Multiple-frequency studies of the high-latitude summer mesosphere : implications for scattering processes

The characteristics of polar mesosphere summer echoes (PMSE) are studied at 53.5 and 224 MHz. Observations at 2.78 MHz, simultaneous with the ones at the other two frequencies, were carefully compared for indications of PMSE, but no obvious relation was found. Relationships between relative scattering cross-section, spectral width and vertical velocity are studied for the 224 MHz radar, and observations at 53.5 MHz are compared with those at 224 MHz. Results of aspect sensitivity measurements at 53.5 MHz are presented. The implications of these characteristics for several possible scattering mechanisms are discussed. We rule out incoherent scatter and chemically induced fluctuations from the evidence that we have. In view of the extremely low temperatures near the high-latitude mesopause in summer, we discuss several scenarios involving heavy cluster ions and charged aerosol particles.     

On the role of dust in the summer mesopause

We propose that dust formed at the cool summer mesopause may have optical properties very different from that measured for bulk material of ice. The smallness of the dust and possible surface impurities may lead to high photoelectric yields and low workfunctions. For such reasons the dust in the summer mesopause may, at least occasionally, be charged to substantial positive surface potentials while pure ice, with its high photoelectric workfunction, would be charged to low and negative potentials by collisions with plasma particles. The presence of ‘dressed’ dust particles, with surface potentials of some volts, can lead to enhanced radar backscatter. We also suggest that the apparent reductions in electron density (‘bite-out’), which have been observed in the radar backscatter region, can be caused by the inability of an electrostatic probe to deflect the massive dust particles.The dust density which is required by our model to explain radar backscatter and electron bite-outs is of the order of 10 cm⁻³ for dust of radius above 5 × 10⁻⁶ cm.     

Postclassic Maya slips and paints and their relationship to socio-political groups in El Petén,Guatemala

LA-ICP-MS analysis of the chemical composition of the exterior slips and red and black pigments used for painted decoration of the three Postclassic Maya slipped ceramic wares suggests that the Itzá and Kowoj used different pigments for exterior slips and decorative motifs. Additionally, different slips and paints were used depending on vessel form and decorative program (red, black, or red-and-black painting or incising). When examined with previous ceramic paste chemical analyses, the data aid in better understanding the changing socio-political alliances and dominance relations in central Petén at the eve of Spanish contact.     

The form of metre-scale turbulence at mesopause heights in summer

Observations with a 46.5 MHz radar system at Aberystwyth (52.4°N, 4.1°W) have been used to examine the characteristics of echoes observed at heights above 80 km in daytime during the summer months of 1990–1992. Particular attention has been paid to the motion field observed during the two types of echo identified previously—spectrally broad, isotropic echoes observed between mid-May and early September, and spectrally narrow, anisotropic echoes observed on certain days in June and July. It has been found that both types of echo are associated with short-period gravity waves, those related to the spectrally narrow echoes being of smaller amplitude. The echoes are identified with isotropic and anisotropic turbulence, respectively, and data for days showing both types of echo have been used to examine the characteristic intervals of height and time over which a transition occurs.     

Electron content measurements in the auroral zone using GPS: preliminary observations of the main trough and a survey of the degree of irregularity in summer

Ionospheric electron content was monitored from sites in or near Tromsø, Norway, for six months of 1993, using the transmissions from the satellites of the Global Positioning System (GPS). The data have been used for preliminary studies of two important phenomena of the high-latitude ionosphere: the main trough and the incidence of large irregularities. The latitude and motion of the trough were determined on several occasions during the spring period, and the results compared with previous data. Best agreement is with the formula of Collis and Haggstrom (1988). The incidence of large irregularities was surveyed during a four-month period, approximately from the summer solstice to the autumnal equinox, and the variation with time of day and magnetic activity has been determined. It was found that irregularities are considerably larger by night than by day, but that they are enhanced during both periods by increased magnetic activity. Statistical results are presented. It is suggested that these irregularities are the same as the “auroral blobs” previously studied by incoherent-scatter radar.     

Sodium density and atmospheric temperature in the mesopause region in polar summer

Sodium lidar measurements have been performed during three summer seasons at a polar latitude (69°N), yielding profiles of sodium number density and temperature of the 85–100 km altitude region. Density measurements were performed during the months of June–August; temperature measurements only were made in August. The sodium layer was found to be both significantly weaker and more variable in summer than in winter. Measurements in summer 1987 yielded an average maximum Na density of about 900 atoms per cm³. The average maximum Na density during summer 1986 and 1988 was near 2600 atoms per cm³. The observed Na column density in summer varied from 3.10⁸ to 3.10⁹ atoms per cm². Temperature measurements were performed in August of 1986 and 1987. Mesopause temperatures of less than 125 K were observed in early August, rising rapidly throughout the month. The mean altitude of the mesopause was found to be about 87 km.     

VHF radar observations of nonlinear interactions in the summer polar mesosphere

VHF radar measurements of velocities and echo power in the summer polar mesosphere have been analysed using maximum entropy, bispectral and cross-spectral methods in order to study wave-wave interactions. The results show nonlinear interactions of second and even third order between the diurnal and semidiurnal tides and planetary waves with periods of 2 and 3 days in the velocity field. Similar analyses of time series of echo power suggest corresponding variations of the temperature field.     

Observations of winds in the Antarctic summer mesosphere using the spaced antenna technique

Observations of winds in the 60–100 km height range were made at Mawson (68°S, 63°E) during December 1981 and January 1982 with the MF spaced antenna technique. The prevailing winds are in accord with other recent observations made at high latitudes and show a peak in the zonal wind near 80 km with westward winds of 30 m s ⁻¹. The meridional winds maximize near 90 km with an equatorward flow of 10 m s⁻¹. The diurnal tidal components are in reasonable agreement with recent model predictions, especially in phase. The amplitudes tend to be larger than the model values. The semidiurnal tide is not as stable as the diurnal tide and shows evidence for interference effects between different modes.     

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%.     

Observational evidence of local turbulence production due to gravity wave saturation in the summer mesosphere

Five foil chaff and two falling sphere rockets flown during the MAC/SINE Campaign on 15 July 1987 at Andenes, Northern Norway (69°17′N). From these rocket measurements, turbulent energy dissipation rates, vertical wind shears and Richardson numbers as functions of height were derived in the range from 82 to 92km. Turbulent energy dissipation rates generally range from 1.4 × 10⁻⁵ to 2.0 × 10⁻²W/kg and are consistent with other experiments performed at the same latitude. Strong wind shears of the order of 50–90 m/s/km are observed at various heights. Good correspondence between turbulence intensity peaks, regions of strong wind shear and low Richardson number is found. Vertical wavenumber spectra of the five scalar winds measured by the foil chaff rockets indicate that there is an excellent agreement with the saturation hypothesis, suggesting that the turbulence intensity peaks measured in this salvo are linked directly to the saturation of gravity wave motions via dynamical instabilities.     

Demanding a safer tomorrow: Japan's anti‐nuclear rallies in the summer of 2012 (Respond to this article at http://www.therai.org.uk/at/debate)

This article discusses Japan's nuclear energy policy and describes the anti‐nuclear protest demonstrations that were held in Japan throughout the summer of 2012, including the author's personal experiences at some of these protests, illuminating the grassroots nature of the current anti‐nuclear movement.     

Estimates of gravity wave momentum fluxes in the winter and summer high mesosphere over northern Scandinavia

As part of the MAP/WINE campaign (winter 1983–1984) and the MAC/SINE campaign (summer 1987) high resolution wind profiles were obtained in the upper mesosphere using the foil cloud technique. Vertical winds were derived from the fall rate of the foil clouds and are used for estimating the momentum fluxes associated with vertical wavelengths shorter than about 10 km. From the ensemble average of 15 observations over an altitude range of 74–89 km we calculate a zonal net momentum flux of +12.6 ± 4.5 m²s⁻² in summer. The average of 14 measurements in winter between 73 and 85 km indicates a zonal net momentum flux of −3.7 ± 2.4 m²2 s⁻².     

Chemical and mineralogical characterization of Aguada Portezuelo pottery from Catamarca,north-western Argentina: PIXE,XRD and SEM-EDS studies applied to surface pre- and post-firing paints,slips and pastes

Particle-induced X-ray emission (PIXE), X-ray diffraction (XRD), electron microprobe analysis (EDS) and scanning electron microscopy (SEM) analytical techniques were used to characterize surface paints in pre- and post-fired Aguada Portezuelo decorated pottery. Surface paintings in black, white, red, brown, burgundy and ochre were analysed. Major, minor and trace elements were detected by PIXE, whereas XRD and SEM-EDS gave information on the main mineral phases and the characteristic morphology for each analysed pigment. The results obtained indicate that the main colour groups can be easily discriminated by PIXE, and they are characterized by only one pigment for each colour: hematite (red) and manganese mineral oxides (black), respectively, whereas white pigments are characterized by calcite, ghelenite and gypsum.     

On the behaviour of wind systems in the upper mesopause region during the transition from summer to winter conditions

Ionospheric drift measurements in the LF range indicate that the phase of the semidiurnal tidal wind oscillation in the upper mesopause, while being approximately equal in summer and in winter, develops characteristic changes near the equinoxes. These changes may either take the form of a complete rotation or, alternatively, an advance and retardation of the phase. What happens in any one year is not predetermined by the initial conditions alone but depends on random processes the nature of which cannot be deduced from the results of wind measurements only.     

Feeling insecure: a personal account in a psychoanalytic voice

The concept of ontological security has been taken up in human geography primarily through Giddens' (1990 Giddens, A. (1990) The Consequences of Modernity. Cambridge: Polity Press. [Google Scholar], 1991 Giddens, A. (1991) Modernity and Self-Identity. Cambridge: Polity Press. [Google Scholar]) formulation, but the idea has its origins in the writings of the existential psychoanalyst R.D. Laing. Returning to the psychoanalytic underpinnings of the concept, I use autobiographical vignettes to evoke and explore what it means to feel insecure. Using psychoanalytically informed illustrations of melancholia, ordinary acute anxiety and unconscious splitting, I develop a personal, subjective emotional geography of insecurity, and I caution against confusing certainty with ontological security.     

FOCUS: Bone Needles in Mallorcan Prehistory: a Reappraisal

A review of bone needles from the Mallorcan earliest prehistory is presented. They are not artifacts, but actually represent natural items, identified as Myotragus balearicus fibular diaphysis. The corpus fibulae ofM. balearicus is here illustrated by first time. Archaeological and paleontological implications of this diagnosis are discussed in this paper.