L-band nighttime scintillations at the northern edge of the EIA along 95°E during the ascending half of the solar cycle 24

The characteristics of nighttime ionospheric scintillations measured at the L-band frequency of 1.575 GHz over Dibrugarh (27.5°N, 95°E, MLAT ～ 17°N, 43° dip) during the ascending half of the solar cycle 24 from 2010 to 2014 have been investigated and the results are presented in this paper. The measurement location is within or outside the zone of influence of the equatorial ionization anomaly depending on solar and geomagnetic activity. Maximum scintillation is observed in the equinoxes irrespective of solar activity with clear asymmetry between March and September. The occurrence frequency in the solstices shifts from minimum in the June solstice in low solar activity to a minimum in the December solstice in high solar activity years. A significant positive correlation of occurrence of scintillations in the June solstice with solar activity has been observed. However, earlier reports from the Indian zone (～75°E) indicate negative or no correlation of scintillation in June solstice with solar activity. Scintillations activity/occurrence in solstices indicates a clear positive correlation with Es recorded simultaneously by a collocated Ionosonde. In equinoxes, maximum scintillations occur in the pre-midnight hours while in solstices the occurrence frequency peaks just after sunset. The incidence of strong scintillations (S₄ ≥ 0.4) increases with increase in solar activity. Strong (S₄ ≥ 0.4) ionospheric scintillations accompanied by TEC depletions in the pre-midnight period is attributed to equatorial irregularities whereas the dusk period scintillations are related to the sporadic-E activity. Present results thus indicate that the current location at the northern edge of the EIA behaves as low as well as mid-latitude location.     

VHF/UHF振幅闪烁和VHF快速法拉弟旋转起伏

本文利用1988年9月至1989年5月在武昌(114.4°E,30.6°N)同时接收日本ETS-Ⅱ卫星(130.0°E)发出的VHF(136MHz)信标信号和苏联静止站-T卫星(99.0°E)发出的UHP(714MHz)广播电视信号时获得的观测记录,对夜间出现的双频(VHF/UHF)闪烁和VHF快速(每分钟大于5次的起伏)法拉弟旋转起伏(以下用FRF表示法拉弟旋转起伏)进行了统计分析,结果发现在临近太阳黑子最大年份观测到的双频夜间闪烁主要为急始型,呈赤道特性,且在临近二分点的月份里有最大出现率,秋季更为明显;伴随VHF振幅闪烁出现的快速FRF常与UHF振幅闪烁共存,以及产生这种现象的不规则体由西向东漂移,东-西向的漂移速度分量,在子夜前为140m/s,在子夜后为90m/s。      

电离层不规则结构的等效厚度和漂移速度对闪烁功率谱的影响

利用由衍射基本原理导出的有限厚薄相屏弱闪烁信号强度的Fourier功率谱表达式研究了不规则结构等效厚度L和水平漂移速度V对Fourier功率谱的影响。结果表明,L加大,Fresnel振幅变小,Presnel半径不变;V加大,Fresnel振幅不变,Fresnel半径变大。功率极小值相应的频率值之比为1:1:2:3:…:n而不是√2:√3:…:√n,与实测资料分析结果一致。对实测闪烁功率谱进行了数值模拟。由此得到了实际电离层不规则结构等效厚度、漂移速度的数值。      

新乡上空Es层不均匀体的闪烁特性

本文介绍新乡1989和1990年夏季ES层不均匀体引起的ETS-II卫星136MHz信号幅度闪烁的观测结果。揭示了闪烁出现与f₀E_s的关系、闪烁强度和持续时间的概率分布、准周期性闪烁特点以及闪烁谱特征。导出了ES层不均匀体的尺度和漂移速度等物理特性。      

Coordinated in situ measurements of plasma irregularities and ground based scintillation observations at the crest of equatorial anomaly

First comparison of in situ density fluctuations measured by the DEMETER satellite with ground based GPS receiver measurements at the equatorial anomaly station Bhopal (geographic coordinates (23.2°N, 77.6°E); geomagnetic coordinates (14.29°N, 151.12°E)) for the low solar activity year 2005, are presented in this paper. Calculation of the diurnal maximum of the strength of the equatorial electrojet, which can serve as precursor to ionospheric scintillations in the anomaly region is also done. The Langmuir Probe experiment and Plasma Analyzer onboard DEMETER measure the electron and ion densities respectively. Irregularities in electron density distribution cause scintillations on transionospheric links and there exists a close relationship between an irregularity and scintillation. In 40% of the cases, DEMETER detects the irregularity structures (dNe/Ne ? 5% and dNi/Ni (O⁺) ? 5%) and GPS L band scintillations (S4 ? 0.2) are also observed around the same time, for the low solar activity period. It is found that maximum irregularity intensity is obtained in the geomagnetic latitude range of 10–20° for both electron density and ion density. As the GPS signals pass through this irregularity structure, scintillations are recorded by the GPS receiver installed at the equatorial anomaly station, Bhopal it is interesting to note that in situ density fluctuations observed on magnetic flux tubes that pass over Bhopal can be used as indicator of ionospheric scintillations at that site. Many cases of density fluctuations and associated scintillations have been observed during the descending low solar activity period. The percentage occurrence of density irregularities and scintillations shows good correspondence with diurnal maximum of the strength of electrojet, however this varies with different seasons with maximum correspondence in summer (up to 66%) followed by equinox (up to 50%) and winter (up to 46%). Also, there is a threshold value of EEJ strength to produce density irregularities ((dNe/Ne)_max ? 5%) and for moderate to strong scintillations (S4 ? 0.3) to occur. For winter this value is found to be ∼40 nT whereas for equinox and summer it is around 50 nT.     

Characteristics and performance of thin LaBr3(Ce) crystal for hard X-ray astronomy

We have developed a new detector using thin lanthanum bromide crystal (32 × 3 mm) for use in X-ray astronomy. The instrument was launched in high altitude balloon flight on two different occasions, December 21, 2007, which reached a ceiling altitude of 4.3 mbs and April 25, 2008 reaching a ceiling altitude 2.8 mbs. The observed background counting rate at the ceiling altitude of 4 mbs was ∼4 × 10⁻³ ct cm⁻² s⁻¹ keV⁻¹ sr⁻¹. This paper describes the details of the experiment, the detector characteristics, and the background behaviour at the ceiling altitude.     

电离层闪烁谱特征分析

本文给出了斜入射和不均匀体各向异性情形下的闪烁强度时间频谱的理论表达式。得出在各向异性不均匀介质中传播的信号,其闪烁谱在低频端既有下降的,又有平坦的,具体视传播的几何条件而定,其中传播角的影响尤为显著。据此,较好地解释了在广州、武昌、新乡等地观测到的ETS～Ⅱ卫星VHF信号闪烁谱在低频端的不同特征。      

A study of GPS ionospheric scintillations observed at Shenzhen

Ionospheric scintillation variations are studied using GPS measurements at the low latitude station of Shenzhen (22.59°N, 113.97°E), situated under the northern crest of the equatorial anomaly region, from the Chinese Meridian Project. The results are presented for data collected during the current phase of rising solar activity (low to high solar activity) from December 2010 to April 2014. The results show that GPS scintillation events were largely a nighttime phenomenon during the whole observation period. Scintillation events mainly occurred along the inner edge of the northern crest of the equatorial anomaly in China. The occurrence of scintillations in different sectors of the sky was also investigated, and the results revealed that it is more likely for the scintillations to be observed in the west sector of the sky above Shenzhen. During the present period of study, a total number of 512 total electron content (TEC) depletions and 460 lock loss events were observed. In addition, both of these events are likely to increase during periods of high solar activity, especially because the strong scintillations are often simultaneously accompanied by TEC depletions and lock losses by GPS receivers.     

Climatology of ionospheric scintillations and TEC trend over the Ugandan region

This study presents results on the investigation of the diurnal, monthly and seasonal variability of Total Electron Content (TEC), phase (_σΦ${\sigma }_{\mathrm{\Phi }}$) and amplitude (S4) scintillation indices over Ugandan (Low latitude) region. Scintillation Network Decision Aid (SCINDA) data was obtained from Makerere (0.34°N, 32.57°E) station, Uganda for two years (2011 and 2012). Data from two dual frequency GPS receivers at Mbarara (0.60°S, 30.74°E) and Entebbe (0.04°N, 32.44°E) was used to study TEC climatology during the same period of scintillation study. The results show that peak TEC values were recorded during the months of October–November, and the lowest values during the months of July–August. The diurnal peak of TEC occurs between 10:00 and 14:00 UT hours. Seasonally, the ascending and descending phases of TEC were observed during the equinoxes (March and September) and solstice (June and December), respectively. The scintillations observed during the study were classified as weak (0.1≤$\le$S4,_σΦ≤${\sigma }_{\mathrm{\Phi }}\le$0.3) and strong (0.3<$<$S4,_σΦ≤${\sigma }_{\mathrm{\Phi }}\le$1.0). The diurnal scintillation pattern showed peaks between 17:00 and 22:00 UT hour, while the seasonal pattern follows the TEC pattern mentioned above. Amplitude scintillation was more dominant than phase scintillation during the two years of the study. Scintillation peaks occur during the months of March–April and September–October, while the least scintillations occur during the months of June–July. Therefore, the contribution of this study is filling the gap in the current documentation of amplitude scintillation without phase scintillation over the Ugandan region. The scintillations observed have been attributed to wave-like structures which have periods of about 2–3 h, in the range of that of large scale travelling ionospheric disturbances (LSTIDs).     

磁赤道异常区电离层F区不均匀体发展过程中的闪烁谱研究

本文对我国磁赤道异常区海口站的夜间电离层不均匀体引起的闪烁进行了谱分析，并进行了理论模拟。大部分闪烁出现在午夜前后且持续时间较长。分析结果发现：这种持续时间较长的闪烁的末期和初期的闪烁谱结构有显著差异，末期闪烁谱高频段较初期要明显陆峭，即谱指数显著增大。由此推测出不均匀体发展末期费涅耳尺度以下的不均匀体首先衰减消失，这与国外某些轨道卫星就地测量结果大致相符。同时还从闪烁谱推测出不均匀体发展末期的漂