Electromagnetic ion cyclotron resonance heating in the VASIMR

Plasma physics has found an increasing range of practical industrial applications, including the development of electric spacecraft propulsion systems. One of these systems, the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) engine, both applies several important physical processes occurring in the magnetosphere. These processes include the mechanisms involved in the ion acceleration and heating that occur in the Birkeland currents of an auroral arc system. Auroral current region processes that are simulated in VASIMR include lower hybrid heating, parallel electric field acceleration and ion cyclotron acceleration. This paper will focus on using a physics demonstration model VASIMR to study ion cyclotron resonance heating (ICRH). The major purpose is to provide a VASIMR status report to the COSPAR community. The VASIMR uses a helicon antenna with up to 20 kW of power to generate plasma. This plasma is energized by an RF booster stage that uses left hand polarized slow mode waves launched from the high field side of the ion cyclotron resonance. The present setup for the booster uses 2–4 MHz waves with up to 20 kW of power. This process is similar to the ion cyclotron heating in tokamaks, but in the VASIMR the ions only pass through the resonance region once. The rapid absorption of ion cyclotron waves has been predicted in recent theoretical studies. These theoretical predictions have been supported with several independent measurements in this paper. The ICRH produced a substantial increase in ion velocity. Pitch angle distribution studies show that this increase takes place in the resonance region where the ion cyclotron frequency is equal to the frequency on the injected RF waves. Downstream of the resonance region the perpendicular velocity boost should be converted to axial flow velocity through the conservation of the first adiabatic invariant as the magnetic field decreases in the exhaust region of the VASIMR. In deuterium plasma, 80% efficient absorption of 20 kW of ICRH input power has been achieved. No evidence for power limiting instabilities in the exhaust beam has been observed.     

Magnetospheric application of high-altitude long-duration balloon technology: Daylight auroral observations

Daylight auroral imaging is a proposed application of the NASA high-altitude long-duration balloon technology. This paper discusses the theoretical background of this application and test observations, for proof of the feasibility. It is demonstrated that nitrogen auroral emissions in the near-infrared band are detectable at altitudes of 35–40 km and above using a near-infrared InGaAs camera. The purpose of such observations is to identify auroral small-scale structures that are manifestations of auroral particle accelerations and the solar wind – magnetosphere – ionosphere interaction. Use of this new approach will enable studies of the dayside aurora, low-latitude aurora, and storm-time and substorm-time auroral conjugacy.     

Polar caps and auroral zones under idealized axisymmetric magnetic fields

The geomagnetic field, modified by the solar wind, determines the shape, area and location of polar caps and auroral zones, among other magnetosphere and upper atmosphere characteristics. Since the field varies greatly with time it is of interest to analyze polar caps and auroral zones variations linked to magnetic field variations of intensity and pattern. Polar caps and auroral zones locations and areas for various single harmonic axial field configurations are obtained analytically assuming a simple magnetopause model. As the axial degree n increases, the polar caps and auroral zones total number, given by n + 1 and 2n respectively, also increase. However, their total areas decrease from a larger value in the case of an axial dipole to a minimum for an axial octupole (n = 3), and then increase for increasing degrees. The increasing rate is much higher in the auroral zones case to the point that it exceeds the dipolar value at n = 5 while in the polar caps case this occurs at n = 8. The absolute latitudes of the auroral zones and polar caps that reside around the geographical poles increase with axial degree. Our results represent an end-member case of the evolution of auroral zones and polar caps during polarity reversals if the transition involves axial dipole energy cascade to higher axial degrees. Evidence for such an energy transfer is found in the historical record of the geomagnetic secular variation.     

Kappa distribution functions and the main properties of auroral particle acceleration

The problem of auroral particle acceleration is analyzed taking into account the filling of the magnetosphere by accelerated particles of ionospheric origin and the trapping of particles between the magnetic and electrostatic barriers. It is taken into account that kappa distributions describe experimentally measured distribution functions better than do maxwellians. The existence of conjugate field-aligned potential drops in the north and south hemispheres is suggested. Field-aligned potential drops are formed if the value of field-aligned current is higher than the threshold determined by the free gazodynamic flow of electrons along field lines. Results of experimental observations showing the possibility of field-aligned potential drop concentration in double layers are summarized. The theory of kinetic double layers is developed taking into account the nonmaxwellian forms of distribution functions. It is shown that the kinetic treatment and the existence of nonmaxwellian distributions lead to real changes in the criteria required for double-layer formation.     

反向赤道电集流与磁层扰动

对印度Trivandrum站第21太阳活动周内地磁H分量分析表明,不仅在磁扰日及其随后的静日内,强磁扰对赤道电集流有显着作用,即使在持续静日期间,较弱的磁扰仍然对赤道电离层有很大影响。磁静日昏侧出现反向(西向)电集流是正常现象,弱磁扰是使此反向电流消失的可能机制。      

反向电集流出现率与大气准两年振荡

本文分析印度Trivandrum地磁台的约两个太阳黑子周期的地磁场水平分量小时值。在部分地消除了太阳黑子周期及一年周期变化后,发现了反向电集流出现率的QBO调制现象:QBO东风相反向电集流出现率增加;QBO西风相反向电集流出现率减小。据此讨论了反向电集流的形成机制,认为大气行星波在其上传过程中与太阳半日波或太阴半日波的相互作用,有可能导致两种半日波的放大和相位移动,并最终导致反向电集流的出现。      

Variations of equatorial electrojet as possible seismo-ionospheric precursor at the occurrence of TEC anomalies before strong earthquake

The measurements of GPS signal delays show that the local areas of increased/decreased Total Electron Content (TEC) of the ionosphere can be observed before strong earthquakes. The main possible cause of these TEC disturbances is the vertical plasma drift under the action of zonal electric field. The spatial pattern of electric potentials for such electric field was proposed. The model calculations were done to investigate the efficiency of the proposed mechanism. The calculation results revealed the agreement with TEC variations observed before strong earthquakes and showed that the equatorial electrojet variations can be considered as precursors of earthquakes.     

ICME期间磁暴的太阳风参数和极光沉降能量

基于1995-2004年ICME驱动的强烈磁暴(SA型)、强磁暴(SB型)和延迟型主相暴(SC型)三种磁暴类型,对1AU处太阳风动压、太阳风速度、行星际磁场、EK-L电场以及极光沉降能量进行时序叠加分析,并分别与-vBz耦合函数和Newell耦合函数进行对比.结果表明,三种磁暴在ICME到达前期的太阳风动压较稳定,背景太阳风、极光沉降能量、行星际磁场和磁层存在相对平静期. ICME到达前期SA型磁暴的背景太阳风速度、行星际磁场南向分量以及极光沉降能量的均值高于另外两种磁暴类型,这说明大型日冕物质抛射在ICME到达前就对行星际磁场、背景太阳风和HP产生了影响.磁暴急始后,SC型磁暴的EK-L电场斜率小,峰值延后且行星际磁场北向分量增强,这些都是磁暴主相延迟的表现,极光沉降能量随着行星际磁场转为南向而增加.     

利用BP神经网络预测AE指数

采用的预报模式是一种全连接的BP网络模型,利用太阳风及行星际磁场的观测数据预报AE指数.神经网络输入选用ACE卫星数据,取5 min平均值,通过比较,选用4个预报参量.构造了预报参量时续为20 min,40 min和60 min依次递增的三个网络,分别进行训练和预测,并对行星际参量对AE指数影响的时续性进行了探讨.预报结果表明,全连接BP神经网络在AE指数的短期预报中是比较有效的,同时还提出了需要进一步改进的环节.      

Variation of F-region critical frequency (foF2) over equatorial and low-latitude region of the Indian zone during 19th and 20th solar cycle

The effect of solar cycle and seasons on the daytime and nighttime F-layer ionization has been investigated over the equatorial and low-latitude region during 19th (1954–1964) and 20th (1965–1976) solar cycle. The F-layer critical frequency (foF2) data observed from the three Indian Ionosonde stations has been used for the present study. The dependence of foF2 on solar cycle has been examined by performing regression analysis between the foF2 values and R₁₂ (twelve month running average sunspot number). The result shows that the magnitude of the cycle, seasons and the location of station has considerable effects on foF2. There is a significant nonlinear relationship between the foF2 values and R₁₂ during 19th solar cycle as compared to 20th solar cycle. Further, the nighttime saturation effect is prominently seen during the 19th solar cycle and summer season. It is also observed that the most profound saturation effect appears at the equatorial ionization anomaly crest region. Seasonally, it is seen that all the stations exhibits semiannual anomaly. The phenomenon of winter anomaly decays as we move higher along the latitude and is prominently seen during the intense solar activity.