Heights of MF radar scatter (1986/87) and the wind field (55–95 km): Saskatoon,Canada

The Saskatoon MF radar (2.2 MHz) at 52°N, 107°W, has been used to measure the heights of occurrence of radar scatter during four seasons, and twelve months of 1986/87. Mean winds, and gravity waves are also available, by the spaced antenna method and from the same radar echoes. Certain heights, called elsewhere ‘preferred heights’, are identified near 60km, 70km, 75km in summer, and 80–86 km. Several layers have seasonal and diurnal variations. Associations with electron density gradients (rocket data), mean wind shear in summer, and gravity wave amplitude-minima in the equinoxes are effectively demonstrated. Case studies, involving 3 h data sets of radar scatter and wind elaborate the comparison: gravity waves of long period (τ > 6 h) are shown to modulate the scattering process.     

Tidal winds at mesopause altitudes over Arecibo (18°N, 67°W), 5–11 April 1989 (AIDA '89)

An imaging Doppler interferometer (IDI) radar was operated during the three AIDA '89 campaigns in Puerto Rico over the period March–May of 1989. The output of the IDI analysis characterizes radar scattering in terms of a number of discrete ‘scattering points,’ also referred to as ‘multiple scattering centers,’ IDI/MSC for short. For each of these points the three-dimensional location, radial velocity and amplitude and phase are determined, similar to the output of meteor radars. We have applied the conventional Groves [(1959) J. atmos. terr. Phys. 16, 344–356] meteor wind radar analysis to the scattering points to produce the mean apparent motions over the height range from 70 to 110 km which are presented here. The mean apparent motion of the scattering centers is the quantity that would correspond to the neutral atmosphere wind or bulk motion if the scattering points are physical entities (such as turbulent eddies) whose motions are determined solely by advection. This is the quantity which is treated as the ‘wind’ in the analysis which follows and which should be compared to the wind measurements as deduced from the other methods employed during this campaign. There is, however, a caveat which supports the contention of Hineset al. [(1993) J. atmos. terr. Phys. 55, 241–287] that extreme care must be used in interpreting the velocities measured by partial reflection radars as winds. The current application of the Groves method of analysis has revealed motions from which one would infer a typical equatorial easterly circulation, with mean meridional circulation becoming significant only above 96 km. A periodogram analysis of the complete data interval (5–11 April) has shown the diurnal tide to be the most significant feature of the wind field at these altitudes, with zonal amplitudes up to some 50 m/s and meridional amplitudes approximately half this value. The 12 and 6 h tides become as significant as the diurnal above 100 km. The two day (48 ± 5 h) wave is the next most significant feature, with zonal amplitude increasing with height up to 30 m/s at 110km. The semidiurnal tide is not at all well developed below 100 km. However, analysis on a day by day basis reveals a significant semidiurnal component which is not phase coherent over the total interval. Mean vertical velocities are of the order of tens of centimeters per second and are considered to be more realistic than the meters per second velocities usually inferred from analyses of meteor trail drifts.     

Field aligned airglow observations of transequatorial bubbles in the tropical F-region

It is possible to form images of the tropical F-region ionization structures, variously labelled as ‘bubbles’, ‘plumes’, or ‘depletions’, in a plane perpendicular to the magnetic field by observing the airglow emissions associated with them in a field aligned direction. Structures which are present at altitudes from 250 km to more than 700 km above the dip equator map down to the 250–350 km region, where recombination and associated airglow emissions occur, ranging from the equator to dip latitudes of 15° or more. The structures can be viewed in a field aligned direction from sites in the range 17°–23° dip latitude. Measurements with high angular resolution (as small as 0.1° in the meridian) could show structures as small as 2 km. It is possible to make simultaneous measurements in both 6300 and 7774 Å recombination emissions, from which the height h_max of the peak plasma concentration n(e)_max on the field line can be estimated from a ratio of the emission rates. It is possible to make maps of n(e)_max and h_max either by raster scanning the sky in the two emissions or by imaging them onto an imaging detector. Useful data can be obtained from one site over a range of 20° in dip latitude and 10° in dip longitude. Observations in the same magnetic meridian as a backscatter radar system are desirable, as also are observations from near magnetic conjugate points. Imaging characteristics for the observation sites in the range of dip latitude 17°–23° have been calculated.     

Lightning-induced perturbations on VLF subionospheric transmissions

Phase and amplitude perturbations on VLF subionospheric transmissions from transmitter NWC to Dunedin have been studied on both MSK frequencies and at spaced receivers, 9 km apart. In any one event (a ‘Trimpi’) the phase and amplitude perturbation can be expressed in terms of a perturbation phasor. This is generally believed to be the result of lightning-induced electron precipitation (LEP) producing a localized increase in ionization near the normal reflection height for subionospheric (waveguide) VLF waves. Most of the Trimpis received on the NWC-Dunedin path can be best explained if the LEP ionization is sufficiently localized so that it acts as a scattering centre for the subionospheric VLF wave from the transmitter. It is then this scattered wave or echo at the receiver which makes the perturbation phasor. We call these ‘echo Trimpis’. The phase of the echo relative to the direct signal will differ on spaced antennae if the angle of arrival of the two signals differ. Similarly, this relative phase will vary with frequency if the group delay of the signals differ. Thus measurement of these differences allows location of the scattering centres, and so too the LEP. Locations made show a significant grouping in a region where the lightning intensity is high. This and other features strongly suggest that these echo Trimpis originate from local (southern hemisphere) lightning. This and other reasons are suggested to explain the high proportion of echo Trimpis on this path.     

Equatorial spread-F: recent results and outstanding problems

Recent results and outstanding problems in the field of equatorial spread-F are reviewed. The discussion is organized about four distinct wavelength regimes: long (≳ 20 km). intermediate (20 km–100 m). transitional (100 m–10 m) and short (≲ 10 m). The intermediate waves are best understood, although the enhanced turbulent power near 1 km wavelength needs explanation, as does the saturation mechanism itself. The role of shear flow and irregularity seeding by ‘geophysical noise’ in the neutral atmosphere form important future research topics at the longest scales. Identification of drift waves in the transitional wavelength range has been a major new step in explaining the full spread-F phenomenon. This drift wave turbulence in the transition regime will be actively studied in the near future, particularly with regard to its role in determining the saturated amplitude of the intermediate waves, as well as in the anomalous diffusion of plasma at high altitudes. Although waves as short as 11 cm have been unambiguously detected and linear theories exist, the origin and amplitude spectra of these short wavelength waves inside topside plumes remain in some doubt and should also be examined in more detail.     

Radio wave turbulent ‘absorption’ due to electron beam injections in the ionosphere

Considered is the collisionless damping of high-frequency radio waves in the ionospheric plasma perturbed by electron beams. Special attention is paid to the attenuation of telemetric signals, observed in the ARAKS experiment with intense electron beam injections, and to the ‘spike’ ionospheric absorption events. It is shown that these phenomena may be explained in terms of the nonlinear scattering of radio waves by plasma turbulence driven by electron beams and accompanied field-aligned currents.     

A revised corrected geomagnetic coordinate system for Epochs 1985 and 1990

A new set of corrected geomagnetic coordinates (CGM) has been calculated from the magnetic field model DGRF for Epoch 1985 and the IGRF model for Epoch 1990. A new approach to determine the ‘dip’ magnetic equator has been developed, which is based on the vertical (along Re) projection on the Earth's surface of the B-minimum value point (apex) on each geomagnetic field line. A strip along the ‘dip’ magnetic equator line has been defined where the corrected geomagnetic coordinates could not be found by the definition of CGM. Linear interpolation between the locations of the two last definable CGM latitudes in both hemispheres has been used to calculate the CGM longitudes in the equatorial region. Interpolation between locations of the last definable CGM latitude and ‘dip’ equator in both hemispheres has been used to calculate the CGM latitudes in this region. The constant B-min geomagnetic coordinate system (CBM) is proposed and analysed to replace CGM in the equatorial region.     

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.     

Wave activity,F1-layer disturbance and a sporadic E-layer over EISCAT

During July 1987 the EISCAT radars were used to study thin layers in the ionospheric E-region. This paper outlines the observing campaign, describes the GEN-type radar program used for the UHF experiments, and discusses the ‘descending’ or ‘sequential’ layer observed on the afternoon of 12 July during a period of strong wave activity, which could be traced throughout the whole E-F1 transition region. Following the descent of one particularly marked wave, a thin layer developed around 120 km height and lasted about 100 min, with temporary disappearances and periods of upward motion which were related to variations of field aligned ion velocity, and in particular to ‘convergent nulls’ in the velocity profile. The layer was eventually dispersed by a rapid upward surge of ion velocity. Composition analysis shows that the layer contains both long-lived light ions and heavy ions, most probably Fe⁺.     

Studies of high latitude mesospheric turbulence by radar and rocket 1: energy deposition and wave structure

During early spring, 1985, the MAE-3 (Middle Atmospheric Electrodynamics) Program was conducted at Poker Flat Research Range, Alaska to study the origin of wintertime mesospheric echoes observed with the Poker Flat MST radar there, by probing the mesosphere with in situ rocket measurements when such echoes occurred. Pre-launch criteria required the appearance of echoes exhibiting some wave structure on the MST radar display; these could be met even under weak precipitation conditions with riometer absorption near or above 1.0 dB. Two morning rockets were launched under such conditions, the first (31.048) on 29 March 1985, at 1703 UT and the second (31.047) on 1 April 1985, at 1657 UT. Both payloads were deployed on a high altitude parachute near a 95 km apogee to provide a stable platform for data acquisition within the mesosphere (below 80 km). Each payload carried a solid state detector to measure energetic electrons between 0.1 and 1.0 MeV and an NaI crystal detector to measure x-rays from >5 to >80 keV. Payload 31.048 also carried a positive ion ‘turbulence’ probe which measured ion density changes (ΔN_i/N_i) during payload descent, whereas 31.047 carried a nose tip ‘turbulence’ probe designed to measure electron density changes (ΔN_e/N_e) during upleg ram conditions plus a Gerdien condenser for the measurement of bulk ion properties during downleg. The energy deposition curves for each event exhibited peak deposition rates between 75 and 80 km with a half width of 16–18 km, almost exclusively induced by precipitating relativistic electrons. They also showed a maximum bottomside gradient between 65 and 75 km. Radar echoes and atmospheric turbulence were observed in the same altitude domain, consistent with the anticipated need for adequate free thermal electron gradients to make such phenomena visible on the radar. The vertical wave structure from radar echoes was found to be consistent with that observed in horizontal wind and temperature profiles measured by Datasondes flown shortly after each large rocket. An analysis of the wave structure from radar data has shown that although large scale waves (λ_z ~ 7 km) were found to be present, a higher frequency shorter wavelength (∼ 1–3 km) component probably played a more significant role in modulating the signal-to-noise structure of the radar echoes.     

Passage of a powerful HF radio wave through the lower ionosphere as a function of initial electron density profiles

The results of numerical modelling of powerful HF radio wave propagation through the ionosphere plasma are presented. Comparison of the heating wave parameters with those of a low powerwave gives the possibility to study the self-action of the powerful HF wave. At low altitudes the ‘translucence’ of the ionosphere plasma takes place. At high altitudes the wave absorption sharply increases. Both self-action effects lead to the reduction of the altitude range of the heated region. The dependence of self-action effects and the resulting electron temperature profiles on the initial electron density profiles are studied.     

Identification of mesospheric heavy ion ledge

For the first time a ground based technique, i.e. incoherent scatter observation of the mesospheric spectra has been utilized in identifying the ‘transition height’ of simple molecular ions to complex cluster ions around 80–90 km in the D-region. This transition height also matches with the electron density ledge. A substantial diurnal variation of this height is observed. The transition height varies by about 10km during the course of a day, the lowest being 80 km, near noon. There is also a strong likelihood that both the neutral temperature and effective positive ion mass vary during the course of a day.     

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.     

Gravity wave saturation and eddy diffusion in the middle atmosphere

A discussion is given of gravity wave saturation and its relation to eddy diffusion in the middle atmosphere. Attention is focused on the saturation process and some of its observable manifestations. It does not serve as a review of all related work. Although a theoretical point of view is taken, the emphasis is on which wave parameters need be measured to predict quantitatively the influence of gravity waves on eddy transport. The following considerations are stressed: the variation of spectra with observation time T; that eddy diffusivities are determined by velocity spectra; the anisotropic nature of diffusivity; a unified approach to saturation; an attempt to make eddy diffusivity more precise; the relationship between eddy diffusivity and wave dissipation.The subjects of ‘wave drag’ (momentum flux deposition) and heat flux need only be treated briefly, because they are related to eddy diffusivity in simple ways. Consideration is also given to two different theoretical mechanisms of wave saturation—wave induced convective instability and strong nonlinear wave interactions. The saturation theory is then used to predict a globally averaged height profile of vertical diffusivity in the middle atmosphere. This calculation shows that gravity waves are a major contributor to eddy diffusion from heights of 40–110 km, and that they are significant down to 20 km. A more detailed calculation of wave induced eddy diffusion, including latitudinal and seasonal variations, can be made if wave velocity spectra become available. The paper closes with recommendations for future research.     

Reflection of electromagnetic waves by density gradients in a magnetised plasma

The reflection of electromagnetic waves by density gradients in a plasma with a magnetic field derived from a scalar potential is studied. Conditions are found for reflection at grazing incidence at a surface S containing field lines. No restriction is placed on the angle between the wave-normal and the field, and account is taken of the curvature of the surface and the anisotropy of the medium. Particular reference is made to whistler-mode waves in the magnetosphere. The minimum electron density enhancement needed for reflection is calculated. Guidance by small-scale irregularities and ‘super whistlers’ (whistlers with upper cut-off above one-half the equatorial electron cyclotron frequency) are briefly discussed.     

‘Motherly Hate’: Gendering Anti–Semitism in the British Union of Fascists

Throughout the interwar period, Britain’s fascist movement was marked by anti–Semitism. That anti–Semitism was such a striking feature of the movement is well known, and studies of British fascism have consequently paid attention to the implications and effects of racial prejudice on Britain’s Jewish community, and on British society more generally. However, the history of women in Britain’s fascist movement has been less well known, and the narrative of racial politics and racial tensions in interwar Britain must now be modified by a consideration of gender relations and women’s activism on the extreme right. The first part of this article is thus concerned with the questions of how British fascist women gave vent to their racial hatreds, the particular tone of their rhetorical invectives against the Jewish community, and the distinctiveness of their expressions of anti–Semitism. From their support for Jew–baiting activities on the streets, to their high level of participation in an anti–war movement dedicated to keeping Britain out of the ‘Jews’ war’, to their choices to educate their young children in the principles of Jew–hating, British fascist women did, in fact, show themselves to be ‘Jew wise’. Their active expression of anti–Semitism certainly challenged the optimistic liberal supposition that the female sex was the more tolerant. The second part of this article is concerned with the theoretical implications of putting women back into the history of British anti–Semitism, and explores how the powerful gender paradigms of feminine tolerance, maternalism, and feminised pacifism were subverted to justify a seemingly incongruous sentiment of ‘motherly hate’.     

High latitude quiet summer ion composition profiles derived from a combined ion line/plasma line incoherent scatter experiment

High latitude quiet summer ion composition values in the altitude range from 200 to 245 km have been derived from a combined ion line/plasma line experiment in a full five-parameter fit. The EISCAT UHF radar was used with a 5 × 14 μs multipulse scheme for the ion line measurements, giving a range resolution of 3 km. Plasma line signals from the same altitudes were measured with a 70 μs pulse using a spectrum analyzer. Significant deviations from the standard EISCAT composition model were found, mainly at the upper altitudes. The O⁺ content was generally lower than predicted by the model. For the largest composition deviations, significant effects were seen in the temperatures, particularly in the electron temperature. The electron temperatures derived by a standard ion line fit applying the model were underestimated by up to 15%.     

Frequency dependence of anomalous absorption caused by high power radio waves

High power radio waves can modify the ionospheric electron density distribution to produce field aligned plasma irregularities which give rise to the anomalous absorption of HF radio waves. The coefficient of anomalous absorption of a vertically propagated radio wave due to scattering from field aligned irregularities has been calculated, taking into account the effects of the geomagnetic field on electron motions. These results are compared with those of other theoretical models. Furthermore, the scale lengths of field aligned irregularities produced by a high power radio wave during recent high latitude modification experiments have been determined from measurements of the anomalous absorption by means of this theory.     

Incoherent scatter observations of thin ionization layers at Sondrestrom

High resolution incoherent-scatter observations of E-region thin (1–3 km) metallic ion layers are presented. Data were collected during three different periods from August 1990 to August 1991, in three different experimental modes. First, the antenna was directed vertically and the entire duty cycle was devoted to Barker coded multi-pulse [Zamlutti (1980) J. atmos. terr. Phys.42, 975–982] measurements to determine the densities and temperatures in the E-region with 300 m resolution. The second experiment measured the F-region electric field as well as the high resolution E-region densities. For the third experiment the antenna was scanned magnetic north-south while only the E-region densities were measured. The experiments were carried out on 16 different nights for a period of 4 h each night at a time near magnetic midnight. Thin ionization layers were observed on 12 of the 16 nights. The first experiment demonstrated that the thin layers are composed of a significant fraction of heavy metallic ions; assuming the layers are composed of a mixture of Fe⁺ and Mg⁺ a composition estimate of 63% Fe⁺ was obtained in one example. The second experiment investigated the relationship between the direction of the electric field and the presence of the thin layers. In these observations thin layers were only present when the electric field was pointed in the magnetic north-west or south-west quadrants, most frequently when the field was near magnetic west. Correlation between layer altitude and field direction was also observed, layers occurring at higher altitudes for fields directed in the north-west, and lower altitudes for fields directed to the south-west. The observations are compatible with the electric field mechanism for thin ionization layer formation. The scanning experiment showed that the layers were of a limited latitudinal extent, typically about 100 km up to a maximum of about 200 km.