Lightning transient fields in the atmosphere—low ionosphere

The complexity of the electric properties of the atmosphere, which influences the excitation and propagation of electromagnetic signals generated by lightning discharges, gives rise to a diversity of the typical signal wave forms and amplitudes in the various space-time domains. This causes difficulties and controversies in the interpretation of the experimental data. In geophysical problems of such a kind, considerations accounting for a broadband spectrum are particularly important.In the present paper, lightning induced ULF-VLF fields in the daytime inhomogeneous atmosphere and D-region of the ionosphere above the thundercloud are analyzed for a standard model of the vertical return stroke. The developed analytical approach makes it possible to unite the canonical model of the electromagnetic radiation into a free-half-space, the discharge (ELF-VLF spectrum) and ‘post-discharge’ (ULF spectrum) low-frequency models and to clarify the temporal scales in the mechanism of lightning coupling with the atmosphere and low ionosphere with respect to the local relaxation time, discharge characteristic time scales and observer location.     

Electric fields and currents in the equatorial electrojet deduced from VHF radar observations—II. Characteristics of electric fields on quiet and disturbed days

Using the Doppler spectra of VHF radar signals, the height profiles of the phase velocity (V_p) of 2.7 m irregularities in the equatorial electrojet (EEJ) over Thumba (dip: 56′S) are obtained. The day-time east-west electric fields (E_y) are deduced by matching experimentally observed V_p profiles with theoretically deduced ones for a number of quiet and disturbed days. The experimental E_y values show: (i) a large day-to-day variability; (ii) a large decrease in the afternoon hours on some days (quiet and disturbed); (iii) the frequent presence of short period fluctuations with amplitudes of 30–50% of the background value and with typical time scales of 30–60 min, on moderately disturbed days (9 ⩽ A_p ⩽ 30); (iv) a significant decrease of the average E_y on disturbed days compared to that on quiet days during 0900–1200 h L.T.     

Electric fields and currents in the equatorial electrojet deduced from VHF radar observations—III. Comparison of observed ΔH values with those estimated from measured electric fields

From VHF backscatter radar measurements at Thumba (dip: 56′S) of the phase velocities of type II irregularities in the equatorial electrojet (EEJ), electric field (E_y) values are estimated for different times of the day. Using the electric field values thus deduced and the Pedersen and Hall conductivities calculated using model values of electron densities and the collision frequencies of ions and electrons, the height integrated current intensity in the EEJ is estimated. The surface level geomagnetic field perturbation ΔH produced by this ionospheric current is then calculated. The calculated values of ΔH are compared with observed values of ΔH (after subtracting the magnetospheric contribution of D_st) for a number of days. The comparisons show good agreement between observed ΔH values and those calculated from measured electric fields. The agreement is found to be good even when type I irregularities are present at higher altitudes in the EEJ. This comparative study demonstrates the validity of estimating electric field values from VHF radar measurements and it indicates the possibility of deducing electric field values from ground level ΔH values, at least for statistical studies.     

Domesticating online games for preteens – discursive fields,everyday gaming,and family life

This article examines families’ everyday practices connected with online games played by children ages seven to eleven in the USA. Based on interviews in homes with children and parents, the article employs domestication theory to account for social experiences and symbolic meanings of games and game devices within private and public contexts of children’s game play. The analysis focuses on the social process through which online games are brought into home environments and incorporated into families’ daily routines. Games are analyzed as both impacting on everyday practices of the family and being shaped by the histories, values, and relationships within the households. The article contributes to an understanding of preteens’ online gaming and highlights the strength of using domestication theory to investigate children’s media practices.     

Foucault, fields of governability, and the population–family–economy nexus in China

It was only in the early twentieth century that China discovered that it had a population, at least if a population is understood not as a simple number of people but instead in terms of such features as variable levels of health, birth and death rates, age, sex, dependency ratios, and so on—as an object with a distinct rationality and intrinsic dynamics that can be made the target of a specific kind of direct intervention. In 1900, such a developmentalist conception of the population simply did not exist in China; by the 1930s, it pervaded the entire social and political field from top to bottom. Through a reading of a series of foundational texts in population and family reformism in China, this paper argues that this birth of the Chinese population occurred as a result of a general transformation of practices of governing, one that necessarily also involved a reconceptualization of the family and a new logic of overall social rationalization; in short, the isolation of a population–family–economy nexus as a central field of modern governing. This process is captured by elaborating and extending Foucault's studies of the historical emergence of apparatuses (dispositifs) into a notion of fields of governability. Finally, this paper argues that the one-child policy, launched in the late 1970s, should be understood not in isolation from the imposition of the “family-responsibility system” in agriculture and market reforms in exactly that period, but as part—mutatis mutandis—of a return to a form of governing that was developed in the first half of the twentieth century.     

Raised fields in the Bolivian Amazonia: a prehistoric green revolution or a flood risk mitigation strategy?

The Llanos de Moxos (LM), Beni, Bolivia, with its impressive number of pre-Columbian earthworks, is an ideal region for studying past human–environment interactions in the Amazonia. Agricultural raised fields are among the most striking of those earthworks. They can offer us valuable information about the region’s agricultural carrying capacity and the nature and extent of human occupation in pre-Columbian times and, therefore, help adopt better informed conservation and development strategies for Amazonia in the future. However, before tackling these issues we need to further our understanding of why pre-Columbian raised fields were built and how they were managed in the past. Published data on raised fields in the LM is contrasted with new data gathered from field and remote sensing images. Raised fields have been analysed in relation to the hydrology, soil, topography and paleoclimate of the areas where they are found. In light of this new data we believe that there are grounds to question the current model that suggests raised field agriculture provided high yields without the need of fallow periods, representing a kind of pre-Columbian green revolution. Our alternative proposal suggests that raised field agriculture allowed pre-Columbian peoples to mitigate the risk of more intense and frequent flooding than is experienced today in the LM. We show that raised fields were built only in those areas where there were no alternatives, which do not coincide with those areas where pre-Columbian societies seem to have flourished and reached high levels of social complexity.     

Plasmaspheric zonal electric fields and coupling fluxes from the Dunedin VLF Doppler experiment,for 180°E,L ≈ 2.3, at solstice and equinox

Group delays and Doppler shifts from ducted whistler-mode signals are measured using the VLF Doppler experiment at Dunedin, New Zealand (45.8°S, 170.5°E). Equatorial zonal electric field and plasmasphere-ionosphere coupling fluxes are determined for L ≈ 2.3 at June solstice and equinox during magnetically quiet periods. The general features of the electric field measured at Dunedin agree with those predicted from ionospheric dynamo theory with a (1,−2) tidal component. Some seasonal variations are observed, with the electric field measured during equinox being smaller and predominantly westward during the night. The electric field at June solstice is also westward during the evening and for part of the night, but turns sharply eastward during the pre-dawn and dawn period at the duct entry site. The June electric field appears to follow a diurnal variation whereas the equinox electric field shows a possible 4-hourly periodic variation. Seasonal variations in the neutral wind pattern, altering the configuration of the ionospheric dynamo field, are the probable cause of the seasonal differences in the electric field. The seasonal variation of the coupling fluxes can be explained by the alteration of the E x B drift pattern, caused by the changes in the electric field.