Ionospheric perturbations in plasma parameters before global strong earthquakes

Based on the electron density (Ne) and temperature (Te) data from DEMETER, the ionospheric perturbations before 82 Ms ? 7.0 earthquakes (EQs) during 2005–2010 were studied, using moving median and space difference methods within 10 days before and 2 days after these events in local nighttime. It was found that the plasma parameters disturbances appeared before 49 EQs, in which more disturbances were detected before shallow-focus earthquakes than deep ones, and there was little difference between continental and oceanic ones, both exceeding 1/2 percentage. For the disturbed time, more perturbations were seen in 1, 3, 5, 6, 8 days before EQs and 1 day after EQs. For the spatial distribution, the anomalies before EQs were not just above the epicenters, but shifted equatorward with several degrees to almost twenty degrees. Most of the abnormities were positive ones, which demonstrate that Ne increases before EQs at the altitude of 670 km of DEMETER. Perturbations of Ne were more than that of Te, which illustrates that Ne is much more sensitive to seismic activity than Te.     

Statistical analysis of the ionospheric ion density recorded by DEMETER in the epicenter areas of earthquakes as well as in their magnetically conjugate point areas

Results of a statistical variation of total ion density observed in the vicinity of epicenters as well as around magnetically conjugated points of earthquakes are presented in this paper. Two data sets are used: the ion density measured by DEMETER during about 6.5?years and the list of strong earthquakes (M_W?≥?4.8) occurring globally during this period (14,764 earthquakes in total). First of all, ionospheric perturbations with 23–120?s observation time corresponding to spatial scales of 160–840?km are automatically detected by a software (64,287 anomalies in total). Second, it is checked if a perturbation could be associated either with the epicenter of an earthquake or with its magnetically conjugated point (distance?<?1500?km and time?<?15?days before the earthquake). The index Kp?<?3 is also considered in order to reduce the effect of the geomagnetic activity on the ionosphere during this period. The results show that it is possible to detect variations of the ionospheric parameters above the epicenter areas as well as above their conjugated points. About one third of the earthquakes are detected with ionospheric influence on both sides of the Earth. There is a trend showing that the perturbation length increases as the magnitude of the detected EQs but it is more obvious for large magnitude. The probability that a perturbation appears is higher on the day of the earthquake and then gradually decreases when the time before the earthquake increases. The spatial distribution of perturbations shows that the probability of perturbations appearing southeast of the epicenter before an earthquake is a little bit higher and that there is an obvious trend because perturbations appear west of the conjugated point of an earthquake.     

Wave-like perturbations in the ionospheric F2-layer observed after the Ms8.1 Samoa earthquake of September 29, 2009

A study of the critical frequency foF2 variations after the large earthquake (M_s = 8.1) which occurred on 29 September, 2009 in the region of Samoa Islands in the Pacific Ocean is carried out using data of the ionospheric station of Kwajalein. The epicenter of the earthquake was located at about 184 km southwest from Apia (the capital of West Samoa). It was found that wave-like perturbations of foF2 were observed for ∼3 h above the station (located approximately 3560 km northwest from the epicenter). The amplitude of the disturbance was as large as ∼20% of the average magnetic quiet day foF2 values. A comparison of the observed perturbations of foF2 with the ones detected at Stanford ionospheric station after the Alaska earthquake of 28 March 1964 (M_s = 8.4) showed a close similarity of the wave-like perturbations of foF2 in both cases.     

Solar MHD Waves and Solar Neutrinos

We analyze here how solar neutrino experiments could detect time fluctuations of the solar neutrino flux due to magnetohydrodynamics (MHD) perturbations of the solar plasma. We state that if such time fluctuations are detected, this would provide a unique signature of the Resonant Spin-Flavor Precession (RSFP) mechanism as a solution to the Solar Neutrino Problem. This revised version was published online in August 2006 with corrections to the Cover Date.     

高精度重力场下回归轨道半解析优化设计

为解决太阳同步回归轨道的标称设计问题,提出一种基于高精度重力场的半解析优化方法。建立地球非球形引力摄动阶数为J15 的高精度重力场解析模型,并分离出引力摄动的长期项和长周期项。构建回归轨道从半长轴到平交点周期的对应关系,平交点周期变化随引力摄动阶数的提高而逐渐收敛。通过微分修正迭代算法所确定的半长轴相对于传统J2摄动模型的半长轴确定值具有更高的精度和更好的稳定性。考察摄动短周期项影响下的密切交点周期,结果表明其受初始位置(平近点角)影响较大,变化范围为0.015s,并由此给出精确回归轨道优化设计的基准：不同的初始位置上满足星下点轨迹严格回归的半长轴期望值。     

气/液界面上Richtmyer-Meshkov不稳定性的实验研究

报道了在国内首次实现的矩形激波管内气/液界面上(即Atwood number,A1)的Richtmyer-Meshkov(RM)不稳定性现象.实验在一台垂直矩形激波管中进行,得到了较低马赫数(M=1.36和1.58)下,多元扰动R-M不稳定性后期阶段气泡和尖钉高度对时间的增长规律,即气泡高度hb~t0.55±0.01,尖钉高度hs~t.当激波马赫数从1.36增加到1.58时,气泡和尖钉高度对时间的指数规律没有发生明显改变,气泡的增长速度没有受到影响,而尖钉增长速度却有大幅度的增加.同时还观察研究了多元扰动R-M不稳定性中典型的气泡竞争现象.     

The flyby anomaly: A case for strong gravitomagnetism?

In the last two decades an anomalous variation in the asymptotic velocity of spacecraft performing a flyby manoeuvre around Earth has been discovered through careful Doppler tracking and orbital analysis. No viable hypothesis for a conventional explanation of this effect has been proposed and its origin remains unexplained. In this paper we discuss a strong transversal component of the gravitomagnetic field as a possible source of the flyby anomaly. We show that the perturbations induced by such a field could fit the anomalies both in sign and order of magnitude. But, although the secular contributions to the Gravity Probe B experimental results and the Lense–Thirring effect in geodynamics satellites can be made null, the detailed orbital evolution is easily in conflict with such an enhanced gravitomagnetic effect.     

Ariane 5 GTO debris mitigation using natural perturbations

GTO objects can potentially collide with operative satellites in LEO and GEO protected regions. Internationally accepted debris mitigation guidelines require that these objects exit these protected regions within 25?years, e.g. by re-entering and burning up in Earth’s atmosphere. In this paper, an inventory of the GTO debris generated from Ariane 5 launches in the period 2012–2017 is provided, and it is expected that none of these objects will re-enter within 25?years. For future launches, natural perturbations can be exploited to increase compliance with mitigation guidelines without the use of extra propellant or complex de-orbiting systems, which is attractive from an economic point of view. The lifetime of GTO objects is very sensitive to initial conditions and some environmental and body-related parameters, mainly due to the effect of solar gravity on the perigee altitude. As a consequence, the lifetime of a specific GTO object cannot be predicted accurately, but its probability of re-entering in less than 25?years can be estimated with proper accuracy by following a statistical approach. By propagating the orbits of over 800,000 simulated Ariane 5 GTO objects, it was found that the launch time leading to the highest probability of compliance with debris mitigation guidelines for GEO launches from Kourou corresponds to about 2 PM local time, regardless of the date of launch, which leads to compliance rates ranging from 60 to 100%. Current practice is to launch at around 5–9?PM, so a change in procedures would be required in order to reach a higher degree of compliance with debris mitigation guidelines, which was predicted to be on average below 20% for the objects generated in the period 2012–2017.     

All-sky-imaging capabilities for ionospheric space weather research using geomagnetic conjugate point observing sites

Optical signatures of ionospheric disturbances exist at all latitudes on Earth—the most well known case being visible aurora at high latitudes. Sub-visual emissions occur equatorward of the auroral zones that also indicate periods and locations of severe Space Weather effects. These fall into three magnetic latitude domains in each hemisphere: (1) sub-auroral latitudes ～40–60°, (2) mid-latitudes (20–40°) and (3) equatorial-to-low latitudes (0–20°).Boston University has established a network of all-sky-imagers (ASIs) with sites at opposite ends of the same geomagnetic field lines in each hemisphere—called geomagnetic conjugate points. Our ASIs are autonomous instruments that operate in mini-observatories situated at four conjugate pairs in North and South America, plus one pair linking Europe and South Africa. In this paper, we describe instrument design, data-taking protocols, data transfer and archiving issues, image processing, science objectives and early results for each latitude domain. This unique capability addresses how a single source of disturbance is transformed into similar or different effects based on the unique “receptor” conditions (seasonal effects) found in each hemisphere. Applying optical conjugate point observations to Space Weather problems offers a new diagnostic approach for understanding the global system response functions operating in the Earth’s upper atmosphere.