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1.
It is now well known that there is a substantial outflow of ionospheric plasma from the terrestrial ionosphere at high latitudes. The outflow consists of light thermal ions (H+, He+) as well as both light and heavy energized ions (H+, He+, O+, N+, NO+, O2+, N2+). The thermal ion outflows tend to be associated with the classical polar wind, while the energized ions are probably associated with either auroral energization processes or nonclassical polar wind processes. Part of the problem with identifying the exact cause of a given outflow relates to the fact that the ionosphere continuously convects into and out of the various high-latitude regions (sunlight, cusp, polar cap, nocturnal oval) and the time-constant for outflow is comparable to the convection time. Therefore, it is difficult to separate and quantify the possible outflow mechanisms. Some of these mechanisms are as follows. In sunlit regions, the photoelectrons can heat the thermal electrons and the elevated electron temperature acts to increase the polar wind outflow rate. At high altitudes, the escaping photoelectrons can also accelerate the polar wind as they drag the thermal ions with them. In the cusp and auroral oval, the precipitating magnetospheric electrons can heat the thermal electrons in a manner similar to the photoelectrons. Also, energized ions, in the form of beams and conics, can be created in association with field-aligned auroral currents and potential structures. The cusp ion beams and conics that have been convected into the polar cap can destabilize the polar wind when they pass through it at high altitudes, thereby transferring energy to the thermal ions. Additional energization mechanisms in the polar cap include Joule heating, hot magnetospheric electrons and ions, electromagnetic wave turbulence, and centrifugal acceleration.Some of these causes of ionospheric outflow will be briefly reviewed, with the emphasis on the recent simulations of polar wind dynamics in convecting flux tubes of plasma.  相似文献   

2.
Plasma patches are regions of enhanced ionization that are created in the dayside cusp or equatorward of the cusp in the sunlit hemisphere during northward interplanetary magnetic field. After formation, and a change to a southward interplanetary magnetic field, they drift across the polar cap with the prevailing convection speed. As a plasma patch propagates, charge exchange reactions occur, which lead to the production of both ion and neutral particles throughout the patch. In the region directly above the patch, an upward jet of H+ and O+ forms. This ion jet, in turn, acts to produce an upward flux of neutral H and O stream particles because of charge exchange reactions between the ion jet and the background neutral atmosphere. A three-dimensional, time-dependent model of the ion and neutral polar winds was used in order to study the evolution of the neutral stream particles that are produced in a ‘representative’ propagating plasma patch, with the anticipation that the neutral stream particles produced by the ion jet would display a distinct signature. However, the outflow of neutral H atoms above a patch is only slightly visible in the simulation due to a continuous outflow flux of H (∼109 cm−2 s−1) across the entire polar cap. On the other hand, the upward flux of neutral O from the patch is more dependent on both the state of the ionosphere and the amount of heating, with increased upward fluxes over areas where the heating is high. Typically, the upward neutral O streams are predominantly located in the pre-midnight auroral oval.  相似文献   

3.
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.  相似文献   

4.
The polar wind is an ambipolar outflow of thermal plasma from the high-latitude ionosphere to the magnetosphere, and it primarily consists of H+, He+ and O+ ions and electrons. Statistical and episodic studies based primarily on ion composition observations on the ISIS-2, DE-1, Akebono and Polar satellites over the past four decades have confirmed the existence of the polar wind. These observations spanned the altitude range from 1000 to ∼50,500 km, and revealed several important features in the polar wind that are unexpected from “classical” polar wind theories. These include the day–night asymmetry in polar wind velocity, which is 1.5–2.0 times larger on the dayside; appreciable O+ flow at high altitudes, where the velocity at 5000–10,000 km is of 1–4 km/s; and significant electron temperature anisotropy in the sunlit polar wind, in which the upward-to-downward electron temperature ratio is 1.5–2. These features are attributable to a number of “non-classical” polar wind ion acceleration mechanisms resulting from strong ionospheric convection, enhanced electron and ion temperatures, and escaping atmospheric photoelectrons. The observed polar wind has an averaged ion temperature of ∼0.2–0.3 eV, and a rate of ion velocity increase with altitude that correlates strongly with electron temperature and is greatest at low altitudes (<4000 km for H+). The rate of velocity increase below 4000 km is larger at solar minimum than at solar maximum. Above 4000 km, the reverse is the case. This suggests that the dominant polar wind ion acceleration process may be different at low and high altitudes, respectively. At a given altitude, the polar wind velocity is highly variable, and is on average largest for H+ and smallest for O+. Near solar maximum, H+, He+, and O+ ions typically reach a velocity of 1 km/s near 2000, 3000, and 6000 km, respectively, and velocities of 12, 7, and 4 km/s, respectively, at 10,000 km altitude. Near solar minimum, the velocity of all three species is smaller at high altitudes. Observationally it is not always possible to unambiguously separate an energized “non-polar-wind” ion such as a low-energy “cleft ion fountain” ion that has convected into a polar wind flux tube from an energized “polar-wind” ion that is accelerated locally by “non-classical” polar-wind ion acceleration mechanisms. Significant questions remain on the relative contribution between the cleft ion fountain, auroral bulk upflow, and the topside polar-cap ionosphere to the O+ polar wind population at high altitudes, the effect of positive spacecraft charging on the lowest-energy component of the H+ polar wind population, and the relative importance of the various classical and non-classical ion acceleration mechanisms. These questions pose several challenges in future polar wind observations: These include measurement of the lowest-energy component in the presence of positive spacecraft potential, definitive determination and if possible active control of the spacecraft potential, definitive discrimination between polar wind and other inter-mixed thermal ion populations, measurement of the three-dimensional ion drift velocity vector and the parallel and perpendicular ion temperatures or the detailed three-dimensional velocity distribution function, and resolution of He+ and other minor ion species in the polar wind population.  相似文献   

5.
It has been clearly established that there is a substantial outflow of ionospheric plasma from the Earth's ionosphere in both the northern and southern polar regions. The outflow consists of both light thermal ions (H+ and He+) and an array of energized ions (NO+, O2+, N2+, O+, N+, He+, and H+). If the outflow is driven by thermal pressure gradients in the ionosphere, the outflow is called the “classical” polar wind. On the other hand, if the outflow is driven by energization processes either in the auroral oval or at high altitudes in the polar cap, the outflow is called the “generalized” polar wind. In both cases, the field-aligned outflow occurs in conjunction with magnetospheric convection, which causes the plasma to drift into and out of the sunlit hemisphere, cusp, polar cap, nocturnal auroral oval, and main trough. Because the field-aligned and horizontal motion are both important, three-dimensional (3-D) time-dependent models of the ionosphere–polar wind system are needed to properly describe the flow. Also, as the plasma executes field-aligned and horizontal motion, charge exchange reactions of H+ and O+ with the background neutrals (H and O) act to produce low-energy neutrals that flow in all directions (the neutral polar wind). This review presents recent simulations of the “global” ionosphere–polar wind system, including the classical, generalized, and neutral polar winds. The emphasis is on displaying the 3-D and dynamical character of the polar wind.  相似文献   

6.
电离层极风的EISCAT-VHF雷达观测   总被引：2，自引：0，他引：2       下载免费PDF全文
极风现象从理论上提出已20多年了,实验上一直没有充分地证实这种现象的存在,以及它的形成区域位于高纬顶部电离层中.我们利用欧洲非相干散射协会（EISCAT）的VHF雷达（在挪威Tromsφ）,对H+离子极风进行了首次实验研究,结果表明,实验期间观测到H+离子在顶部电离层中的运动速度始终向上,且随高度的增加而增大,从而证实在高纬顶部电离层中确实存在着一个永久向上的H+离子流,即H+离子极风,其速度在1000km 高度上达到1km/s,其通量在此高度上接近于饱和,达到1012ms（-1）,而温度小于0.26eV.在我们的探测高度上仍未发展成超声速极风.  相似文献   

7.
The high-latitude ionospheric response to a major magnetic storm on May 15, 1997 is studied and different responses in the polar cap and the auroral oval are highlighted. Depletion of the F2 region electron density occurred in both the polar cap and the auroral zone, but due to different physical processes. The increased recombination rate of O+ ions caused by a strong electric field played a crucial role in the auroral zone. The transport effect, however, especially the strong upward ion flow was also of great importance in the dayside polar cap. During the main phase and the beginning of the recovery phase soft particle precipitation in the polar cap showed a clear relation to the dynamic pressure of the solar wind, with a maximum cross-correlation coefficient of 0.63 at a time lag of 5 min.  相似文献   

8.
The magnetospheric ion composition spectrometer MICS on the Swedish Viking satellite provided measurements of the ion composition in the energy range 10.1 keV/e\leqE/Q\leq326.0 keV/e. Data obtained during orbit 842 were used to investigate the ion distribution in the northern polar cusp and its vicinity. The satellite traversed the outer ring current, boundary region, cusp proper and plasma mantle during its poleward movement. H+ and He++ ions were encountered in all of these regions. He+ ions were present only in the ring current. The number of O+ and O++ ions was very small. Heavy high-charge state ions typical for the solar wind were observed for the first time, most of them in the poleward part of the boundary region and in the cusp proper. The H+ ions exhibited two periods with high intensities. One of them, called the BR/CP event, appeared at energies up to 50 keV. It started at the equatorward limit of the boundary region and continued into the cusp proper. Energy spectra indicate a ring current origin for the BR/CP event. Pitch angle distributions show downward streaming of H+ ions at its equatorward limit and upward streaming on the poleward side. This event is interpreted as the result of pitch angle scattering of ring current ions by fluctuations in the magnetopause current layer in combination with poleward convection. The other of the two periods with high H+ ion intensities, called the accelerated ion event, was superimposed on the BR/CP event. It was restricted to energies \leq15 keV and occurred in the poleward part of the boundary region. This event is regarded as the high-energy tail of magnetosheath ions that were accelerated while penetrating into the magnetosphere. The cusp region thus contains ions of magnetospheric as well as of magnetosheath origin. The appearance of the ions depends, in addition to the ion source, on the magnetic field configuration and dynamic processes inside and close to the cusp.  相似文献   

9.
Pulsating of the generalized ion and neutral polar winds   总被引：1，自引：1，他引：0  
A three-dimensional, time-dependent model of the ion and neutral polar winds was used to study their dynamic evolution during the May 4, 1998 magnetic storm. The simulation tracked the dynamics of five species (O+, H+, Hs, Os, and electrons) and covered a 9-h period. During the storm, Dst decreased to −210 nT, Ap reached 300, and Kp was elevated. The IMF Bz component was southward at the start of the storm and for several hours thereafter and then turned northward. However, the magnetospheric energy input to the ionosphere exhibited a 50-min oscillation, with the plasma convection and particle precipitation patterns expanding and contracting in a periodic manner. As a consequence, the ion and neutral polar winds pulsated with an approximate 50-min period. The H+ and O+ ions displayed cyclic upflows and downflows in the topside ionosphere as well as a highly structured spatial distribution that varied with time. The vertical flux of the neutral Hs atoms was upward at the top of the ionosphere, but the magnitude varied in a cyclic manner in response to the oscillating stormtime energy input. The vertical flux of neutral Os atoms was downward at the top of the ionosphere and varied significantly with the stormtime energy input. For H+, O+, and Hs, the maximum total (integrated) vertical flux during the storm was upward at the top of the ionosphere, with values of 8–9×1025 particles/s for H+, 2–4×1026 particles/s for O+, and 2–3×1027 particles/s for Hs. The corresponding total vertical Os flux was predominately downward, with only localized areas with positive fluxes.  相似文献   

10.
Ion composition measurements on board the ACTIVE satellite during the recovery phase of a strong geomagnetic storm of 10–12 April 1990 revealed extremely high concentrations (up to 103 cm−3) of the NO+, O+2, N+2 molecular ions in the topside F2-region of the European high-latitude zone. Concentrations of O+, N+, He+, H+ light ions were slightly decreased relative to prestorm quite conditions. Theoretical calculations were used to analyze the observed variations in ion concentration. Increased neutral temperature and [O2], [N2] are shown to be the main reasons for the observed ion concentration variations.  相似文献   

11.
This tutorial review examines the role of O+ in the dynamics of magnetosphere–ionosphere coupling. The life cycle of an O+ plasma element is considered as it circulates from the mid- to high-latitude ionosphere. Energization and diversion of the convecting plasma element into outflows involves Alfvénic turbulence at the low-altitude base of the cusp and plasmasheet boundary layer and in downward-current “pressure cookers.” Observational evidence indicating that O+ dominates the plasmasheet and ring current during extreme storm intervals is reviewed. The impacts of an O+-enriched plasma on solar wind–magnetosphere–ionosphere coupling are considered at both the micro and global scales. A synthesis of results from observation, theory and simulations suggests that the presence of O+ in the magnetosphere is both a disruptive and a moderating agent in maintaining the balance between dayside and nightside magnetic merging.  相似文献   

12.
New results on the information that can be extracted from simulated non-Maxwellian incoherent radar spectra are presented. The cases of a pure ionosphere and of a composite ionosphere typical of a given altitude of the auroral F region are considered. In the case of a pure ionosphere of NO+ or O+ ions it has been shown that the electron temperature and the electron density can be derived from a Maxweilian analysis of radar spectra measured at aspect angles of 0° or 21° respectively; the ion temperature and ion temperature anisotropy can be derived from a non- constraining model such as the ID Raman fitting of a complementary measurement made at an aspect angle larger than 0° for the NO+ ions, or at an aspect angle larger than 21° for the O+ ions. Moreover with such measurements at large aspect angles, the shape of the velocity ion distribution functions can simultaneously be inferred. The case of a composite ionosphere of atomic O+ and molecular NO+ions is a difficult challenge which requires simultaneously a complementary measurement of the electron temperature to provide the ion composition and the electron density from the incoherent radar spectra at a specific aspect angle of 21°; hence, a model dependent routine is necessary to derive the ion temperatures and ion temperature anisotropies. In the case where the electron temperature is not given, a routine which depends on ion distribution models is required first: the better the ion distribution models are, the more accurately derived the plasma parameters will be. In both cases of a composite ionosphere, the 1D Raman fitting can be used to keep a check on the validity of the results provided by the ion distribution model dependent routine.  相似文献   

13.
The results from the numerical calculations of the global distribution of topside ionospheric parameters such as H+ ions and ion and electron temperatures up to 1500 km height are presented for equinoctial conditions at solar minimum. Calculations are carried out using the Global Self-consistent Model of Thermosphere, Ionosphere and Protonosphere (GSM TIP) developed in WD IZMIRAN, and using a new calculation block for electric fields due to dynamo and of magnetospheric origin. A comparison of two sets of calculations of magnetospheric convection electric field for a given potential difference is carried out, one through polar caps and other through field aligned currents of first zone. It is shown that the distribution of the electric potential obtained through field aligned currents of first zone is more self-consistent than that through polar caps. The light ion trough in H+ ions is deeper and occupies larger region for the potential difference through polar cap. For a given potential difference through field aligned current, at 1500 km, the maximum ion temperature is 150 K higher, minimum ion temperature is 200 K lower and maximum electron temperature is 100 K higher than those obtained for the same potential difference through polar caps. It is concluded that for modeling the electric field of magnetospheric origin, it is necessary to use the potential difference through field aligned current of first zone instead of through polar caps.  相似文献   

14.
The results of studying the ionospheric response to solar flares, obtained from the data of the GPS signal observations and incoherent scatter radars and as a result of the model calculations, are presented. It is shown that, according to the GPS data, a flare can cause a decrease in the electron content at altitudes of the topside ionosphere (h > 300 km). Similar effects of formation of a negative disturbance in the ionospheric F region were also observed during the solar flares of May 21 and 23, 1967, with the Arecibo incoherent scatter radar. The mechanism by which negative disturbances appear in the topside ionosphere during solar flares has been studied in this work based on the theoretical model of the ionosphere-plasmasphere coupling. It has been indicated that the formation of the electron density negative disturbance in the topside ionosphere is caused by an intense removal of O+ ions into the overlying plasmasphere under the action of an abrupt increase in the ion production rate and thermal expansion of the ionospheric plasma.  相似文献   

15.
The high-latitude ionosphere interfaces with the hot, tenuous, magnetospheric plasma, and a heat flow into the ionosphere is expected, which has a large impact on the plasma densities and temperatures in the high-latitude ionosphere. The value of this magnetospheric heat flux is unknown. In an effort to estimate the value of the magnetospheric heat flux into the high-latitude ionosphere, and show its effect on the high-latitude ionospheric plasma densities, we ran an ensemble of model runs using the Ionosphere Forecast Model (IFM) with different values of the heat flux through the upper boundary. These model runs included heating from both auroral and solar sources. Then, for each heat flux value, the plasma densities obtained from the model runs, at 840 km, were compared to the corresponding values measured by the DMSP F13 satellite. The heat flux value that gave the best comparison between the measured and calculated plasma densities was considered to be the best estimate for the topside heat flux. The comparison was conducted for a 1-year data set of the DMSP F13 measured plasma densities (4300 consecutive orbits). Our systematic IFM/DMSP plasma density comparisons indicate that when a zero magnetospheric downward heat flux is assumed at the upper boundary of the IFM model, on the average, the IFM underestimates the measured plasma densities by a factor of 2. A good IFM/DMSP plasma density comparison was achieved for each month in 1998 when for each month a constant heat flux was assumed at the upper boundary of the model. For the 12-month period, the heat flux values that gave the best IFM/DMSP plasma density comparisons varied on the average from −0.5×1010 to −1.5×1010 eV cm−2 s−1.  相似文献   

16.
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17.
It has been previously demonstrated that a two-ion (O+ and H+) 8-moment time-dependent fluid model was able to reproduce correctly the ionospheric structure in the altitude range probed by the EISCAT-VHF radar. In the present study, the model is extended down to the E-region where molecular ion chemistry (NO+ and O+2, essentially) prevails over transport; EISCAT-UHF observations confirmed previous theoretical predictions that during events of intense E×B induced convection drifts, molecular ions (mainly NO+) predominate over O+ ions up to altitudes of 300 km. In addition to this extension of the model down to the E-region, the ionization and heating resulting from both solar insolation and particle precipitation is now taken into account in a consistent manner through a complete kinetic transport code. The effects of E×B induced convection drifts on the E- and F-region are presented: the balance between O+ and NO+ ions is drastically affected; the electric field acts to deplete the O+ ion concentration. The [NO+]/[O+] transition altitude varies from 190 km to 320 km as the perpendicular electric field increases from 0 to 100 mV m−1. An interesting additional by-product of the model is that it also predicts the presence of a noticeable fraction of N+ ions in the topside ionosphere in good agreement with Retarding Ion Mass Spectrometer measurements onboard Dynamic Explorer.  相似文献   

18.
The general features of the region of interaction of the solar wind with the ionosphere of Venus and Mars are compared using data obtained with the Mariner 5 and the Pioneer Venus Orbiter (PVO) spacecraft for Venus and with the Phobos II, the Mars Global Surveyor (MGS) and the Mars Express spacecraft for Mars. Despite the overall weak intrinsic global magnetic field that is present in both planets there are significant differences in the manner in which the interplanetary magnetic field accumulates and is organized around and within their ionosphere. Such differences are unrelated to the crustal magnetic field remnants inferred from the MGS measurements around Mars. In fact, while in Venus and Mars there is a region in which the magnetic field becomes enhanced as it piles up in their plasma environment it is shown that such a region exhibits different regimes with respect to changes in the ion composition measured outside and within the ionosphere. At Venus the region of enhanced magnetic field intensity occurs in general above the ionopause which represents the boundary across which there is a change in the ion composition with dominant solar wind protons above and planetary O+ ions below. At Mars the region of enhanced magnetic field is located below a magnetic pileup boundary across which there is also a comparable change in the ion composition (solar wind protons above and planetary O+ ions below). It is argued that this difference in the relative position of the region of enhanced magnetic field with respect to that of a plasma boundary that separates different ion populations results from the peculiar response of the ionosphere of each planet to the oncoming solar wind dynamic pressure. While at Venus the peak ionospheric thermal pressure is in general sufficient to withhold the incident solar wind kinetic pressure there is a different response in Mars where the peak ionospheric thermal pressure is in general not large enough to deviate the solar wind. In this latter case the ionosphere is unable to force the solar wind to move around the ionosphere and as a result the oncoming electron population can reach low altitudes where it is influenced by neutral atmospheric particles (the solar wind proton population is replaced at the magnetic pileup boundary which marks the upper extent of the region where the interplanetary magnetic field becomes enhanced). Peculiar conditions are expected near the magnetic polar regions and over the terminator plane where the solar wind is directed along the sides of the planet.  相似文献   

19.
The structure and dynamics of the ionosphere and plasmasphere at high solar activity under quiet geomagnetic conditions of June 2–3, 1979, and January 5–6, 1980, over Millstone Hill station and Argentine Islands ionosonde, the locations of which are approximately magnetically conjugate, have been theoretically calculated. The plasma drift velocity, determined by comparing the calculated and measured heights of the F 2 layer maximum (hmF2), and the correction of [N2] and [O2], found in the NRLMSISE-00 model, make it possible to coordinate the electron densities (NmF2) calculated at the hmF2 height and the measured anomalous variations in NmF2 over the Argentine Islands ionosonde as well as the calculated and measured NmF2 and electron temperature at the hmF2 height over Millstone Hill station. It has been shown that, if the interference of the diffusion velocities of O+(4S) and H+ ions is taken into account, the additional heating of plasmaspheric electrons leads to an increase in the flux of O+(4S) ions from the topside ionosphere to lower F 2 layer altitudes, as a result of which an anomalous nighttime increase in NmF2 6, observed on January 6, 1980, over Millstone Hill station, is mainly produced. The second component of the formation of anomalous night-time NmF2 is the plasma drift along the magnetic field caused by the neutral wind, which shifts O+(4S) ions to higher altitudes where the recombination rate of O+(4S) with N2 and O2 is lower and slows down a decrease in NmF2 in the course of time. It has been shown that the influence of electronically excited O+ ions and vibrationally excited N2 and O2 molecules on electron density (N e ) considerably differs under winter and summer conditions. This difference forms significant part of the winter anomaly in N e at heights of the F 2 region and topside ionosphere over Millstone Hill station.  相似文献   

20.
We analyze the data obtained using the Arecibo incoherent scatter radar to examine the response of the topside ionosphere to a moderate geomagnetic storm that occurred during the period March 7–11, 2008. During this time period a magnetic storm with a non-monotonic main phase decrease in the Dst index occurred. The recovery phase also exhibited a secondary Dst decrease. During the initial phase of the storm, Te and Ti increased coincident with the arrival of the solar wind. The main phase registered an increase in proton concentration proportional to Ne while temperatures reached the lowest values. Variations in O+ concentration were not significant but a reduction in helium fraction was observed. Soon after the peak of the storm, the transition height between the topside ionosphere and the protonosphere, where H+ ions dominate composition, was lower than would be expected during quiet conditions and this behavior lasted for approximately 12 h.  相似文献   

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