Using the combined resources of amateur radio observations and ionosonde data in the study of temperate zone sporadic-E

This paper discusses how key characteristics of temperate zone sporadic-E can be determined by making use of the combined experiences of amateur radio observations and ionosonde data. There are advantages to using this unified approach in the study of the phenomenon, and to understand and draw conclusions from the data. A brief history of amateur radio involvement in the phenomenon is provided along with actual radio observations in the 50 MHz band. Long term ionosonde data collected at Boulder, Colorado were examined using the benefit of radio experience in order to find what correlations may exist with other phenomena. Some significant conclusions regarding characteristics of temperate zone sporadic-E can be drawn through this approach.     

Night-time equatorial F-region zonal plasma drifts from VHF backscatter radar observations

Night-time equatorial F-region plasma drifts are deduced from VHF backscatter radar observations of F-region irregularities. The zonal drifts reveal large vertical shears. It is found that the irregularity polarization electric field (though small compared to the ambient field) is significant in affecting the observed zonal drifts.     

Mechanisms for vertical separation of ions in sporadic-E layers

A model of the ionospheric E-region between 90 and 130 km altitude is constructed with normal molecular ions and two species of metal ion with different masses. This paper investigates whether the vertical structure observed in sporadic-E layers can be accounted for by separation of different ion species according to their mass. The result of the investigation is substantially negative. Another mechanism for range spread sporadic-E has signatures that may be sought in observational data.     

Multi-instrument observations of mesospheric motions over Arecibo: comparisons and interpretations

The MF/HF partial-reflection technique of observing the mesosphere and lower thermosphere has been employed for more than two decades to measure motions, but there has never been complete agreement as to what motions were being detected. This paper reports on observations made during a major international campaign—AIDA '89—that was initiated with the objective of resolving this question.The partial-reflection system employed was an Imaging Doppler Interferometer operating at 3.175 MHz, but it stands here as a prototype for all MF/HF partial-reflection radar systems: its raw data were analyzed both in its own basic mode, derived on the assumption that it sees wind-borne multiple scattering centers and in modes adopted by other interferometric and ‘spaced antenna’ systems. The motions thus revealed are compared here with those found by what we consider to be more certain measurers of winds: an incoherent-scatteer radar at heights of 65–95 km, a meteor-wind radar at heights of 80–100 km and a Fabry-Perot interferometer measuring 0(¹S) emissions near a height of 97 km.Comparisons of the different sets of observations oblige us to conclude that

• 1.(1) MF/HF partial-reflection systems may be expected to give a good representation of ambient winds up to a height of about 80 km;
• 2.(2) they fail to give a consistently reliable measurement of the ambient winds above a height of about 80 km
• 3.(3) they yield, at the greater heights, what appears in our data to be some convolution of the horizontal phase velocities of atmospheric gravity waves, with the wave spectrum having been modified by passage through the underlying wind system and containing, on occasion, locally generated Kelvin-Helmholtz waves; and
• 4.(4) when the underlying winds change, the local wave spectrum will change in response and, in MF/HF partial-reflection measurements, will give the appearance of a changing local wind: if the underlying winds undergo tidal changes, the wave spectrum will undergo tide-like changes that will masquerade as true tidal winds.

These results are, of course, limited to a single site over a limited period of observation. Nevertheless, taken at face value they suggest that current methods of data reduction are inappropriate for partial-reflection velocities at heights above 80 km and that new methods of data reduction, perhaps extending certain older methods that have been applied successfully in the past to total-reflection measurements, should be employed in their place if the full potential of the MF/HF partial-reflecton technique is to be realized.     

The amplitude of auroral backscatter: II. Topology of the backscatter range-azimuth distribution

The range-azimuth distribution of auroral backscatter echoes received at Essoyla at frequencies of 93 and 45 MHz is predicted for a model which includes the effects of electron density, magnetic aspect angle, and the azimuth of current flow and also takes into account ionospheric refraction. The distribution is in the form of an arc with maxima of backscatter in both eastern and western wings. As the electron density increases, the intensity of the backscatter increases more rapidly and the azimuths of maximum backscatter separate even further. For currents flowing along the L-shells, the backscatter is strongest in the eastward wing. This asymmetry is intensified if the current flow is rotated anti-clockwise but if the current flow is rotated sufficiently in a clockwise direction the backscatter is stronger in the westward wing. These predictions are supported by observations made at Essoyla.     

美英在新中国参与对日媾和问题上的争议

旧金山会议前后 ,美英围绕究竟“哪一个中国”将参与对日媾和的问题 ,立场一度严重对立 :美国支持台湾国民党政权而英国支持新中国。双方为此持续争议 ,直到美国以非常手段迫英国就范。文章认为 ,围绕中国签约权问题的分歧实际上反映了美英两国在远东存在的重大利害冲突、不同的现实处境以及两国外交的不同理念 ,也揭示出即使在冷战高峰时期 ,国家利益和历史传统在一国外交中仍发挥着不可忽视的作用。     

HF Doppler observations of 23 October, 1976 total solar eclipse over south-eastern Australia

Observations of the Doppler shift of HF transmissions on 2.5 MHz and 4.5 MHz propagated via the ionosphere during the 23 October, 1976 eclipse over south-eastern Australia are reported. The 4.5 MHz signal, reflected from the F-region, showed the characteristic frequency shift attributable to recombination and/or motion of the reflection height after first contact. Spreading of the Doppler signal occurred after totality. Some wave activity was present in the record which is normal for this time of day. The 2.5 MHz observations showed little activity up to totality when sporadic E conditions set in, masking the detection of the response of the normal E-region to the eclipse.     

Response of high frequency radar to meteor backscatter

The response of a High Frequency (HF) Radar System to echoes backscattered from underdense meteor trails is calculated. Three propagation modes are identified according to whether the echo is received along the direct (line-of-slight) path, or along two possible paths from beyond the horizon involving ionospheric reflection. The system response contours in terms of meteor radiant position on the sky are presented in the altitude-azimuth and celestial ecliptic coordinate systems. Diurnal echo rate curves are deduced for point radiants, which correspond to meteor showers and for a density distribution of radiants which is appropriate to sporadic meteors.The calculations are compared with observations of integrated meteor echo power from sporadic meteors made with an experimental radar system at frequencies throughout the HF band. Satisfactory agreement is reached between predictions and observations as functions of time of day, radar frequency and range. The extension of observations to include ionospherically propagated echoes permits meteor echo rates to be simultaneously monitored over an area of the Earth's surface of the order of 10⁶ km² with a single radar system.A greater than normally accepted echo rate is required to explain our observations. However, we believe that this enhanced rate is consistent with the true echo height distribution and the attenuating effects of trail initial radius and diffusion, which are particularly severe at the radar frequencies normally used for meteor detection near and beyond the top of the HF band. Our echo rate is consistent with the meteoroid cumulative mass distribution which may be inferred from a simple interpolation between satellite and visual measurements.     

On the role of auroral electric fields in the formation of low altitude sporadic-E and sudden sodium layers

The characteristics of metallic and molecular ion sporadic-E (E_s) layers, formed by the action of strong electric fields at auroral latitudes, are examined using computer simulations. It is found that, for electric fields directed between northward and westward (northern hemisphere), thin metallic ion layers (<2 km thick) can be formed above about 105 km altitude. For electric fields directed from westward, through southward, to south-eastward, slightly thicker (4–6 km thick) metallic ion layers can form between 90 and 105 km altitudes. Thin layers of molecular ions can be formed by electric fields directed between north and west if the ion density is low. Examples of E_s layers observed by the EISCAT radar, together with simultaneous observations of electric fields and ion drifts are presented which show good agreement with the simulations. The relationship between the lower-altitude E_s layers and sudden sodium layers (SSLs) is discussed leading to an explanation of some of the characteristics of SSLs at high latitude. A possible involvement of smoke particles in the formation of both E_s layers and SSLs is proposed.     

Upper atmosphere wind observations over Southern Australia during the total solar eclipse of 23 October 1976

Observations of winds in the 80–100 km height region were made at three locations in South Australia during the total solar eclipse of 23 October 1976. One station (Tantanoola) was located in the eclipse path while the others (Adelaide and Woomera) were situated several hundred kilometers north of the path of totality. Wind variations caused either directly by cooling of the 90 km region or by the propagation of a bow wave generated in the lower atmosphere were searched for but no events were found that could be ascribed unambiguously to the eclipse.     

抗战胜利前后国民政府忠烈祠功能之嬗变——以江苏省为例

忠烈祠是国民政府为祭祀在战争中为国家忠勇牺牲的官兵和民众的神圣场所.国民党江苏省地方各县市筹建忠烈祠的活动经历了抗战胜利前后两个不同的历史时期.国民政府根据变化了的社会、政治环境,对忠烈祠功能进行了有利于自身利益的诠释.忠烈祠功能的嬗变,使民众与政府之间在国家象征体系的构造上,产生了或互补、或冲突的关系.这对江苏地方忠烈祠的筹建产生了深层影响,从而导致前后两个时期不同的建祠结果.     

Reconstruction of horizontally-inhomogeneous ionospheric structure from oblique-incidence backscatter experiments

Fridman and Fridman [(1994) J. atmos. terr. Phys. 56, 115] suggested a method of reconstructing the horizontally-inhomogeneous ionospheric structure using vertical- and oblique-incidence backscatter sounding (OBS) ionograms measured at a single location. In the present paper this technique has been used to analyze experimental data and tested against independent vertical sounding (VS) measurements. By using the OBS and VS ionograms measured at Irkutsk as source data for the method we reconstructed ionization profiles over Tomsk (1050 km to the west of Irkutsk). We found that the reconstructed profiles are in reasonable agreement with the profiles obtained from VS measurements at Tomsk.     

Ionospheric disturbances over Japan due to the 18 May 1980 eruption of Mount St. Helens

The effects of the Mount St. Helens eruption at 1532 UT on 18 May 1980 on the ionosphere over Japan are examined using data on total electron content obtained at three closely-spaced stations and HF (5 and 8 MHz) Doppler recordings together with microbarograph data for the surface pressure perturbation. The results strongly suggest that ionospheric perturbations having a predominant period of about 9 min propagated from north to south approximately along the great circle path with a horizontal velocity of about 300 m s⁻¹. The observed time variations of perturbations can be well explained in terms of Lamb waves propagating through the atmospheric sound channel while launching up-going waves to produce the ionospheric oscillations.     

Interpretation of elevation-scan HF backscatter data from Losquet Island radar

Most methods using HF ground backscatter radar data to estimate the ionospheric bottomside electron density profile rely upon multi-frequency measurements of the minimum group delay. However, information of the same nature can also be extracted at a single frequency if the elevation angle can be precisely controlled. We outline the analysis of this technique, known as elevation-scan backscatter sounding. The relevant parameter estimation problem is studied using a Bayesian approach. We report on an experiment using the Losquet Island radar to illustrate this method. The performance is compared to ionosonde data. This technique provides a method of teledetection of the bottomside F-region electron density profile hundreds of km from the radar site: however, further development is needed to provide increased reliability of the estimates.     

Comparison of boundaries for HF auroral backscatter and VHF scintillation

A study is described of the equatorwards boundary of high-latitude ionospheric irregularities using measurements obtained by two different experimental techniques. Auroral traces observed on backscatter ionograms from an HF radar have been used to identify the boundary of the decametre scale-size irregularities responsible for the coherent backscatter. Simultaneous observations of scintillation on the 150 MHz signals from NNSS satellites have enabled the boundary for irregularities in the sub-kilometre scale regime to be located. Comparisons of the results from the two techniques indicate that reconciliation between boundary positions can be made in only about 50% of the cases considered. In general the scintillation boundary lies on average well polewards of that identified by the HF radar, suggesting that caution should be exercised in the mapping of irregularity boundary positions.     

A method of determining horizontal structure of the ionosphere from backscatter ionograms

We have developed a technique lor oblique backscatter sounding (OBS) ionogram inversion as a diagnostic tool for the horizontally inhomogeneous structure of the ionosphere. Input data for the method include the leading edge of a backscalter ionogram that is measured through soundings in a given direction, and the vertical electron density profile measured over the sounding station or over some other site lying in the sounding direction. The method may be useful for reconstructing the two-dimensional electron density distribution in a vertical plane aligned with the direction of sounding. The inverse problem has been solved using the Newton Konlorovich method and the Tikhonov regularization method. The algorithm we have developed was tested against model data, that is, OBS ionograms synthesized using geometrical optics calculations for different models of the inhomogeneous ionosphere. Test results demonstrate that our method converges reliably, is stable to measurement errors and provides a good accuracy of reconstruction of inhomogeneous structures with scales of 100 2000 km. This indicates that this method shows promise as an operative remote diagnostic tool for ionospheric irregularities of natural and artificial origin.     

Gravity wave activity in the upper mesosphere over Urbana,Illinois: lidar observations and analysis of gravity wave propagation models

We analyze 375 h of Na Wind/Temperature lidar measurements of the mesopause region (≈ 80–105 km) Na density and temperature profiles on 57 nights distributed over 2 yr at Urbana, Illinois. These observations yield a high-resolution seasonal data set of gravity wave activity in the upper mesosphere. From this data, we present measurements of the Brunt-Väisälä period, the relative atmospheric density perturbations and their spectra, and the parameters of 143 quasi-monochromatic gravity waves. The direct measurement of the Brunt-Väisälä period allows accurate calculation of the horizontal velocity perturbations and vertical displacement perturbations from the density measurements. The horizontal velocity and vertical displacement vertical wave number spectrum magnitudes and indices show considerable seasonal and nightly variability. The gravity wave amplitudes, wavelengths, and observed periods exhibit systematic relationships similar to those found in previous studies, and are consistent with the MU radar measurements of intrinsic gravity wave parameters. Here, we present a detailed analysis of the observations in terms of Diffusive-Filtering Theory models of gravity wave propagation. The magnitudes of the vertical wave number spectrum, the form of the joint vertical wave number and frequency spectrum, and the systematic relationships between the monochromatic gravity wave parameters are consistent with the Diffusive-Filtering model. We compare these results with a variety of radar, lidar, and airglow observations from other sites. This observational study suggests that the complex nonlinear interactions of the gravity wave field may be modeled successfully as a diffusive damping process, where the effective diffusivity is a function of the total wave variance.     

Reduction of the effects of non-stationarity in studies of amplitude statistics of radio wave backscatter

By studying the statistics of fluctuations in amplitude of radio signals backscattered from the atmosphere and lower ionosphere, it is possible to obtain information about the scatterers. This procedure has been applied previously, but often relatively long data series have been used (e.g. 10–30 min) in order to produce reliable amplitude distributions. Unfortunately, the nature of the scatterers can often change considerably over such a time interval and this can distort the amplitude distributions. An alternative approach, applied in this work, is to use much shorter data sets, derive a parameter representative of each data set (e.g. the Rice parameter) and then examine the statistics of this derived parameter over a longer period. Computer modelling was used to examine the statistics of such a parameter and some surprising results emerged, even for relatively long data series. Several examples of the application of this new method will be presented.