Transmission of large-scale TIDs in the ionospheric F2-region

Large-scale travelling ionospheric disturbances (1.s. TIDs) have been investigated in order to derive the horizontal velocity dispersion by using f₀F2 data from four ionospheric observatories in Japan. It was found that the horizontal phase trace velocity lies between 300 and 1000ms⁻¹ with periods in the range 50 to 150 min. There is evidence that the derived velocity generally increases with increase of wave period. This is consistent with the dispersion predicted by the theory of the internal gravity waves. The azimuthal angles are distributed in ±35° sectors centered around 197° (measured clockwise from north), indicating that 1.s. TIDs may be obtainable when they are excited along the auroral zone of the same sector in longitude as that of the observatories. The average propagation direction shifts by 17° from south towards west. This clockwise shift is consistent with the rotation caused by the Coriolis effect. This means that the Coriolis effect cannot be ignored for the wave propagation of 1.s. TIDs. In addition to the positive correlation between TID speed and geomagnetic activity, the direction of wave propagation is found to be correlated with polar magnetic activity. The propagation direction is mostly southward during the period of large polar magnetic disturbances, while during the period of low magnetic activity the direction scatters considerably.     

Experimental daytime VLF ionospheric parameters

Measured field strengths from VLF transmitters are used to determine improved daytime values of ionospheric parameters to enable improved VLF propagation predictions. These parameters are the traditional H′ (height in km) and β (sharpness in km⁻¹) as used by Wait and by NOSC in their Earthionosphere waveguide computer program. They are found by comparing the predictions of the NOSC program with the observed VLF field strengths over both long and short paths.Experimental observations from two nearly north-south paths are used to determine the solar zenith angle dependence of both H′ and β for low latitude (or summer mid-latitude) conditions. These results are then used to predict the daytime variations in VLF field strengths with solar zenith angle (and hence time) on other suitable paths and good agreement is found with measurements made on these paths.The absolute value of β for overhead Sun is found to be 0.45 km⁻¹ and is principally determined by the attenuation on the very long, west to east, fully sunlit, 14.4 Mm path from NWC (Australia, 22°S) to San Francisco (37°N), after applying small corrections for the solar zenith angle variations along the path at midday. Further support is obtained from results from the 8.6 Mm path NDT (Japan) to San Francisco, an 8.2 Mm path NPM (Hawaii) to New Zealand, and an east to west 7.5 Mm path from NPM to Townsville, Australia. The conditions studied are solar maximum. The frequencies studied are 15–30 kHz.     

Field-aligned and field-perpendicular velocities in the ionospheric F2-layer

Incoherent scatter observations have shown that there is sometimes a detailed anticorrelation or ‘mirroring’ between V_∥ and V_⊥, the components of F2-layer plasma velocity parallel to and perpendicular to the geomagnetic field. In this paper we develop a simple theoretical model of the F2-layer and compute its response to applied perturbations of V_⊥, both steplike and oscillatory; in particular we investigate the phase and amplitude relationships between V_∥ and V_⊥ resulting from ion-drag and plasma diffusion. For periods of a few hours, the oscillations of V_∥ lag behind exact anticorrelation with V_⊥ by 0.1–0.2 cycle, but the time lags corresponding to these phase differences are only a fraction of 1 h and seem broadly compatible with observations previously reported from Arecibo and Malvern. We do not study the question of what causes the velocities to fluctuate in the first place.     

Latitudinal variation in the ionospheric parameters: a Soviet-Indian experiment by simultaneous launchings

Coordinated ion-neutral composition and electron density measurements have been carried out over Thumba (India) and Volgograd (U.S.S.R.), near sunrise. One of the launchings from Thumba revealed the turbopause to be around 110 km. Large fluctuations in ion and electron densities were also registered in the altitude region 105–125 km, along with oscillatory structures in the neutral composition, indicating that unusual conditions prevailed during this measurement. Contrary to expectations, ‘time synchronous’ launchings from Thumba and Volgograd revealed nearly identical distributions of neutral species. The turbopause altitudes during these flights were also the same within the limits of experimental uncertainty. These measurements confirm that the role of the turbopause and temperature are mutually independent in governing the distribution of neutral composition in the thermosphere.     

Reconstruction of travelling ionospheric disturbances parameters by a tomographic method

A tomographic method is proposed to reconstruct parameters of the inhomogeneous ionosphere on the basis of model representations using angles of arrival or total electron content. With such an approach, determining the function of the inhomogeneous ionosphere implies finding a set of parameters of TIDs. Suitable signals can be generated by satellites.     

Measurements of gradients in ionospheric parameters with a new nine-position experiment at Millstone Hill

A new nine-position experiment is now routinely carried out with the Millstone Hill incoherent scatter radars which allows estimation of spatial gradients in the measured ionospheric scalar parameters N_e, T_e, and T_i, and in the components of the ion velocity vector v_i. Use of this technique results in improved estimates of basic and derived parameters from incoherent scatter data at times of significant gradients. We detail the data analysis method and present the first results from this new experiment. The gradients in N_e and in the components of vi are used to compute the motion term in the ionospheric F region continuity equation ▿ · (Nv), which is then combined with ∂N/∂t to estimate the O⁺ recombination rate β at night. Meridional neutral winds U_mer are computed from the field-aligned ion velocity v_∥ and a calculation of the O⁺ diffusion velocity v_d, and it is found that horizontal gradients in the ion velocity field at times significantly affect the calculation of the neutral winds.     

Power spectra of VHF intensity scintillations from F2- and E-region ionospheric irregularities

An experiment is described for the routine study of scintillations and ionospheric irregularities at high-latitudes using NNSS satellites with additional coordinated observations by means of the EISCAT ionospheric radar facility. Early results, obtained during the development phase of the experiment, are presented of the power spectra of intensity fluctuations at 150 MHz observed at the equatorwards edge of the high-latitude irregularity zone. The spectra of 165 samples of night-time scintillation recorded during October 1982 to May 1983 show a spectral index with a mean value of −3.58 and a steepening of the spectral slope with increasing S₄. Some examples of scintillation arising from irregularities at E-layer height show spectral indices of magnitude generally smaller than for F-region cases. A few spectra have been found with a clear break in spectral slope at around 10 Hz, suggesting two regimes for irregularities of different scale sizes.     

The phase relationships of the ionospheric signatures of Pc1 geomagnetic pulsations

In this study we consider the phase relationships between the oscillations of various ionospheric signatures associated with Pcl geomagnetic pulsations. Investigations using a simple analytical method and a numerical model, which has proved successful when applied to longer period pulsations, both suggest that Doppler velocity oscillations should be predominantly in anti-phase with oscillations of the rates of change of group range and echo amplitude. However, observations indicate that the Doppler velocity oscillations are in quadrature with the other two types of oscillations. Possible causes for this discrepancy are suggested.     

Nonlinear solitary wave in the ionospheric E-region

A nonlinear wave equation for a solitary one-dimensional inhomogeneity is studied. It is similar to the diffusion equation with the diffusion coefficient depending on the phase velocity. The phase velocity depends, in turn, on the electron density. A weak inhomogeneity moves with the velocity close to that of the electric drift. If this velocity exceeds the ion acoustic speed the effective diffusion is negative, and the inhomogeneity grows and contracts. The velocity of the growing inhomogeneity becomes smaller. It absorbs weaker and faster moving inhomogeneities from the back side. In a stationary regime, the ionosphere will be filled with rare but strong inhomogeneities with sharp back sides.     

Travelling ionospheric disturbances and the effectiveness of powerful HF transmitters in ionospheric modification and radio location of the Moon

Using ray tracing we investigate, on a qualitative level and in the linear approximation, the effects of medium-scale travelling ionospheric disturbances (MS TIDs) arising when powerful HF radio transmitters are operated in conjunction with antenna arrays designed for ionospheric modification (heating) and for radio location of the Moon. It is shown that the HF radio wave focusing effect, arising during the movement of the MS TIDs, can give rise to a strong inhomogeneous and nonstationary modulation of the space-time distribution of the field intensity of a powerful radio transmitter both at heights near the reflection region (in heating experiments) and at the exit from the ionosphere (in radio location of the Moon). The excess of intensity over an unperturbed value for typical parameters of MS TIDs in experiments on ionospheric modification can reach values of hundreds of percent: a ‘spot’ of increased intensity of the wave field can have the size of about 1–10 km, and can move with a velocity close to the MS TID phase velocity.In the case of lunar radio location, the inhomogeneity and nonstationarity of the wave field intensity distribution at the exit from the ionosphere substantially complicates the evaluation of the corresponding distribution on the Moon's surface and the interpretation of the Moon-reflected radio signal characteristics.     

The accuracy of simple methods for determining the height of the maximum electron concentration of the F2-layer from scaled ionospheric characteristics

The techniques for estimating hmF2 from M(3000)F2 are reviewed with particular stress put upon those in which the effects of underlying ionization are accounted for by a correction (ΔM) to M(3000)F2, formulated in terms of the ratio foF2/foE(=x_E). The simplifying assumptions involved in the three practical implementations (Bradley and Dudeney, 1973; Dudeney, 1974; Bilitza et al., 1979) are emphasised and their consequences investigated quantitatively using a numerical simulation. The factors considered are the dependence upon ymF2, the importance of the underlying layer shape (in particular the significance of the F1-ledge), and the influence of the geomagnetic field.It is demonstrated that the correction technique relies upon ymF2 being a direct polynomial function of hmF2. Analysis of observational data suggests that this relationship holds in practice. Fluctuations in ymF2 about this mean variation are shown to produce only small effects which decrease in magnitude as the amount of underlying ionization increases. The results indicate that underlying layer shape becomes very important when a large amount of underlying ionization is present (x_E<2.5). However, the global morphology of the occurrence of the F1-ledge is such that it is invariably present in such circumstances (ignoring the polar regions). Hence, the ionosphere tends to assume a specific profile form for low x_E cases. The three implementations are shown all to fortuitously incorporate this behaviour. It is demonstrated that exclusion of the geomagnetic field introduces a very small extra uncertainty dependent upon gyrofrequency and geomagnetic latitude, which decreases as the amount of underlying ionization increases.The three implementations are compared and it is concluded that the Dudeney (1974) scheme gives the best overall performance. The more modern and complex Bilitza et al. (1979) scheme appears to have no performance advantages, whilst containing a sunspot number dependent geomagnetic term whose behaviour is irreconcilible with the numerical simulation. The Dudeney (1974) equation is shown to be accurate to between 4 and 5% at magnetic mid-latitudes. The scope for further refinement is considered but rejected as being unlikely to produce an increase in accuracy commensurate with the effort required.     

Internal structure of the equatorial ionospheric dynamo

Using the Sq current profiles measured with rocket born magnetometer, off the coast of Peru, by Daviset al. (J. geophys. Res. 72, 1845) comparison is made between measured and calculated profiles near noon on geomagnetic dip equator, and a mismatch is pointed out in the height pattern of Sq current. Theory is worked out to determine the eastward electric field (E_y) with which computed j_y (eastward current density) coincides with the observed one. It is found that the neutral wind plays very important rôle in keeping E_y height-independent. E_y is found to be about 0.6 mVm⁻¹, ranging from 0.5 to 0.7 mVm⁻¹ in some cases. Flow of meridional current is obtained and its effect on jet current construction is discussed.     

倍耐力F1赛道上的主角

F1赛道轮胎展实力 赛场外,来自世界各地的车迷们尽情享受着节日的狂欢,赛场上,咆哮的发动机和刺耳的轮胎摩擦声则给现场观众带来最直接的感官刺激,比赛中轮胎成了主角,上演了一幕幕戏剧性的瞬间：最受关注的车王舒马赫第—次进站就因为轮胎更换失误退赛,     

Ground and in situ excitation of waves in the ionospheric plasma

A review is presented of seven papers the contents of which range from ULF to VLF wave excitation in the ionospheric plasma by ground-based radio wave and acoustic wave sources, to in situ plasma wave excitation by satellite- and rocket-borne radio transmitters.     

Temporal variations of ionospheric waves in the D- and F-regions

It is shown that mesoscale ionospheric wave disturbances in the D- and F-regions regularly occur at all times of day, night and season (characteristic periods ~100, 24, 12.6 min) and are a characteristic property of dynamic processes in the ionosphere.     

Investigations of the winter anomaly in ionospheric absorption in January 1981

Ground-based and rocket-borne investigations were carried out in January 1981 in the Volgograd region to study space-time peculiarities of the winter anomaly in ionospheric radio wave absorption (WA). Electron-density altitude profiles N_e(h) were measured with rockets, by the coherent frequency method and by using electrostatic probes; temperature profiles T(h) were measured by a resistance thermometer: wind velocity and direction were measured by radio-observations of a chaff cloud and of the payload parachute drift. At the same time, ionospheric radio wave absorption was measured in Volgograd at two frequencies, 2.2 and 2.7 MHz, by the A1 method. The condition of the lower ionosphere could be determined from absorption data and from f min parameter data obtained from vertical sounding ionograms. “Salvo” launchings of the rockets were performed on 14 January, when absorption was anomalously large, and on 21 and 28 January, which were days of normal winter absorption.Data analysis has shown that N_e values on the day with excessive absorption exceeded the same values on a normal day at altitudes from 72 to 95 km; on 21 January N_c values exceeded those of 29 February 1980 (without WA) at all altitudes below ~ 90 km. The absorption at Volgograd on 28 January was somewhat higher than on 21 January and than at stations at higher latitude, which may be due to a stable local increase of N_e values in the altitude range 80–90 km. The temperature in the region of the N_e-enhanced values (up to the limit altitude of measurements, about 80 km) was below the standard temperature (COSPAR, 72), both on 14 January and on the normal days. Measurements carried out at night have shown that winter N_c values considerably exceeded those during the autumn. The zonal and meridional wind profiles (up to about 80 km) at Volgograd exhibit a stable eastward flux, both in the stratsophere and in the mesosphere. The value of the wind velocity meridional component on 21 January is close to zero at all altitudes. On 14 and 28 January the wind profiles show an irregular structure with large velocity gradients at all altitudes above about 50–60 km.The absorption data and f min data from a number of stations, viz. from Juliusruh to Yakutsk (in longitude) and from Arkhangel'sk to Rostov-on-Don (in latitude), show that anomalously excessive absorption occurred over a vast distance exceeding 100° of longitude at ~ 55° latitude and that, based on the dates of absorption maxima (f min), one may conclude that the source of the disturbance was moving from west to east. Data on the motion of the air as shown by rocket and radiometeoric observations, indicate the same wind direction in the stratosphere as in the mesosphere. These data and the constant pressure charts point to the conclusion that the enhanced radio absorption values at mid-latitudes may be explained by a transport of dry air rich in nitric oxide from the auroral zone towards lower latitudes. The transport is provided by a stable circumpolar vortex existing in winter time. This mechanism may explain both the normal and anomalous winter absorption, as well as the post-storm effect.     

Distributions of the irregularities which produce ionospheric scintillations

The distribution of nighttime irregularities which produce satellite scintillation has been examined for a midlatitude location using a large array of receivers. The irregularities are aligned along the earth's magnetic field and appear to extend from top to bottom of the F-region, being preferentially observed near the F-region ionization peak where they produce the strongest scintillations. A new method of mapping the horizontal distribution shows patches of various shapes and sizes but with no systematic structure.