ISSN:0048-6604    

DOI:10.1029/RS021i003p00285

年代:1986

数据来源: WILEY

摘要:

Oblique propagation traces observed by an airborne ionosonde at different ranges from the Platteville heater facility during a period of overdense heating have been simulated by using a representative ionospheric model and standard ray‐tracing techniques. The heater frequency used during the time discussed in this paper was 6.2 MHz, whilef0F2was approximately 8 MHz. The plasma frequency of 6.2 MHz was deduced to occur at approximately 260‐km altitude. The simulated ionograms are found to reproduce accurately the main features of the observed ionograms, over a wide range of ionosonde to heater distances. Comparison of the simulated and observed ionograms indicates that the irregularities created by the heater existed at altitudes of 200 to at least 280 km, over an area of radius approximately 100

ISSN:0048-6604    

DOI:10.1029/RS021i003p00286

年代:1986

数据来源: WILEY

摘要:

A recently developed ionosonde (called a disonde) designed for low‐budget research projects, is described briefly. It is capable of measuring the comparative signal strengths and the angles of arrival of signals returning from the ionosphere. In addition, phase‐path information is available. The capabilities of the system are illustrated by some sample recordings and there is some discussion on these recordings. In addition, the capacity of this system (and a similar system which it replaced) to obtain research results is illustrated by discussing some results already produ

ISSN:0048-6604    

DOI:10.1029/RS021i003p00297

年代:1986

数据来源: WILEY

摘要:

Recent angle of arrival measurements of echoes reflected from sporadicElayers show that those layers are frequently tilted in different directions with deviations from the horizontal ranging up to 30°. The observations also indicate that structure sizes ofEsare relatively small, on the order of 50 km. Strong tilts ofEscan launch HF rays into the whispering gallery mode, and can cause large errors in HF direction finding. They also permit the interpretation of nonblanketingEsas a geometrical effect and not an optical property. The consequences of those findings for HF modelling will be discussed

ISSN:0048-6604    

DOI:10.1029/RS021i003p00304

年代:1986

数据来源: WILEY

摘要:

By using an HF radar which produces a steerable beam about 4° wide and measures angle of arrival and Doppler shift of radio echoes, the structure of various types of mid‐latitude sporadicE(Es) has been determined. Totally reflectingEsis a very smooth layer, tilted less than 1° from the horizontal. Partially reflectingEsconsists of clouds of ionization. These clouds vary in size from a few kilometers to 25 km in the direction of movement and larger in the transverse direction. Echoes often disappear rapidly: the clouds either disappear quickly or have sharp edges. SpreadEshas a curious structure of small clouds, each of which reflects only for a few seconds, but each cloud moves with the same velocity, typically 100 m/s, even though the heights of the clouds vary up to 10 km. It is difficult to reconcile this finding with the presence of wind she

ISSN:0048-6604    

DOI:10.1029/RS021i003p00309

年代:1986

数据来源: WILEY

摘要:

A technique is described for obtaining photographs of the patterns produced by the infrared hydroxyl airglow emission in the night sky by using exposure times of less than l min, and some examples of such patterns are shown. A photometer capable of obtaining the temperature of the emitting region at 3‐min intervals is also described, and an example of a temperature run on a dynamically disturbed night, with accompanying pattern photographs, is presented. Some references to work on the influence of gravity waves upon the hydroxyl airglow intensity are given and briefly discussed in relation to the present observational result

ISSN:0048-6604    

DOI:10.1029/RS021i003p00313

年代:1986

数据来源: WILEY

摘要:

The availability of representative empirical models of the variation of the electron concentration with height in the ionosphere is one critical element in the development of practical schemes for providing reliable HF radio propagation predictions. The degree to which a specific model succeeds must be judged against three criteria: (1) quality of profile match: the model must reproduce the range ofN(h) profiles encountered in practice; this match should be maintained in the first and second derivatives with height; (2) availability and simplicity of the external data required for profile specification: input data which consist of only those parameters routinely scaled from ionograms and available from CCIR predictions best fit this criterion; (3) numerical complexity: preferably the mathematical algorithms describing the model should be as simple as possible. These criteria conflict so that schemes have been developed optimized with respect to one or two of them at the expense of the other(s), the choice being driven by the application. In this paper, four such schemes are reviewed and contrasted in the light of these criteria and usage in practice. It is concluded that the Booker (1977) “skeleton” profile approach is best for simulating a known profile for precision radio wave studies, while the Dudeney (1978) technique provides good overall performance for general purpose communications predictions. The performance of the scheme currently recommended by the CCIR (Bradley and Dudeney, 1973a) cannot match these two, and should be superceded except where the need for mathematical simplicity is of overriding importance. The International Reference Ionosphere profile is found to have significant disadvantages for communications work with respect to all three crite

ISSN:0048-6604    

DOI:10.1029/RS021i003p00319

年代:1986

数据来源: WILEY

摘要:

Rapid progress in the integrated circuit market has led to new advanced techniques in the remote probing of the ionosphere with HF radio waves. The classical ionosonde which measured virtual height as a function of frequency expanded into a geophysical research tool by measuring all the observables contained in the electromagnetic signals reflected from the ionosphere: amplitude, phase, Doppler, incidence angle, and polarization. A receiving antenna array and high speed digital processing provide the desired spatial and temporal resolution. The current emphasis is on both the on‐line and off‐line postprocessing of the multiparameter ionogram data to extract the geophysically important ionospheric characteristics: the vertical electron density profiles, horizontal gradients (tilts and waves), plasma drift, the mid‐latitudeFregion trough, and auroral and equatorial spreadF. Digital ionosonds deployed in the polar cap and the auroral zone have helped to obtain a better understanding of some of the high‐latitude features, and measurements of the equatorial spreadFhave shown the development and motion of theFregion bubbles. HF coherent radar techniques for studying ionospheric irregularity structures measure the velocity of irregularities with scale sizes of one half the radio wavelength. They have mainly been used in the northern auror

ISSN:0048-6604    

DOI:10.1029/RS021i003p00331

年代:1986

数据来源: WILEY

摘要:

An introduction to the history and intentions of the International Reference Ionosphere (IRI) is given and future plans are outlined. The description of the topside electron density profile in the IRI is based on Bent's summary of topside sounder measurements, mainly Alouette. Instead of Bent's tabular form, the IRI has the advantage of an analytical description. Our comparison with AEROS satellite data shows that the IRI model is inaccurate in its description of the latitudinal behavior of the electron density in the topside ionosphere close to the magnetic equator. An improved IRI formula is proposed that closely follows the experimental data. The present IRI is restricted to solar activities reached during the last solar cycle 20. Measurements during the present solar cycle indicate a saturation effect for very high solar activities.

ISSN:0048-6604    

DOI:10.1029/RS021i003p00343

年代:1986

数据来源: WILEY

摘要:

During 1984 total electron content (TEC) data were gathered from Melbourne, a mid‐latitude station, and from Macquarie Island in the southern auroral zone, using the Faraday rotation of geostationary satellite signals. Large‐scale fluctuations in the TEC due to auroral activity were observed from Macquarie Island, and some of these disturbances were seen to propagate towards Melbourne with speeds of 200 to 1,000 m/s. Large‐scale rapid decreases in TEC were observed during the evening hours of about one third of autumn equinox days studied. These decreases occurred at a geomagnetic latitude of approximately 60°S and could be associated with the main ionospheric trough travelling through the ray path from the satellite to the receiving s

ISSN:0048-6604    

DOI:10.1029/RS021i003p00347

年代:1986

数据来源: WILEY