Sensing the Earth’s low ionosphere during solar flares using VLF signals and goes solar X-ray data

An analysis of D-region electron density height profile variations, induced by four isolated solar X-ray flares during period from September 2005 to December 2006, based on the amplitude and the phase delay perturbation of 22.1 kHz signal trace from Skelton (54.72 N, 2.88 W) to Belgrade (44.85 N, 20.38 E), coded GQD, was carried out. Solar flare data were taken from NOAA GOES12 satellite one-minute listings. For VLF data acquisition and recordings at the Institute of Physics, Belgrade, Serbia, the AbsPAL system was used. Starting from LWPCv21 code (Ferguson, 1998), the variations of the Earth-ionosphere waveguide characteristic parameters, sharpness and reflection height, were estimated during the flare conditions. It was found that solar flare events affected the VLF wave propagation in the Earth-ionosphere waveguide by changing the lower ionosphere electron density height profile, in a different way, for different solar flare events.     

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.      

低纬100—200km间电子数密度的变化

利用光化平衡模式计算了低纬100—200km间白天电子数密度的变化。求得E-F₁谷区的谷深,谷宽、谷高的变化特征。获得如下结果:a.太阳活动明显影响电子数密度随高度及太阳天顶角的变化,发现太阳活动指数与电子数密度间不仅存在正相关,而且存在负相关;b.太阳活动明显影响E-F₁谷区的形态。在一定太阳活动条件下,对同一太阳赤纬和地理纬度,谷深、谷宽与太阳天顶角的关系难以用一简单函数来表示;c.太阳耀斑、地磁活动对该区电子密度有明显影响;d.在讨论100—200km间电子密度时不能忽略O+（2P）和NO的光电离率。      

Ionospheric heating due to solar flares as measured by SROSS-C2 satellite

The data on thermal fluctuations of the topside ionosphere have been measured by Retarding Potential Analyser (RPA) payload aboard the SROSS-C2 satellite over the Indian region for half of the solar cycle (1995–2000). The data on solar flare has been obtained from National Geophysical Data Center (NGDC) Boulder, Colorado (USA) and other solar indices (solar radio flux and sunspot number) were download from NGDC website. The ionospheric electron and ion temperatures show a consistent enhancement during the solar flares. The enhancement in the electron temperature is 28–92% and for ion temperature it is 18–39% compared to the normal day’s average temperature. The enhancement of ionospheric temperatures due to solar flares is correlated with the variation of sunspot and solar radio flux (F10.7cm). All the events studied in the present paper fall in the category of subflare with almost same intensity. The ionospheric electron and ion temperatures enhancement have been compared with the IRI model values.     

From solar nanoflares to stellar giant flares: Scaling laws and non-implications for coronal heating

In this study we explore physical scaling laws applied to solar nanoflares, microflares, and large flares, as well as to stellar giant flares. Solar flare phenomena exhibit a fractal volume scaling, V(L)  L^1.9, with L being the flare loop length scale, which explains the observed correlation between the total emission measure EM_p and flare peak temperature T_p in both solar and stellar flares. However, the detected stellar flares have higher emission measures EM_p than solar flares at the same flare peak temperature T_p, which can be explained by a higher electron density that is caused by shorter heating scale height ratios s_H/L ≈ 0.04–0.1. Using these scaling laws we calculate the total radiated flare energies E_X and thermal flare energies E_T and find that the total counts C are a good proxy for both parameters. Comparing the energies of solar and stellar flares we find that even the smallest observed stellar flares exceed the largest solar flares, and thus their observed frequency distributions are hypothetically affected by an upper cutoff caused by the maximum active region size limit. The powerlaw slopes fitted near the upper cutoff can then not reliably be extrapolated to the microflare regime to evaluate their contribution to coronal heating.     

Nitric oxide density enhancements due to solar flares

A differential emission measure technique is used to determine flare spectra using solar observations from the soft X-ray instruments aboard the Thermosphere Ionosphere Mesosphere Energetics Dynamics and Solar Radiation and Climate Experiment satellites. We examine the effect of the solar flare soft X-ray energy input on the nitric oxide (NO) density in the lower thermosphere. The retrieved spectrum of the 28 October 2003 X18 flare is input to a photochemical thermospheric NO model to calculate the predicted flare NO enhancements. Model results are compared to Student Nitric Oxide Explorer Ultraviolet Spectrometer observations of this flare. We present results of this comparison and show that the model and data are in agreement. In addition, the NO density enhancements due to several flares are studied. We present results that show large solar flares can deposit the same amount of 0.1–2 and 0.1–7 nm energy to the thermosphere during a relatively short time as the Sun normally deposits in one day. The NO column density nearly doubles when the daily integrated energy above 5 J m⁻² is doubled.     

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。     

Study of the 28 October 2003 and 20 January 2005 solar flares by means of 2.223 MeV gamma-emission line

By the data on intensity-time profiles of the neutron capture line of 2.223 MeV we have studied some characteristics of two solar flares, 28 October 2003 and 20 January 2005 (INTEGRAL and CORONAS-F observations, respectively). The SINP code was applied making allowance for the main processes of neutron interactions and deceleration in the solar plasma, character of neutron source, losses of neutrons and density model of the solar atmosphere. Comparison of the computed time profiles of 2.223 MeV line with observed ones for the flare of 28 October 2003 confirms the results obtained earlier for three other flares. Namely, the effect of density enhancement (EDE) in the sub-flare region, as well as the variations (hardening) of accelerated particle spectrum in the course of the event have been confirmed. The usual modeling procedure by the SINP code, however, seems to be inapplicable to the event of 20 January 2005. Possible causes of density enhancements during some flares and peculiarities of the 20 January 2005 flare are discussed.     

基于PCA方法对太阳活动区主要参量的分析

太阳耀斑与太阳质子事件的发生通常与太阳活动区存在非常密切的关系, 对这种关系的深入分析有助于太阳耀斑和太阳质子事件预报模型的建立. 本文利用主成分分析(Principal Component Analysis, PCA)方法对1997-2010年太阳质子事件所在活动区的主要参量进行分析, 选取的参量包括黑子磁分类、 McIntosh分类、太阳黑子群面积、10.7 cm射电流量、耀斑指数、质子耀斑位置和软X射线耀斑强度. 结果得到81个太阳活动主成分得分值排序(得分值代表每个事件的强弱), 与太阳质子事件峰值流量、太阳黑子年均值以及10.7 cm射电流量年均值的对比显示相似度非常高, 表明主成分得分值一定程度上可以反映太阳活动的强弱规律.      

2009年7月22日日全食电离层效应观测

首次利用廊坊中频雷达和武汉、嘉兴、廊坊等三站GPS对2009年7月22日日全食电离层效应进行了观测．日食期间,中频雷达D层78km高度上电子密度减小了约67％,电子密度为200cm^-3的高度上升了近10km,GPS／TEC减小了1TECU左右,其变化的最大相位与日食最大相位几乎同步;日食后,观测到周期为2个多小时的电离层扰动现象．     

MHD simulation of magnetic field configuration above the active region NOAA 10365

The current sheet (CS) creation before a flare in the vicinity of a singular line above the active region NOAA 10365 is shown in numerical experiments. Such a way the possibility of energy accumulation for a solar flare is demonstrated. These data and results of observation confirm the electrodynamical solar flare model that explains solar flares and CME appearance during CS disruption. The model explains also all phenomena observed in flares. For correct reproduction of the real boundary conditions the magnetic flux between spots should be taken into account. The full system of 3D MHD equations are solved using the PERESVET code. For setting the boundary conditions the method of photospheric magnetic maps is used. Such a method permits to take into account all evolution of photospherical magnetic field during several days before the flare.     

Theoretical modelling of X-ray fluorescence signals for different lunar compositions and dependence on solar activity

We present a forward modelling technique for calculating the surface X-ray spectra for a variety of lunar terrains. Our calculations considered variations in solar fluxes from solar quiescent condition to large flare activity (M1 flare), and expected elemental concentrations in the target, as well as yield, instrumental, and viewing geometry parameters for X-ray induced fluorescence from the lunar surface. Additionally, we present estimates of anticipated XRF signals from prominent K_α lines observable by a collimated 14 cm² X-ray detector from a 100 km lunar orbit with ∼20 km spatial resolution. Our results show that Mg, Al and Si characteristic K_α lines can be observed for all solar conditions. The Ca K_α lines line can be differentiated from a fixed background during more energetic solar conditions such as C1 and M1 flares, whereas Ti and Fe lines are identifiable only during C1 and M1 solar flare conditions for Apollo 12 site composition. Both the K_α X-ray intensity ratios of Mg/Si and Al/Si correlate well with concentration ratios of Mg/Si and Al/Si, respectively, for B1 and M1 solar conditions. The K_α X-ray intensity ratios of Fe/Si and Ca/Si correlates with concentration ratios of Fe/Si and Ca/Si, respectively, for M1 solar condition. In principle, the modelling technique outlined here can be used to determine absolute elemental abundances (Mg, Al, Si, Ca, Ti and Fe) from X-ray spectra measured during recent and future lunar missions.     

Lower ionosphere response to external forcing: A brief review

There are two ways of external forcing of the lower ionosphere, the region below an altitude of about 100 km: (1) From above, which is directly or indirectly of solar origin. (2) From below, which is directly or indirectly of atmospheric origin. The external forcing of solar origin consists of two general factors – solar ionizing radiation variability and space weather. The solar ionization variability consist mainly from the 11-year solar cycle, the 27-day solar rotation and solar flares, strong flares being very important phenomenon in the daytime lower ionosphere due to the enormous increase of the solar X-ray flux resulting in temporal terminating of MF and partly LF and HF radio wave propagation due to heavy absorption of radio waves. Monitoring of the sudden ionospheric disturbances (SIDs – effects of solar flares in the lower ionosphere) served in the past as an important tool of monitoring the solar activity and its impacts on the ionosphere. Space weather effects on the lower ionosphere consist of many different but often inter-related phenomena, which govern the lower ionosphere variability at high latitudes, particularly at night. The most important space weather phenomenon for the lower ionosphere is strong geomagnetic storms, which affect substantially both the high- and mid-latitude lower ionosphere. As for forcing from below, it is caused mainly by waves in the neutral atmosphere, i.e. planetary, tidal, gravity and infrasonic waves. The most important and most studied waves are planetary and gravity waves. Another channel of the troposphere coupling to the lower ionosphere is through lightning-related processes leading to sprites, blue jets etc. and their ionospheric counterparts. These phenomena occur on very short time scales. The external forcing of the lower ionosphere has observationally been studied using predominantly ground-based methods exploiting in various ways the radio wave propagation, and by sporadic rocket soundings. All the above phenomena are briefly mentioned and some of them are treated in more detail.     

Variability of the ionospheric electron density at fixed heights and validation of IRI-2007 profile’s prediction at Ilorin

A study on the variability of the equatorial ionospheric electron density was carried out at fixed heights below the F2 peak using one month data for each of high and low solar activity periods. The data used for this study were obtained from ionograms recorded at Ilorin, Nigeria, and the study covers height range from 100 km to the peak of the F2 layer for the daytime hours and height range from 200 km to the peak of the F2 layer for the nighttime hours. The results showed that the deviation of the electron density variation from simple Chapman variation begins from an altitude of about 200 km for the two months investigated. Daytime minimum variability of between 2.7% and 9.0% was observed at the height range of about 160 and 200 km during low solar activity (January 2006) and between 3.7% and 7.8% at the height range of 210 and 260 km during high solar activity (January 2002). The nighttime maximum variability was observed at the height range of 210 and 240 km at low solar activity and at the height range of 200 and 240 km at high solar activity. A validation of IRI-2007 model electron density profile’s prediction was also carried out. The results showed that B0 option gives a better prediction around the noontime.     

Chromospheric line emission in seismically active flares

Some flares are known to drive seismic transients into the solar interior. The effects of these seismic transients are seen in helioseismic observations of the Sun’s surface thousands of km from their sources in the hour succeeding the impulsive phase of the flare. Energetic particles impinging from the corona into the chromosphere are known to drive strong, downward-propagating shocks in active region chromospheres during the impulsive phases of flares. H observations have served as an important diagnostic of these shocks, showing intense emission with characteristic transient redshifts. In most flares no detectable transients penetrate beneath the active region photosphere. In those that do, there is a strong correlation between compact white-light emission and the signature of seismic emission. This study introduces the first known H observations of acoustically active flares, centered in the core of the line. The morphology of line-core emission H in the impulsive phase of the flare is similar to that of co-spatial line-core emission in NaD₁, encompassing the site of seismic emission but more extended. The latter shows a compact red shift in the region of seismic emission, but a similar feature is known to appear in a conjugate magnetic footpoint from which no seismic emission emanates. Radiative MHD modelling based on the profiles of chromospheric line emission during the impulsive phases of flares can contribute significantly to our understanding of the mechanics of flare acoustic emission penetrating into the solar interior and the conditions under which it occurs.     

用半经验模型研究耀斑大气的能量耗散

本文利用南京大学太阳塔多波段光谱资料推求出的两个耀斑(一个SB级,一个2B级)的半经验模型;计算了耀斑不同时刻的辐射损失速率,并与电子束轰击和X线作用下的产能率作了比较.结果表明,耀斑不同时刻的色球辐射损失变化可达一个量级以上;耀斑脉冲相前后电子束轰击加热相当有效;耀斑强度极大时,电子束轰击和X线加热都有作用;耀斑主相时,X线加热更能有效地平衡辐射损失.但是,尤其是对大耀斑来说,色球低层和光球上层的加热既不能用电子束轰击,也不能用X线的作用来解释;可能存在某种把能量从色球上层向低层转移的机制.研究也表明,耀斑随时间变化的半经验模型为研究耀斑的能量耗散过程提供了很好的工具.      

Distinctive spatial configuration of a class ofmicrowave flaring sources

We discuss a class of microwave flares whose source regions exhibit a distinctive spatial configuration; the primaryenergy release in these flares results from the interaction between emerging magnetic flux and an existing overlying region. Such events typically exhibit radio, X-ray and EUV emission at the main flare site (the site of interaction) and in addition radio emission at a remote site up to 1 × 10⁵ km away in another active region. We have identified and studied more than a dozen microwave flares in this class, in order to arrive at some general conclusions on reconnection and energy release in such solar flares. Typically, these flares show a gradual rise showing many subsidiary peaks in both radio and hard X-ray light curves with a quasi-oscillatory nature with periods of 5–6 seconds, a bright compact X-ray & EUV emitting loop in the main flare source, a delay of the radio emission from the remote source relative to the main X-ray-emitting source. The magnetic field in the main flare site changes sharply at the time of the flare, and the remote site appears to be magnetically connected to the main flare site.     

太阳耀斑硬X射线能谱演变特征

太阳硬X射线是耀斑高能电子束流与太阳大气相互作用产生的韧致辐射,根据简单的太阳耀斑环物理模型,假定具有流量与能谱同步变化的高能电子束流从耀斑环顶部注入,计算了硬X射线辐射在不同的靶物质密度区的能谱演变特征。结果表明:硬X射线辐射在低大气密度靶区呈现软一硬一硬的能谱演变特征,在高密度靶区硬X射线能谱则具有软一硬一软的变化特征。高能电子束流持续时间影响谱型转变区域在耀斑环中的高度。      

Relationships of a growing magnetic flux region to flares

Some sites for solar flares are known to develop where new magnetic flux emerges and becomes abutted against opposite polarity pre-existing magnetic flux (review by Galzauskas/1/). We have identified and analyzed the evolution of such flare sites at the boundaries of a major new and growing magnetic flux region within a complex of active regions, Hale No. 16918. This analysis was done as a part of a continuing study of the circumstances associated with flares in Hale Region 16918, which was designated as an FBS target during the interval 18 – 23 June 1980. We studied the initiation and development of both major and minor flares in Hα images in relation to the identified potential flare sites at the boundaries of the growing flux region and to the general development of the new flux. This study lead to our recognition of a spectrum of possible relationships of growing flux regions to flares as follows: (1) intimate interaction with adjacent old flux — flare sites centered at new/old flux boundary, (2) forced or “intimidated” interaction in which new flux pushes old field having lower flux density towards a neighboring old polarity inversion line where a flare then takes place, (3) “influential” interaction — magnetic lines of force over an old polarity inversion line, typically containing a filament, reconnect to the new emerging flux; a flare occurs with erupting filament when the magnetic field overlying the filament becomes too weak to prevent its eruption, (4) inconsequential interaction — new flux region is too small or has wrong orientation for creating flare conditions, (5) incidental — flare occurs without any significant relationship to new flux regions.     

Solar flares,CMEs and solar energetic particle events during solar cycle 24

We present here a study of Solar Energetic Particle Events (SEPs) associated with solar flares during 2010–2014 in solar cycle 24. We have selected the flare events (≥GOES M-class), which produced SEPs. The SEPs are classified into three categories i.e. weak (proton intensity?≤?1?pfu), minor (1?pfu?<?proton intensity?<?10?pfu) and major (proton intensity?≥?10?pfu). We used the GOES data for the SEP events which have intensity greater than one pfu and SOHO/ERNE data for the SEP event less than one pfu intensity. In addition to the flare and SEP properties, we have also discussed different properties of associated CMEs.