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1.
EISCAT radar experiments over a full solar cycle between January 1984 and March 1995 have been used to construct meridional neutral wind patterns in the ionospheric F region. For locally geomagnetically quiet periods the neutral winds have been binned according to season, solar activity, and universal time. The diurnal and seasonal behaviors and the effect of the solar flux are described. An empirical model of the meridional neutral wind for the high latitudes at eight altitudes in the ionospheric F region over a full solar cycle is presented. Results are compared with other recent empirical models.  相似文献   

2.
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   

3.
A mathematical model of the middle and high latitude ionosphere   总被引：5，自引：0，他引：5  
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4.
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   

5.
Three-dimensional structures of the ionospheric dynamo currents are examined using the neutral winds in a general circulation model of the middle atmosphere at Kyushu University. A quasi-three-dimensional ionospheric dynamo model is constructed assuming an infinite parallel conductivity in the ionosphere. This model is able to simulate both the equatorial electrojet and the global Sq current system successfully. The simulated results reveal that the equatorial electrojet is confined in quite narrow latitudes around the equator accompanied with meridional current circulations and satisfies a non-divergent structure mainly within the E region. A vertically stratified double layered structure is seen in the east–west current density near the focus latitude of the global Sq current system. It is shown that the stratified structure mainly consists of the east–west Hall current associated with the eastward wind of zonal wavenumbers 1 and 2 in the lower altitudes and the westward wind of zonal wavenumber 2 in the upper altitudes. The day-to-day variation of the neutral winds can significantly vary the induced ionospheric dynamo current system, which is recognized as changes of the focus latitude and/or the maximum value of the equatorial electrojet.  相似文献   

6.
通过求解中性大气Navier Stokes动量方程建立了一个时变的三维风场理论模式，利用目前新版的中性大气模式NRLMSISE 00及国际电离层参考模式IRI2000作为输入参数给出热层风场. 基于该模式，计算得到中等太阳活动年磁静日风场的变化形态及其受电场和离子曳力的影响. 同时，将Navier Stokes动量方程作不同形式的简化，并利用简化模式与本文的模式计算结果的对比，分析中性大气Navier Stokes动量方程中黏性项以及非线性项(U·Δ)U的作用. 结果表明，本文所建立伪三维风场模式给出的结果更为合理，而简化模式在某些地区尤其在低纬和赤道区不适用，黏性项及非线性项的作用不可忽略. 本文所建立的风场模式将对研究电离层动力学过程、电离层与热层的耦合过程以及空间天气学研究都有着重要意义.  相似文献   

7.
The MICADO instrument, consisting of a Michelson interferometer, has observed winds and temperatures during three winter campaigns in the auroral zone, and during 2 years at the Observatoire de Haute-Provence. The instrument observed the O(1S) oxygen emission line. Emission from this line originates from both the E- and F-regions. A method to separate the contribution from these two regions is presented for cases when the thermospheric component is comparable to that for the mesosphere. For the auroral latitudes, a mean model of the meridional and zonal neutral wind components as a function of magnetic activity and time is presented and compared to predictions from recent empirical models. For the mid-latitudes, several properties of the semi-diurnal tides are shown and compared to radar observations and predictions from recent theoretical models.  相似文献   

8.
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   

9.
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10.
The meridional propagation velocities of the ionospheric F2-region response to 268 geomagnetic storms are calculated. Ionospheric vertical sounding data of 1 h time resolution from several stations located in a longitude sector approximately centred along the great circle that contains both the geomagnetic poles and the geographic poles are used.Most meridional propagation velocities from high to low latitudes are less than 600 m/s. The smaller velocities are typical of global neutral meridional wind circulation and the larger are representative of traveling atmospheric disturbances.Simultaneous disturbances at several locations are more frequent during positive phases than during negative phases. Negative phase meridional propagation velocities associated with meridional neutral winds are less frequent in the southern hemisphere when compared with corresponding velocities observed in the northern hemisphere. This may be related to the fact that the distance between the geomagnetic pole and the equator is smaller in the northern hemisphere.Most negative phase onsets are within the 06–10 LT interval. For middle geomagnetic latitudes a “forbidden time interval” between 11 and 14 LT is present. The positive phase onsets show the “dusk effect”.  相似文献   

11.
Common programme observations by the EISCAT UHF radar revealed an extended interval, post geomagnetic local noon on 03 April 1992, during which the F-region ion velocity orthogonal to the geomagnetic field was significantly enhanced, to values exceeding 2 km s−1 corresponding to a perpendicular electric field of some 100 mV m−1. Observations from this interval are used to illustrate a method by which estimates of the E-region ion-neutral collision frequency may be derived in the presence of enhanced electric field. From both the rotation of the ion velocity vector and the reduction in the ion velocity magnitude relative to that in the F-region, independent estimates of the normalised ion-neutral collision frequency are made at the UHF E-region tristatic altitudes; the derived values are, in general, lower than model predictions. Although initial calculations assume a stationary neutral atmosphere, first-order estimates of the E-region neutral wind are subsequently employed to calculate revised estimates of the normalised ion-neutral collision frequency; these neutral winds are derived by attributing the difference between predicted and observed enhancements in field-parallel ion temperature to thermospheric motion. The inclusion of neutral winds, which are themselves not inconsiderable, appears to have only a limited effect on the normalised collision frequencies derived.  相似文献   

12.
Formation mechanism of the spring–autumn asymmetry of the F2-layer peak electron number density of the midlatitudinal ionosphere, NmF2, under daytime quiet geomagnetic conditions at low solar activity are studied. We used the ionospheric parameters measured by the ionosonde and incoherent scatter radar at Millstone Hill on March 3, 2007, March 29, 2007, September 12, 2007, and September 18, 1984. The altitudinal profiles of the electron density and temperature were calculated for the studied conditions using a one-dimensional, nonstationary, ionosphere–plasmasphere theoretical model for middle geomagnetic latitudes. The study has shown that there are two main factors contributing to the formation of the observed spring–autumn asymmetry of NmF2: first, the spring–autumn variations of the plasma drift along the geomagnetic field due to the corresponding variations in the components of the neutral wind velocity, and, second, the difference between the composition of the neutral atmosphere under the spring and autumn conditions at the same values of the universal time and the ionospheric F2-layer peak altitude. The seasonal variations of the rate of O+(4S) ion production, which are associated with chemical reactions with the participation of the electronically excited ions of atomic oxygen, does not significantly affect the studied NmF2 asymmetry. The difference in the degree of influence of O+(4S) ion reactions with vibrationally excited N2 and O2 on NmF2 under spring and autumn conditions does not significantly change the spring–autumn asymmetry of NmF2.  相似文献   

13.
Tomographic imaging provides a powerful technique for obtaining images of the spatial distribution of ionospheric electron density at polar latitudes. The method, which involves monitoring radio transmissions from the Navy Navigation Satellite System at a meridional chain of ground receivers, has particular potential for complementing temporal measurements by other observing techniques such as the EISCAT incoherent-scatter radar facility. Tomographic reconstructions are presented here from a two-week campaign in November 1995 that show large-scale structuring of the polar ionosphere. Measurements by the EISCAT radar confirm the authenticity of the technique and provide additional information of the plasma electron and ion temperatures. The dayside trough, persistently observed at high latitudes during a geomagnetically quiet period but migrating to lower latitudes with increasing activity, is discussed in relationship to the pattern of the polarcap convection.  相似文献   

14.
We present combined observations made near midnight by the EISCAT radar, all-sky cameras and the combined released and radiation efects satellite (CRRES) shortly before and during a substorm. In particular, we study a discrete, equatorward-drifting auroral arc, seen several degrees poleward of the onset region. The arc passes through the field-aligned beam of the EISCAT radar and is seen to be associated with a considerable upflow of ionospheric plasma. During the substorm, the CRRES satellite observed two major injections, 17 min apart, the second of which was dominated by O+ ions. We show that the observed are was in a suitable location in both latitude and MLT to have fed O+ ions into the second injection and that the upward flux of ions associated with it was sufficient to explain the observed injection. We interpret these data as showing that arcs in the nightside plasma-sheet boundary layer could be the source of O+ ions energised by a dipolarisation of the mid- and near-Earth tail, as opposed to ions ejected from the dayside ionosphere in the cleft ion fountain.  相似文献   

15.
Results of studying the ionospheric response to solar flares, obtained based on the incoherent scatter radar observations of the GPS signals and as a result of the model simulations, are presented. The method, based on the effect of partial “shadowing” of the atmosphere by the globe, has been used to analyze the GPS data. This method made it possible to estimate the value of a change in the electron content in the upper ionosphere during the solar flare of July 14, 2000. It has been shown that a flare can cause a decrease in the electron content at heights of the upper ionosphere (h > 300 km) according to the GPS data. Similar effects in the formation of a negative disturbance in the ionospheric F region were also observed during the solar flares of May 21 and 23, 1967, at the Arecibo incoherent scatter radar. The mechanism by which negative disturbances are formed in the upper ionosphere during solar flares has been studied based on the theoretical model of the ionosphere-plasmasphere coupling. It has been shown that an intense ejection of O+ ions into the above located plasmasphere under the action of a sharp increase in the ion production rate and the thermal expansion of the ionospheric plasma cause the formation of a negative disturbance in the electron concentration in the upper ionosphere.  相似文献   

16.
Geomagnetic activity dependence of O in transit from the ionosphere   总被引：1，自引：0，他引：1  
Energetic O+ ions have important dynamic effects on the ring current. Insights into the effects of O+ on ring current dynamics have come primarily from models, not observations. Here, we discuss observations of O+ populations escaping from the ionosphere and their access to the plasma sheet and ring current. We review data establishing that a significant flux of O+ escapes the ionosphere during geomagnetically quiet intervals. We then estimate the relative magnitude of the O+ population in transit between the ionosphere and ring current during quiet intervals before geomagnetic storms. Our analysis suggests that dynamic reconfigurations of the magnetosphere during geomagnetic storms significantly alter the O+ transport paths from the ionosphere to the ring current. During these reconfigurations some of the pre-existing, quiet time, in-transit O+ populations are captured on magnetic field lines leading to the ring current. The prompt appearance of this O+ population in the ring current could modify the evolution of the ring current in the storm growth phase. Our analysis suggests that the consequences of an activity-dependent O+ transport path to the ring current should be systematically investigated.  相似文献   

17.
The zonally averaged UK Meteorological Office (UKMO) zonal mean temperature and zonal winds for the latitudes 8.75°N and 60°N are used to investigate the low-latitude dynamical response to the high latitude sudden stratospheric warming (SSW) events that occurred during winter of the years 1998–1999, 2003–2004 and 2005–2006. The UKMO zonal mean zonal winds at 60°N show a short-term reversal to westward winds in the entire upper stratosphere and lower mesosphere and the low-latitude winds (8.75°N) show enhanced eastward flow in the upper stratosphere and strong westward flow in the lower mesosphere during the major SSW events at high latitudes. The mesosphere and lower thermosphere (MLT) zonal winds acquired by medium frequency (MF) radar at Tirunelveli (8.7°N, 77.8°E) show a change of wind direction from eastward to westward several days before the onset of SSW events and these winds decelerate and weak positive (eastward) winds prevail during the SSW events. The time variation of zonal winds over Tirunelveli is nearly similar to the one reported from high latitudes, except that the latter shows intense eastward winds during the SSW events. Besides, the comparison of daily mean meridional winds over Tirunelveli with those over Collm (52°N, 15°E) show that large equatorial winds are observed over Tirunelveli during the 2005–2006 event and over Collm during the 1998–1999 events. The variable response of MLT dynamics to different SSW events may be explained by the variability of gravity waves.  相似文献   

18.
Seasonal variations in the auroral E-region neutral wind for different solar activity periods are studied. This work is based on neutral wind data obtained over 56 days between 95–119 km altitude under geomagnetic quiet conditions (Ap<16) during one solar cycle by the European Incoherent Scatter radar located in northern Scandinavia. In general, the meridional mean wind shifts northward, and the zonal mean wind increases in eastward amplitude from winter to summer. The zonal mean wind blows eastward in the middle and lower E-region for each season and for each solar condition except for the equinox, where the zonal mean wind blows westward at and below 104 km. Solar activity dependence of the mean wind exists during the winter and equinox seasons, while in summer it is less prominent. Under high solar activity conditions, the altitude profiles of the horizontal mean winds in winter and the equinoxes tend to resemble those in summer. The horizontal diurnal tide is less sensitive to solar activity except during summer when the meridional amplitude increases by ∼10 m s−1 and the corresponding phase shifts to a later time period (1–2 h) during high solar activity. Seasonal dependence of the semidiurnal tide is complex, but is found to vary with solar activity. Under low solar activity conditions the horizontal semidiurnal amplitude shows seasonal dependence except at upper E-region heights, while under high solar activity conditions it becomes less sensitive to seasonal effects (except for the meridional component above 107 km). Comparisons of mean winds with LF and UARS observations are made, and the driving forces for the horizontal mean winds are discussed for various conditions.  相似文献   

19.
Latitudinal variations in the nighttime plasma temperatures of the equatorial topside ionosphere during northern winter at solar maximum have been examined by using values modelled by SUPIM (Sheffield University Plasmasphere Ionosphere Model) and observations made by the DMSP F10 satellite at 21.00 LT near 800 km altitude. The modelled values confirm that the crests observed near 15° latitude in the winter hemisphere are due to adiabatic heating and the troughs observed near the magnetic equator are due to adiabatic cooling as plasma is transported along the magnetic field lines from the summer hemisphere to the winter hemisphere. The modelled values also confirm that the interhemispheric plasma transport needed to produce the required adiabatic heating/cooling can be induced by F-region neutral winds. It is shown that the longitudinal variations in the observed troughs and crests arise mainly from the longitudinal variations in the magnetic meridional wind. At longitudes where the magnetic declination angle is positive the eastward geographic zonal wind combines with the northward (summer hemisphere to winter hemisphere) geographic meridional wind to enhance the northward magnetic meridional wind. This leads to deeper troughs and enhanced crests. At longitudes where the magnetic declination angle is negative the eastward geographic zonal wind opposes the northward geographic meridional wind and the trough depth and crest values are reduced. The characteristic features of the troughs and crests depend, in a complicated manner, on the field-aligned flow of plasma, thermal conduction, and inter-gas heat transfer. At the latitudes of the troughs/crests, the low/high plasma temperatures lead to increased/decreased plasma concentrations.  相似文献   

20.
Data from the VLF Doppler experiment at Faraday, Antarctica (65○ S, 64○ W) are used to study the penetration of the high-latitude convection electric field to lower latitudes during severely disturbed conditions. Alterations of the electric field at L-values within the range 2.0 - 2.7 are studied for two cases at equinox (10 - 12 September 1986 and 1 - 3 May 1986). The recovery of the electric field is found to be approximately an exponential function of time. Values for the equatorial meridional E×B drift velocity, inferred from the data, are used as inputs to a model of the plasmasphere and ionosphere. The model and experimental results are used to investigate the post-storm alteration of ionospheric coupling processes. The magnitude of the effect of ionosphere-plasmasphere coupling fluxes on NmF2 values and the O+-H+ transition height is dependent on the local time of storm commencement, and on the orientation of the electric field. The coupling fluxes appear to have a maximum influence on ionospheric content during the main phase of geomagnetic activity that produces outward motion of plasmaspheric whistler ducts.  相似文献   

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