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1.
This paper considers a dataset of ionograms recorded by the CADI ionosonde installed at São José dos Campos (SJC; 23.2°S, 45.9°W, magnetic latitude 14.1°S), Brazil, to compare two autoscaling systems: Autoscala, developed by the Istituto Nazionale di Geofisica e Vulcanologia, and the UDIDA-scaling, developed by the Universidade do Vale do Paraíba. The analysis, focused on the critical frequency of the F2 layer, foF2, shows that the two systems work differently. The UDIDA-scaling gives always a value of foF2 as output, regardless of the presence of the ionogram trace and its definition, while Autoscala tends to reject ionograms for which the digital information is considered insufficient. As a consequence, the UDIDA-scaling can autoscale more foF2 values than Autoscala, but Autoscala can discard a larger number of ionograms for which the trace is unidentifiable. Discussions are made on the accuracy of the foF2 values given as output, as well as on the main shortcomings characterizing the two systems.  相似文献   

2.
This work describes a simple filter able to eliminate the traces caused by second-order reflection from ionograms. This filter is applied to Autoscala in order to smooth out cases in which the autoscaling of the ionogram is mistaken because the second-order F2 layer reflection is identified as first order. A dataset of 32,626 ionograms recorded at the ionospheric observatory of Rome was used to test the filter.  相似文献   

3.
The performance of a computer program, called Autoscala, for the automatic scaling of foF2 and MUF(3000)F2 from ionograms has been extensively tested. Results of comparisons between automatically and manually scaled data are shown both for Autoscala and for ARTIST (release 4.01). Particular attention has been paid to the cases in which the ionograms have a truncated trace. The problem of the rejection of bad quality ionograms has been also considered. The analysis of data shows that the reliability of values automatically given as output by Autoscala is good. For the data set considered Autoscala seems to operate better than ARTIST.  相似文献   

4.
The changing state of the ionosphere is generally monitored by networks of vertical ionosondes that provide us with regular ionospheric sounding. Many ionospheric applications require determination of the true-height electron density profiles. Therefore, ionograms must be further inverted into real-height electron density profiles. The paper presents the comparison study of the true-height electron density profiles inverted from ionograms using two different methods POLAN (Titheridge, 1985) and NHPC (Huang and Reinish, 1996; Reinish et al., 2005), widely used by the ionospheric research community. Our results show significant systematic differences between electron density profiles calculated by these two inversion methods. pkn@ufa.cas.cz  相似文献   

5.
Lacuna on ionograms indicate conditions where the usual ionospheric reflections of vertically propagating radio waves transmitted from and subsequently received by an ionosonde are missing over a range of frequencies. Reflections from the lowermost E-region should still be observable contrary to the more usual cases where absorption processes in the underlying D-region removes the low-frequency part of the ionospheric reflections appearing in ionograms. It is emphasized below that lacuna cases related to E-region processes should be distinguished from lacunae related to processes in the F1 and F2 regions. This distinction appears to have been neglected in a recent paper.  相似文献   

6.
《Journal of Atmospheric and Solar》2003,65(14-15):1309-1314
Equatorial spread-F (ESF) dynamics is studied based on quarter-hourly series of ionograms recorded in West Africa during the year December 1994 to November 1995. The time evolution of F layer at the typical equatorial site OUAGADOUGOU (Burkina Faso) differs slightly from that at DAKAR (Senegal), located at the northern edge of the magnetic equatorial belt. Comparing ESF occurrences at both stations with the pre-sunrise ones at FORTALEZA (Brazil), we find generally antisymmetric variations on both sides of the Atlantic, except for a common December solstice maximum. We stress the convergence of the multiple-scale morphologies drawn from new radars with those from high-quality ionosonde density (h′,t) plots. This revives the analysis of ESF dynamics and points toward long-term network studies of ESF coupling phenomena.  相似文献   

7.
The Dynasonde is a digital ionosonde which measures the amplitude and phase of radio echoes reflected from the ionosphere. In addition to the frequency and virtual range of each echo, one parameter of particular interest is the direction of arrival which allows horizontal structures in the ionosphere to be studied. Under suitable ionospheric conditions, namely where structures or strong gradients are present in the electron concentration, echoes may be observed out to horizontal distances of several hundred kilometres. We describe an automated method for latitudinally mapping these gradients in F-region peak electron concentration using the Dynasonde. Good agreement is found when the results are compared with a co-located incoherent scatter radar lending credibility to observations of electron concentration gradients by a Dynasonde alone. This is significant for sites where no supporting instruments exist. Although Dynasondes account for only a small fraction of digital ionosondes in use today, the techniques described in this paper could be extended to other digital ionosondes with similar directional capabilities. The combination of routine soundings, and the worldwide distribution of such instruments, would provide a powerful means to monitor ionospheric structures on a regular basis.  相似文献   

8.
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10.
The variations in the electron density measured with the incoherent scatter radar, DPS-4 digisonde, and FMCW ionosonde are compared in this work. The main regularities in differences are explained by the effect of different-scale ionospheric irregularities. Considerable morning gradients of electron density result in that ionosondes give increased values as compared to the incoherent scatter radar data. Electron density disturbances measured with different instruments can be of correlated and uncorrelated character. Uncorrelated disturbances are explained by intense medium-scale ionospheric irregularities. Correlated disturbances are caused by large-scale irregularities. Observation of such disturbances can be used to determine the velocity and direction of a disturbance.  相似文献   

11.
本文基于我国西南地区电离层垂测网普洱站和乐山站的基础数据,结合空间天气事件指数,通过限定不同阈值的滑动平均方法,提出靠近南部的普洱站应选取中值M±1.5σ(标准差)作为限定阈值,靠近北部的乐山站应选取中值M±IQR(四分位距)作为限定阈值.在此基础上,利用本文提出的扰动识别方法,对2015年4月25日尼泊尔MS 8.1地震予以分析.研究结果显示,震前1天普洱站和乐山站均出现了正向扰动,震前3小时乐山站持续出现负异常.根据规划,我们还将在西南地区建立1—2个垂测台站,架设数台被动接收垂测仪信号的电离层斜向探测仪,通过组网对西南地区上空的电离层进行监测,为分析震前电离层扰动提供数据支持.   相似文献   

12.
Calculations using the Sheffield University plasmasphere ionosphere model have shown that under certain conditions an additional layer can form in the low latitude topside ionosphere. This layer (the F3 layer) has subsequently been observed in ionograms recorded at Fortaleza in Brazil. It has not been observed in ionograms recorded at the neighbouring station São Luis. Model calculations have shown that the F3 layer is most likely to form in summer at Fortaleza due to a combination of the neutral wind and theE × B drift acting to raise the plasma. At the location of São Luis, almost on the geomagnetic equator, the neutral wind has a smaller vertical component so the F3 layer does not form.  相似文献   

13.
Global positioning system (GPS) networks have provided an opportunity to study the dynamics and continuous changes in the ionosphere by supplementing ionospheric studies carried out using various techniques including ionosondes, incoherent scatter radars and satellites. Total electron content (TEC) is one of the physical quantities that can be derived from GPS data, and provides an indication of ionospheric variability. This paper presents a feasibility study for the development of a Neural Network (NN) based model for the prediction of South African GPS derived TEC. Three South African locations were identified and used in the development of an input space and NN architecture for the model. The input space included the day number (seasonal variation), hour (diurnal variation), Sunspot Number (measure of the solar activity), and magnetic index (measure of the magnetic activity). An analysis was done by comparing predicted NN TEC with TEC values from the IRI-2001 version of the International Reference Ionosphere (IRI), validating GPS TEC with ionosonde TEC (ITEC) and assessing the performance of the NN model during equinoxes and solstices. For this feasibility model, GPS TEC was derived for a limited number of years using an algorithm still in the early phases of validation. However, results show that NNs predict GPS TEC more accurately than the IRI at South African GPS locations, but that more good quality GPS data is required before a truly representative empirical GPS TEC model can be released.  相似文献   

14.
15.
Spatial and time variations in the critical frequencies foF2 before the strong earthquake of August 15, 1963, with the magnitude M = 7.75 are analyzed. The epicenter of the earthquake was located in the vicinity of the magnetic equator in the American longitudinal sector. The data of the topside ionosonde on board Alouette-1 and of the series of ground-based ionosondes has been used for this purpose. The ground-based ionosondes made it possible to detect an insignificant anomalous decrease in foF2 within the zone of earthquake preparation a few days prior to the earthquake. This result confirms the conclusion drawn earlier on the basis of the satellite data. The modification of the ionosphere at the F-region level is more evident in the satellite than in the ground-based data. It is also noted that the character of the time variations in foF2 a day before the earthquake is similar to the so called “quiet time” Q-disturbances in the ionosphere, when the electron concentration at the F region maximum differs from the median values by more than 20% under undisturbed geophysical conditions.  相似文献   

16.
The measurements of the critical frequencies of the ionospheric F2 layer based on vertical radiosounding, which was performed with a CADI digital ionosonde at the Voeykovo magnetic–ionospheric observatory in February 2013, have been considered. The observations have been compared with the upper atmosphere numerical model (UAM) data for three days that differ in the amplitude and the character of solar and magnetic activity and correspond to quiet and moderately disturbed states of the ionosphere. The work was performed in order to improve the methods for determining the ionospheric state by vertical sounding ionograms. The time variations in the F2 layer critical frequency, electric field vector zonal component, and thermospheric wind velocity meridional component have been analyzed. Calculations were performed with three UAM variants. The UAM version providing the best agreement with the CADI ionosonde data was the version in which the neutral temperature, neutral composition, and pressure gradients are calculated according to the MSIS empirical model and the horizontal neutral wind velocity is determined by the equation of motion with pressure gradients from MSIS. The calculated values corresponded to the measurements, except those for the evening, because the electron density at the ionospheric F2 layer maximum depends more strongly on electric fields and thermospheric wind velocities during this period. Thus, the indicated UAM version with the above limitations can be used to determine the state of the subauroral ionosphere.  相似文献   

17.
The virtual (or minimum) height of the F-region (h′F), recorded over a number of solar cycles for 11 equatorial and mid-latitude ionosonde stations, was used to deduce the hemispheric (i.e. southern or northern hemisphere) character of equatorial stations. The semi-annual median monthly height (h′F) variations consist of two components: major local summer maximum and winter sub-maximum (about 5 percent of the summer maximum). This hemispheric pattern was most consistently observed for equatorial stations (within 5° of the geomagnetic equator) in a period centred on the local midnight (21-03 LT) but was also present, to a lesser extent, at mid-latitude stations and at other time intervals. It is evident that the physical parameter h′F defines the hemispheric character of an equatorial station which has different (sometimes opposite) geographic and geomagnetic latitudes.There is a sharp transition in the latitudinal character of the stations on both sides of the equator leading to hypothesis that the equal maxima in h′F in December and June solstices are observed at a near-equator position labelled as ionosonde deduced equator (IDE). Such a signature was observed for an American equatorial (both geographic and geomagnetic) station Talara (Peru) which is an experimental support of the hypothesis. The IDE can be another useful parameter characterising the equatorial ionosphere. This finding reveals a new application of the standard ionosonde data in defining the geophysical character of equatorial stations, being an important contribution to space climatology.  相似文献   

18.
万卫星  李钧 《地球物理学报》1989,32(06):609-620
为了充分发挥现代数字式电离层探测仪在电离层结构与优动研究中的潜力,必须在传统的频高图真高换算的基础上,发展新的反演理论和算法.本文介绍了随时空缓变的各向异性电离层介质中无线电波包传播的广义射线方程组,讨论了计算波包射线几何路径以及计算波包参数,如频移、波矢、群时延等沿射线路径变化的传播正问题,并详细讨论了根据波包参量的测定值反演介质结构和扰动伏态的传播反问题.文中若干实验实例表明,这种反演理论和算法可用于数字式电离层探测仪记录的分析,它使高频无线电波探测技术成为研究全球电离层声重波一类扰动的有力工具。  相似文献   

19.
Various authors, analysing the set of accelerograms recorded at Gubbio Piana (GBP) (central Italy), have demonstrated that strong amplification occurs at this accelerometric station, which is installed within an alluvial basin. In particular, Ambraseys et al. [(2005a), Bull Earthq Eng 3:1–53; (2005b), Bull Earth Eng 3:55–73] observed that the strong motion peaks at GBP greatly exceed the median values predicted by the attenuation relationships they derived for Europe. In this work, we analyse and discuss some characteristics of the ground motion recorded at the GBP station. We show that the ground motion parameters, such as peak-ground acceleration and peak-ground velocity, are strongly influenced by the presence of locally induced surface waves that produce both a lengthening of the significant shaking duration and an increase in the peak values with respect to a nearby bedrock site. The basin-induced surface waves are observed in the three components of motion and their effects on the peak values are particularly evident in the vertical component. In the frequency domain, the energy of the surface waves is mostly restricted to the frequency band 0.4–0.8 Hz for both the horizontal and vertical components. The horizontal and vertical Fourier amplitudes are also very similar, and this indicates that the H/V spectral ratio technique is not applicable to describing the site response due to the propagation of seismic wave in a complex 2D/3D geological structure. Finally, a preliminary polarization analysis shows that the directions of polarization, as well as the degree of elliptical polarization, exhibit a strong variability with time, that may be related to a complex propagation of Love and Rayleigh waves within the basin.  相似文献   

20.
电离层声重波扰动的高频无线电诊断   总被引:1,自引:1,他引:1  
为了充分发挥现代数字式电离层探测仪在电离层结构与优动研究中的潜力,必须在传统的频高图真高换算的基础上,发展新的反演理论和算法.本文介绍了随时空缓变的各向异性电离层介质中无线电波包传播的广义射线方程组,讨论了计算波包射线几何路径以及计算波包参数,如频移、波矢、群时延等沿射线路径变化的传播正问题,并详细讨论了根据波包参量的测定值反演介质结构和扰动伏态的传播反问题.文中若干实验实例表明,这种反演理论和算法可用于数字式电离层探测仪记录的分析,它使高频无线电波探测技术成为研究全球电离层声重波一类扰动的有力工具。  相似文献   

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