The effects of neutral air winds on the electron content of the mid-latitude ionosphere and protonosphere in summer     

G.C. Sethia  G.J. Bailey  R.J. Moffett  J.K. Hargreaves 《Planetary and Space Science》1983,31(4):377-387

The effects of neutral air winds on the electron content (N_T) and other parameters of the mid-latitude ionosphere have been modelled by means of mathematical solutions of the time-dependent continuity and momentum equations for oxygen and hydrogen ions. The geometry is chosen to represent a propagation path between a geosynchronous satellite and a ground station, and the computations are compared with results from slant path observations of the ATS-6 radio beacon made at Lancaster (U.K.) and Boulder, Colorado (U.S.A.).It is demonstrated that the electron content responds markedly to the magnitude and phase of the neutral air winds and that the effect induced by the wind on the electron content shows a consistent quantitative relationship with the wind velocity, especially during daytime. Reasonable variations in the phase and magnitude of the wind produce a range of daily electron content patterns which encompass the range of daily variations observed.The computations show that the wind gives rise to enhanced filling of the protonosphere. This shows as a depressed value of the shape factor (F), which by definition means that a greater fraction of the ionization is at higher altitudes. The depression of F is enhanced by a poleward wind and is suppressed or even superseded by an equatorward wind through changes of the electron density distribution with altitude.  相似文献   

Mid-latitude electron content modelling: The role of interhemispheric coupling     

G.C. Sethia  G.J. Bailey  R.J. Moffett  J.K. Hargreaves 《Planetary and Space Science》1985,33(3):321-332

A modelling study of the electron content of the mid-latitude ionosphere and protonosphere has been carried out for solstice conditions using the mathematical model of Bailey (1983). In the model calculations coupled time-dependent O⁺, H⁺ continuity and momentum equations and O⁺, H⁺ and electron heat balance equations are solved for a magnetic shell extending over both hemispheres. The inclusion of interhemispheric flow of plasma and of heat balance has enabled us to investigate the role of interhemispheric coupling on the electron content and related shape parameters. The computed results are compared with results from slant path observations of the ATS-6 radio beacon made at Lancaster (U.K.) and Boulder, Colorado (U.S.A.).It has been found that the conjugate photoelectron heating has a major effect on the shape of the daily variation of slant slab thickness (τ) and also on the magnitude of the protonospheric content (N_p). Some of the main features of τ are closely related to the sunrise and sunset times in the conjugate ionosphere. Also it is found that night-time increases in total electron content (N_T) and F2 region peak electron density (N_max) in winter are natural consequences of ionization loss at low altitudes causing an enhanced downward flow of plasma from the protonosphere which is coupled to the summer hemisphere. One other important consequence of the coupled protonosphere is that the effects on N_T of the neutral air wind are not much different in winter from those in summer.  相似文献   

Ion transport in the mid-latitude F1-region     

R.J. Footitt  G.J. Bailey  R.J. Moffett 《Planetary and Space Science》1983,31(6):671-687

A study is made of electron concentration altitude profiles within the F1-layer. By using a mathematical model with a variety of atmospheric conditions and neutral air wind patterns we demonstrate the appearance of a daytime valley. Such valleys have been observed at St. Santin during summer for low-to-moderate levels of solar activity by Taieb et al. (1975,1978). Our calculations show that a valley occurs when there is a vertical shear in the meridional component of the neutral air wind velocity. This wind component must be directed poleward below the shear and equatorward above the shear. A valley will also occur when the meridional component of the neutral air wind velocity is directed poleward at all altitudes within the F1-region provided there is a rapid change in the velocity. We conclude from our results that the non-appearance of a valley at St. Santin during the winter and solar maximum observation periods of Taieb et al. (1975) is due to the neutral air wind pattern having an inappropriate form. Thus, it appears from observational evidence of the F1-layer that the pressure gradients existing in the neutral air during winter and at a solar maximum are unable to produce a wind pattern capable of producing a valley in the electron concentration profile.  相似文献   

The high latitude circulation and temperature structure of the thermosphere near solstice     

R.G. Roble  R.E. Dickinson  E.C. Ridley  B.A. Emery  P.B. Hays  T.L. Killeen  N.W. Spencer 《Planetary and Space Science》1983,31(12):1479-1499

The neutral gas temperature and circulation of the thermosphere are calculated for December solstice conditions near solar cycle maximum using NCAR's thermospheric general circulation model (TGCM). High-latitude heat and momentum sources significantly alter the basic solar-driven circulation during solstice. At F-region heights, the increased ion density in the summer hemisphere results in a larger ion drag momentum source for the neutral gas than in the winter hemisphere. As a result there are larger wind velocities and a greater tendency for the neutral gas to follow the magnetospheric convection pattern in the summer hemisphere than in the winter hemisphere. There is about three times more Joule heating in the summer than the winter hemisphere for moderate levels of geomagnetic activity due to the greater electrical conductivity in the summer E-region ionosphere.

The results of several TGCM runs are used to show that at F-region heights it is possible to linearly combine the solar-driven and high-latitude driven solutions to obtain the total temperature structure and circulation to within 10–20%. In the lower thermosphere, however, non-linear terms cause significant departures and a linear superposition of fields is not valid.

The F-region winds at high latitudes calculated by the TGCM are also compared to the meridional wind derived from measurements by the Fabry-Perot Interferometer (FPI) and the zonal wind derived from measurements by the Wind and Temperature Spectrometer (WATS) instruments onboard the Dynamics Explorer (DE−2) satellite for a summer and a winter day. For both examples, the observed and modeled wind patterns are in qualitative agreement, indicating a dominant control of high latitude winds by ion drag. The magnitude of the calculated winds (400–500 m s⁻¹) for the assumed 60 kV cross-tail potential, however, is smaller than that of the measured winds (500–800 m s⁻¹). This suggests the need for an increased ion drag momentum source in the model calculations due to enhanced electron densities, higher ion drift velocities, or some combination that needs to be further denned from the DE−2 satellite measurements.  相似文献   

The influence of the magnetospheric convection on the current and wind systems in the lower ionosphere     

M. V. Samokhin 《Astrophysics and Space Science》1976,44(1):141-150

The distributions of the current and the neutral winds driven by the electric field of convection are calculated in the dynamo-region of the ionosphere. At high latitudes the convection field drives the current and wind systems which consist of two cells with the centres at about 6 and 18 hours LT. In the northern hemisphere in the dawn cells winds and currents are clockwise, in the dusk cells they are counterclockwise. The appearance of the wind system shows that the upper atmosphere moves in the direction inverse to the displacement of the ionospheric ends of the magnetic flux tubes taking part in the convection. In the disturbed conditions the calculated wind system has the directions and velocities of the winds which are in a satisfactory agreement with the data of the irregularity drifts in the lower ionosphere in the winter season.  相似文献   

Ionospheric winds in the F-region and their effects on the limiting periods of gravity waves     

K. Davies  T.B. Jones  P.F. Weaver 《Planetary and Space Science》1973,21(1):147-149

Spectrum analyses of ionospheric electron density and content fluctuations show periods with a lower limit near 5 min. Interpretation of this cut off in terms of gravity waves in a windless atmosphere leads to unacceptably low thermospheric temperatures near 180°K. It is concluded that neutral winds reduce the apparent cut-off period in the ionosphere. The maximum horizontal wind speed obtained from cut-off data is about 100 m/sec.  相似文献   

Storm associated protonospheric depletion and recovery     

L. Kersley  J.A. Klobuchar 《Planetary and Space Science》1980,28(5):453-458

The average response of the protonosphere to geomagnetic activity has been determined from measurements of protonospheric electron content, line integrals along the transmission paths from the ATS-6 geostationary satellite to several stations. The results indicate an abrupt depletion of the protonosphere starting in the dusk sector on the first day of the storm. Minimum contents are found early on the third day, with greatest absolute departures from average levels being found at the station for which the transmission path intersects the lowest L-shells, although the percentage depletion is greater where the L-shells are higher. The recovery to mean levels is achieved by about days six–eight for the stations studied, but complete refilling of the protonospheric flux tubes is not achieved unless some two weeks of quiet have elapsed before the next onset of geomagnetic activity. Recovery in the winter hemisphere is found to be faster than that in summer. The results are discussed in terms of convective movements of the plasmapause and field aligned interactions of the protonospheric plasma with the underlying ionosphere.  相似文献   

The composition,structure, temperature and dynamics of the upper thermosphere in the polar regions during October to December 1981     

D. Rees  R. Gordon  T.J. Fuller-Rowell  M. Smith  G.R. Carignan  T.L. Killeen  P.B. Hays  N.W. Spencer 《Planetary and Space Science》1985,33(6):617-666

During the period October to December 1981, the Dynamics Explorer-2 (DE-2) spacecraft successively observed the South polar and the North polar regions, and recorded the temperature, composition and dynamical structure of the upper thermosphere. In October 1981, perigee was about 310 km altitude, in the vicinity of the South Pole, with the satellite orbit in the 09.00–21.00 L.T. plane. During late November and December, the perigee had precessed to the region of the North Pole, with the spacecraft sampling the upper thermosphere in the 06.00 18.00 L.T. plane. DE-2 observed the meridional wind with a Fabry-Perot interferometer (FPI), the zonal wind with the wind and temperature spectrometer (WATS), the neutral temperature with the FPI, and the neutral atmosphere composition and density with the neutral atmosphere composition spectrometer (NACS). A comparison between the South (summer) Pole and the North (winter) Pole data shows considerable seasonal differences in all neutral atmosphere parameters. The region of the summer pole, under similar geomagnetic and solar activity conditions, and at a level of about 300 km, is about 300 K warmer than that of the winter pole, and the density of atomic oxygen is strongly depleted (and nitrogen enhanced) around the summer pole (compared with the winter pole). Only part of the differences in temperature and composition structure can be related to the seasonal variation of solar insolation, however, and both polar regions display structural variations (with latitude and Universal Time) which are unmistakeable characteristics of strong magnetospheric forcing. The magnitude of the neutral atmosphere perturbations in winds, temperature, density and composition within both summer and winter polar regions all increase with increasing levels of geomagnetic activity.The UCL 3-dimensional time dependent global model has been used to simulate the diurnal, seasonal and geomagnetic response of the neutral thermosphere, attempting to follow the major features of the solar and geomagnetic inputs to the thermosphere which were present during the late 1981 period.In the UCL model, geomagnetic forcing is characterized by semi-empirical models of the polar electric field which show a dependence on the Y component of the Interplanetary Magnetic Field, due to Heppner and Maynard (1983), It is possible to obtain an overall agreement, in both summer and winter hemispheres, with the thermospheric wind structure at high latitudes, and to explain the geomagnetic control of the combined thermal and compositional structure both qualitatively and quantitatively. To obtain such agreement, however, it is essential to enhance the polar ionosphere as a consequence of magnetospheric particle precipitation, reflecting both widespread auroral (kilovolt) electrons, and “soft” cusp and polar cap sources. Geomagnetic forcing of the high latitude thermosphere cannot be explained purely by a polar convective electric field, and the thermal as well as ionising properties of these polar and auroral electron sources are crucial components of the total geomagnetic input.  相似文献   

A numerical study of polar ionospheric currents     

Hiroshi Maeda  Koichiro Maekawa 《Planetary and Space Science》1973,21(8):1287-1300

Numerical calculations for the electric current in the polar ionosphere have been made by assuming some realistic distributions of the electric field and conductivity. Two dynamo actions are taken into account; one of which is induced by ionospheric winds and the other by the solar wind. For the solar wind dynamo action, it is found that the secondary polarization field caused by non-uniform distribution of ionospheric conductivity is much larger than the primary field induced by the solar wind, suggesting its important effect on charged particles in the magnetosphere, and that the irrotational current having a source and sink is of the same order of magnitude as the solenoidal current closing its circuit in the ionosphere. It is also found that the solar wind is, in general, more effective than the ionospheric winds in producing polar current systems such as DP 1 and 2, but in some cases the ionospheric winds have a significant effect on the current distribution.  相似文献   

Interhemispheric flow of thermal plasma in a closed magnetic flux tube at mid-latitudes under sunspot minimum conditions     

G.J. Bailey  R.J. Moffett  J.A. Murphy 《Planetary and Space Science》1978,26(8):753-765

The coupled H⁺ and O⁺ time-dependent continuity and momentum equations are solved within a region of the L = 3 magnetic flux tube lying between (and including) the F2-layers of conjugate hemispheres. The method of solution is an extended and modified version of the Murphy et al. (1976) method. The model is used to study the coupling between the F2-layers of conjugate hemispheres during magnetically quiet periods.The results of the calculations strongly indicate that the protonosphere acts as a reservoir, with variable H⁺ content, which prevents direct coupling between the F2-layers of conjugate hemispheres. However there is generally a significant interhemispheric flow of plasma. This flow is caused by conditions in the summer and winter topside ionospheres and it maintains continuity in the plasma concentration within the protonosphere. There are times when the direction of flow is from the winter hemisphere to the summer hemisphere. It is suggested that maintenance of the winter F2-layer at night is not assisted directly by the F2-layer of the conjugate summer hemisphere.It is shown that during the first few days of protonosphere replenishment after a magnetic storm there is an upflow of H⁺ in the topside ionosphere at all times in the summer hemisphere. There is also an upflow of H⁺ during the daytime in both hemispheres. A comparison with the results obtained when the interhemispheric H⁺ flux is held permanently at zero shows that both F2-layers are little affected by the interhemispheric H⁺ flux. Nevertheless both F2-layers are affected by the H⁺ tube content of the protonosphere. When the H⁺ flux at 1000 km in one hemisphere is much greater than the H⁺ flux at 1000 km in the conjugate hemisphere, there is a corresponding signature in the interhemispheric H⁺ flux.The results suggest that there is insufficient time between magnetic storms for complete replenishment of the protonosphere to occur.  相似文献   

Ionospheric warming by neutral winds     

P. Stubbe 《Planetary and Space Science》1971

The effect of frictional heating by means of neutral winds on the ion and electron temperature in the undisturbed ionosphere is studied theoretically by solving a system of basic ionospheric and atmospheric equations. The study shows that both the electron and ion temperatures are increased in the night-time ionosphere through friction. In the region between 150 and 200 km T_i may exceed T₆ by as much as 130°. The increase of T_i due to friction amounts to about 100–200°, depending on the atmospheric model employed in calculating the neutral wind velocity. It is illustrated that frictional heating may be very important for the determination of the neutral temperature from measured ion temperature values.  相似文献   

Thermospheric winds in the cusp: Dependence of the latitude of the cusp     

R.W. Smith  K. Henriksen  C.S. Deehr  D. Rees  F.G. McCormac  G.G. Sivjee 《Planetary and Space Science》1985,33(3):305-313

The dayside thermospheric wind pattern as observed from Spitsbergen generally shows moderately strong westward winds with a small poleward component. The flow is almost zonal, frequently with sufficient westward velocity that parcels of air cross the noon meridian travelling towards the morning before turning antisunward towards the nightside across the polar cap. There have been some exceptions which are characterized by much weaker winds having been increased in the poleward direction but with a very much reduced westward component. Making use of the meridian scanning photometer data obtained simultaneously on the same site, it is clearly shown that the normal behaviour occurs when the cusp, as indicated by the region of high $\text{630}\text{428}\text{nm}$ and $\text{630}\text{558}\text{nm}$ photometric intensity ratios, is to the North of the station. Just below the latitude of the cusp, the strong thermospheric flow generated by neutral coupling to the strong westward convection in the dusk sector continues across the dayside. It is maintained in the zonal direction because of the balance between the poleward Coriolis force and the equatorward pressure force caused by cusp heating. Poleward of the high pressure region at the cusp the flow is diverted northward and initially makes much slower progress across the Polar Cap. When the auroral oval has expanded such that the cusp is well to the South of our Spitsbergen station, the thermosphere in the sampled region has been found to be within this slow flow zone. On such occasions, the nightside speeds are well in excess of those on the dayside, in contrast to the normal behavior of comparable dayside and nightside wind speeds.  相似文献   

The topside equatorial ionosphere during daytime: Elevated plasma temperatures,the transequatorial O⁺ breeze and the dynamics of minor ions     

G.I. Bailey  R.I. Moffett 《Planetary and Space Science》1979,27(8):1075-1085

Steady-state calculations are performed for the daytime equatorial F2-region and topside ionosphere. Values are calculated of the electron and ion temperatures and the concentrations and field-aligned velocities of the ions O⁺, H⁺ and He⁺. Account is taken of upward $\text{E × B}$ drift, a summer-winter horizontal neutral air wind and heating of the electron gas by thermalization of fast photoelectrons.The calculated plasma temperatures are in accord with experiment: at the equator there is an isothermal region from about 400–550 km altitude, with temperatures of about 2400 K around 800 km altitude. The transequatorial O⁺ breeze flux from summer to winter in the topside ionosphere is not greatly affected by the elevated plasma temperatures. The field-aligned velocities of H⁺ and He⁺ depend strongly on the O⁺ field-aligned velocity and on the presence of large temperature gradients. For the minor ions, ion-ion drag with O⁺ cannot be neglected for the topside ionosphere.  相似文献   

A numerical investigation of the formation and evolution of magnetospheric irregularities by the interchange of magnetic flux tubes     

P.G. Richards  K.D. Cole 《Planetary and Space Science》1979,27(11):1351-1360

The formation and evolution of magnetospheric irregularities by interchange of tubes of force, is studied through the solution of the electron and ion heat, and ion density equations. These calculations indicate that interchange of magnetic flux tubes may cause irregularities in the ionosphere and protonosphere. Ionospheric irregularities result from disturbance of the F-layer through electrodynamic movement vertically while the protonospheric irregularities result from variations in flux tube volume. It has been found that the temperature profile plays an important role in the variation of irregularity magnitude along flux tubes and that irregularities will persist for many hours at night. After several hours a small growth of the irregularities has been observed.  相似文献   

A numerical investigation of thermosphere-ionosphere interaction over Millstone Hill     

M.E. Hagan  J.M. Forbes  M. Codrescu   《Planetary and Space Science》1990,38(12):1541-1549

The upper thermosphere and F-region ionosphere system at 43°N is modelled for equinox and moderate solar conditions via a series of iterative calculations employing a thermospheric wind model and a one-dimensional ionospheric model which are mutually coupled. Several feedback loops within the system involving F₂-layer peak height, F₂-layer peak density, zonal wind, meridional wind, and Coriolis force are investigated to better understand the interactive aspect of ionosphere-thermosphere coupling. The interplay of primary importance involves the night-time ascent/descent of the F-layer due to equatorward/poleward neutral winds, the resulting changes in ion drag presented to the meridional and zonal wind fields, and the Coriolis force modification of the ion drag coupling. Wind shear and plasma profile shape are not significantly coupled. For magnetically undisturbed conditions, self-consistent treatment of these effects modifies a non-interactive “control” calculation by 20–35 m s⁻¹ in the wind field. During geomagnetically disturbed periods interactive processes play a more crucial role in determining thermospheric and ionospheric storm responses. Our calculations reveal wind enhancements of up to 100 m s⁻¹ associated with the lifting and negative-phase depletion of the F-region for prolonged magnetic disturbance conditions, the former mechanism accounting for a major portion of the effect.  相似文献   

Ion temperature troughs induced by a meridional neutral air wind in the night-time equatorial topside ionosphere     

G.J. Bailey  R.A. Heelis 《Planetary and Space Science》1980,28(9):895-906

A mathematical model has been developed to calculate consistent values for the O⁺ and H⁺ concentrations and field-aligned velocities and for the O⁺, H⁺ and electron temperatures in the night-time equatorial topside ionosphere. Using the results of the model calculations a study is made to establish the ability of F-region neutral air winds to produce observed ion temperature distributions and to investigate the characteristics of ion temperature troughs as functions of altitude, latitude and ionospheric composition. Solar activity conditions that give exospheric neutral gas temperatures 600 K, 800 K and 1000 K are considered.It is shown that the O⁺-H⁺ transition height represents an altitude limit above which ion cooling due to adiabatic expansion of the plasma is extremely small. The neutral atmosphere imposes a lower altitude limit since the neutral atmosphere quenches any ion cooling which field-aligned transport tends to produce. The northern and southern edges of the ion temperature troughs are shown to be restricted to a range of dip latitudes, the limiting dip latitudes being determined by the magnetic field line geometry and by the functional form of the F-region neutral air wind velocity. Both these parameters considerably influence the interaction between the neutral air and the plasma within magnetic flux tubes.  相似文献   

Jupiter's radiation belts     

Neil Brice  Thomas R. Mcdonough 《Icarus》1973,18(2):206-219

A model for the production and loss of energetic electrons in Jupiter's radiation belt is presented. It is postulated that the electrons originate in the solar wind and are diffused in toward the planet by perturbations which violate the particles' third adiabatic invariant. At large distances, magnetic perturbations, electric fields associated with magnotospheric convection, or interchange instabilities driven by thermal plasma gradients may drive the diffusion. Inside about 10 R_J the diffusion is probably driven by electric fields associated with the upper atmosphere dynamo which is driven by neutral winds in the ionosphere. The diurnal component of the dynamo wind fields produces a dawn-dusk asymmetry in the decimetric radiation from the electrons in the belts, and the lack of obvious measured asymmetries in the decimetric radiation measurements provides estimates of upper limits for these Jovian ionospheric neutral winds. The average diurnal winds are less than or comparable to those on earth, but only modest fluctuating winds are required to drive the energetic electron diffusion referred to above.The winds required to diffuse the energetic particles across the orbit of the satellite lo in a time equal to their drift period are also estimated. If Io is non-conducting, modest winds are required, but if Io is conducting, only small winds are needed. It is concluded that both protons and electrons are diffused in from the solar wind to small distances without serious losses occurring due to the particles being swept up by the satellites.Consideration of proton and electron diffusion in energy shows that once the electrons become relativistic, the ratio of proton to electron energy increases. Thus, if protons and electrons have the same energy in the solar wind, when the electrons reach nMeV, the protons will be nMeV if n ? 1 or n² MeV if n ? 1. If the proton-to-electron energy ratio is initially, e.g., 5, then these figures are 5n and 5n², respectively.  相似文献   

A New look at the ionosphere of Jupiter in light of the UVS occultation results     

J.C. McConnell  J.B. Holberg  G.R. Smith  B.R. Sandel  D.E. Shemansky  A.L. Broadfoot 《Planetary and Space Science》1982,30(2):151-167

Simple photochemical models cannot reconcile Jupiter's ionospheric electron density profiles with the observed neutral atmosphere. The location of the peak electron density predicted when the neutral atmosphere determined by theVoyager Ultraviolet Spectrometer is combined with simple models falls about 1000km lower than the peak determined by radio occultation. The locations and magnitudes of the peaks in electron density can be accounted for by including the effects of vertical transport of ions in the ionospheric models. This vertical transport may be induced by meridional winds in the neutral atmosphere or external electric fields. It is probable that precipitating particles and an altitude-variable H₂ vibrational temperature play important roles in determining the character of the iono?phere. In view of the complex relationship between the ionosphere and neutral atmosphere, an attempt to infer one from the other cannot succeed. However, combining independent information on the two leads to new insights into the coupling of the neutral atmosphere, the ionosphere and the magnetosphere.  相似文献   

The spectrum of electron content fluctuations in the ionosphere     

J. E. Titheridge 《Planetary and Space Science》1971,19(12):1593-1608

Continuous records of the electron content of the ionosphere, from 1965 to 1970, are used to obtain power spectra covering periods from 30 sec to 2 yr at latitudes of 34°S and 42°S. At periods up to 5 min, amplitudes were less than 0.2 per cent of the total electron content. Variations produced by gravity waves were very common in the range 20–80 min, with no preferred periods. The r.m.s. amplitude per octave A₀ was about 10¹⁵ electrons/m², or 0.6 per cent of the mean electron content. The amplitude increased during the day, particularly in winter when periodic components predominated. The cut-off at about 17 min was sharply defined, giving a mean scale height for the neutral atmosphere (at 300 km) of about 43 km in summer, 47 km on winter days and 42 km on winter nights.

From 12 hr to 1 month A₀ was about 12 per cent of the mean electron content in both summer and winter at 34°S, and 10 per cent at 42°S. The 24 hr and 27 day peaks were largest just before sunspot maximum, and almost disappeared near sunspot minimum. Variations between 1 and 27 days reflect the random occurrence of ionospheric storms and show no consistent peaks. Day to day and night to night variations were both about 10 per cent of the background content for periods from 2 days to 2 yr, apart from a slight decrease between 1 and 6 months.  相似文献   

Formation of blanketing sporadic E-layers at the magnetic equator due to horizontal wind shears     

C.A. Reddy  C.V. Devasia 《Planetary and Space Science》1973,21(5):811-817

A careful survey of quarter-hourly ionograms for the year 1969 has shown that blanketing layer type ionization irregularities occur on many occasions in the E-region of the ionosphere over Trivandrum (dip ～ 0.6°S). It is shown that horizontal shears of horizontal neutral winds are the most likely sources of such layer type irregularities at the magnetic equator. The horizontal wind shears of required magnitude are shown to be provided by internal gravity waves of short period. The rarity of E_s-layer occurrence is attributed to the stringent requirements on the amplitude and wave vector orientation of the relevant gravity waves generating the E_s-layers.  相似文献