护结构含水率的同面散射场式电容传感器设计

目前常用的测量含水率的方法有微波法、红外线法和电容法.由于基于电容法的传感器具有分辨力高、响应速度快、体积小、结构简单等优点,被广泛应用.针对围护结构含水率测试深度的要求和测试特点,本文通过仿真和实验,对同面电容传感器探头的结构尺寸进行了优化设计,并采取了保护电极以提高其抗干扰能力;运用改进的充放电电容检测电路,设计出一种测量围护结构含水率的新型同面散射场式电容传感器,该传感器具有宽范围的测试深度和较高的测试灵敏度.     

Relative amplitude of the total electron content variations depending on geomagnetic activity

We developed a method of estimation of a relative amplitude dI/I of the total electron content (TEC) variations in the ionosphere as deduced from the data of the global GPS receivers network. To obtain statistically significant results we picked out three latitudinal belts provided in the Internet by the maximum number of GPS sites. They are high-latitudinal belt (50–80°N, 200–300°E; 59 sites), mid latitude belt (20–50°N, 200–300°E; 817 sites), and equatorial belt (±20°N, 0–360°E; 76 sites). The results of the analysis of the diurnal and latitudinal dependencies of dI/I and dI/I distribution probability for 52 days with different levels of geomagnetic activity are presented. It was found that on average the relative amplitude of the TEC variations varies within the range 0–10% proportionally to the value of the K_p geomagnetic index. In quiet conditions the relative amplitude dI/I of the TEC variations at night significantly exceeds the daytime relative amplitude. At high levels of magnetic field disturbances, the geomagnetic control of the amplitude of TEC variations at high and middle latitudes is much more significant than the regular diurnal variations. At the equatorial belt, on average, the amplitude of TEC variations in quiet and disturbed periods almost does not differ. The obtained results may be useful for development of the theory of ionospheric irregularities.     

Seasonal dependence of TEC and SLAB thickness

Several years of hourly daily GPS measurements of the vertical total electron content (TEC) and of the equivalent slab thickness made at different European locations are analysed by using the linear regression technique to demonstrate the response of these two ionospheric parameters to seasonal variations. It is found that both TEC and slab thickness are highly correlated with season. Analytical relationships are determined expressing the seasonal dependence of the vertical TEC and of the equivalent slab thickness as a function of the seasonal parameter cos χ at noon in each location.