低轨航天器弹道系数估算及热层大气模型误差分析

利用低轨（LEO）航天器在轨期间两行轨道根数（TLEs）数据,结合经验大气密度模型NRLMSISE00,反演计算得到其在轨期间的弹道系数B’,以31年B’的平均值代替弹道系数真值,分别通过标准球形目标卫星对比以及物理参数基本相同的非球形目标卫星对比,对弹道系数真值进行了检验;利用不同外形目标卫星弹道系数在不同太阳活动周内的变化规律,结合太阳和地磁活动变化,估计经验大气密度模型的误差分布. 结果表明,利用反演弹道系数31年的平均值来代替真值,其在理论值的正常误差范围内;大气密度模型误差在210～526km高度范围内存在相同的变化趋势,且模型误差随高度增加而增大;在短周期内B’变化与太阳活动指数F_10.7存在反相关性;密度模型不能有效模拟2008年出现的大气密度异常低. 以上结果表明,经验大气密度模型结果需要修正,尤其是在太阳活动峰年和谷年,此外,磁暴期间模型误差的修正对卫星定轨和轨道预报等也具有重要意义.      

Semi-empirical model of middle atmosphere wind from the ground to the lower thermosphere

During recent years, special attention has been paid to understanding the background circulation of the middle atmosphere. Particularly in the mesosphere/lower thermosphere (MLT) region, this has involved including data from a range of new radar measurements. It has also involved the comparison of existing empirical middle atmosphere wind models, such as CIRA-86 and HWM-93 to the new data. This has led to the construction of empirical models of MLT winds such as the Global Empirical Wind Model (GEWM). Further investigations are aimed at the construction of new empirical and semi-empirical wind models of the entire middle atmosphere including these new experimental results. The results of a new wind climatology (0–100 km) are presented here, based upon the GEWM, a reanalysis of stratospheric data, and a numerical model which is used to fill the gap between data from the stratospheric and MLT regions.     

Recent advances in upper atmospheric structure

A possible quantitative explanation of the semi-annual variation in thermospheric density has been obtained in terms of a semi-annual variation in the computed globally averaged vertical energy carried by propagating tides from the lower and middle atmosphere into the thermosphere. The effect is primarily due to seasonal changes in the distribution of water vapor and in the solar declination angle and Sun-Earth distance. An MSIS-83 empirical model of the thermosphere, representing a revision of the earlier MSIS models, has been prepared. The database used covers a wider range of solar activity than previous models and an improved magnetic storm representation is included. Atomic oxygen profiles in the 100 to 160 km altitude region of the auroral thermosphere have been recalculated from measured quenching of N₂(A³∑_u⁺) using the latest laboratory rates and the results are in good agreement with the mean CIRA 1972 profile. A new empirical model of thermospheric variations with geomagnetic activity has been developed incorporating variations with local magnetic time, latitude dependent terms which can vary with the magnitude of the geomagnetic disturbance, and an altitude dependent expression for the equatorial wave. A new index ML, derived from the AL index, has been developed that appears to have promise to represent the variations of thermospheric species with geomagnetic activity. Satellite measured values of solar UV flux, ground-based observations of CaK plages, sunspot numbers and 10.7 cm solar radio flux have been analyzed for temporal variations. Some differences have been identified and the significance to empirical and theoretical upper atmosphere models is discussed.     

Climatology of extreme upper atmospheric heating events

We use a trio of empirical models to estimate the relative contributions of solar extreme ultraviolet heating, Joule heating and particle heating to the global energy budget of the earth’s upper atmosphere. Daily power values are derived from the models for the three heat sources. The SOLAR2000 solar irradiance specification model provides estimates of the daily extreme EUV solar power input. Geomagnetic power comes from a combination of satellite-derived electron precipitation power and an empirical model of Joule power derived from hemispherically integrated estimates of high-latitude heating, which we discuss in this paper. From 1975 to mid-2002, the average daily contributions were electrons: 51 GW, Joule: 95 GW and solar: 784 GW. Joule and particle heating combine to provide more than 17% of the total global upper atmospheric heating. For the top 10% and 1% of heating events, contributions rise to 20% and 25%, respectively. In the top 15 heating events, geomagnetic power contributed more than 50% of the total power budget. During three events, the Joule power alone exceeded solar power.     

A global empirical orthogonal function model of plasmaspheric electron content

Based on the method for establishing a global plasmaspheric model using observations from COSMIC and MetOp-A orbit determination GNSS receivers, Chen et al. (2017) obtained a global plasmaspheric total electron content product with a spatial resolution of 2.5° × 5° and a time resolution of 4 h. In this paper, we use those global plasmaspheric electron content product in 2008, 2010, 2011, 2012, 2014 for 1446 days to establish a global plasmaspheric empirical model based on empirical orthogonal function (EOF). The model can well characterize the spatiotemporal variation of plasmaspheric electron content (PEC) and the influence of solar radiation on it. Only the first four orders of EOF sequences can characterize the 98.43% features of the original PEC dataset. The principal component coefficient Pk is decomposed twice during modeling, and the combination of trigonometric function and linear function is used to model Pk to characterize the solar cycle, annual cycle, semi-annual cycle and quarter-cycle variation. We compare the PEC model values with the actual observation data, the results show that the empirical PEC model values are highly correlated with the actual observations. The correlation between the two is above 0.96, and the RMS maximum of the difference between the PEC model values and the observed values are 0.70 TECU, and the average of the difference between the PEC model values and the observed values are −0.18 TECU, respectively. In addition, we validate the reliability of the global plasmaspheric model established by two empirical orthogonal function decomposition method using actual observation data, according to the global distribution of the differences between the PEC model values and the observed values in low solar activity and high solar activity, it can be seen that under low solar activity and high solar activity conditions, the model has good adaptability.     

Thermospheric storm effects

A brief review is given of our current understanding of the atmospheric perturbations in the thermosphere and exosphere that are related to geomagnetic disturbances and of current efforts to represent these in empirical models of the upper atmosphere. A particular model, based on ESRO4 mass spectrometer observations of neutral composition and density, is presented in detail. This model gives the effects on the principal constituents of the upper atmosphere as a function of the geomagnetic coordinates and the K_p geomagnetic index. It is a modification of an earlier model, the most important difference being the inclusion of the variation with magnetic local time.     

The effect of surface reflection function and of atmospheric parameters on the shortwave radiation budget

Errors in the determination of the shortwave radiation budget from broadband satellite measurements at the top and at the bottom of a cloudless atmosphere due to uncertainties of the actual parameters of the atmosphere and the surface are derived by computer modelling. The model uses measured bidirectional reflectance functions and realistic values of the optical parameters of the atmosphere. Examples are presented which show the range of such uncertainties. Neglecting the anisotropy of the reflection function of land surfaces results in high uncertainties of the shortwave radiation budget, both at the top and the bottom of the atmosphere. The uncertainties caused by actual uncertain atmospheric parameters are low if data of the meteorological network are properly used.     

太阳10.7cm射电流量中期预报模型研究(Ⅰ)

采用时间序列模型中的自回归方法开展了F_(10.7)中期预报研究.预报试验和误差分析结果表明,在太阳活动水平较低、F_(10.7)的27天周期性明显时自回归预报方法的预报精度高,具有较为理想的预报效果,但在日面有大活动区产生和消亡时预报效果不理想.这说明时间序列模型中的自回归方法能够较好地反映太阳F_(10.7)的27天周期性特征,对F_(10.7)中期预报模型的建立有一定适用性.通过对2005年9月21日至2007年6月7日期间预报结果的比较可以看出,自回归分析方法预报的精度与美国空军预报的相当。     

How to address the accuracy of empirical magnetic field models?

Empirical magnetic field models are compared with high-altitude magnetic field measurements and results from an MHD simulation. Comparison of the T96 model and observations from GOES-8 and GOES-9 shows that if the observed solar wind and IMF parameters are used to compute the model field, the model field is more stretched than the observed field. On the other hand, if measurements made by one spacecraft are used to find the model parameters that give a best-fit field at that location, the RMS error can be reduced also at the other spacecraft four hours away in local time. Comparison of T96 model and MHD simulation results shows that the empirical models have a thinner current sheet than the MHD simulation, but that the lobe field values are quite similar to each other. Furthermore, a comparison of an event-oriented, modified T89 model and MHD simulation by Pulkkinen et al. [2000] reveals that if the empirical model is constructed by fitting to in-situ measurements, the resulting model is very similar to the MHD simulation magnetic field. These results indicate that an efficient method of utilizing the present-day empirical models is to select model parameters based on measurements from a few individual points.     

基于神经网络的磁平静期赤道电集流预测

利用BP神经网络技术分别对2008年后磁平静期印度扇区、秘鲁扇区以及CHAMP卫星的赤道电集流(EEJ)变化进行预测,其中神经网络训练数据为对应的2000-2007年磁平静期EEJ观测数据,输入参量为天数、地方时、太阳天顶角、太阳活动指数(F10.7)、太阴时以及卫星地理经度,输出参量为EEJ.对EEJ预测结果进行了统...     

火星进入的气动力特性预测模型分析

火星大气环境对飞行器进入带来了新的挑战,气动力预测是首先需要解决的问题.针对火星探测器的高超声速进入问题,利用三维并行程序求解流体力学Navier-Stokes方程,分别考虑真实气体模型和完全气体模型,分析模型及参数对气动力特性预测的影响,旨在得到准确、高效和可靠的火星进入器气动力特性预测模型.采用真实气体模型对海盗号进行了沿飞行轨道的数值模拟,气动力特性预测结果与飞行数据一致,验证了火星大气热化学模型及数值方法.分别采用真实气体模型和完全气体模型对海盗号升力式进入和探路者号零攻角进入进行了气动力特性预测,结果表明采用等效比热比的完全气体模型的预测值非常接近真实气体模型,偏差均在1%左右,配平攻角相差约0.4°,来流比热比模型的气动力特性预测值偏差很大.火星进入器的气动力预测建议采用真实气体模型和等效比热比完全气体模型.      

Empirical model of cosmic ray spectrum in energy interval 1 MeV–100 GeV during 11-year solar cycle

The galactic cosmic rays (GCR) are the main ionization source at altitude of ∼3–35 km in the atmosphere. For high latitude anomalous cosmic ray (ACR) component has also a significant influence on the atmospheric ionization. We propose an empirical model for differential spectra D(E) of galactic and anomalous cosmic rays in energy interval 1 MeV–100 GeV during solar cycle. In the model data are used which cover three solar cycles: 20, 22 and 23. The LEAP87, IMAX92, CAPRICE94, AMS98 and BESS experimental spectra for protons and alpha particles are fitted to the proposed empirical model. The modulated GCR differential spectra are compared with force-field approximation to the one-dimensional transport equation and with solutions of two-dimensional cosmic ray transport equation. For experimental spectra, the calculation of the model parameters is performed by Levenberg–Marquardt algorithm, applied to the special case of least squares. Algorithm that combines the rapid local convergence of Newton–Raphson method with globally convergent method for non-linear systems of equations is applied for theoretically obtained differential spectra. The described programmes are realized in algorithmic language C++. The proposed model gives practical possibility for investigation of experimental data from measurements of galactic cosmic rays and their anomalous component.     

基于电离层暴时f_0F_2经验模型Kalman滤波短期预报

利用时间累积地磁指数印ap(T),建立了强地磁扰动条件下电离层f0F2与月中值相对偏差经验模型.该经验模型只在春秋季节和夏季特强地磁扰动条件ap(T)>100,即时间累积地磁指数大于100时达到理想精度.尝试利用气象预报中常用的Kalman滤波方法对模型的系数进行实时修正,以提高预报精度,并对长春站1986-1995年近一个太阳周f0F2数据进行提前一小时预报试验.冬季预报均方根误差为0.76MHz,春秋季节为0.68MHz,夏季为0.61MHz.在特强地磁扰动条件下,预测误差在0.87～1.43MHz之间.该预报方法同时与包含暴时修正模型STORM的国际参考电离层IRI2001进行了比较,展示了Kalman滤波方法实时修正模型系数的能力和良好的应用前景.     

Solar EUV energy budget of the thermosphere

Using the accumulation of experimental data and theoretical studies conducted on the terrestrial thermosphere since the mid seventies, we have re-evaluated the channels by which solar UV energy is transferred to the atmosphere. As an outcome of this evaluation we have redetermined the solar EUV heating efficiency for the thermosphere and find this to be considerably different from that established in earlier studies. The heating efficiency has strong altitude, solar cycle and diurnal dependencies. The values of this parameter vary from less than 10% to greater than 100%, with peak midday values of 50–55% In recent papers we have presented the results of this new UV heating efficiency determination using a steady state solution of the ionospheric model. In this paper we present the results obtained solving a time dependent model over a diurnal cycle. The time dependent effects are found to be significant, with certain longlived species acting as temporary reservoirs of latent heat that is released to the neutral atmosphere at later times.     

Model for induced ionization by galactic cosmic rays in the Earth atmosphere and ionosphere

The ionization profiles produced by galactic cosmic rays in the Earth atmosphere and ionosphere are obtained on the basis of Monte Carlo simulations. Cascade processes in the atmosphere are simulated using CORSIKA 6.52 code with FLUKA 2006 and QGSJET II hadronic interaction subroutines. Proton induced showers are considered using a realistic atmospheric model (US Standard Atmosphere). The energy deposit from different components is taken into account, namely electromagnetic, hadron and muon components. The curvature of the atmosphere is considered in the computer code. On the basis of the computed ionization yield function the ion pair production rate in the atmosphere is obtained for different conditions and locations. The model is applicable to the entire atmosphere, from ground level to upper atmosphere. Several applications of the obtained results are discussed. The Monte Carlo simulation model considers nuclear interactions below the altitude of 35 km. It is compared with analytical–numerical electron production rate model. The latter model which takes into account the electromagnetic interactions above altitudes of 35 km has two main regions of application: above 50 km (thin target model) and between 35 and 50 km (intermediate target model). A good agreement between the CORSIKA results and analytical–numerical model results is found above altitude of 35 km.     

Validation of satellite-derived atmospheric temperature and water vapor concentration using radiosonde and rocketsonde measurements

Measurements of the spectral radiance of the earth's atmosphere from satellites can be related to the vertical structures of temperature and humidity. Derived profiles of these quantities are compared with radiosonde and rocketsonde observations, as well as with horizontal and vertical cross-sections of the atmosphere. In some regions of the atmosphere, particularly where large gradients are found, significant differences occur. A method for overcoming these by use of Typical Shape Functions is discussed. Transmittances computed from theory require modifications which are not well defined, and radiances measured from some satellite instruments disagree with computed values in ways which suggest calibration or instrument problems.     

电波折射误差的经验-分层修正算法

建立了一种新的电波折射修正算法——经验-分层电波折射修正算法。经过与电波折射误差的经验修正和分层实测指数修正方法修正效果的比较，证实了该算法效果接近分层实测指数修正方法，明显优于经验修正方法。该方法为一些不其备提供分层电波折射参数的航天测控站电波折射误差修正问题，提供了行之有效的技术手段，对航天测控工程具有应用价值。     

武汉上空对流层与平流层大气密度和温度探测的初步结果

利用武汉大学Rayleieh/钠荧光散射激光雷达和无线电探空仪进行联合探测的数据,反演出武汉地区上空(30.5°N,114.4°W)0—65km处的密度和温度分布曲线,并简单阐述了激光雷达的工作原理。将测量结果和MSISE-90参考大气模式比较,二者结果基本符合,温度廓线在中层顶附近和模式的差别约为3K。同时利用激光雷达探测到了中层大气中的重力波活动。     

Model calculations of middle atmospheric wind and temperature fields

The zonally-averaged circulation of the middle atmosphere between 10 and 110 km is calculated from a two-dimensional grid point model for steady solstice conditions. Using the temperatures of CIRA 72 in a diagnostic study of the vertical-meridional circulation we have investigated the influence of a latitude dependent static stability and the consequences of meridional temperature advection. In the summer mesopause region we found an area of subsidence which is located near the equatorward boundary of the noctilucent cloud region. In a self-consistent dynamical study we have assumed an empirical momentum source in the lower summer thermosphere in addition to the well-known Rayleigh friction to obtain an eastward zonal flow in this region.