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1.
Under magnetically quiet conditions, ionospheric plasma in the midlatitude F-region corotates with the Earth and relative east-west drifts are small compared to the corotation velocity. During magnetic storms, however, the enhanced dawn-to-dusk magnetospheric convection electric field often penetrates into the midlatitude region, where it maps into the ionosphere as a poleward electric field in the 18:00 LT sector, producing a strong westward plasma drift. To evaluate the ionospheric response to this east-west drift, the time-dependent O+ continuity equation is solved numerically, including the effects of production by photoionization, loss by charge exchange and transport by diffusion, neutral wind and E × B drift. In this investigation only the neutral wind's meridional component and east-west E × B drift are included. It is found that an enhanced equatorward wind coupled with westward drift produces an enhancement in the peak electron density (NMAX(F2)) and in the electron content (up to 1000 km) in the afternoon sector and a subsequent greater-than-normal decay in ionization after 18:00 LT. These results agree in general with midlatitude F-region ionospheric storm observations of NMAX(F2) and electron content which show an afternoon enhancement over quiet-time values followed by an abrupt transition to lower-than-normal values. Westward drift appears to be a sufficient mechanism in bringing about this sharp transition.  相似文献   

2.
The effect of lunar tides on the apparent ionospheric drift velocity (V) for an equatorial station Thumba (0.6°S dip) is computed by using nearly six years of data at fixed solar hours. Significant tides are observed in the E-region drifts, particularly around 12.00 hr and in the F-region drifts around 15.00 hr.A good correlation in the phases of the lunar tides in H and V is found to exist, suggesting a strong electrojet control of the horizontal ionospheric drift around these hours.  相似文献   

3.
A rocket C.W. radio propagation experiment has been used to measure electron density profiles and the results compared with values calculated from ionograms. In general the agreement is satisfactory but significant discrepancies in the rocket measurements, during the up-leg portions of several rocket flights above 110 km were observed and possible causes are discussed. In one flight the effect of a travelling ionospheric disturbance on the N(h) profile was recorded. Sporadic E strata with thicknesses of 0.6–0.8 km were recorded in these flights.  相似文献   

4.
Structured Pc 1 signals propagate in the ionospheric F2 region duct from their secondary sources at high latitudes to lower latitudes. Propagation directions to low latitude stations can be inferred from measurements of polarization parameters. The analysis of five events recorded at two low latitude stations (L = 1.9) are presented. Direction of arrival measurements are used to investigate the spatial and temporal structure of Pc 1 sources. Results show a close relationship between the structure of events identified in the frequency-time representation and direction of arrival measurement patterns. Multiple sources are sometimes indicated.  相似文献   

5.
Simultaneous spaced measurements of medium-latitude VLF/ELF emissions were carried out during the three northern winters from 1976 to 1979. The experiment was making use of two different kinds of direction-finding systems (a field-analysis method and a goniometer network) at two stations in Europe, namely Brorfelde in Denmark (L = 2.9) and Chambron-la-Foret in France (L = 1.9); this enabled us to locate the ionospheric exit regions of emissions over a wide range of L-values up to and beyond 4.0, the average plasmapause location. In order to study the time delay in the temporal evolution of VLF emissions or the longitudinal drift of the emissions, observations from the Moshiri Observatory in Japan, widely separated in longitude, are also used. The overall system of the VLF equipment installed at the three stations is described. Then we present the VLF/ELF data of good quality obtained during the final year's campaign (Nov. 1978–Feb. 1979). By making use of the direction-finding data, we were able to classify the observed emissions into several categories, and some early results for some of the emissions are presented.  相似文献   

6.
A numerical model of current F-region theory is use to calculate the diurnal variation of the mid-latitude ionospheric F-region over Millstone Hill on 23–24 March 1970, during quiet geomagnetic conditions. From the solar EUV flux, the model calculates at each altitude and time step primary photoelectron spectra and ionization rates of various ion species. The photoelectron transport equation is solved for the secondary ionization rates, photoelectron spectra, and various airglow excitation rates. Five ion continuity equations that include the effects of transport by diffusion, magnetospheric-ionospheric plasma transport, electric fields, and neutral winds are solved for the ion composition and electron density. The electron and ion temperatures are also calculated using the heating rates determined from chemical reactions, photoelectron collisions, and magnetospheric-ionospheric energy transport. The calculations are performed for a diurnal cycle considering a stationary field tube co-rotating with the Earth; only the vertical plasma drift caused by electric fields perpendicular to the geomagnetic field line is allowed but not the horizontal drift. The boundary conditions used in the model are determined from the incoherent scatter radar measurements of Te, Ti and O+ flux at 800km over Millstone Hill (Evans, 1971a). The component of the neutral thermospheric winds along the geomagnetic field has an important influence on the overall ionospheric structure. It is determined from a separate dynamic model of the neutral thermosphere, using incoherent scatter radar measurements.The calculated diurnal variation of the ionospheric structure agrees well with the values measured by the incoherent scatter radar when certain restrictions are placed on the solar EUV flux and model neutral atmospheric compositions. Namely, the solar EUV fluxes of Hinteregger (1970) are doubled and an atomic oxygen concentration of at least 1011cm3 at 120 km is required for the neutral model atmosphere. Calculations also show that the topside thermal structure of the ionosphere is primarily maintained by a flow of heat from the magnetosphere and the night-time F2-region is maintained in part by neutral winds, diffusion, electric fields, and plasma flow from the magnetosphere. The problem of maintaining the calculated night-time ionosphere at the observed values is also discussed.  相似文献   

7.
The principal advance of the ATS-6 satellite beacon experiment was the ability to deduce continuously the electron content along the entire slant path from ground-based measurements of the signal group delay. This feature has been exploited in conjunction with the more usual Faraday rotation technique to separate the total electron content into ionospheric and protonospheric components. The physical validity of the deduced quantities is investigated using a mathematical model of the plasmasphere in which integration of the time-dependent continuity and momentum equations for oxygen and hydrogen ions along selected L shells yields the ion concentrations and field-aligned fluxes. The ion concentrations are then integrated along the propagation path to various ground stations from ATS-6 to give computed values for comparison with observations. The mathematical model is used with different sets of atmospheric parameters to investigate the significance of ionospheric and protonospheric contents as derived from beacon data.The calculated electron concentrations are able to reproduce mid-latitude equinoctial electron content observations. The shape parameters τ and F can also be simulated by day, but night-time values do not match the observations well, a greater protonospheric content being required. The calculations show that the quantity Np, which is readily derived from ATS-6 observations, may be interpreted as the slant H+ content above some fixed height in the case of some stations (but not others) if the plasmasphere is reasonably full. The total slant content of H+ is approx. twice the value of Np, though it appears that for the Lancaster raypath a closer relationship exists between Np and the H+ tube content at L = 1.8. In general,Np is most closely related to the tube content for an L value slightly greater than the minimum L intersected along the raypath.  相似文献   

8.
《Icarus》1987,72(3):635-646
The occultation of a bright (K∼6) infrared star by Neptune revealed a central flash at two stations and provided accurate measurements of the limb position at these and several additional stations. We have fitted this data ensemble with a general model of an oblate atmosphere to deduce the oblateness e and equatorial radius a0 of Neptune at the 1-μbar pressure level, and the position angle pn of the projected spin axis. The results are e=0.0209±0.0014, a0=25269±10 km, pn=20.1°±1°. Parameters derived from fitting to the limb data alone are in excellent agreement with parameters derived from fitting to central flash data alone (E. Lellouch, W.B. Hubbard, B. Sicardy, F. Vilas, and P. Bouchet, 1986, Nature 324, 227–231), and the principal remaining source of uncertainty appears to be the Neptune-centered declination of the Earth at the time of occultation. As an alternative to the methane absorption model proposed by Lellouch et al., we explain an observed reduction in the central flash intensity by a decrease in temperature from 150 to 135°K as the pressure rises from 1 to 400 μbar. Implications of the oblateness results for Neptune interior models are briefly discussed.  相似文献   

9.
A method of estimating ionospheric drift velocities using single-site scintillation measurements is applied to determine a correlation coefficient of 0.55 between magnetic activity and F-region drift velocity near the auroral ionosphere. This method is based on the relationship between the drift velocity and the scintillation spectral breakpoint.  相似文献   

10.
A self-consistent, time-dependent numerical model of the aurora and high-latitude ionos-phere has been developed. It is used to study the response of ionospheric and atmospheric properties in regions subjected to electron bombardment. The time history of precipitation events is arbitrarily specified and computations are made for a variety of electron spectral energy distributions and flux magnitudes. These include soft electron precipitation, such as might occur on the poleward edge of the auroral oval and within the magnetospheric cleft, and harder spectra representative of particle precipitation commonly observed within and on the equatorward edge of the auroral oval. Both daytime and night-time aurorae are considered. The results of the calculations show that the response of various ionospheric and atmospheric parameters depends upon the spectral energy distribution and flux magnitudes of the precipitating electrons during the auroral event. Various properties respond with different time constants that are influenced by coupling processes described by the interactive model. The soft spectrum aurora affects mainly the ionospheric F region, where it causes increases in the electron density, electron temperature and the 6300 Å red line intensity from normal quiet background levels during both daytime and night-time aurora. The fractional variation is greater for the night-time aurora. The hard spectrum aurorae, in general, do not greatly affect the F-2 region of the ionosphere; however, in the F-1 and E regions, large increases from background conditions are shown to occur in the electron and ion temperatures, electron and ion densities, airglow emission rates and minor neutral constituent densities during the build-up phase of the auroral event. During the decay phase of the aurora, most of these properties decrease at nearly the same rate as the specified particle precipitation flux. However, some ionospheric and atmospheric species have a long memory of the auroral event. The odd nitrogen species N(4S) and NO probably do not ever reach steady-state densities between auroral storms.  相似文献   

11.
Using the combined measurements from a rocket flight through a stable intense sporadic E-layer, we examine the shortcomings of conventional wind shear theory of ion layer formation, principally in underestimating the role of the ambient ionospheric electric field. Our results imply that the ionospheric electric field may control the stability and precise location of such ionisation layers within a region of convergent ion flow.  相似文献   

12.
An attempt is made to analyse known experimental data on electron density and ion composition of the night-time ionosphere; the main ideas on the night-time E region ionization source are considered; the role of dynamic processes in the irregular structure formation of the night-time ionospheric E region is discussed.  相似文献   

13.
The polarization method of source location has been used on data from two low latitude stations (L = 1.9) to determine the exit region of structured Pc1 emissions from the magnetosphere into the ionosphere. Propagation directions in the ionospheric F2 duct can be inferred from measurements of polarization parameters made at the low latitude recording station. Measurements on six events indicated an average source L value of 3.2, which represented the sources being on the average 1.0 ± 0.5 Re inside the corresponding statistical plasmapause position.  相似文献   

14.
Rocket borne Langmuir probe measurements of electron temperature in the E-region are examined in relation to recent laboratory investigations of surface drift effects which can lead to erroneously high and time-dependent electron temperature measurements. The rocket data is consistent with the laboratory expectations thus supporting the suggested importance of surface effects in rocket measurements and in relation to the E-region discrepancy with simultaneous incoherent radar scatter measurements.  相似文献   

15.
Ionospheric drifts using total reflections from the E-region have been compared with neutral winds measured by meteor radar. Close agreement was found when both measurements were made in a common volume of atmosphere. Even with a separation of 700 km between the measuring regions the results were very similar. It is concluded that the drift technique does measure the movement of the neutral atmosphere in the altitude range 95–120 km. The agreement between measurements from widely separated regions indicates the horizontal scale of the wind structure is at least 700 km.  相似文献   

16.
When observed noontime values of the maximum electron density, NMAX(F2), in the ionospheric F2 region are plotted as a function of magnetic latitude, a curve is produced which has two peaks, one on either side of the dip equator at ±16° dip latitude. This paper theoretically investigates the daily variation of this latitudinal distribution in NMAX(F2) (the so-called Appleton or equatorial anomaly) and specifically attempts to account for the longitudinal differences observed between the American and Asian sectors.In Part II, models of the neutral atmosphere, production, loss and diffusion rates, neutral wind, and electric field are described and the electron densities obtained by solving the continuity equation utilizing these models are presented. In each sector, the extent to which the equatorial anomaly's daily variation is affected by changes in the geomagnetic field configuration, neutral wind, and E × B drift is examined. It is found that development of the anomaly is most sensitive to the electric field model assumed, and that the observed differences at the magnetic equator between the American and Asian sectors could be accounted for by an upward E × B drift which commences an hour or two earlier in the Asian sector.  相似文献   

17.
Photoelectrons of ionospheric origin have been observed for the first time at high altitudes (up to 7RE geocentric distance) using the suprathermal plasma analysers (SPA) on the GEOS satellites. At such high altitudes the photoelectron flux is confined within a few degrees of the magnetic field direction. We show how this flux may be identified and extracted from the background which is a combination of locally produced photoelectrons and ambient plasma. GEOS-2 results are presented to illustrate the “turn-on” of the photoelectron flux at dawn in the ionosphere. Data from GEOS-1 are used to study the behaviour of the photoelectron flux with equatorial geocentric distance from 3 to 7RE. The results compare favourably with theoretical models and with ionospheric observations at mid latitudes.  相似文献   

18.
Galactic cosmic rays (GCRs) encounter an outward-moving solar wind with cyclic magnetic-field fluctuation and turbulence. This causes convection and diffusion in the heliosphere. The GCR counts from the ground-based neutron monitor stations show intensity changes that are anti-correlated with the sunspot numbers with a lag of a few months. GCRs experience various types of modulation from different solar activity features and influence space weather and the terrestrial climate. In this work, we investigate certain aspects of the GCR modulation at low cut-off rigidity (R c≈1 GV) in relation to some solar and geomagnetic indices for the entire solar cycle 23 (1996?–?2008). We separately study the GCR modulation during the ascending phase of cycle 23 including its maximum (1996?–?2002) and the descending phase including its minimum (2003?–?2008). We find that during the descending phase, the GCR recoveries are much faster than those of the solar parameters with negative time-lag. The results are discussed in light of modulation models, including drift effects and previous results.  相似文献   

19.
This paper presents a picture of the north polar F layer and topside ionosphere obtained primarily from three satellites (Alouette 2, ISIS 1, ISIS 2), that passed over the region within a time interval of ca. 50 min on 25 April 1971, a magnetically quiet day. The horizontal distribution of electron densities at the peak of the F layer is found to be similar to synoptic results from the IGY. Energetic particle and ionospheric plasma data are also presented, and the F layer data are discussed in terms of these measurements, and also in terms of electric field and neutral N2 density measurements made by other satellites on other occasions. The major features observed are as follows: A tongue of F region ionization extends from the dayside across the polar cap, which is accounted for by antisunward drift due to magnetospheric convection. In the F layer and topside ionosphere, the main effect of auroral precipitation appears to be heating and expansion of the topside. A region of low F layer density appears on the morning side of the polar cap, which may be due to convection and possibly also to enhanced N2 densities.  相似文献   

20.
The paper describes a comparison of vertical electron drift in the F-region (Vz) measured by VHP incoherent scatter radar at Jicamarca with the corresponding variations of geomagnetic horizontal field (H) and the maximum frequency reflected from The Es layer (Es) at Huancayo during the geomagnetic storm period 7–9 March, 1970. The Vz is generally upward during the daytime at the equator, but during 7–9, March, 1970, Vz was negative for brief periods associated with negative bays in H. These periods of abnormally low or of downward Vz correspond closely with the period of complete disappearance of the q type of Es layer. The magnetic bays associated with the intensification of ring current do not affect the equatorial Es- q and it is only the negative bays in H at the equator due to the ionospheric current flowing westward, that cause sudden disappearance of Es? q. It is suggested that the q type of Es is due to cross-field instability created in the electrojet region due to interaction of northward magnetic field and vertical upward Hall polarization electric field when the plasma density gradient is upward. The sudden disappearances of Es? q are due to the reversal of the horizontal electric field in the equatorial ionosphere and thereby due to the reversal of the equatorial electrojet currents. These reversals of electric field may be due to the imposition on the normal Sq field of another westward electric field.  相似文献   

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