电离层电场半年变化的模拟研究

利用一个中低纬电离层电场理论模式,模拟太阳活动低年、地磁活动平静情况下,中低纬地区电离层电场全年的变化情况。结果显示,单独计算南、北半球（去耦合）得到电离层电场具有明显的周年变化特征,且两个半球电场的相位相差半年左右。而同时计算南、北半球（计及耦合）时,电场则是以半年变化为主,且这种半年变化的幅度和相位随地方时和地磁纬度有变化。提出一个南、北半球耦合电路的简单物理模型给予解释。电路模型初步计算发现,即使两个半球电离层电场分别具有周年变化,只要它们变化的幅度相当,相位相差半年左右,由于跨越南北半球磁力线的耦合效果,耦合的电离层电场会产生明显的半年变化分量。由于缺少连续的电离层电场观测资料,将模拟结果与Richmond基于非相干散射雷达数据建立的经验模式（ISR Model）相比较,结果符合较好。     

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.     

Determination of orbital drag perturbations caused by atmospheric effects

Atmospheric perturbations of the elements of the artificial satellites orbits are determined using a special model of distribution and variations of the total density of the upper atmosphere between 200–500 km. The model includes diurnal and semi-annual density variations, variations with solar activity and geomagnetic index and latitudinal changes. The height profile is expressed by multiple exponential functions. The equations of motion are solved analytically.     

Large-scale circulation of atomic oxygen in the upper mesosphere and lower thermosphere

The variability of the atomic oxygen green line airglow at 557.7 nm, originating from the O(¹S) level, has a long history of observation. Only recently, global observations of the oxygen airglow, interpreted with the help of global circulation models have provided some understanding. Satellite observations of winds and temperatures clearly demonstrate the dynamical influence of tides on the daily variations. Both annual and semi-annual components of the variation have been identified as occurring over the course of the year. From the large-scale circulation of the atmosphere one expects downwelling in the winter at high latitudes, causing enhanced atomic oxygen and enhanced airglow while the opposite is expected in summer. In the present investigation a search is made for this large-scale signature using data from the WIND Imaging Interferometer on the Upper Atmosphere Research Satellite, model results from the Thermosphere–Ionosphere–Mesosphere-Electrodynamics-Global Circulation Model, and earlier published results. A well-defined semi-annual variation of emission rate is found in the tropics, apparently the result of the semi-annual variation of the diurnal tide. Annual and semi-annual patterns are found at mid-latitudes, in satellite and model data, while ground-based observations detect only an annual variation, with a maximum in the autumn. At still higher latitudes the fall peak persists, but with a deep depletion of atomic oxygen in the springtime; this appears to be the signature of the large-scale circulation.     

The solar cycle variation of plasma parameters in equatorial and mid latitudinal areas during 2005–2010

Based on the ISL data detected by DEMETER satellite, the solar cycle variation in electron density (Ne) and electron temperature (Te) were studied separately in local daytime 10:30 and nighttime 22:30 during 2005–2010 in the 23rd/24th solar cycles. The semi-annual, annual periods and decreasing trend with the descending solar activity were clearly revealed in Ne. At middle and high latitudes, there exhibited phase shift and even reversed annual variation over Southern and Northern hemisphere, and the annual variation amplitudes were asymmetrical at both hemispheres in local daytime. In local nighttime, the annual variations of Ne at south and north hemispheres were symmetrical at same latitudes, but the annual variation amplitudes at different latitudes differed largely, showing obviously zonal features. As for Te, the phase shift in annual variations was not as apparent as Ne with the increase of latitudes at Southern and Northern hemisphere in local daytime. While in local nighttime the reversed annual variations of Te were shown at low latitudinal areas, not at high latitudes as those in Ne. The correlation study on Ne and Te illustrated that, in local daytime, Ne and Te showed strong negative correlation at equator and low latitudes, but during the solar minimum years the correlation between Ne and Te changed to be positive at 25–30° latitudes in March 2009. The correlation coefficient R between Ne and Te also showed semi-annual periodical variations during 2005–2010. While in local nighttime, Ne and Te exhibited relatively weak positive correlation with R being about 0.6 at low latitudes, however no correlation beyond latitudes of 25° was obtained.     

Periodic and aperiodic ozone variations in the middle and upper stratosphere

Umkehr, ozonesonde and satellite observations were used to determine the height/latitude distribution of the amplitude and phase of the periodic components of the variation of the ozone mixing ratio in the middle and upper stratosphere. The amplitude of the first (annual) harmonic is small in the subtropics and increases to a maximum at polar latitudes. It also increases with height in the mid and upper stratosphere to an apparent maximum just below the stratopause. The second (semi-annual) harmonic has an amplitude that is largest in tropical regions and in subpolar regions at a level of about 40 km. There seems to be very little ozone variation above 30 km with dominant periods close to the quasi-biennial period of total ozone observed in the tropics. The percent of the total variance of the ozone mixing ratio accounted for by the first harmonic is larger than 60 percent at all heights from 20° – 60° latitude in both hemispheres (except near 40 km in the Northern Hemisphere). The percent of the total variance accounted for by the second harmonic is maximum at a height of about 40 km in the tropics and at subpolar latitudes where, as mentioned, its amplitude is also largest.The phase of the first harmonic shows a marked transition from a winter/spring maximum below 30 km to a summer maximum at 30 km, changing rapidly to a maximum in winter in both hemispheres. The regions of minimum amplitude of the annual variation and the marked phase shifts with height both indicate the separation by levels of the dominant physical control mechanisms on the periodic changes of the ozone mixing ratio in the middle and upper stratosphere. Changes below 30 km respond primarily to dynamic influences in the lower stratosphere while above 30 km the periodic variations result mainly from photochemical processes. Above 40 km these variations are strongly temperature dependent.     

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 global,hemispheric and regional electron content variations during the solar cycles 23 and 24

We present the results of study on the variations of ionospheric total electron content (TEC) by using global, hemispheric, and regional electron contents computed from the global ionospheric maps (GIMs) for the period from 1999 to 2020. For a low and moderate solar activity, the global and regional electron contents vary linearly with solar 10.7 cm radio flux and EUV flux. While a saturation effect in the electron content verses EUV and F10.7 is found during the high solar activity periods at all regions, the maximum effect is observed at low-latitudes followed by high and mid-latitudes region. The extent of saturation effect is more pronounced for F10.7 as compared to EUV. A wavelet transform is applied to global and hemispheric electron contents to examine the relative strength of different variations. The semi-annual variations dominate in the northern hemisphere, whereas annual variations dominate in the southern counterpart. The amplitude of annual variations in southern hemisphere is found to be higher than northern counterpart at all latitudes. This asymmetry in the amplitude of annual variation is maximum at low-latitudes, followed by mid and high-latitudes, respectively. The semi-annual variations are in-phase in both hemisphere and follow the solar cycle. The northern hemisphere depicts relatively large amplitude of semi-annual variations and exhibit the maximum effect at high-latitudes.     

北京地区大气温度及重力波活动的季节变化

利用瑞利激光雷达观测数据,分析了北京地区35~70km高度范围内大气温度和重力波活动的季节变化.发现北京地区30~70km高度范围内的大气温度有明显的年周期变化：平流层顶最高温度出现在6,7月份,大约为270K;中间层70km高度最低温度也出现在6,7月份,大约为200K.以2014年10月14日晚数据为例,分析重力波势能密度,发现50km以下重力波势能存在耗散,而在50km以上重力波近乎无耗散地向上传播.通过对比35~50km高度范围内的平均势能密度,对北京地区重力波活动强弱的季节变化进行了研究.研究结果表明,北京上空重力波活动强度具有明显的年周期变化,冬季平均势能密度为18J·kg^-1,夏季为8J·kg^-1,且冬季重力波活动强度约为夏季的两倍.此外,还分析了春夏秋冬四个季节重力波势能密度随高度的变化.结果表明,不同季节和不同高度的重力波势能密度不同.     

基于激光测距的飞艇净重在线计算方法研究

通过对三维建模软件CATIA中的飞艇副气囊模型进行切片分割,获得了不同副气囊高度下的对应体积值,使用最小二乘法建立了副气囊中心点高度与副气囊体积的三次曲线拟合公式,采用相位式激光测距仪对副气囊中心高度测量,使用该公式可以估算出副气囊的实时体积大小,从而推算飞艇净重大小,掌握飞艇的压力高度和起降能力。使用某次飞行试验对副气囊高度测量的数据计算出的飞艇净重值,与多次地面称重数据一致性较好,验证了使用激光测距仪对大型飞艇净重进行在线评估的可行性,并使用该方法对某飞艇某次飞行试验过程中的净重进行了分析,对飞艇的压力高度进行了核算。     

基于激光测距的飞艇净重在线计算方法研究

通过对三维建模软件CATIA中的飞艇副气囊模型进行切片分割,获得了不同副气囊高度下的对应体积值,使用最小二乘法建立了副气囊中心点高度与副气囊体积的三次曲线拟合公式,采用相位式激光测距仪对副气囊中心高度测量,使用该公式可以估算出副气囊的实时体积大小,从而推算飞艇净重大小,掌握飞艇的压力高度和起降能力。使用某次飞行试验对副气囊高度测量的数据计算出的飞艇净重值,与多次地面称重数据一致性较好,验证了使用激光测距仪对大型飞艇净重进行在线评估的可行性,并使用该方法对某飞艇某次飞行试验过程中的净重进行了分析,对飞艇的压力高度进行了核算。     

倾斜轨道小卫星太阳高度角分析与机动方案设计

针对倾斜轨道小卫星必然会面对的光学姿态敏感器受阳光干扰的问题,分析太阳高度角的变化规律,提出了计算太阳高度角的经验公式,并在此基础上提出了平台偏航姿态机动方案,可以使光学姿态敏感器规避阳光干扰,并可以简化整星热控和帆板驱动设计,提高了整星的可靠性.     

Geometry of the “exponential” middle ionosphere

The required numbers of exponential sections fitting an electron density profile between the E- and F-layer peak heights of the ionosphere are considered. The range of the scale height variation and the angles of slope of the F region sub-peak profile are obtained under the different solar-geophysical conditions.     

电离层等离子体主动释放试验研究

等离子体主动释放试验是空间物理研究的一种主动、有效手段. 2013年4月中国科学院空间科学与应用研究中心在海南进行了中国第一次空间等离子体主动释放试验. 探空火箭在190 km高度释放了近1 kg碱金属钡, 形成一团由钡原子和钡离子组成的云团. 利用地面光学观测手段, 记录了钡云从释放初期到末期的演化全过程, 获取了钡云亮度、粒子密度、成分及扩散范围随时间的变化规律. 通过对钡云漂移的研究, 得到低纬度地区释放点处电离层的中性风场特性, 其分析结果对于研究低纬度地区电离层动力学特性具有一定指导意义.     

The low and middle latitude semi-annual anomaly in NmF2 near noon: A statistical study

Hourly values of the F2-layer peak density, NmF2, measured by 99 ionosonde stations near noon from 1957 to 2010 at low and middle geomagnetic latitudes of the northern and southern geographic hemispheres are used in a statistical study of the F2-region semi-annual anomaly. The equinox/winter and equinox/summer geomagnetically quiet NmF2 ratios, X and Y, taken near noon over each ionosonde for approximately the same winter, equinox, and summer solar activity conditions are analyzed. The conditional probabilities of occurrences of X and Y in intervals of X and Y, the most frequent values of X and Y, the mean expected values of X and Y, and the conditional probability to observe the F2-region semi-annual anomaly are calculated and studied for the fist time for low, moderate, and high solar activity conditions. These statistical parameters are averaged over 5° geomagnetic latitude interval in the northern and southern geographic hemispheres, and the trends in these averaged statistical characteristics of the NmF2 semi-annual anomaly are calculated and studied for the fist time. It is shown that the median approach can produce the incorrect conclusions about the absence of the NmF2 semi-annual anomaly.     

Study the behavior of the ionospheric frequencies at Karachi during three consecutive solar minima of cycle 21, 22 & 23 and their comparison with IRI-2016

The behavior of critical frequencies of ionospheric E and F2 layers (foE & foF2) along with minimum ionospheric frequency (fmin) is studied for solar minima of cycle 21 (1986), 22 (1996) and 23 (2008) over Karachi (24.95$°$N, 67.13$°$E), Pakistan. The station is located at the crest of equatorial ionization anomaly region. Beside seasonal differences, pronounced change in the values of frequencies is noted from one solar minimum to another solar minimum. A strong and direct correlation of foF2 with Smoothed Sunspot Number (SSN) and F10.7?cm solar flux is observed. In the minimum of cycle 23, reduction in foF2 is noted due to reduction of solar EUV as compared to other minima. Also disappearance of semi-annual variations in foF2 is noted in cycle 23 minimum. Unexpectedly higher values of foE and fmin are observed in minimum of cycle 23 as compared to other minima. It is difficult to explain this unusual behavior of fmin and foE along with disappearance of semi-annual variation in foF2. It is possible that during very low solar activity, thermospheric conditions are changed which in turn altered the ionosphere. Further investigation of atmosphere-ionosphere coupling is required to understand this complex behavior. On comparison of observed values with IRI-2016, higher deviations are observed in foE before noon hours while in case of foF2, large deviations are noted during daytime. The absence of foF2 semi-annual variation in cycle 23 is not reproduced by IRI-2016. It is suggested that IRI-2016 need some modification for extremely low solar activity condition.     

利用曙暮气辉光度观测研究钠层

通过对钠原子曙暮气辉的18次观测确定了北京北郊上空不同季节钠原子气柱总含量和钠层重心高度等结构参数。结果表明:春夏季钠层重心位置高,秋冬季位置低.冬季观测的平均钠层重心高度为85.67公里;钠原子气柱总含量冬季明显高于其它季节,1月和12月的含量约为6月的7.5倍;冬季钠层也相对地厚.钠层重心高度及总含量的季节变化不仅受D层顶中性和离子化学的制约,而且受到垂直风及子午向或纬向环流的很大影响.     

一氧化氮冷却率的变化及其作用

利用最新的NO经验公式,计算了近两个太阳活动周期100-200km间NO的冷却率,研究了太阳和地磁活动对NO和O冷却率的影响。进一步证明了NO冷却是120km以上热层的主要冷却过程。     

Quality Assessment of the IDS Contribution to ITRF2008

Doppler Orbitography Radiopositionning Integrated by Satellite (DORIS) is one of the four fundamental techniques contributing to the ITRF. The optimal coverage over the globe of the DORIS observing sites and sites co-located with GPS, allow a strong embedding of DORIS within the ITRF network. DORIS contributes to the access to ITRF through precise orbit determination of altimetric satellites with onboard DORIS receivers. The DORIS contribution to the ITRF2008 is enhanced by the fact that the solutions of seven analysis centers were included in the submitted combined time series of weekly station positions and daily polar motion. We evaluate the quality of the DORIS combined solution in terms of its agreement with the other techniques (VLBI, SLR, GPS) contributing to the ITRF2008 combination. We show in particular that the precisions of the current IDS products range between 1.5 to 2.6 mm for station positions (at the epochs of minimum variances); better than 1 mm/yr in velocities and between 170 and 260 micro-arc-seconds for polar motion, a significant improvement by a factor of three to five, compared to past data used in the ITRF2005 combination. This improvement is certainly due to improved analysis strategies employed by the seven IDS analysis centers that contributed to the combined weekly submitted solutions of station positions and polar motion. A spectral analysis of DORIS station height time series indicates that annual and semi-annual signals are dominant. However, TOPEX draconitic period of about 118 days is still detected in about 20% of the station position power spectra. DORIS height annual signals correlate well with GPS annual signal estimated at some co-located stations, which show that DORIS technique is able to detect loading signals.