An experiment to study solar flare effects on radio-communication signals

The occurrence of radio signal fading events caused by ionospheric absorption plays an important role in the performance of radio-communication systems. It is necessary to know the magnitude and time-scale of such events in order to specify technical parameters of the communication system to be used. Generally, fading events are associated with solar flares, which are characterized by sudden increase in the solar X-ray flux that causes an increase in the ionization in the lower ionosphere. The abrupt increase of ionization causes the absorption of radio waves propagating in the Earth–ionosphere wave-guide and is reported as radio signal fading events. A simple experiment to monitor the behavior of lower ionosphere has been carried out at the Southern Space Observatory-SSO/INPE (29.43°S, 53.8°W), located in southern Brazil. The experiment is basically a computer controlled radio receiver that records the received signal strength of Amplitude Modulated (AM) radio signals in the HF (High Frequencies) range. We analyzed data of the 6 MHz beacon signal that has been transmitted by a broadcasting radio station located about 400 km from the observation site. In this work we present initial results of daily variation of the received signal strength and fading events associated with solar flares observed in the 6 MHz signal monitored by the experiment during 2001. X-ray solar flux data from the GOES-8 satellite were used to identify X-ray solar bursts associated with solar flares. Based on the one-year data collected by the experiment, a statistical summary of fading occurrences and their correlation with solar flares, as well as the distributions of time-scales and magnitudes of such events are presented.     

太阳质子事件警报

采用人工神经网络预报方法,利用太阳耀斑的日面位置、X射线辐射的峰值流量及其上升时间、2695MHz和8800MHz微波辐射的半积分流量等5个物理参量,提出了一个新的太阳质子事件警报方案,预报太阳质子事件的发生及其流量和时间．该方案在本文检验中达到93．75％的预报准确率．     

第21,22周峰年太阳射电爆发中毫秒级精细结构的分析

本文对第21周的2840MHz及22周峰年的2545MHz，2645MHz和2840MHz波段上所观测到的285个快速事件进行分析，发现两个峰年的快速事件具有多种多样的快速活动（快速精细结构）．它们与耀斑的对应关系也做了统计分析．     

质子事件上升时间及峰值强度的统计研究

在耀斑已基本确定为质子耀斑的情况下, 为了对即将到达地球的太阳质子作出半定量的粗略预报(警报), 即估计从观测到光学耀斑开始, 需经多长时间质子通量将到达峰值;峰值强度有多大。为此, 我们收集了1967年5月—1972年12月约五年半期间国外发表的比较系统的质子事件资料, 以及相应的太阳耀斑和太阳射电资料。      

A prediction model of short-term ionospheric foF2 based on AdaBoost

In this paper, the AdaBoost-BP algorithm is used to construct a new model to predict the critical frequency of the ionospheric F2-layer (foF2) one hour ahead. Different indices were used to characterize ionospheric diurnal and seasonal variations and their dependence on solar and geomagnetic activity. These indices, together with the current observed foF2 value, were input into the prediction model and the foF2 value at one hour ahead was output. We analyzed twenty-two years’ foF2 data from nine ionosonde stations in the East-Asian sector in this work. The first eleven years’ data were used as a training dataset and the second eleven years’ data were used as a testing dataset. The results show that the performance of AdaBoost-BP is better than those of BP Neural Network (BPNN), Support Vector Regression (SVR) and the IRI model. For example, the AdaBoost-BP prediction absolute error of foF2 at Irkutsk station (a middle latitude station) is 0.32 MHz, which is better than 0.34 MHz from BPNN, 0.35 MHz from SVR and also significantly outperforms the IRI model whose absolute error is 0.64 MHz. Meanwhile, AdaBoost-BP prediction absolute error at Taipei station from the low latitude is 0.78 MHz, which is better than 0.81 MHz from BPNN, 0.81 MHz from SVR and 1.37 MHz from the IRI model. Finally, the variety characteristics of the AdaBoost-BP prediction error along with seasonal variation, solar activity and latitude variation were also discussed in the paper.     

Solar physics with the Square Kilometre Array

The Square Kilometre Array (SKA) will be the largest radio telescope ever built, aiming to provide collecting area larger than 1?km². The SKA will have two independent instruments, SKA-LOW comprising of dipoles organized as aperture arrays in Australia and SKA-MID comprising of dishes in South Africa. Currently the phase-1 of SKA, referred to as SKA1, is in its late design stage and construction is expected to start in 2020. Both SKA1-LOW (frequency range of 50–350?MHz) and SKA1-MID Bands 1, 2, and 5 (frequency ranges of 350–1050, 950–1760, and 4600–15,300?MHz, respectively) are important for solar observations. In this paper we present SKA’s unique capabilities in terms of spatial, spectral, and temporal resolution, as well as sensitivity and show that they have the potential to provide major new insights in solar physics topics of capital importance including (i) the structure and evolution of the solar corona, (ii) coronal heating, (iii) solar flare dynamics including particle acceleration and transport, (iv) the dynamics and structure of coronal mass ejections, and (v) the solar aspects of space weather. Observations of the Sun jointly with the new generation of ground-based and space-borne instruments promise unprecedented discoveries.     

Interpretation of 6 and 21 cm observations of Jupiter

Observations of Jupiter's radio emission were made at a frequency of 1412 MHz (21cm) in 1977 and at 4885 MHz (6cm) in 1978 using the Westerbork Synthesis Radio telescope in the Netherlands. The thermal disk temperatures at these wavelengths yield values of 320±20 K at 21 cm and 220±8 K at 6 cm. The first value requires an overabundance of ammonia by a factor of three with respect to the solar value, the second one is in agreement with the value expected for a convective model atmosphere with solar abundances for all chemical elements. The data at this wavelength however show no or very little limb darkening on the planet, indicating that there is a layered rather than a uniformly mixed atmosphere. A sudden increase in the ammonia abundance by a factor of about three below the 210–220 K level is proposed to explain this fact and also both derived disk temperatures.     

1000兆赫≤f≤9400兆赫太阳射电流量与黑子数的关系

本文给出了9400、3750、2800、2000和1000兆赫太阳射电流量与黑子数的统计相关关系式,采用了最小二乘法、百分最小二乘法和复合最小二乘法三种处理方法.结果表明:百分最小二乘法得出的三次方程为最佳拟合关系式.由此得出的宁静太阳射电频谱与用射电干涉仪实测结果符合.      

Statistical ionospheric E layer properties measured with the Cyprus Digisonde and comparisons with IRI predictions

This paper reports the diurnal, seasonal, and long term variability of the E layer critical frequency (foE) and peak height (hmE) derived from Digisonde measurements from 2009 to 2016 at the low-middle latitude European station of Nicosia, Cyprus (geographical coordinates: 35°N, 33°E, geomagnetic lat. 29.38°N, I = 51.7°). Manually scaled monthly median values of foE and hmE are compared with IRI-2012 predictions with a view to assess the predictability of IRI. Results show that in general, IRI slightly overestimates foE values both at low and high solar activity. At low solar activity, overestimations are mostly limited to 0.25?MHz (equivalent electron density, 0.775?×?10³?el/m^?3) but can go as high as 0.5?MHz (equivalent electron density, 3.1?×?10³?el/m^?3, during noon) around equinox. In some months, underestimations, though sporadic in nature, up to 0.25?MHz are noted (mostly during sunrise and sunset). At high solar activity, a similar pattern of over-/underestimation is evident. During the entire period of study, over-/under estimations are mostly limited to 0.25?MHz. In very few cases, these exceed 0.25?MHz but are limited to 0.5?MHz. Analysis of hmE reveals that: (1) hmE remains almost constant during ±2 to ±4?h around local noon, (2) hmE values are higher in winter than in spring, summer and autumn, (3) there are two maxima near sunrise and sunset with a noontime minimum in between. During the entire period of study, significant differences between observed hmE and the IRI predictions have been noted. IRI fails to predict hmE and outputs a constant value of 110?km, which is higher than most of the observed values. Over- and under estimations range from 3 to 13?km and from 0 to 3?km respectively.     

Monthly mean foF2 model for an African low-latitude station and comparison with IRI

We have employed the hourly values of the ionospheric F-region critical frequency (foF2) obtained from Ouagadougou ionosonde, Burkina Faso (geographic coordinates 12° N, 1.8° W) during the interval of 1985–1995 (solar cycle 22) and solar radio flux of 10 cm wavelength (F10.7) to develop a local model (LM) for the African low-latitude station. The model was developed from regression analysis method, using the two-segmented regression analysis. We validated LM with foF2 data from Korhogo observatory, Cote d’Ivorie (geographical coordinates 9.3° N, 5.4° W). LM as well as the International Reference Ionosphere (IRI) agrees well with observations. LM gave some improvement on the IRI-predicted foF2 values at the sunrise (06 LT) at all solar flux levels and in all seasons except June solstice. The performance of the models at the representing the salient features of the equatorial foF2 was presented. Considering daytime and nighttime performances, LM and IRI are comparable in low solar activity (LSA), LM performed better than IRI in moderate solar activity (MSA), while IRI performed better than LM in high solar activity (HSA). CCIR has a root mean square error (r.m.s.e), which is only 0.10 MHz lower than that of LM while LM has r.m.s.e, which is about 0.05 MHz lower than that of URSI. In general, our result shows that performance of IRI, especially the CCIR option of the IRI, is quite comparable with the LM. The improved performance of IRI is a reflection of the numerous contributions of ionospheric physicists in the African region, larger volume of data for the IRI and the diversity of data sources, as well as the successes of the IRI task force activities.     

Relative importance of solar X-rays below 10 Å and pulsed HF radiowave absorption at 2.132 MHz frequency over Delhi under solar flare conditions

The computed photoionization rates in the discrete wavelength bands in the XUV spectra under quiet sun, moderate flare, strong flare and outstanding flare conditions have been presented graphically as a function of altitude in the height range 50 – 90 km to show the relative importance of solar X-rays below 10 Å. Ionospheric absorption data, measured by A₁ technique at the Ionosphere Research Centre at the University of Delhi, Delhi (28.6°N) at a single radio wave frequency of 2.132 MHz have been analyzed under solar flare conditions, with a special emphasis on a solar flare event on 3 February, 1983 which started at 1115 IST, reached its peak at 1140 IST and persisted till 1400 IST, during which time the radio wave absorption exceeded 60 or 65 dB for nearly three and half hours. During solar flare, a direct correlation between large enhancements of solar X-ray flux and ionospheric absorption is observed.     

A roadmap towards a space-based radio telescope for ultra-low frequency radio astronomy

The past two decades have witnessed a renewed interest in low frequency radio astronomy, with a particular focus on frequencies above 30 MHz e.g., LOFAR (LOw Frequency ARray) in the Netherlands and its European extension ILT, the International LOFAR Telescope. However, at frequencies below 30 MHz, Earth-based observations are limited due to a combination of severe ionospheric distortions, almost full reflection of radio waves below 10 MHz, solar eruptions and the radio frequency interference (RFI) of human-made signals. Moreover, there are interesting scientific processes which naturally occur at these low frequencies. A space or Lunar-based ultra-low-frequency (also referred to as ultra-long-wavelength, ULW) radio array would suffer significantly less from these limitations and hence would open up the last, virtually unexplored frequency domain in the electromagnetic spectrum.A roadmap has been initiated by astronomers and researchers in the Netherlands to explore the opportunity of building a swarm of satellites to observe at the frequency band below 30 MHz. This roadmap dubbed Orbiting Low Frequency Antennas for Radio Astronomy (OLFAR), a space-based ultra-low frequency radio telescope that will explore the Universe’s so-called dark ages, map the interstellar medium, and study planetary and solar bursts in the solar system and search them in other planetary systems. Such a radio astronomy system will comprise of a swarm of hundreds to thousands of satellites, working together as a single aperture synthesis instrument deployed sufficiently far away from Earth to avoid terrestrial RFI. The OLFAR telescope is a novel and complex system, requiring yet to be proven engineering solutions. Therefore, a number of key technologies are still required to be developed and proven. The first step in this roadmap is the NCLE (Netherlands China Low Frequency Explorer) experiment, which was launched in May 2018 on the Chinese Chang’e 4 mission. The NCLE payload consists of a three monopole antenna system for low frequency observations, from which the first data stream is expected in the second half of 2019, which will provide important feedback for future science and technology opportunities.In this paper, the roadmap towards OLFAR, a brief overview of the science opportunities, and the technological and programmatic challenges of the mission are presented.     

中国典型区域Es特性研究

利用中国海口、长春和拉萨三个站1976-1986年一个太阳周的观测数据, 对中国典型区域的Es特性进行了研究. 分析了不同强度Es (f₀E_s > 3, 5, 7, 9MHz)出现概率随本地时、季节以及太阳活动的变化规律, 并对电离层Es遮蔽情况(包括全遮蔽和半遮蔽)进行了系统分析. 研究结果表明, 各种强度的Es出现概率均是白天大于夜间, 夏季高于其他季节, 随太阳活动性变化规律不明显, 地区差异较大, 大部分情况拉萨站Es出现概率最高; 对于全遮蔽和半遮蔽特性, 不同站也表现出不同的分布规律.      

太阳电池阵列模拟器计量测试方法研究

对太阳电池阵列模拟器(SAS)的设计原理和技术要求进行了分析,并根据分析结果对太阳电池阵列模拟器计量测试方法进行了研究。     

Study on solar sources and polar cap absorption events recorded in Antarctica

Particularly intense events occurred on the Sun in a period around minimum of solar activity during cycle 23. We investigated the characteristics of September 2005 and December 2006 events and the properties of the correlated observations of ionospheric absorption, obtained by a 30 MHz riometer installed at Mario Zucchelli Station (MZS-Antarctica), and of geomagnetic activity recorded at Scott Base (Antarctica). Solar events are studied using the characteristics of CMEs measured with SoHO/LASCO coronagraphs and the temporal evolution of solar energetic protons in different energy ranges measured by GOES 11 spacecraft.     

根据行星际闪烁(IPS)的双频互谱估计太阳风速度

本文讨论了观测频率为232MHz和327MHz时,利用互谱的方法估计太阳风速度的可能性、考虑路径积分效应,结果表明在17°≤ε≤50°范围内,对于几种可能的太阳风速度分布,由互谱所得结果与太阳风速度值差别小于15%.      

同无黑子耀斑相协的微波爆发机制的探讨

1980—1984年期间,我们在云南天文台9375MHz,3653MHz和2902 HHz三个波段的射电观测资料中,查到11组微波爆发与无黑子耀斑相伴随。本文研究了这些爆发与耀斑的大气层高度,射电爆发类型以及通过落进峰值流量-时间图的位置,确认出爆发机制是活动区中作麦克斯韦分布电子的热轫致辐射。     

Difficulties in the study of cosmic radio noise absorption at 30 MHz using riometer at low latitude station,Kolhapur (Lat-16.8°N,Long-74.25°E)

A dual dipole antenna has been installed at low latitude station Kolhapur (Geographic 16.8°N, 74.25°E), Maharashtra, India for the study of cosmic radio noise absorption using Solid State Riometer (which operates at 30 MHz) during pre phase of 24th solar maxima. The aim for this type of study over Kolhapur was to know the response of lower (D region) ionosphere over low latitude by cosmic radio noise absorption using riometer technique during quite period as well as sudden ionospheric disturbances (SID). The observations are being taken for 3 years. Two different sites (∼40 km away from each other) were used for the installation of riometer equipment assuming minimum local noise. It is found that solar noise to cosmic radio noise hence resulting in signal saturation. The night time signal is relatively free of interference but sometimes local noise is responsible for spike-like signatures. Hence it is concluded that Kolhapur (a low latitude station) is not suitable for the study of cosmic radio noise absorption on 30 MHz with riometer and dual dipole antenna. Proper choice for operating frequency of riometer and antenna gain is suggested for low latitude use of this technique for ionospheric deviative and nondeviative absorption studies.     

太阳质子事件预报和射电Ⅰ型噪暴

太阳是一个异常活跃的天体,其爆发过程会对地球周围空间环境产生重要影响. 通常,单个高能质子即足以引起飞行器中微电子器件出现异常,因此太阳质子事件预报是空间天气预报的重要内容. 关于预报模型的参数选择尚有值得改进之处. 研究认为,Ⅰ型噪暴与日冕加热磁重联具有密切关系,可以作为预报参数. 通过两个典型太阳爆发事件的详细资料分析,说明了Ⅰ型噪暴与质子事件及CME的相关性.      

VHF radio response of the near Earth space during solar activity growth in October, 2003

The analysis of observations of very high frequency radio noise intensity at the middle latitude on a frequency f = 500 MHz from 14th till 26th of October, 2003 is presented. These data are compared with the solar radio bursts in the range of frequencies 1–14 MHz registered by RAD2 receiver of the WAVES device installed on board the WIND spacecraft.