Directional currents in nocturnal E-region layers     

H. Rishbeth  J.C.G. Walker 《Planetary and Space Science》1982,30(2):209-214

In the mid-latitude E-region, the wind-shear mechanism produces thin ionized layers at levels where the vertical ion velocity is zero. We show that such layers conduct electric current only towards the magnetic equator, and not in the zonal direction. We surmise that this property may influence the electric field distribution in the nocturnal ionosphere, and possibly also the coupling between ion drifts and neutral air winds in the F-region. Detailed case studies of nocturnal layers located near the peak of ion Pedersen conductivity (around 130km) are needed to test this idea.  相似文献   

Theoretical ion densities in the lower ionosphere     

R.W. Schunk  J.C.G. Walker 《Planetary and Space Science》1973,21(11):1875-1896

We have solved the coupled momentum and continuity equations for NO⁺, O₂⁺, and O⁺ions in the E- and F-regions of the ionosphere. This theoretical model has enabled us to examine the relative importance of various processes that affect molecular ion densities. We find that transport processes are not important during the day; the molecular ions are in chemical equilibrium at all altitudes. At night, however, both diffusion and vertical drifts induced by winds or electric fields are important in determining molecular ion densities below about 200 km. Molecular ion densities are insensitive to the O⁺ density distribution and so are little affected by decay of the nocturnal F-region or by processes, such as a protonospheric flux, that retard this decay. The O⁺ density profile, on the other hand, is insensitive to molecular ion densities, although the O⁺ diffusion equation is formally coupled to molecular ion densities by the polarization electrostatic field. Nitric oxide plays an important role in determining the NO⁺ to O₂⁺ ratio in the E-region, particularly at night. Nocturnal sources of ionization are required to maintain the E-region through the night. Vertical velocities induced by expansion and contraction of the neutral atmosphere are too small to affect ion densities at any altitude.  相似文献   

Atmospheric expansion from Joule heating     

Howard F. Bates 《Planetary and Space Science》1974,22(6):925-937

An expression for the vertical velocity of the neutral atmosphere in the F-region is derived for Joule heating by the electric field that drives the auroral electrojet. When only vertical expansion is allowed, it is found that the vertical wind must always increase monotonically with altitude. The heating rate is proportional to the F-region ion density, so that appreciable heating, even during high electric fields, requires some production mechanism of ionization such as auroral secondary ionization or solar photoionization, in the lower F-region. Once started at night, when an ionizing source is present in the lower F-region, the expansion of the atmosphere transports ionization upward, thereby increasing the heating rate, and hence the expansion rate, i.e. positive feedback. Electric field strengths and F-region ion densities of 50 mV/m and 2 × 10¹¹e/m³, respectively, will produce vertal neutral wind speeds of several tens of m/sec in the 300–500 km altitude range. During periods of high magnetic activity, i.e. high electric field, Joule heating can produce large increases in the relative N₂ concentration in the upper F-region; computations made with a simple model suggest that tenfold increases can occur at 400 km altitude $\text{1}\text{2?1}\text{hr}$ after the onset of magnetic activity, a result in agreement with satellite observations. When the Joule heating theory is applied to incoherent scatter data taken during one period of high heating, the horizontal electric field in the F-region is found to decrease markedly, possibly approaching zero as the field penetrates a weak, discrete auroral arc; the decrease began 10–20 km from the arc.  相似文献   

Modeling the midlatitude F-region ionospheric storm using east-west drift and a meridional wind     

D.N. Anderson 《Planetary and Space Science》1976,24(1):69-77

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 $\text{E}\text{×}\text{B}$ drift. In this investigation only the neutral wind's meridional component and east-west $\text{E}\text{×}\text{B}$ 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   

Electrical coupling of the E- and F-regions and its effect on F-region drifts and winds     

R.A. Heelis  P.C. Kendall  R.J. Moffett  D.W. Windle  H. Rishbeth 《Planetary and Space Science》1974,22(5):743-756

Electric currents, generated by thermospheric winds, flow along the geomagnetic field lines linking the E-and F-regions. Their effects on the electric field distribution are investigated by solving the electrical and dynamical equations. The input data include appropriate models of the F-region tidal winds, the thermospheric pressure distribution and the E-and F-layer concentrations. At the magnetic equator, the calculated neutral air wind at 240 km height has a prevailling eastward component of 55 m sec^-1 and the west-east and vertical ion drifts agree in their general form with incoherent scatter data from Jicamarca  相似文献   

The calculated and observed diurnal variation of the ionosphere over Millstone Hill on 23–24 March 1970     

R.G. Roble 《Planetary and Space Science》1975,23(7):1017-1033

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 T_e, T_i 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 $\text{10}{}^{11}\text{cm}{}^3$ 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   

Comparative studies of E-region ionospheric drifts and meteor winds     

D.G. Felgate  A.N. Hunter  S.P. Kingsley  H.G. Muller 《Planetary and Space Science》1975,23(3):389-400

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   

Time-dependent behaviour of a stable auroral red arc excited by an electric field     

R.G. RobleR.E. Dickinson 《Planetary and Space Science》1972

We examine the electric field hypothesis as a possible explanation of a stable auroral red arc. An electric field perpendicular to the geomagnetic field in the ionosphere heats the ambient F-region electrons and ions. Given large enough electric fields, the electrons can be heated sufficiently to excite the OI (¹D) term of atomic oxygen by electron impact, giving rise to the λ6300 emission characteristic of the red arc. The electron and ion heating rates are determined by the relative drift between the plasma and neutral gas.  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   

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   

Ion momentum and energy transfer rates for charge exchange collisions     

J. Horwitz  P.M. Banks 《Planetary and Space Science》1973,21(11):1975-1981

The rates of momentum and energy transfer have been obtained for charge exchange collisions between ion and neutral gases having arbitrary Maxwellian temperatures T_i and T_n and bulk transport velocities c_i and c_n. The results are directly applicable to the F-region of the ionosphere where O⁺ - O charge is the dominant mechanism affecting ion momentum and energy transfer.  相似文献   

Evidence that auroral zone electric fields act in opposition to superrotation of the upper atmosphere     

Michael C. Kelley 《Planetary and Space Science》1976,24(4):355-357

The average auroral zone electric field pattern has been studied to determine whether such fields can, as has been suggested, drive the super-rotation of the upper atmosphere. It is shown that the local time averaged meridional electric field is small and, in fact, poleward, which would tend to drive a prevailing westerly wind. When averaged only over the dayside, where ion drag should be most important due to the higher ion density, the poleward average is even more pronounced. Thus at high latitudes ion drag acts to drive a prevailing neutral wind to the west. Model calculations indicate that without including electric fields the prevailing wind at mid-latitudes should be to the west, due to higher ion drag on the dayside. Including the present results will increase ion drag on the dayside and further enhance this effect. These results thus suggest that at middle and high latitudes the upper atmosphere does not superrotate.  相似文献   

Transport equations for aeronomy     

R.W. Schunk 《Planetary and Space Science》1975,23(3):437-485

In this paper we present results for a general system of transport equations appropriate to a multi-constituent gas mixture. This system includes a continuity, momentum, internal energy, pressure tensor and heat flow equation for each species. The results can be applied to both collision dominated and collisionless plasmas with there being explicit limits derived for the validity of the various expressions. In the limit of very frequent collisions the pressure tensor and heat flow equations give the usual Navier-Stokes results for the viscous stress tensor and heat flow vector. Furthermore, the momentum equation includes thermal diffusion and thermoelectric transport coefficients equivalent to the second approximation of Chapman and Cowling. The basic system of equations has been applied to different regions of the ionosphere and neutral atmosphere. It is found that: (1) The viscous stress tensor and heat flow expressions used in previous studies of the neutral thermosphere may not be appropriate; (2) The transport coefficients normally used for mid-latitude F2-region and topside studies seem to be adequate; (3) The high speed flow of plasma in the polar topside ionosphere is likely to be strongly affected by stresses and heat flow; and (4) E- and F-region ionization at high latitudes is substantially affected by stresses and heat flow.  相似文献   

Auroral ion velocity distributions for a polarization collision model   总被引：1，自引：0，他引：1  

J.-P. St-Maurice  R.W. Schunk 《Planetary and Space Science》1977,25(3):243-260

We have calculated the effect that convection electric fields have on the velocity distribution of auroral ions at the altitudes where the plasma is weakly-ionized and where the various ion-neutral collision frequencies are much smaller than the ion cyclotron frequencies, i.e. between about 130 and 300 km. The appropriate Boltzmann equation has been solved by expanding the ion velocity distribution function in a generalized orthogonal polynomial series about a bi-Maxwellian weight factor. We have retained enough terms in the series expansion to enable us to obtain reliable quantitative results for electric field strengths as large as 90 mV m^?1. Although we have considered a range of ion-neutral scattering mechanisms, our main emphasis has been devoted to the long-range polarization interaction. In general, we have found that to lowest order the ion velocity distribution is better represented by a two-temperature or bi-Maxwellian distribution than by a one-temperature Maxwellian, with there being different ion temperatures parallel and perpendicular to the geomagnetic field. However, the departures from this zeroth-order bi-Maxwellian distribution become significant when the ion drift velocity approaches (or exceeds) the neutral thermal speed.  相似文献   

Radar Backscatter from Underdense Meteors and Diffusion Rates     

Werner Singer  Ralph Latteck  Luis Federico Millan  Nick J. Mitchell  Jens Fiedler 《Earth, Moon, and Planets》2008,102(1-4):403-409

Many meteoroids burn up between about 120 km and 70 km, deposit metals and dust and form ionized trails which are detected by radars. Model studies about the influence of neutral or positively charged background dust on the ambipolar diffusion indicate that significant smaller decay times should be observed for weak meteor echoes compared to strong meteor echoes which can affect the estimation of temperatures. The variation of meteor decay times in dependence on echo strength, height, and season was studied using radar observations at 69° N, 22° S, and 67° S. Significantly reduced decay times were found for weak echoes below about 88 km at low latitudes throughout the year, and at high latitudes with the exception of summer. In summer at high latitudes, decreasing decay times of weak and strong meteors are observed at altitudes below about 85 km during the appearance of noctilucent clouds. The impact of reduced decay times on the estimation of neutral temperatures from decay times is discussed.  相似文献   

An analysis of auroral E region neutral winds based on incoherent scatter radar observations at Chatanika     

R.H. Comfort  S.T. Wu  G.R. Swenson 《Planetary and Space Science》1976,24(6):541-560

Auroral E region neutral winds determined from incoherent scatter radar observations at Chatanika, AK, during geomagnetic disturbances (15 May 1974) are compared with detailed theoretical calculations of neutral velocities for these conditions. The theoretical velocities are obtained by numerically solving the ion and neutral momentum equations in the ion drag approximation, including coriolis and viscous forces, using observed electric fields and electron densities. Large vertical gradients are found in the calculated velocities for altitudes below about 130 km. As a consequence of this structure and fluctuations in the electron density profiles, the data analysis procedure of Brekke et al. (1973) for obtaining neutral winds from radar data is found to underestimate the wind speed by up to 40%, but it determines the direction and temporal structure reasonably well. Comparison of observed neutral velocities with calculated values shows that ion drag alone cannot account for the observations. An equation is derived to estimate the pressure gradients required to resolve the discrepancy between calculated and observed neutral winds. Accelerations due to these pressure gradients are of the same order as those due to ion drag, but at least an order of magnitude larger than those due to solar heating. Directions of the horizontal pressure gradients are consistent with expected locations of auroral heating. During geomagnetic disturbances, ion drag and auroral heating both appear to play important roles in the generation and modification of neutral winds.  相似文献   

Auroral ion velocity distribution function: Generalized polynomial solution of Boltzmann's equation     

D. Hubert 《Planetary and Space Science》1983,31(1):119-127

The ion distribution function is calculated for the E and the F regions of the auroral latitudes. In these regions the plasma is weakly ionized and there exist convective electric fields which may attain very significant intensities. Boltzmann's equation is solved in the limit where the ion-neutral collision frequency is much lower than the ion gyrofrequency. This solution is obtained in the form of a generalized polynomial series expansion starting from a good zeroth-order approximation. With this weight function, and considering a development to the order of the 32 moments, good approximations are obtained for high electric fields. The resonant charge exchange model and the polarization model are successively considered. The Post-Rosenbluth instability threshold is discussed for the above two models.  相似文献   

The behaviour of the midlatitude F-region at the time of four magnetospheric substorms during the night of 29/30 October 1973     

M.M. Gogoshev  K.B. Serafimov  Ts.N. Gogosheva  K.M. Kazakov 《Planetary and Space Science》1976,24(3):293-298

The data from observations of the geomagnetic field, ionospheric parameters and atmospheric emissions, carried out at four midlatitude station in Bulgaria are analysed. The observations refer to the geomagnetic disturbance on 28/30 October 1973 (K_p^max = 7) and also to a very quiet period before it. It is shown that all four geomagnetic substorms during the night of 29/30 October influenced the midlatitude F-region. This is indicated by a lowering of the height of the F-region by ca. 50–70 km. Owing to this downward drift of ionisation the dissociative recombination and the intensity of the red line is accordingly increased. As an explanation of this phenomenon we suggest the action of the electric fields, which can at the same time be transported from the magnetosphere to the ionosphere.  相似文献   

Thermal balance of the mid-latitude F2-region at night     

G.J. Bailey  R.I. Footitt  R.I. Moffett 《Planetary and Space Science》1979,27(8):1063-1073

The thermal balance of the plasma in the night-time mid-latitude F2-region is examined using solutions of the steady-state O⁺ and electron heat balance equations. The required concentrations and field-aligned velocities are obtained from a simultaneous solution of the time-dependent O⁺ continuity and momentum equations.The results demonstrate the systematic trend for the O⁺ temperature to be 10–20 K greater than the electron temperature during the night at around 300 km, as observed at St. Santin by Bauer and Mazaudier. It is shown that frictional heating between the O⁺ and neutral gases is the cause of the O⁺ temperature being greater than the electron temperature; the greater the importance of frictional heating in the thermal balance the greater is the difference in the O⁺ and electron temperatures. A study is made of the roles played in the thermal balance of the plasma by the thermal conductivity of the O⁺ and electron gases; collisional heat transfer between O⁺ electrons and neutrals; frictional heating between the O⁺ and neutral gases; and advection and convection due to field-aligned O⁺ and electron motions. The results of the study show that, at around 300 km, electron cooling by excitation of the fine structure of the ground state of atomic oxygen plays a major role in the thermal balance of the electrons and, since the temperature of the ions is little affected by this electron cooling process, in determining the difference between the ion and electron temperatures.  相似文献   

Thermospheric observations combining chemical seeding and ground-based techniques—II. Ionospheric drifts and the Sq current system     

D. Rees  G. Haerendel  D.G. Felgate  K.H. Lloyd  C.H. Low 《Planetary and Space Science》1973,21(7):1237-1249

Two Skylark sounding rockets carrying chemical seeding payloads were launched from Woomera, South Australia in October 1969. In conjunction with these firings, the F-region drifts were determined with the Buckland Park aerial array and the results compared with the observed motion of the barium ion clouds. The local ionospheric Sq current system was calculated both from the observed ionospheric parameters and from ground-based magnetograms and the differences between the two results are discussed.  相似文献