银河宇宙线在电离层D层中电离的全球分布

本文从带电粒子对D层大气电离出发, 给出了宇宙线相对论粒子、非相对论粒子及低能粒子在地球大气中的电离公式, 从而给出了宇宙线在电离层D层中电子产生率q(h)和电子密度N(h)的全球分布.结果表明, 宇宙线产生的q(h)和N(h)具有明显的纬度效应, 在极区产生的q(h)和N(h)要比低纬高得多, 当截止刚度R_c=10—18GV时, q(h)的变化相差很小.太阳活动11年调制对q(h)的影响是明显的, 但远小于R_c对q(h)的影响.大气密度ρ(h)对q(h)的影响主要是随高度的变化.      

大气中子实时计算模式

为实时评估0~100km高度范围内的大气中子全球分布,对宇宙线在地磁场和大气中的传输过程进行了分析.利用蒙特卡罗方法工具包Geant4,预先计算不同能量的粒子在大气层中产生的次级粒子能谱分布,形成大气次级粒子数据库,并与相关模型进行对比,验证了该数据库的有效性和可靠性.以实测或预报的空间环境参数作为输入,计算同步轨道银河宇宙线和太阳质子事件能谱以及100km高度上的地磁垂直截止刚度,最终得到大气层顶上的粒子能谱.通过对大气次级粒子数据库的线性插值,实现1h分辨率的大气中子能谱和辐射剂量全球分布的实时计算.      

太阳宇宙线源物质的高色球层模式和重离子丰度过量机制的探讨

本文利用太阳能量粒子事件中重离子平均丰度过量的资料,计算得到太阳能量粒子源物质的温度,提出了描述太阳宇宙线能量粒子源物质的新模式——高色球层模式;太阳耀斑观测确定,太阳宇宙线耀斑的加速区一般最可能出现在低日冕甚至高达几万公里的高度,从而,太阳宇宙线的源和加速区通常不位于同一区域;进而提出了描述太阳能量粒子事件中重离子丰度过量的可能机制——其源物质是通过太阳黑子的冻结型无力场从高色球层输送到活动区,形成耀斑前加速区内重离子丰度大和耀斑后宇宙线中重元素丰度的过量.      

太阳宇宙线的传播效应(Ⅱ)——峰值谱的传播改正

根据太阳宇宙线传播方程的量纲分析解, 讨论了传播对宇宙线事件峰值谱的影响, 着重指出对其进行传播改正的重要性。太阳风对流是低能谱变坦的可能原因之一, 在一定条件下, 幂律型发射谱可以变成指数型观测谱, 动能幂律谱也可以变成刚度幂律谱。能谱的幂指数随源耀斑的磁方位角而增加, 分布有明显的东西不对称性。进一步对第20周的相对论性太阳质子事件进行传播改正, 求出发射谱, 其中有些可表达成统一指数的幂律谱, 有些仍有低能段趋坦现象。      

E10.7指数在软X射线谱段的修正应用

表征EUV辐射通量的E10.7指数在越来越多的研究和应用中被用来代替传统的F10.7指数.X射线对地球D层和E层的电离起着重要作用,但由于D层观测数据的不足和E层电离源的多样性,难以被用来考虑X射线对电离层的影响.火星电离层下层的电离源几乎是单一的软X射线,这为研究X射线对电离层的作用提供了可能性.通过研究火星电离层下层的峰值电子浓度对E10.7的依赖关系,发现即便经过必要的修正,这种关系对不同的观测时段并不具备一致性.通过理论推导和数据分析,得到了一种特别用于描述太阳软X射线辐射通量的新指数,即Xs指数,用来替代E10.7指数.Xs指数在描述火星电离层下层对太阳辐射的依赖关系时,不同的观测时段有很好的一致性,表明Xs指数在表征太阳软X射线辐射强度方面比E10.7指数更加合适.      

太阳纯电子事件和质子-电子事件的电子能谱的机制

本文计算、分析了太阳耀斑加速电子在日冕中传输时激发的等离子体尾场的效应,认为耀斑电子的高能成份激发的尾场,能够加速低能耀斑电子,低能耀斑电子的能量增值可达几十keV至上百keV,这种尾场加速将软化约100keV以下的能量范围内(探测阈之上)的耀斑电子能谱。结合考虑尾场效应,本文提出了太阳耀斑加速电子从加速区到形成电子事件之间的能谱演化模式,说明了太阳纯电子事件的双幂律电子能谱和太阳质子-电子事件的单幂律电子能谱的形成,认为两类事件的电子能谱差异为耀斑电子日冕传输中不同程度的尾场效应所致,前者尾场效应弱,电子能谱呈双幂律,后者尾场效应较强,电子能谱为单幂律谱。      

由大气密度的季变化所造成的中、低层大气电离率的季变化

本文对CIRA 1972 模式下的中、低层大气密度季变化所造成的电离率的季变化作了理论计算, 利用宇宙线电离源函数对全球中、低层大气的电离率作了数值计算.计算结果表明, 在70km以下的大气电离率的季变化幅度为百分之几十.在电离峰值高度(约15km)以下幅度为约百分之十, 高度越高变幅越大, 到70km处达35%.在20km以上电离率的季变化趋势与大气密度的季变化趋势大致相同, 夏季比冬季大, 20km以下变化稍为复杂.      

日照边缘区域电离层对耀斑的响应特点研究

利用MSIS模型和背景太阳辐射谱模型,在一定大耀斑辐射谱假设的前提下,计算了耀斑期间日照边缘区域的电子产生率,分析了这一区域电离层电子密度的变化特点.结果表明,大耀斑期间在日照边缘区域,甚至大于太阳天顶角90°的区域都有明显的电子产生率的增加.从不同太阳天顶角处的电子产生率剖面的形态来看,随着天顶角的增加最大电离率减少,但高度增加.计算还显示了在太阳天顶角小于90°的区域内电子产生率的垂直分布有明显的双峰结构,这种结构对应着电离层的E区和F区,但在天顶角大于90°区域,F区的电子产生率要大得多.考虑到离子和电子的复合过程,这一区域的总电子含量的增加主要产生在高F区.      

利用地面宇宙线强度变化预报地磁暴方法初步研究

分析了Nagoya宇宙线闪烁体望远镜探测数据的变化特点,定性地探讨了CME可能引起的地面宇宙线的变化特征,通过实例证实了地面宇宙线通量的异常波动是地磁暴发生的重要先兆特征,并且将8 h内宇宙线通量与该时间段内平均通量的偏差D8(t)参数应用到宇宙线数据分析中.通过数据分析与讨论,认为D8(t)参数达到一定阈值是地磁暴的重要先兆特征,但不是充分条件,虚假信号仍占多数;D8(t)参数与太阳质子事件探测结果相结合,对于大地磁暴的预报有较好的效果.      

太阳质子事件与大气臭氧扰动

本文利用统计分析方法分析了1960至1982年间1级以上的太阳质子事件与四个不同地理纬度大气臭氧含量的相互关系.分析结果表明,对于中、低纬度地区,1、2级太阳质子事件基本上不影响大气臭氧含量,只有3、4级的大事件才对臭氧含量产生扰动,而且具有明显的纬度效应;对于极区,1级以上的太阳质子事件就能对臭氧含量产生影响,随着质子事件级别的增高,对臭氧含量的扰动也加大.通常,太阳质子事件发生的当天,臭氧含量开始下降,在第4天下降达最小值,整个扰动持续数日.由太阳质子事件扰动大气臭氧明显的纬度效应证明了太阳质子事件的确是使大气臭氧含量变化的重要因素.此外,分析结果表明,冬天出现的太阳质子事件对臭氧的扰动要大于夏天质子事件对臭氧的扰动.这些结果给出了太阳质子事件影响大气臭氧的一个总轮廓,而且从理论上得到了较好的解释.      

Response of low latitude D-region ionosphere to the total solar eclipse of 22 July 2009 deduced from ELF/VLF analysis

Response of the D-region of the ionosphere to the total solar eclipse of 22 July 2009 at low latitude, Varanasi (Geog. lat., 25.27° N; Geog. long., 82.98° E; Geomag. lat. = 14° 55’ N) was investigated using ELF/VLF radio signal. Tweeks, a naturally occurring VLF signal and radio signals from various VLF navigational transmitters are first time used simultaneously to study the effect of total solar eclipse (TSE). Tweeks occurrence is a nighttime phenomena but the obscuration of solar disc during TSE in early morning leads to tweek occurrence. The changes in D-region ionospheric VLF reflection heights (h) and electron density (n_e: 22.6–24.6 cm⁻³) during eclipse have been estimated from tweek analysis. The reflection height increased from ∼89 km from the first occurrence of tweek to about ∼93 km at the totality and then decreased to ∼88 km at the end of the eclipse, suggesting significant increase in tweek reflection height of about 5.5 km during the eclipse. The reflection heights at the time of totality during TSE are found to be less by 2–3 km as compared to the usual nighttime tweek reflection heights. This is due to partial nighttime condition created by TSE. A significant increase of 3 dB in the strength of the amplitude of VLF signal of 22.2 kHz transmitted from JJI-Japan is observed around the time of the total solar eclipse (TSE) as compared to a normal day. The modeled electron density height profile of the lower ionosphere depicts linear variation in the electron density with respect to solar radiation as observed by tweek analysis also. These low latitude ionospheric perturbations on the eclipse day are discussed and compared with other normal days.     

Periodic variations of ionization rate in the low and middle atmosphere

The cosmic ray ionization source functions which were obtained using a simplified extensive air shower model are used to calculate the eleven year cycle, seasonal and diurnal variations of ionization rate in the low and middle atmosphere. The ionization source function, as a function of the penetrating depth and the energy of cosmic ray particles, is the ionization rate per unit depth for a unit flux of incoming cosmic ray particles with certain energy.The calculation of the eleven year cycle variation of ionization rate in the low and middle atmosphere due to the modulation of galactic cosmic ray intensity by solar activity shows that the amplitude is larger at a higher magnetic latitude and is generally larger at higher altitudes. The relative amplitude of fluctuation of the ionization peak value (at altitudes near 15 km) is up to 45% in the magnetic polar region. The ionization rate, due to the seasonal variation of the atmospheric density, varies from several per cent below the ionization peak to several tens per cent above the peak. This seasonal variation of ionization rate reaches 35% at 70 km. The diurnal variation of atmospheric densities caused by atmospheric tidal oscillation can produce a diurnal variation of the ionization rate to an amplitude of several per cent at altitudes above 40 km. The diurnal oscillation is less than 1% below 35 km.     

Response of the mid-latitude D-region ionosphere to the total solar eclipse of 22 July 2009 studied using VLF signals in South Korean peninsula

In this paper, we analyze VLF signals received at Busan to study the the D-region changes linked with the solar eclipse event of 22 July 2009 for very short (∼390 km) transmitter–receiver great circle path (TRGCP) during local noon time 00:36–03:13 UT (09:36–12:13 KST). The eclipse crossed south of Busan with a maximum obscuration of ∼84%. Observations clearly show a reduction of ∼6.2 dB in the VLF signal strength at the time of maximum solar obscuration (84% at 01:53 UT) as compared to those observed on the control days. Estimated values of change in Wait ionospheric parameters: reflection height (h′) in km and inverse scale height parameter (β) in km⁻¹ from Long Wave Propagation Capability (LWPC) model during the maximum eclipse phase as compared to unperturbed ionosphere are 7 km and 0.055 km⁻¹, respectively. Moreover, the D-region electron density estimated from model computation shows 95% depletion in electron density at the height of ∼71 km. The reflection height is found to increase by ∼7 km in the D-region during the eclipse as compared to those on the control days, implying a depletion in the Lyman-α flux by a factor of ∼7. The present observations are discussed in the light of current understanding on the solar eclipse induced D-region dynamics.     

Latitudinal influences on the quiet daytime D-region

Four versions of a steady-state quiet D-region model are presented. They differ from each other as a result of latitudinal differences in total neutral particle concentrations, nitric oxide concentrations and cosmic ray ionization rates. The total ion concentration profiles of all four versions have minima near 70 km which range from about 10⁸ m^?3 at high latitudes to 3.5 × 10⁷ m^?3 at equatorial latitudes for a solar zenith angle of 60°. Neutral density differences among the four cases result in important vertical shifts for the respective D-region profiles relative to one another. A “C-layer” is evident for the high and mild-latitude models at large solar zenith angles. The altitude where the negative ion/electron concentrations ratio is unity varies from about 63 to 67 km. The computed results are compared briefly with the extensive data base in the literature.     

超高能宇宙线电子在星际介质中的传播

本文研究能量高达1012eV以上宇宙线电子在星际介质中的传播特征, 得到了一些有趣的结果。作为一种自然的猜测, 宇宙线电子高能成份的区域性特征, 可能是导致银河系γ射线辐射的非均匀成团状分布结构的直接原因。      

D-region IRI profiles in relation to radio observations

The D-region IRI profiles are compared with the direct rocket measurements as well as with ground-based radio observations by a variety of techniques. The characteristics of D-region IRI profiles and the dependence of electron density on solar zenith angle, sunspot number, latitude and season are discussed. The sensitivity of certain reflection coefficients on the height distribution of electron density below 70 km is illustrated with a typical example. For D-region modelling, the results show the importance of simultaneous measurement of reflection and conversion coefficients together with polarization phase over a wide frequency range.     

Galactic cosmic ray composition and energy spectra.

Galactic cosmic ray nuclei represent a significant risk to long-duration spaceflight outside the magnetosphere. We review briefly existing measurements of the composition and energy spectra of heavy cosmic ray nuclei, pointing out which species and energy ranges are most critical to assessing cosmic ray risks for spaceflight. Key data sets are identified and a table of cosmic ray abundances is presented for elements from H to Ni (Z = 1 to 28). Because of the 22-year nature of the solar modulation cycle, data from the approaching 1998 solar minimum is especially important to reducing uncertainties in the cosmic ray radiation hazard. It is recommended that efforts to model this hazard take advantage of approaches that have been developed to model the astrophysical aspects of cosmic rays.