A scintillation theory of fading in long distance HF ionospheric communications

Scintillation theory is used to study the fading of radio waves returned from the ionospheric F-region in the HF band at oblique incidence. For both low and high penetration frequencies calculations are made as a function of wave frequency, but emphasis is given to behaviour near the maximum usable frequency for one-hop F-transmission over distances up to 4000 km. Estimates are made of

• 1.(i) the fluctuations of phase both for long-term (~ 1h) and for short-term (~ the fading correlation time),
• 2.(ii) the fading correlation distance,
• 3.(iii) the quasi-period of fading,
• 4.(iv) the twinkling correlation distance,
• 5.(v) the quasi-period of twinkling,
• 6.(vi) the angular departure of the arrival azimuth from the mean and
• 7.(vii) the correlation bandwidth.

The slow fluctuations often experienced in long distance HF radio communications are a manifestation of twinkling, rather than fading. Under normal conditions in the F-region the correlation bandwidth is so large that the bandwidth of transmission at HF is controlled by the dispersive properties of the ionosphere, rather than by the scattering properties. The reverse is true in the presence of spread-F. For sufficiently strong spread-F the correlation bandwidth for long distance HF radio communications is of the order of only 10 Hz, thereby creating the phenomenon known as flutter fading. Theoretical estimates of the scintillation parameters are compared with experience in long distance HF ionospheric communications over the last 60 years. Agreement is promising, but future experiments should be designed in the light of theory; existing observational data do not provide some of the information needed.     

VHF radio wave scattering due to range and frequency types of equatorial spread-F

Comparing vertical incidence ionograms during spread-F conditions at the equatorial station Huancayo and modified range time interrsity records of 50 MHz scatter echoes at Jicamarca, it has been shown that the range type of spread-F is very efficient for the back-scattering of VHF radio waves. On the otherhand, the frequency type of spread-F does not seem to produce strong echoes. It is suggested that the range type of spread-F ionogram is due to the reflection (ω = ω_p) of radio waves from large scale irregularities with structure as small as 3 m below or near the base of the F-region The frequency type spread-F ionogram is suggested due to scattering from large scale irregularities with no 3 m counterpart situated around the region of peak ionisation density.     

Weak nonlinear theory of the ionospheric response to atmospheric gravity waves in the F-region

The nonlinear ionospheric response to atmospheric gravity waves is studied in an approximate fashion using a new approach. The concept of nonlinear travelling ionospheric disturbances (TIDs) is outlined, and the nonlinear behaviour of atmospheric gravity waves is calculated. A principal result is that harmonics are generated which cause the wave velocity perturbation to deform. The ionospheric response is investigated by solving the continuity equation for ionization in the F-region. The distortion of the TIDs waveform produced by the nonlinear interactions is depicted. The nonlinear TIDs depart seriously from a cosinusoidal wave described by previous linear TID theory. The distorted TIDs appear as ‘sharp peak’ and ‘sawtooth’ waveform shapes. The ‘peaks’ can be upward or downward, and the ‘sawteeth’ forward or backward, depending on the wave parameters. The nonlinearly distorted TIDs show a good agreement with various observed ionospheric irregularities produced by atmospheric gravity waves.     

Automatic fitting of quasi-parabolic segments to ionospheric profiles with application to ground range estimation for single-station location

A method of automatically fitting a quasi-parabolic segment (QPS) model to measured profiles of electron concentration is described. The model consists of many smoothly joined quasi-parabolic segments. The base of the ionosphere is represented by a quasi-linear segment. This model has the advantage of possessing analytic solutions for ray quantities in a spherical ionosphere (neglecting the effect of the Earth's magnetic field). It is also able to represent measured vertical ionospheric profiles to within a few percent in electron concentration.The usefulness of the model is illustrated by an application to the single-station location (SSL) of a distant radio transmitter from angle-of-elevation measurements. The no magnetic field results can represent the ordinary mode and approximate results for the extraordinary mode can be obtained using a frequency scaling technique.     

Application of a scattering theory of VHF transequatorial propagation

Numerical application is made of the theory of scattering by long, curved, field-aligned irregularities of ionization density in the F-region developed by Ferguson and Booker. Using an intermediate-scale regime of irregularities with an outer scale equal to the scale height of the F-region and an inner scale equal to the ion gyroradius, combined with a small-scale regime with an outer scale equal to the ionic gyroradius and an inner scale equal to the electron gyroradius, calculations are made corresponding to (i) equatorial spread-F in the VHF and UHF bands, (ii) long-range transequatorial propagation of the type observed by Nielson and (iii) short-range transequatorial propagation of the type observed by Cohen and Bowles. The same ionospheric model yields field-strengths of the right order of magnitude in all three cases. The theory also predicts a focusing phenomenon that should be looked for experimentally.     

Auroral riometer absorptions and the F-region disturbances observed over a wide range of latitudes

Standard riometer data from a southern auroral station were compared with ionograms obtained at five stations positioned from sub-auroral to equatorial latitudes. The rapid onset in riometer absorption, during intense substorm activities in an equinoctial period, was associated with a sequential propagation of ionospheric disturbances deduced from the F-region parameters h′F and range spread-F. The time shift between absorption maxima and extrapolated commencement times of the disturbances was consistent with the presence of large-scale travelling ionospheric disturbances (TIDs), propagating equatorwards with velocities lying typically in the range 600–900 m s⁻¹, and with a median velocity of 720 m s⁻¹. It is suggested that the onset of TIDs is associated with high-energy particle precipitation, manifested by the occurrence of auroral absorption events. Similarity of absorption increases at the southern and northern conjugate points, found from a previous riometer study, would indicate that large-scale TIDs are simultaneously generated in both hemispheres.     

Sara Ruddick's theory of maternal thinking applied to traditional Irish mothering

This paper uses Sara Ruddick's theory of maternal thinking to explain patterns of Irish mothering that developed in Ireland following the Great Famine of 1845-1852. Ruddick's central thesis, that maternal thinking develops strategies for preserving the life of the child, fostering the child's growth, and shaping an acceptable child, is applied to the intersecting influences of famine memory, religion, education, and emigration in post-famine Ireland. The strict, moralistic, and highly inhibiting features of Irish culture that dominated the nineteenth and twentieth centuries are traceable to patterns of mothering that developed after the famine. While Irish mothers are often blamed for instilling values that stressed sexual repression and guilt, other cultural factors influenced maternal thinking. Mothers did foster highly repressive moral values that encouraged permanent celibacy and delayed marriage. This paper examines the larger cultural features that derived from political oppression and the famine as they imprinted these values.     

Application of refractive scintillation theory to radio transmission through the ionosphere and the solar wind,and to reflection from a rough ocean

The results of Booker and Majidiahi (1981) concerning refractive scattering by large-scale irregularities in a phase-changing screen are combined with the theory of diffractive scattering by small-scale irregularities in order to study three intensity scintillation phenomena. The first is the reflection of radio and optical waves from an ocean surface disturbed by a spectrum of water waves. The second is the scintillation of VHP, UHF and SHF radio waves traversing the ionospheric F-region. The third is the scintillation of VHF, UHF and SHF radio waves traversing the solar wind. In each case appropriate values are chosen for the mean square fluctuation of phase, for the outer scale, for the inner scale and for the spectral index. Spectral diagrams are drawn to show how the outer scale, the inner scale, the Fresnel scale, the focal scale, the lens scale and the peak scale vary with a relevant parameter (electromagnetic wave-frequency for the ocean, RMS fractional fluctuation of ionization density for the ionosphere, and distance of closest approach to the Sun for the solar wind). For the ionosphere and the solar wind, multiple refractive scattering by weak irregularities occurs in practice whereas it is strong single scattering that is assumed in the thin-screen theory ; potential consequences of this are discussed qualitatively.     

Simultaneous observations of travelling ionospheric disturbances by two-dimensional radio interferometry and the differential Doppler technique applied to satellite signals

The main object of the campaign reported here was to compare TID characteristics obtained from two essentially different observation techniques: (1) observation of the apparent angular position shifts of Virgo A by the Nançay radioheliograph (47.33°N, 2.15°E) gave azimuths and periods of travelling ionospheric disturbances (TIDs); (2) differential Doppler shifts of signals from NNSS-satellites recorded simultaneously at Tours (47.35°N, 0.70°E), Nançay and Besançon (47.32°N, 5.99°E) provided azimuths and latitudinal wavelengths. Observations were made during the period 10–30 November 1987, between 6 and 12 h UT. It is found that azimuths obtained from the two techniques are consistent if sufficient averaging over wave trains is performed: averaging over several hours for radio interferometry and averaging over the whole satellite trace for the differential Doppler technique. Averaging is necessary because of (1) the intrinsic dispersion in wave azimuth, (2) the broadness of observed wave spectra and the dispersive properties of gravity waves, and (3) the spatial separation of ionospheric points for the two techniques. Good agreement between the azimuths was achieved by setting the altitude of the TIDs, which is used in the differential Doppler analysis, to about 250 km, appreciably lower than the maximum in electron density (about 350 km). The mean azimuth of observed TIDs was 12° East from South with a standard deviation of about 30°. The dominant period and horizontal wavelength of the observed TIDs were 40 min and 450 km. The East-West coherence length of the TIDs was found to be only of the order of 200 km.     

Design and realization of a goniopolarimeter with application to the study of ionospheric tilts

The purpose of the paper is to describe a high frequency goniopolarimeter operating in the range of 3–30 MHz. The system uses four sensors, each of them is composed of two cross polarization active loop antennas oriented east-west and north-south. By “goniopolarimeter” we mean a system which determines both arrival angles (goniometer function), the type of the mode (O or X), the magnitude of this mode and the corresponding Doppler shift. It works with known broadcast transmitters and permits measurements over a large geographic area. The signal process deals with narrowband signals, polarization filtering, nonlinear frequency analysis and interferometry technique. We present some experimental results and discuss the application of this system to the study of ionospheric tilts.     

Evidence for a large scale electric field gradient at the onset of equatorial spread-F

Barium-strontium release experiments were conducted at Sriharikota Rocket Range (SHAR. 5.5 N dip latitude) at the onset of equatorial spread-F. We report here an unusual phenomenon of the development of two barium ion clouds from a single release around 200 km altitude, moving with different speeds indifferent directions. This is the first experimental evidence for the presence of large scale electric field gradients with a scale size of 15km. By incorporating neutral wind measured during spread-F into a numerical model for equatorial electrojet we interpret these gradients to be the manifestation of effects due to the meridional winds and wind shears. It is possible that the electric field gradients observed may lead to the generation of plasma holes during the onset of equatorial spread-F.     

From values to narrative: a new foundation for the conservation of historic buildings

Since its inception, modern conservation has derived the significance of a heritage asset from the identification and prioritisation of distinct classes of values. Different systems of values have been proposed, and the focus of the debate has been on the competing merits of such systems, with little attention paid to the genealogy of their theoretical foundation. If such values-based systems were ever appropriate, they are increasingly out of step with other areas of cultural life, and the resulting tensions are particularly manifested when considering change to historic buildings and environments. The currently under-theorised state of conservation is positively harmful both to the conservation professions and to the buildings we seek to protect. It is increasingly urgent therefore that we understand conservation’s philosophical origins, that we question the application of a late-nineteenth-century modernist approach to culture, and that we seek a better theoretical foundation.     

A comparison of foF2 obtained from a time-dependent ionospheric model with Argentine Islands' data for quiet conditions

In this study a comparison is made of the Utah State University Time-Dependent Ionospheric Model (TDIM) and an ionosonde data set from Argentine Islands. This study is unique in that the Argentine Islands data set of foF2 spans complete diurnal, seasonal and solar cycle conditions for low geomagnetic activity. The TDIM reproduces these foF2 variations extremely well. Although the observed winter and summer solstice foF2 diurnal curves have opposite phases, they are readily modelled. At equinox where a sharp transition occurs from winter to summer, or vice versa, the monthly average is complicated by this feature and hence the TDIM does not reproduce the diurnal fine structure.The neutral wind induced vertical plasma drift is the only free parameter in this study. All the other inputs are fixed for the specific solar, seasonal and diurnal conditions. A vertical plasma drift variation is presented; although simplistic, it couples the geographic and geomagnetic frames. With additional information such as hmF2, it would be possible to deduce a unique vertically induced drift pattern.     

Applicability of the two-layer model for simulation of non-linear evolution of a large scale plasma cloud in the ionospheric F-region

The adequacy of the two-layer model of Lloyd and Haerendel for describing the behaviour of an ionospheric irregularity is verified by numerical simulation of large plasma cloud dynamics. The background ionosphere is approximated by a set of conductive layers with ion mobilities and concentrations corresponding to the real ionospheric conditions. Polarization electric field produces positive and negative image clouds, i.e. plasma density enhancements and depletions in each layer. Their intensity, form and orientation turn out to change with height depending on the local conditions. However, the drift and deformation of the released cloud slightly differ from the case when the ionosphere is characterized by constant, height averaged parameters, at least if altitude dependent neutral wind and photochemical processes are ignored.     

Mixed results of seven methods for organic residue analysis applied to one vessel with the residue of a known foodstuff

Several methods of archaeological organic residue analysis were applied to a single unglazed and unseasoned ceramic vessel that had absorbed residues of heated camel milk. Sections of the wall of this vessel were sent to eleven archaeological laboratories. Seven reported their results before the identity of the residue was revealed, during the 70th Annual Meeting of the Society for American Archaeology. Methods included stable carbon and nitrogen isotope ratio analysis, protein analysis and lipid analysis. These laboratory techniques provide a biochemical analysis of the residue in a ceramic matrix, the archaeological interpretation of which can be rather difficult. The exact source of the residue was not identified by any laboratory, but it is evident that residue analysis can provide valuable information, especially when combined with additional archaeological and historical data. We therefore support a close cooperation of those working in this field to develop it to its full potential.     

Application of a simplified theory of ELF propagation to a simplified worldwide model of the ionosphere

The approximate theory of ELF propagation in the Earth-ionosphere transmission line described by Booker (1980) is applied to a simplified worldwide model of the D- and E-regions, and of the Earth's magnetic field. At 1000 Hz by day, reflection is primarily from the gradient on the underside of the D-region. At 300 Hz by day, reflection is primarily from the D-region at low latitudes, but it is from the E-region at high latitudes. Below 100 Hz by day, reflection is primarily from the gradient on the underside of the E-region at all latitudes. By night, reflection from the gradient on the topside of the E-region is important. There is then a resonant frequency (~300 Hz) at which the optical thickness of the E-region for the whistler mode is half a wavelength. At the Schumann resonant frequency in the Earth-ionosphere cavity (~8Hz) the nocturnal E-region is almost completely transparent for the whistler mode and is semi-transparent for the Alfvén mode. Reflection then takes place from the F-region. ELF propagation in the Earth-ionosphere transmission line by night is quite dependent on the magnitude of the drop in ionization density between the E- and F-regions. Nocturnal propagation at ELF therefore depends significantly on an ionospheric feature whose magnitude and variability are not well understood. A comparison is made with results based on the computer program of the United States Naval Ocean Systems Center.     

New technologies applied to family history: a particular case of southern Europe in the eighteenth century

In this article, the author explains how the support of new technologies has helped historians to develop their research over the last few decades. The author, therefore, summarizes the application of both database and genealogical programs for the southern Europe family studies as a methodological tool. First, the author will establish the importance of the creation of databases using the File Maker program, after which they will explain the value of using genealogical programs such as Genopro and Heredis. The main aim of this article is to give detail about the use of these new technologies as applied to a particular study of southern Europe, specifically the Crown of Castile, during the late modern period. The use of these computer programs has helped to develop the field of social sciences and family history, in particular, social history, during the last decade.     

Evaluation of Fe isotope values as a provenance tool for chert artefacts from the north-eastern United States

Iron (Fe) isotope compositions of prehistoric stone tools and geological sources were compared to evaluate the robustness of this isotopic fingerprinting technique. Artefacts and source materials were collected from the Hatch site in central Pennsylvania, United States, where both veined chert (Bald Eagle chert) and stone tools coexist within several metres. Yellow artefacts (δ⁵⁶Fe = 0.38 ± 0.1, n = 7) and source materials (δ⁵⁶Fe = 0.42 ± 0.1, n = 8) isotopically matched within error. The source values also overlap yellow chert samples from three other Bald Eagle chert locations in the area. These values are different from six other chert locations in the north-eastern United States. These data suggest that the Fe isotope composition of chert artefacts reflect distinct geological sources. To enhance the mechanical characteristics of the stone tools, the chert experienced heat treatment, which induced a phase shift of the Fe oxide mineral goethite to hematite. This phase shift changes the colour of the chert to red. The red chert artefacts and source material also have overlapping Fe isotope values, but are 0.2‰ higher than the initial yellow chert. Experimental work where cherts were heated with different clays shows that Fe exchange with site soils induces the +0.2 fractionation. These data demonstrate that predictable Fe isotope fractionation occurs during heating, resulting in isotopically distinct artefacts.     

Detection of chloride from pottery as a marker for salt: A new analytical method validated using simulated salt-making pottery and applied to Japanese ceramics

Salt is an essential mineral in the human diet, and ancient peoples obtained salt either directly from rock salt, from salt lakes, or by concentrating saline waters from salt springs or seawater in pottery vessels. However, because sodium chloride, the major component of salt, is soluble in water, it has been thought unlikely that any trace of salt would remain in the pottery after a long period of time. A new methodology for retrieval of water-insoluble (retainable) chloride ion trapped within a pottery matrix is presented as a method for detecting previous use of the pottery for salt making. Simulated salt-making pottery was used to make salt by repeatedly boiling seawater over a fire. After chloride had been extracted with distilled water, to mimic the removal of chloride by natural waters such as rainwater and groundwater, an aqueous ammonium fluoride solution was shown to be capable of extracting chloride ions remaining in the pottery. A chloride-selective electrode was used to quantify the amount of extracted chloride in the presence of fluoride. This method was then successfully applied to excavated Japanese pottery vessels suspected of having been used for making salt. Identification of retainable chloride in pottery can offer insights into salt trading networks, which reflect the growth and affluence of an ancient society.