南京地区低电离层加热效应的初步模拟

从电子能量方程和连续性方程出发,利用国际参考电离层(IRI-2007)和中性大气模型(NRLMSISE-00)得出背景参数,数值计算了大功率无线电波加热南京地区低电离层的电子温度和电子密度扰动幅度,并对比了不同加热条件下的电离层扰动效应.结果表明,大功率无线电波入射到电离层后,与等离子体相互作用,能够有效造成电子温度的升高而产生电子温度扰动;由于电子温度升高,等离子体碰撞频率增加且电子的复合系数减小,导致电子密度扰动;电子温度和电子密度的扰动幅度随着加热时间的推移而减小,即扰动逐渐趋于饱和;电子温度扰动的弛豫时间尺度为微秒量级,电子密度扰动的弛豫时间尺度为毫秒量级;在欠密加热条件下,X波模比O波模更容易吸收.     

Modelling of the lower ionosphere

The model of calculations of electron density profiles in D-region is suggested. The model includes four positive ions, four negative ions and electrons. The effective rate coefficients were received from detailed models of ionization-recombination cycle. The calculations, which were made, and the comparisons with experimental data (Ne-profiles and their variations, absorption of radiowaves) have showed, that in general the model described the basic features of D-region parameters.     

Effect of geomagnetic storms (substorms) on the ionosphere: 1. A review

The result of the effect of magnetospheric storms and substorms on the ionosphere (the so-called main effect) has been studied. The effect consists in that the critical frequency and altitude of the F region vary specifically during a disturbance. The critical frequency first increases before the storm (substorm) active phase, then decreases during the active phase, and increases again after this phase. On the contrary, the F region altitude increases during the active phase and decreases after this phase. An approach to the short-term (2–3 h) prediction of the development of storms (substorms) as the main disturbed space weather elements has been proposed.     

Diurnal asymmetry in the lower ionosphere — seasonal variability

Summary On the basis of long period measurements of ionospheric absorption in five A3 circuits in Central Europe, it is shown that the considerable seasonal variation of the diurnal asymmetry of absorption, found in[1], exhibits practically no year-to-year variability and is well-developed at equivalent frequencies f _eq 1 MHz, while it vanishes at F _eq 2 MHz. The limited data on the diurnal asymmetry of the D-region electron concentration are consistent with the seasonal pattern of the diurnal asymmetry in absorption. A tentative hypothesis of nitric oxide variability as the cause of the seasonal variation of the asymmetry is proposed.     

Response of the midlatitude ionosphere to extreme geomagnetic storms of the 23rd solar cycle

The ionospheric response in the Irkutsk region (52.3° N, 104.3° E) to the extreme geomagnetic storms of solar cycle 23 was studied based on the data of the Irkutsk incoherent scatter radar (ISR) and DPS-4 vertical sounding digital ionosonde. The deviations of parameters from the undisturbed level, i.e., from the monthly medians or the values obtained on a quiet day, were considered as an ionospheric response. Values of the electron concentration maximum (N _mF2) and electron temperature (T _e) at a height of 350 km were chosen as parameters. The ionospheric response is interpreted in the scope of the concept of a thermospheric storm and penetration of the magnetospheric electric field.     

2002年10月Millstone Hill地区电离层暴时特性研究

磁暴期间电离层行为是电离层物理的重要研究内容.本文利用美国Millstone Hill非相干散射雷达以及GPS-TEC数据资料,分析了2002年10月13-17日和22-26日磁暴事件期间电离层电子密度响应在不同高度存在的差异.结果表明：正、负相暴电子密度的变化幅度随高度变化趋势相同,但不同高度上响应的时间、相位和幅度存在差异;负相暴最大变化幅度所在高度值同静时峰高值非常吻合,二者有很好的线性关系,但正相暴最大变化幅度所在高度值同静时峰高值无关,波动较大,意味着电离层正相暴响应更易到达各个高度上;特别地,22-26日负相暴在能量初次耦合进入电离层时高高度有极小的变化,其最大绝对变化量仅为低高度的4%.大气成分和风场的共同作用是两次负相暴发生的主要原因,但前者成分效应明显,后者动力学作用明显,有时甚至700 km以上电离层的贡献也是不可忽略的.

     

A numerical model of ion concentration profiles in the lower ionosphere

Summary A one-dimensional numerical model has been developed which gives the vertical profiles of the electron and ion concentrations at altitudes between 50 and 100 km. The model has been constructed for day-time ionization conditions in midlatitudes and yields a slightly abbreviated scheme of ion-molecular reactions. Neutral species concentrations have been compiled from various authors. Seasonal variations of temperature and the most important neutral species have been taken into account. For the purpose of this paper moderate solar fluxes in all required radiation bands have been considered.     

Some possibilities of predicting radio wave absorption in the lower ionosphere

Summary An attempt is made to show possible ways of predicting radio wave absorption in the midlatitude lower ionosphere using relations between absorption and the intensity of solar ionizing radiation and/or common solar activity indices, and between absorption and f₀F2.

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Day-time variations of the equivalent electron concentration in the non-sounded lower ionosphere

Summary Based on data on the lowest reflected frequencyf _min and on information on the lower and upper boundaries of the non-sounded lower ionosphere, an equivalent electron concentration for all concentrations below the correspondingf _min was determined. Day-time variations of the equivalent concentration are investigated, confirming that there is a cosine relation to the solar zenith angle. The power index of that relation has an outlined seasonal course with a maximum in April and October, while the absolute seasonal minimum is during the winter (the summer minimum is slightly outlined). The mean yearly values of the index are almost constant:n _N 0.5 for solaractivity,I ₁₅₀₀ to 115.10^–22 W Hz^–1 m². During higher activityn _N changes correspondingly toI ₁₅₀₀ according to relation (12). The variations ofn _N during high solar activity show that the altitude gradient and temperature gradient in the low ionosphere are becoming proportional toI ₁₅₀₀ when the solar x-ray radiation exceeds a certain level. The results obtained confirm the reliability of the method developed for employingf _min in aeronomic investigations.     

Response of the lower equatorial ionosphere to strong tropospheric disturbances

A morphological analysis of the results of sounding the lower equatorial ionosphere (the D region) in the region of action of strong tropospheric vortex disturbances (tropical cyclones, TC) is presented in this work. Based on the rocket sounding of the lower ionosphere at Thumba rocket site (8° N, 77° E) in May–June 1985 and on the satellite monitoring of TC in the northern Indian Ocean, it is demonstrated that a sharp depletion (by a factor of 2–4) of the electron concentration at altitudes of 60–80 km could be a response of the ionosphere during the TC active phase. In this case the lower boundary of the D region rose by several kilometers (not more than 5 km), and the temperature in the region of the stratopause slightly (by 2°–3°) increases. It is assumed that internal gravity waves (IGWs) generated by TC cause the effect on the lower ion-osphere.     

Upper-atmospheric effects of magnetic storms: a brief tutorial

The physical processes underlying several phenomena of upper-atmospheric storms are described: magnetospherically driven ion convection and Joule heating and their impact on the high-latitude thermosphere and ionosphere; global changes in thermospheric circulation and composition; traveling atmospheric disturbances; and effects of electric-field penetration to middle and low latitudes. Examples from the 1997 January 10–11 storm are used to illustrate some of these features. It is pointed out that not only the magnitude, but also the sign of many storm-time changes at any given location depend sensitively on the temporal and spatial variations of auroral particle precipitation and high-latitude electric fields. In order for simulation models to be able to predict upper-atmospheric storm effects accurately, improved determination of the high-latitude inputs will be required.     

磁暴期间高纬顶部电离层离子上行特征——DMSP卫星观测

本文利用DMSP F13和F15卫星观测数据,对2001—2005年58个磁暴(-472 nT≤Min.Dst≤-71 nT)期间高纬顶部电离层离子整体上行特征进行了统计研究.观测表明,磁暴期间,顶部电离层离子上行主要发生在极尖区和夜间极光椭圆区.在北半球,磁正午前,高速的离子上行(≥500 m·s-1)多集中在65° MLat以上;午后,高速离子上行区向低纬度扩展,上行速度要略高于午前;在南半球,磁午夜前,DMSP卫星在考察区域内几乎所有的纬度上都观测到了高速上行的离子;午夜后,各纬度上观测到上行离子的速度明显降低.离子上行期间,DMSP卫星在极区顶部电离层高度上也频繁地观测到电子/离子增温,且电子增温发生的频率要远高于离子增温.O+密度变化分析显示,DMSP卫星磁暴期间观测到的上行离子更多地源于顶部电离层高度.这些结果表明电子增温在驱动暴时电离层离子整体上行过程中起着重要作用.     

Contribution of the X-ray emission lines to ionization of lower ionosphere

Summary In the case of solar flares, X-ray flux shorter than 8 Å fully controls the ionization conditions of the lower ionosphere. Therefore, it should be expected that the energy spectrum distribution shorter than 8 Å determines the form of the height profile of the electron production rate. It is shown analytically that the existing emission lines within the range of 1–8 Å under flare conditions contribute insignificantly to the ionization state of the lower ionosphere. Only two of the most powerful lines Fe XXV (1.850 Å) and the triplet Ca XIX (3.174 Å; 3.187 Å; 3.187 Å; 3.207 Å) are considered for ionization effects. It is shown that the increase of the electron production rate at the height of the maximum ionization of these lines is negligibly small.     

Dust storms in northern China and their significance for the concept of the Anthropocene

Science China Earth Sciences - A key scientific issue in the study of the Anthropocene is the determination of the corresponding stratigraphic marker in geological archives. The arid and semi-arid...     

Effective radius of heating of the lower ionosphere by intense shortwave radiation

The results of a theoretical analysis of the radial distribution of electron temperature T _e in the area of heating of the lower ionosphere by intense shortwave radiation are presented. It was established that effective radius r _eff of heating at a certain height may differ significantly from the characteristic radius of illumination of the ionosphere (a) by radiation at this height. At the boundary of the heating area (r = r _eff ), the characteristic radial scale of T _e changes is less than the corresponding scale of changes in the squared amplitude of the radiation electric field, and it is almost independent of the amplitude value; i.e., the formation of a relatively strong T _e gradient at such a boundary is a common feature of heating of the lower ionosphere by intense shortwave radiation.     

考虑电子吸附效应的低电离层加热研究

基于低电离层自洽加热模型,综合考虑了低电离层中电子的复合效应及典型吸附效应,本文数值仿真了大功率高频无线电波持续加热低电离层所产生的电子温度、电子密度的扰动,并且首次模拟分析了由于电子温度扰动造成的加热电波自吸收效应.结果表明：电子吸收大功率加热电波能量导致了电子温度的增加,同时改变了电离层的吸收指数,引起了加热电波的自吸收效应.加热电波的自吸收效应对低电离层较高区域的电子温度扰动有重要的抑制作用.因此,随着加热频率的减小或有效辐射功率的增大,低电离层较低区域的电子温度增量明显增大而在高度100 km以上区域的电子温度增量始终较小.另一方面,随着电子温度的增加,电子的复合系数减小而电子的吸附系数增加,导致了电子密度在低电离层中较高区域出现正扰动而在较低区域出现负扰动.当饱和电子温度较大时,继续减小加热频率或增大有效辐射功率对电子密度扰动所造成的改变较小,尤其当电子温度超出复合系数和吸附系数的温度敏感区间.此外,电子温度与电子密度的饱和时间相差较大,电子温度的饱和时间为微秒量级而电子密度的饱和时间为秒量级.

     

Variations of daytime and nighttime electron temperature and heat flux in the upper ionosphere,topside ionosphere and lower plasmasphere for low and high solar activity

A database of the electron temperature (T_e) comprising of most of the available LEO satellite measurements is used for studying the solar activity variations of T_e. The T_e data are grouped for two levels of solar activity (low LSA and high HSA), five altitude ranges between 350 and 2000 km, and day and night. By fitting a theoretical expression to the T_e values we obtain variation of T_e along magnetic field lines and heat flux for LSA and HSA. We have found that T_e increases with increase in solar activity at low and mid-latitudes during nighttime at all altitudes studied. During daytime the T_e response to solar activity depends on latitude, altitude, and season. This analysis shows existence of anti-correlation between T_e and solar activity at mid-latitudes below 700 km during the equinox and winter day hours. Heat fluxes show small latitudinal dependence for daytime but substantial for nighttime.