Simultaneous observations of the enhanced plasma line and of the reflected HF wave at Arecibo

A suitably devised pulsing sequence of the powerful HF transmissions radiated towards the ionosphere below the penetration frequency made it possible to separate the attenuation of the reflected HF wave due to thermal and to ponderomotive type parametric instabilities. The separation was possible on account of the different growth times of the thermal and ponderomotive type parametric instabilities. At the same time the power in the 430 MHz enhanced plasma line was recorded.The results show that previously accepted explanations of the overshoot in the 430 MHz enhanced plasma line for 5.3 MHz HF transmissions are invalid. A strong overshoot was observed but the attenuation of the powerful HF wave was too small to be observed. For 3.175 MHz HF transmissions substantial attenuation was observed on both time scales.     

Gyro line observations with the EISCAT VHF radar

This paper reports the first successful gyro line experiment with the EISCAT VHF (224 MHz) radar. The incoherent scatter gyro line (also known as ‘resonance line’ and ‘whistler line’ in the literature) corresponds to the electrostatic wave mode ω ≈ Ω cos α known to be present in a weakly magnetized plasma (Ω is the electron gyro frequency and α is the angle between the scattering wave vector and the magnetic field). The line is very weak, but has the great advantage from an observational point of view that its position in the scattered spectrum is only marginally dependent on the electron density and temperature. This means that filter offsets can be easily predicted and that a long pulse and long integration times can be used in the experiment. Measurements were made at angles of 55 and 69° with the geomagnetic field where the gyro line frequencies are approximately 800 and 500 kHz, respectively. The line was seen in the altitude region 100–220 km, being most intense at 160–170 km. The strong dependence of the gyro line on the magnetic field may be used to study variations in the field. Other interesting aspects of the line to be investigated in future experiments are the effects of suprathermal particles, the possible effects of stimulated scattering, and the heating effects in an ionospheric modification experiment.     

Simultaneous ground-based observations of the plasmapause and the F-region mid-latitude trough

The plasmapause and the mid-latitude ionospheric trough have been observed simultaneously from two Antarctic stations, Halley and Faraday, during five winter nights covering a range of geomagnetic disturbance conditions. The equatorial radius of the plasmapause was measured using whistlers recorded at Halley, whilst the poleward edge of the trough was located from ionospheric soundings at one or other of the stations.Before midnight the trough was well poleward of the plasmapause (by 1–2 L) when first observed (typically at ~21 LT), but then moved rapidly equatorwards. After local magnetic midnight the two features were roughly coincident, and in general moved slowly to lower L-shells with increasing local time. At no time were there simultaneous and identical movements of the two features, suggesting a lack of coupling between them. Agreement of the observations with statistical studies and models was fair, given the considerable variability among the five cases studied. For the geomagnetically quieter nights the trough data fit the Spiro model predictions, whereas in the most disturbed case, agreement is better with the Quegan et al. model. The latter model predicts a difference in L between the two features which would fit the data better if shifted 1–2 h later in local time.     

Atomic oxygen concentrations from rocket airglow observations in the equatorial region

A rocket payload designed to measure mesospheric sodium, hydroxyl and oxygen nightglow emissions, in addition to electron density and temperature, was launched from the Alcantara Launch Center (2°S, 44°W), Brazil, at 23:52 LST on 31 May 1992. The height profiles of the atomic oxygen OI557.7 nm and molecular oxygen Atmospheric (0-0) band emissions showed maxima at 100±3 km and 98±3 km, respectively. The emission data are used to calculate the atomic oxygen concentration profiles. The results show the validity for the equatorial region of the empirical parameters proposed by McDade et al. (1986).     

Simultaneous optical observations of long-period gravity waves during AIDA '89

Ground-based optical instrumentation supported the AIDA '89 wind measurement comparisons by describing the gravity waves affecting the 80–100 km altitude region during clear dark hours over Puerto Rico. This study tabulates the characteristics of gravity waves with fractional column emission rate amplitudes up to 30% and with periods greater than 45 min as seen in the O₂ airglow layer by MORTI, a sensor of O₂ rotational temperature and column emission rate in twelve look directions. Data from seven other sensors operating at Guanica and the Arecibo Observatory are then compared with the MORTI data to check the consistency of the entire data set with the wave parameters, primarily velocities, deduced from MORTI. Nine nights of visually distinct crests and troughs were found, one of which was dominated by an evanescent wave and the rest by internal waves. The nights of 5/6 April and 4/5 May 1989 were selected for multi-sensor comparisons. The comparisons showed substantial agreement between the MORTI characterizations and the observations by others, and most differences were attributed to complexities introduced by higher frequency components with shorter coherence distances. Nightly summaries of the O₂ rotational temperature and column emission rate are also given.     

Simultaneous nightglow and Na lidar observations at Arecibo during the AIDA-89 campaign

Simultaneous nightglow and Na lidar observations made at Arecibo during the AIDA-89 campaign are reported from between 0000 and 0530 LT (Local Time) on 6 April 1989 and on 9 April 1989. On 9 April the observations are consistent with the presence of a large amplitude 8.5 km vertical wavelength, 4 h period wave propagating through the 85–91 km region. A lower amplitude 80 min period wave is also observed. The results imply that the O₂ atmospheric band intensity peaked near 91 km while the OH Meinel (6,2) band intensity peaked near 85 km. The OH Meinel temperature and intensity are 160° out of phase which can be explained by low eddy diffusion and high ozone densities near the mesopause. The integrated Na abundance from 87 to 89 (90–92) km correlates well with the OH Meinel (O₂ atmospheric) band intensity. On 5–6 April the OH Meinel and O₂ atmospheric band intensities are not well correlated. The OH Meinel intensity is correlated with the integrated Na abundance from 86 to 88 km. Both the Na and OH measurements reveal the presence of an approximately 1 h period wave. The OH temperature data appear to be consistent with the OH Meinel band originating near 85 km. The O₂ atmospheric band data show the presence of a 2 h period wave. The integrated Na abundance data suggest that the O₂ atmospheric band peaks between 90 and 94 km. A large sporadic Na event which occurs near 6 UT appears related to the presence of a gravity wave near 95 km. In all of the observed waves there is good agreement between the wave parameters derived separately by the optical airglow and Na lidar techniques.     

Simultaneous observations of E and F region electric field fluctuations at the magnetic equator

Simultaneous daytime observations of E region horizontal irregularity drift velocities in the equatorial electrojet and F region vertical plasma drifts were made on a few magnetically quiet days at the magnetic equatorial station of Trivandrum (dip 0.5°N). Measurements of the electrojet irregularity velocities by VHF backscatter radar and the F region vertical plasma drifts by HF Doppier radar are used to deduce the daytime East-West electric fields in the E and F regions, respectively. The fluctuating components of the electric fields are separated and subjected to power spectral analysis. The E and F region electric field fluctuations are found to be well correlated; the estimated correlation coefficient is in the range of 0.52–0.8. The fluctuation amplitudes are of the order of 15% over the background for the E region and 25% for the F region. The spectral analysis reveals dominant components in the range of 30–90 min with F region components stronger than those of the E region by a factor of about 1.5 on the average. The F region electric fields during daytime being coupled from the low latitude E region, the good correlation observed between the E and F region perturbations suggests that the electric fields in the E region at low and equatorial latitudes are coherent for the temporal scales of the order of few tens of minutes. The spectral characteristics are such that the commonly occurring medium scale gravity waves could possibly be the source for the observed fluctuations in the E and F region electric fields.     

Simultaneous ground-based observations of polar cap arcs and spacecraft measurements of particle precipitation

In order to investigate the particles which produce the polar cap aurora at the Vostok station in Antarctica, charged particle data obtained by the DMSP satellites for some days in a period from April to August 1985 were surveyed. Due to the satellite orbit the local time range in which the data were available was the morning sector. For all the events when sun-aligned arcs were observed on the ground the simultaneous DMSP measurements on almost the same field line showed an increased integral number flux J. > 10⁸ (cm⁸/s/sr)⁻¹ of the precipitating electrons with energy E_e > 200 eV. The electron spectra with double peaks are typical of intense electron precipitation in the polar cap arcs. The most noticeable feature of ion spectra in the polar cap arcs is the prominent minimum in ion flux in the energy range 0.1 < E_i < 1 keV in contrast with the oval precipitation ; this feature gives the possibility to separate the polar arcs from the aurora in the oval. In some events the satellite crossed the system of two widely separated arcs ; one of them was a sun-aligned arc whereas the other was circular at constant latitude according to the Vostok data. The analysis of the DMSP electron and ion precipitation data has shown that in these events the latitude-oriented arcs are located in the polar cap and not in the auroral oval.     

Observational technique and parameter estimation in plasma line spectrum observations of the ionosphere by chirped incoherent scatter radar

With the 430 MHz incoherent scatter radar facility at the Arecibo Observatory, the plasma line spectrum has been measured with a linearly frequency modulated or ‘chirped’ pulse. On reception the signal is demodulated (‘dechirped’). The paper describes the experimental set-up and the parameter estimation for day-time ionosphere observations. Using a non-linear least squares fit it is possible to determine the linear and quadratic coefficients of a locally parabolic plasma line frequency versus height profile. The strength of the plasma line and the point of tangency of the locally parabolic plasma line frequency profile can be determined very accurately. In measurements of the day-time ionosphere the plasma line was found to be enhanced by about 70 times over the thermal equilibrium level.     

Simultaneous observations of the quasi 2-day wave at Mawson,Antarctica, and Adelaide,South Australia

Observations of the Austral quasi 2-day wave at Mawson, Antarctica (67°S, 63°E) are presented and compared with those from Adelaide (35°S, 138°E). The data were obtained from partial-reflection radars which have been measuring winds continuously since mid-1984, and the results presented here are the first to record the 2-day wave in middle atmosphere winds from Mawson. They show that 2-day period oscillations of 10–15 m s⁻¹ are a regular feature of the high latitude southern hemisphere summer. The wide longitude and latitude separation of the radar stations permits estimates of propagation velocity and latitude phase structure, and results are consistent with the passage of a westward travelling Rossby-gravity (3, 3) wave.     

Magnetic activity (Kp) and quasi-periodic variations of intensity of the oxygen green and red lines

The association between magnetic activity (K_p) and quasi-periodic variations of intensity of the oxygen green and red lines is studied. It is found that, when K_p is greater, the association between K_p and quasi-periodic intensity variations is generally better. It is suggested that some relationship exists between quasi-periodic intensity variations of nightglow emissions and the activity of travelling ionospheric disturbances or magnetospheric substorms.     

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.     

天纲地常考

本文依据历史文献与出土古文献《十大经》中有关的资料,提出"纲常"二字的本源,是指中国古代建立天地系统模型中的两个极点。天之极曰纲,地之极曰常,天纲与地常上下相对,天旋于上,地静于下,形成了"有晦有明,有阴有阳"现象。后世运用纲常二字,盖出乎此,但其原本之义,已经隐晦不明,故为考证。     

Lived experience and the present: New directions in anthropological writing

Fox, Richard G., ed. Recapturing Anthropology: Working in the Present. Santa Fe, NM: School of American Research Press, 1991. viii + 248 pp. including references and index. $15.95 paper.

Ellis, Carolyn and Michael G. Flaherty, eds. Investigating Subjectivity: Research on Lived Experience. Newbury Park, CA: Sage Publications, 1992. vii + 259 pp. including subject and author indices and information on authors. $21.95 paper.     

The red line over European colonialism: comparison of the Macao museum and Hong Kong museum of history after their return to China

Hong Kong and Macao were once European colonies. A unique, hybrid culture of East and West now flourishes in these two Special Administrative Regions (SARs) of China. Both cities opened new history museums in 1998, but they adopted remarkably different approaches in their representation of their complicated and politically sensitive history. The Hong Kong Museum of History (HKMH) represents history by closely following the orientation of traditional Chinese nationalism. The postcolonial characteristics adopted by the Macao Museum to reproduce history, in contrast, are likely amongst the richest of all history museums in China. What are the reasons behind the different historical representations by Hong Kong and Macao, which were both promised a ‘One country, Two systems’ policy by the Chinese central authority? This paper argues that both museums reveal two faces of a rising China; the one in Hong Kong emphasises national dignity, and the people’s identification with and loyalty to the nation when it is engaged in state building. The one in Macao emphasises the multiple roles in finding a balanced position to coexist with superpowers, forging friendships with developing countries and building an idealised image of a (re-)rising nation through historical construction. The difference between these two museums indicates the exceptional flexibility of China’s postcommunist regime in engaging in soft power diplomacy.     

EISCAT observations of tidal modes in the lower thermosphere

EISCAT has made regular measurements of plasma velocity at heights between 101 and 133 km in the E-region and at 279 km in the F-region as part of the Common Programme CP1. Correcting for the effect of the electric field as determined in the E-region, it is possible to estimate the neutral wind velocity in the E-region for a number of days in the period 1985–1987 when magnetic conditions were relatively quiet. These velocities display diurnal and semi-diurnal tidal oscillations. The diurnal tide varies considerably from day to day in both amplitude and phase. The semi-diurnal tide also varies in amplitude but displays a fairly consistent phase at each height and the variation of phase with height below 110 km indicates a dominant (2,4) mode. Above 120 km the variation of phase with height is slower which suggests that at these heights the (2, 4) mode is attenuated and the (2, 2) mode is more important. The results agree well with previous measurements at high latitude.