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1.
This study compares the Isis II satellite measurements of the electron density and temperature, the integral airglow intensity and volume emission rate at 630 nm in the SAR arc region, observed at dusk on 4 August, 1972, in the Southern Hemisphere, during the main phase of the geomagnetic storm. The model results were obtained using the time dependent one-dimensional mathematical model of the Earth’s ionosphere and plasmasphere (the IZMIRAN model). The major enhancement to the IZMIRAN model developed in this study to explain the two component 630 nm emission observed is the analytical yield spectrum approach to calculate the fluxes of precipitating electrons and the additional production rates of N+2, O+2, O+(4S), O+(2D), O−(2P), and O+(2P) ions, and O(1D) in the SAR arc regions in the Northern and Southern Hemispheres. In order to bring the measured and modelled electron temperatures into agreement, the additional heating electron rate of 1.05 eV cm−3 s−1 was added in the energy balance equation of electrons at altitudes above 5000 km during the main phase of the geomagnetic storm. This additional heating electron rate determines the thermally excited 630 nm emission observed. The IZMIRAN model calculates a 630 nm integral intensity above 350 km of 4.1 kR and a total 630 nm integral intensity of 8.1 kR, values which are slightly lower compared to the observed 4.7 kR and 10.6 kR. We conclude that the 630 nm emission observed can be explained considering both the soft energy electron excited component and the thermally excited component. It is found that the inclusion of N2(v > 0) and O2(v > 0) in the calculations of the O+(4S) loss rate improves the agreement between the calculated Ne and the data on 4 August, 1972. The N2(v > 0) and O2(v > 0) effects are enough to explain the electron density depression in the SAR arc F-region and above F2 peak altitude. Our calculations show that the increase in the O+ + N2 rate factor due to the vibrationally excited nitrogen produces the 5–19% reductions in the calculated quiet daytime peak density and the 16–24% decrease in NmF2 in the SAR arc region. The increase in the O+ + N2 loss rate due to vibrationally excited O2 produces the 7–26% decrease in the calculated quiet daytime peak density and the 12–26% decrease in NmF2 in the SAR arc region. We evaluated the role of the electron cooling rates by low-lying electronic excitation of O2(a1δg) and O2(b1σg+), and rotational excitation of O2, and found that the effect of these cooling rates on Te can be considered negligible during the quiet and geomagnetic storm period 3–4 August, 1972. The energy exchange between electron and ion gases, the cooling rate in collisions of O(3P) with thermal electrons with excitation of O(1D), and the electron cooling rates by vibrational excitation of O2 and N2 are the largest cooling rates above 200 km in the SAR arc region on 4 August, 1972. The enhanced IZMIRAN model calculates also number densities of N2(B3πg+), N2(C3πu), and N2(A3σu+) at several vibrational levels, O(1S), and the volume emission rate and integral intensity at 557.7 nm in the region between 120 and 1000 km. We found from the model that the integral integral intensity at 557.7 nm is much less than the integral intensity at 630 nm.  相似文献   

2.
This study compares the OV1-10 satellite measurements of the integral airglow intensities at 630 nm in the SAR arc regions observed in the northern and southern hemisphere as a conjugate phenomenon, with the model results obtained using the time-dependent one-dimensional mathematical model of the Earth ionosphere and plasmasphere (the IZMIRAN model) during the geomagnetic storm of the period 15–17 February 1967. The major enhancements to the IZMIRAN model developed in this study are the inclusion of He+ ions (three major ions: O+ H+ and He+ and three ion temperatures), the updated photochemistry and energy balance equations for ions and electrons, the diffusion of NO+ and O+2 ions and O(1D) and the revised electron cooling rates arising from their collisions with unexcited N2, O2 molecules and N2 molecules at the first vibrational level. The updated model includes the option to use the models of the Boltzmann or non-Boltzmann distributions of vibrationally excited molecular nitrogen. Deviations from the Boltzmann distribution for the first five vibrational levels of N2 were calculated. The calculated distribution is highly non-Boltzmann at vibrational levels v > 2 and leads to a decrease in the calculated electron density and integral intensity at 630 nm in the northern and southern hemispheres in comparison with the electron density and integral intensity calculated using the Boltzmann vibrational distribution of N2. It is found that the intensity at 630 nm is very sensitive to the oxygen number densities. Good agreement between the modeled and measured intensities is obtained provided that at all altitudes of the southern hemisphere a reduction of about factor 1.35 in MSIS-86 atomic oxygen densities is included in the IZMIRAN model with the non-Boltzm-ann vibrational distribution of N2. The effect of using of the O(1D) diffusion results in the decrease of 4–6% in the calculated integral intensity of the northern hemisphere and 7–13% in the calculated integral intensity of the southern hemisphere. It is found that the modeled intensities of the southern hemisphere are more sensitive to the assumed values of the rate coefficients of O+(4S) ions with vibrationally excited nitrogen molecules and quenching of O+(2D) by atomic oxygen than the modeled intensities of the northern hemisphere.  相似文献   

3.
We present a study of statistical relationships between SAR arc intensities acquired by the Pacific Northwest Laboratory Photometer Network during 1978–1988 and solar and geomagnetic activity indices Dst, F10.7, and Kp by use of the method of multiple regression analysis. We found significant correlations between intensity and all of the indices involved. In the present work we show for the first time that the partial correlation coefficients depend on the time offset, t, between the time of SAR arc intensity observations and the onset of the geomagnetic storm recovery phase, with the largest correlations being observed when 8 d t d 16 h. It is also shown that there are significant differences between partial correlation coefficients calculated for SAR arcs associated with strong (Dstmin > −100 nT) and weak (Dstmin > −100 nT) geomagnetic storms. We observe also that the multiple correlation coefficients for strong storms are much larger than for weak ones. We found that the variations in the electron temperature, Te, in the SAR arc region are not mainly produced by variations in the electron density of the ionosphere but are strongly driven by the additional heating of the electron gas due to an interaction of the ring current ions and the plasmaspheric electrons. As a result, variations of Te in the SAR arc region with characteristic time scales from several minutes to several hours are stipulated by time variations of ring current parameters.  相似文献   

4.
Millstone Hill ionospheric storm time measurements of the electron density and temperature during the ionospheric storms (15-16 June 1965; 29–30 September 1969 and 17–18 August 1970) are compared with model results. The model of the Earth’s ionosphere and plasmasphere includes interhemispheric coupling, the H+, O+(4S), O+(2D), O+(2P), NO+, O+2 and N+2 ions, electrons, photoelectrons, the electron and ion temperature, vibrationally excited N2 and the components of thermospheric wind.In order to model the electron temperature at the time of the 16 June 1965 negative storm, the heating rate of the electron gas by photoelectrons in the energy balance equation was multiplied by the factors 5–30 at he altitude above 700 km for the period 4.50-12.00 LT, 16 June 1965. The [O]/[N2] MSIS-86 decrease and vibrationally excited N2 effects are enough to account for the electron density depressions at Millstone Hill during the three storms. The factor of 2 (for 27–30 September 1969 magnetic storm) and the & actor 2.7 (for 16–18 August 1970 magnetic storm) reduction in the daytime peak density due to enhanced vibrationally excited N2 is brought about by the increase in the O++N2 rate factor.  相似文献   

5.
An abrupt decrease in the solar wind pressure and its effect on the magnetosphere and ionosphere during the event occurring on April 4, 1971, are studied. This event differs fundamentally from a typical sudden commencement (SC) of a geomagnetic storm or from a positive sudden impulse (SI+) and is determined as a negative sudden impulse (SI–). The geomagnetic variations at different latitudes and the cosmic radio emission in the auroral zone are analyzed. From the data of low-latitude geomagnetic observatories, several subsequent negative impulses observed with a periodicity of ~45 min were found. At the same time, a sudden decrease in the absorption of cosmic radio emission in the auroral zone was revealed. Possible physical explanations of the observed changes are discussed.  相似文献   

6.
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7.
A comparative study of the geomagnetic and ionospheric data at equatorial and low-latitude stations in India over the 20 year period 1956–1975 is described. The reversal of the electric field in the ionosphere over the magnetic equator during the midday hours indicated by the disappearance of the equatorial sporadic E region echoes on the ionograms is a rare phenomenon occurring on about 1% of time. Most of these events are associated with geomagnetically active periods. By comparing the simultaneous geomagnetic H field at Kodaikanal and at Alibag during the geomagnetic storms it is shown that ring current decreases are observed at both stations. However, an additional westward electric field is superimposed in the ionosphere during the main phase of the storm which can be strong enough to temporarily reverse the normally eastward electric field in the dayside ionosphere. It is suggested that these electric fields associated with the V × Bz electric fields originate at the magnetopause due to the interaction of the solar wind and the interplanetary magnetic field.  相似文献   

8.
We investigate the features of the planetary distribution of wave phenomena (geomagnetic pulsations) in the Earth’s magnetic shell (the magnetosphere) during a strong geomagnetic storm on December 14–15, 2006, which is untypical of the minimum phase of solar activity. The storm was caused by the approach of the interplanetary magnetic cloud towards the Earth’s magnetosphere. The study is based on the analysis of 1-min data of global digital geomagnetic observations at a few latitudinal profiles of the global network of ground-based magnetic stations. The analysis is focused on the Pc5 geomagnetic pulsations, whose frequencies fall in the band of 1.5–7 mHz (T ～ 2–10 min), on the fluctuations in the interplanetary magnetic field (IMF) and in the solar wind density in this frequency band. It is shown that during the initial phase of the storm with positive IMF Bz, most intense geomagnetic pulsations were recorded in the dayside polar regions. It was supposed that these pulsations could probably be caused by the injection of the fluctuating streams of solar wind into the Earth’s ionosphere in the dayside polar cusp region. The fluctuations arising in the ionospheric electric currents due to this process are recorded as the geomagnetic pulsations by the ground-based magnetometers. Under negative IMF Bz, substorms develop in the nightside magnetosphere, and the enhancement of geomagnetic pulsations was observed in this latitudinal region on the Earth’s surface. The generation of these pulsations is probably caused by the fluctuations in the field-aligned magnetospheric electric currents flowing along the geomagnetic field lines from the substorm source region. These geomagnetic pulsations are not related to the fluctuations in the interplanetary medium. During the main phase of the magnetic storm, when fluctuations in the interplanetary medium are almost absent, the most intense geomagnetic pulsations were observed in the dawn sector in the region corresponding to the closed magnetosphere. The generation of these pulsations is likely to be associated with the resonance of the geomagnetic field lines. Thus, it is shown that the Pc5 pulsations observed on the ground during the magnetic storm have a different origin and a different planetary distribution.  相似文献   

9.
This study compares the observed behavior of the F region ionosphere over Millstone Hill with calculations from the IZMIRAN model for solar minimum for the geomagnetically quiet period 23–25 June 1986, when anomalously low values of hmF2(<200 km) were observed. We found that these low values of hmF2 (seen as a G condition on ionograms) exist in the ionosphere due to a decrease of production rates of oxygen ions resulting from low values of atomic oxygen density. Results show that determination of a G condition using incoherent scatter radar data is sensitive both to the true concentration of O+ relative to the molecular ions, and to the ion composition model assumed in the data reduction process. The increase in the O+ + N2 loss rate due to vibrationally excited N2 produces a reduction in NmF2 of typically 5–10%, but as large as 15%, bringing the model and data into better agreement. The effect of vibrationally excited NO+ ions on electron densities is negligible.  相似文献   

10.
A possible mechanism of earthquake triggering by ionizing radiation of solar flares is considered. A theoretical model and results of numerical calculations of disturbance of electric field, electric current, and heat release in lithosphere associated with variation of ionosphere conductivity caused by absorption of ionizing radiation of solar flares are presented. A generation of geomagnetic field disturbances in a range of seconds/tens of seconds is possible as a result of large-scale perturbation of a conductivity of the bottom part of ionosphere in horizontal direction in the presence of external electric field. Amplitude-time characteristics of the geomagnetic disturbance depend upon a perturbation of integral conductivity of ionosphere. Depending on relation between integral Hall and Pedersen conductivities of disturbed ionosphere the oscillating and aperiodic modes of magnetic disturbances may be observed. For strong perturbations of the ionosphere conductivities amplitude of pulsations may obtain ~102 nT. In this case the amplitude of horizontal component of electric field on the Earth surface obtains 0.01 mV/m, electric current density in lithosphere –10–6 A/m2, and the power density of heat release produced by the generated current is 10–7 W/m3. It is shown that the absorption of ionizing radiation of solar flares can result in variations of a density of telluric currents in seismogenic faults comparable with a current density generated in the Earth crust by artificial pulsed power systems (geophysical MHD generator " Pamir-2” and electric pulsed facility " ERGU-600”), which provide regional earthquake triggering and spatiotemporal variation of seismic activity. Therefore, triggering of seismic events is possible not only by man-made pulsed power sources but also by the solar flares. The obtained results may be a physical basis for a novel approach to solve the problem of short-term earthquake prediction based on electromagnetic triggering phenomena.  相似文献   

11.
The purpose of this research was to study the complexity of the energization of the ring current during a geomagnetic storm, produced during southern Bz(IMF) by the injection of plasma sheet ions, accelerated by enhanced convective electric fields. This model assumes that the plasma sheet is continuously populated by H+ from the sun and the ionosphere, and sporadically by ionospheric O+, making the ring current a coupled system whose energy can hardly be expressed analytically. When Bz(IMF) turns north, the ring current becomes uncoupled, and the energy decays exponentially if the storm is weak, or can be expressed as a combination of exponentials during strong storms representing the quick decay of O+ and the slower decay of H+, as has been shown.  相似文献   

12.
The paper is dedicated to the studies of formation mechanisms of additional layers in the equatorial ionosphere carried out using numerical simulations with use of the Global Self-Consistent Model of the Thermosphere, Ionosphere, and Protonosphere (GSM TIP) modified in the part of the solution of the electric field equation in the Earth’s ionosphere. Calculations were preformed for quiet geomagnetic conditions using the MSIS-90 model for the calculation of thermospheric parameters. The obtained spatio-temporal pattern of thermospheric circulation and the variations in the dynamo electric field obtained on its basis make it possible to reproduce the stratification effect of the F2 layer and the appearance of the F3 layer in the equatorial ionosphere due to the action of the nonuniform in height zonal electric field at the geomagnetic equator. On the basis of the earlier presented results of calculations using the modified GSM TIP model, the appearance of a maximum in the vertical profile of the electron density at a height of ∼1000 km formed by H+ ions, which we called the G layer, has been predicted. Numerical simulations showed that this layer is formed by the meridional component of the thermospheric wind and is related to the formation of the nighttime midlatitude maximum at heights of the ionospheric F region.  相似文献   

13.
A mathematical model of the middle and high latitude ionosphere   总被引：5，自引：0，他引：5  
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14.
This paper presents an investigation of geomagnetic storm effects in the equatorial and middle-low latitude F-region in the West Pacific sector during the intense geomagnetic storm on 13–17 April, 2006. The event, preceded by a minor storm, started at 2130 UT on April 13 while interplanetary magnetic field (IMF) Bz component was ready to turn southward. From 14–17 the ionosphere was characterized by a large scale enhancement in critical frequency, foF2 (4～6 MHz) and total electron content (TEC) (～30TECU, 1TECU=1×1016el/m2) followed by a long-duration negative phase observed through the simultaneous ionospheric sounding measurements from 14 stations and GPS network along the meridian 120°E. A periodic wave structure, known as traveling ionospheric disturbances (TIDs) was observed in the morning sector during the initial phase of the storm which should be associated with the impulsive magnetospheric energy injection to the auroral. In the afternoon and nighttime, the positive phase should be caused by the combination of equatorward winds and disturbed electric fields verified through the equatorial F-layer peak height variation and modeled upward drift of Fejer and Scherliess [1997. Empirical models of storm time equatorial electric fields. Journal of Geophysical Research 102, 24,047–24,056]. It is shown that the large positive storm effect was more pronounced in the Southern Hemisphere during the morning-noon sector on April 15 and negative phase reached to lower magnetic latitudes in the Northern Hemisphere which may be related to the asymmetry of the thermospheric condition during the storm.  相似文献   

15.
The observations of the variations in the vertical component of the atmospheric electric field (E z ) at Swider midlatitude Poland observatory (geomagnetic latitude 47.8°) under the conditions of fair weather during 14 magnetic storms have been analyzed. The effect of the magnetic storm main phase in the daytime midlatitude variations in E z in the absence of local geomagnetic disturbances has been detected for the first time. Considerable (～100–300 V m?1) decreases in the electric field strength (E z ) at Swider observatory were observed in daytime simultaneously with the substorm onset in the nighttime sector of auroral latitudes (College observatory). The detected effects indicate that an intensification of the interplanetary electric field during the magnetic storm main phase, the development of magnetospheric substorms, and precipitation of energetic electrons into the nighttime auroral ionosphere can result in considerable disturbances in the midlatitude atmospheric electric field.  相似文献   

16.
Ionospheric effects of a large number (51) of severe geomagnetic storms are studied using total electron content (TEC) and VHF/UHF scintillation data from Calcutta, situated near the northern crest of equatorial ionization anomaly and equatorial spread-F (ESF) data from Kodaikanal. The susceptibility of the equatorial ionosphere to develop storm time plasma density irregularities responsible for ESF and scintillation is found to be largely modulated by the local times of occurrences of main and recovery phases as seen in the Dst index. While inhibition of premidnight scintillation for lower TEC values compared to the quiet day averages is omnipresent, occurrence of scintillation for enhancements of TEC is largely dependent on initiation time and amplitude of the said deviations. An overall reduction in threshold values of h′F for observing storm induced ESF and scintillation compared to reported quiet time values is noted. The results are discussed in terms of storm time variabilities in electric fields, neutral wind system and composition changes.  相似文献   

17.
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18.
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   

19.
Numerical calculations of the thermospheric and ionospheric parameters above EISCAT are presented for quiet geomagnetic conditions in summer. The Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) was used. The numerical results were obtained both with a self-consistent calculation of the electric fields of magnetospheric and dynamo-action origin and with the magnetospheric electric fields only. It was found that the dynamo-electric field has some effect on the ionospheric convection pattern during quiet geomagnetic conditions. It has a marked effect mainly on the zonal neutral wind component above EISCAT (±20m/s at 140 km altitude). We have studied the effects of various field-aligned current (FAC) distributions on thermosphere/ionosphere parameters and we show that a qualitative agreement can be obtained with region-I and -II FAC zones at 75° and 65° geomagnetic latitude, respectively. The maximum FAC intensities have been assumed at 03–21 MLT for both regions with peak values of 2.5 × 10–7 Am–2 (region I) and 1.25 × 10–7 A m–2 (region II). These results are in agreement with statistical potential distribution and FAC models constructed by use of EISCAT data. The lack of decreased electron density in the night-time sector as observed by the EISCAT radar was found to be due to the spatial distribution of ionospheric convection resulting from electric fields of magnetospheric origin.  相似文献   

20.
Summary Direct measurements of the thermal plasma parameters in the topside ionosphere reveal variations of the plasmasphere boundary in the dusk sector. The ACTIVE satellite's near-polar orbits at altitudes of 500 – 1800 km around winter solstice 1989 were used to study the bulge region of the plasmasphere during intervals with different levels of geomagnetic agitation. The narrow, sharply defined trough in electron concentration corresponding to the plasmapause under quiet conditions situated at L = 6 – 7 moved to lower L-values with increasing geomagnetic activity. This narrow trough can be found in all main ion constituents. During periods of moderate geomagnetic activity, following the onset of a weak magnetic storm, a portion of the plasmaspheric bulge region was separated from the main plasmaspheric body. This can be seen in the outer ionosphere as an inner narrow trough at lower L-value. Troughs in light ions need no longer coincide with this in electron concentration. He+ is the most sensitive constituent reflecting the dusk sector plasmaspheric situation at this altitude.Dedicated to the Memory of Professor Karel P  相似文献   

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