Analysis of Jovian kilometric radiation simultaneously observed by voyagers 1 and 2

first_imgBroadband Jovian radio emission in the kilometric wavelength range (bKOM) observed by the Voyagers 1 and 2 (V1 and V2) planetary radioastronomy, PRA, experiments have been analysed for the period January to December 1979 which includes the Jupiter encounters. The pre-encounter observations were made on the nightside, the difference in local time between the two spacecraft being about one hour. It is therefore possible to study local time, and source – observer distance effects. bKOM beaming exhibits large temporal variations. The beaming is believed to arise from the manner in which the source electrostatic upper-hybrid waves are converted to electromagnetic radiation in the plasma density gradients at the Io torus. In this case the beaming depends on the characteristic frequencies of the source plasma, and temporal variations in the beaming are expected to reflect fluctuations in the Io torus. Remote-sensed density profiles have been computed from V1 and V2 simultaneous bKOM observations and compared with in situ measurements by V1 when it passed through the torus. Good agreement is found between the density gradients obtained, and the in situ measurements. The differences between V1 and V2 profiles may possibly be explained by the difference in local time of the two spacecraft. The computed profiles from dayside and nightside observations are nearly coincident. A large temporal variability of the Io torus density, or of the latitudinal position of the source, is apparent.last_img read more

The annual variation in quiet time plasmaspheric electron density, determined from whistler mode group delays

first_imgWhistler mode group delays from the VLF Doppler experiment at Faraday, Antarctica (65°S, 64°W) show an annual variation that has a maximum in December and a minimum in June/July. Assuming signal propagation at constant L (L = 2.5), this implies an annual equatorial electron density (Neq) variation, with December values 3 times higher than in June (during solar minimum—1986). This annual variation in Neq can be modelled from the combined ƒƒoF2medians at each end of the field line (Argentine Islands and Wallops Island), by assuming that diffusive equilibrium is maintained from the F2 layer to the equator over long (≥ 1 month) time scales during quiet magnetic conditions. The use of this model enables the longitude dependence of the annual Neq variation to be investigated. ƒƒoF2data from two other pairs of near-conjugate stations at ∼ 50°E and ∼ 180°E suggest that there are probably no other regions where there are such large annual variations in Neq at L = 2.5. Whistler mode group delays from a similar VLF Doppler experiment at Dunedin, New Zealand (45.8°S, 170.5°E) show an annual variation that is much smaller, and in agreement with the model results at that longitude. At Faraday during solar maximum conditions, the phase of the annual variation is similar to that observed at solar minimum, but the amplitude is smaller, the December–June ratio in Neq being about 2:1.last_img read more

A one-dimensional model of ice shelf-ocean interaction

first_imgLarge‐scale oceanic circulation beneath Antarctic ice shelves is driven by the thenmohaline differences which result from mass and energy exchange at the ice‐ocean interface. Dense, saline waters are drawn underneath the ice shelves and emerge, cooled and diluted, as plumes of Ice Shelf Water. A simple, one‐dimensional model of this process has been developed, in which the Ice Shelf Water plume is treated as a turbulent gravity current, initiated at the inland margin by a flow of fresh meltwater emerging from beneath the grounded ice. Subsequent evolution of the plume, as it ascends along an ice shelf base of specified geometry, can be simulated. The model has been applied to a flow line on Ronne Ice Shelf, Antarctica, to explain the observed distribution and rate of basal melting and freezing. Calculations indicate that the present mean melt rate of 0.6 m yr−1 would increase to 2.6 m yr−1 if the underlying water were to warm by 0.6°C. This would not only lead to significant thinning of the ice shelf but could also cause a profound change in ocean circulation on the open continental shelf.last_img read more

Electrical response of the Summit-Greenland ice core to ammonium, sulphuric acid, and hydrochloric acid

first_imgElectrical and chemical analysis of the GRIP ice core from Summit in central Greenland confirms that the ECM current is controlled solely by acids in the ice, though there could be different responses for different acids. The dielectric conductivity is dependent on strong acid, on sea salt chloride, and also on ammonium concentrations in the ice. The response to NH4+ is similar to that of sea salt chloride, as they both conduct only at AC frequencies, but NH4+ is approximately twice as conductive per mole. The response to the strong acids shows results consistent with earlier work, with similar responses throughout the length of the core. It seems as if all the thousands of electrical peaks in the GRIP core may be explained by the response to just three chemical species: acidity, ammonium salts, and a third component which is probably chloride.last_img read more

Fish in the diet of Antarctic fur seals (Arctocephalus gazella) at South Georgia during winter and spring

first_imgThe occurrence of fish in the diet of the Antarctic fur seal (Arctocephalus gazella) at Bird Island, South Georgia was investigated by analysis of fish otoliths in scats (faeces) collected during late May to early November 1983. Of the 55 scats examined, 49 contained fish remains, and 45 contained fish otoliths. Ten fish species were represented by 415 otoliths, and 33 otoliths were too digested to be identified unequivocally. Fish size was estimated from otolith size based on published allometric equations. Four coastal notothenioid fishes dominated the fish component of the diet: Champsocephalus gunnari and Gobionotothen gibberifrons each comprised about 40% of the total fish mass; Chaenocephalus aceratus was ranked third by mass and the smaller Lepidonotothen larseni occurred in one quarter of the scats but was of lower importance in terms of mass. The length-frequency distribution of C. gunnari landed by the commercial fishery in October 1982 to June 1983 is similar to that which comprised the bulk of the diet in the present study. Compared with recent studies on the fish component of the diet in the literature, the dominance of C. gunnari is generally similar, however, there was a greater proportion of G. gibberifrons during the 1983 winter and spring than reported for recent winters.last_img read more

Automatic Whistler Detector and Analyzer system: Implementation of the analyzer algorithm

first_imgThe full potential of whistlers for monitoring plasmaspheric electron density variations has not yet been realized. The primary reason is the vast human effort required for the analysis of whistler traces. Recently, the first part of a complete whistler analysis procedure was successfully automated, i.e., the automatic detection of whistler traces from the raw broadband VLF signal was achieved. This study describes a new algorithm developed to determine plasmaspheric electron density measurements from whistler traces, based on a Virtual (Whistler) Trace Transformation, using a 2-D fast Fourier transform transformation. This algorithm can be automated and can thus form the final step to complete an Automatic Whistler Detector and Analyzer (AWDA) system. In this second AWDA paper, the practical implementation of the Automatic Whistler Analyzer (AWA) algorithm is discussed and a feasible solution is presented. The practical implementation of the algorithm is able to track the variations of plasmasphere in quasi real time on a PC cluster with 100 CPU cores. The electron densities obtained by the AWA method can be used in investigations such as plasmasphere dynamics, ionosphere-plasmasphere coupling, or in space weather models.last_img read more

Either taking it easy or feeling too tired: old Cory’s shearwaters display reduced activity levels while at sea

first_imgIt has long been known that birds change their behaviour, reproductive performance and survival as they mature, including in the first few years after recruitment into the breeding population. However, and contrasting with the description of patterns of actuarial and reproductive senescence in later years, there are surprisingly few studies documenting changes in behaviour in old individuals. Such studies are important, as birds provide particularly interesting models for studying the biology of senescence. It has been suggested that, unlike mammals, birds may remain physically fit until an advanced age, yet this has limited empirical support. In this paper, we used activity (immersion) loggers to show that old (>26 years) Cory’s Shearwaters Calonectris diomedea are less active when foraging at sea, spend more time resting on the water and have a smaller number of take-offs and landings during darkness, when compared to experienced mid-aged individuals (13–20 years old). Old individuals also tended to have reduced immune response against an experimental challenge using phytohaemagglutinin. These results are in line with observed reductions in activity levels with age in a wide range of non-avian taxa, and may suggest that old seabirds are physically less fit than younger individuals. Alternatively, old birds might simply be more experienced and their reduction in activity might reflect a strategic regulation of investment in different activities. Our study illustrates the potential for gaining insights into avian aging patterns and processes by looking into the behaviour of model organisms. We therefore encourage more research focusing on behavioural parameters that may reflect variations in physical condition or strategic choices, during both the breeding and non-breeding seasons.last_img read more

Area protection in Antarctica: how can conservation and scientific research goals be managed compatibly?

first_imgThe footprint of human activities within Antarctica is increasing, making it essential to consider whether current conservation/protection of environmental and scientific values is adequate. The Antarctic protected area network has developed largely without any clear strategy, despite scientific attempts to promote protection of representative habitats. Many Antarctic Specially Protected Area (ASPA) Management Plans do not state clearly if conservation or science is the priority objective. This is problematic as science and conservation may have conflicting management requirements, i.e. visitation may benefit science, but harm conservation values. We examined recent estimated mean annual levels of visitation to ASPAs. On average, ASPAs protecting scientific research interests were visited twice as often as ASPAs conserving Antarctic habitat and biological communities. However, ASPAs protecting both science and conserving habitat were visited three times as often as ASPAs conserving habitat alone. Examination of visitation data showed that the proportion of visitors entering ASPAs for science, environmental management and/or education and tourism purposes, did not reflect the primary reason for designation, i.e. for science and/or conservation. One third of APSAs designated since the Environmental Protocol entered into force (1998) did not describe clearly the main reason for designation. Policy makers should consider (i) for all Management Plans stating unambiguously the reason an area has ASPA designation, e.g. either to protect habitat/environmental values or scientific research, in accordance with adopted guidance, (ii) designating new protected areas where visitation is kept to an absolute minimum to ensure the long-term conservation of Antarctic species and habitats without local human impacts (possibly located far from areas of human activity), and (iii) encouraging the use of zoning in ASPAs to help facilitate the current and future requirements of different scientific disciplines.last_img read more

Sexual segregation in habitat use is smaller than expected in a highly dimorphic marine predator, the southern sea lion

first_imgSexual segregation in habitat use is widely reported in many taxa and can profoundly influence the distribution and behaviour of animals. However, our knowledge of the mechanisms driving sexual segregation is still in its infancy (particularly in marine taxa) and the influence of extrinsic factors in mediating the expression of sex differences in foraging behaviour is underdeveloped. Here, we combine data from biologging tags, with stable isotope analysis of vibrissae, to assess sexual segregation in southern sea lions (SSL) (Otaria flavescens) breeding at the Falkland Islands in the South Atlantic. We found evidence to support segregation, most notably in δ13C and δ15N values. However, in spite of extreme sexual size dimorphism and differing constraints related to female-only parental care, adult male and adult female SSL overlapped considerably in isotopic niches and foraging area, and shared similar foraging trip characteristics (such as distance and duration). This is in contrast to SSL breeding in Argentina, where prior studies report sexual differences in foraging locations and foraging trip characteristics. We posit that sexual segregation in SSL is influenced by habitat availability (defined here as the width of the Patagonian Shelf) and individual foraging preferences, rather than commonly invoked individual-based limiting factors per se.last_img read more

Molecular mechanisms of biomineralization in marine invertebrates

first_imgMuch recent marine research has been directed towards understanding the effects of anthropogenic-induced environmental change on marine biodiversity, particularly for those animals with heavily calcified exoskeletons, such as corals, molluscs and urchins. This is because life in our oceans is becoming more challenging for these animals with changes in temperature, pH and salinity. In the future, it will be more energetically expensive to make marine skeletons and the increasingly corrosive conditions in seawater are expected to result in the dissolution of these external skeletons. However, initial predictions of wide-scale sensitivity are changing as we understand more about the mechanisms underpinning skeletal production (biomineralization). These studies demonstrate the complexity of calcification pathways and the cellular responses of animals to these altered conditions. Factors including parental conditioning, phenotypic plasticity and epigenetics can significantly impact the production of skeletons and thus future population success. This understanding is paralleled by an increase in our knowledge of the genes and proteins involved in biomineralization, particularly in some phyla, such as urchins, molluscs and corals. This Review will provide a broad overview of our current understanding of the factors affecting skeletal production in marine invertebrates. It will focus on the molecular mechanisms underpinning biomineralization and how knowledge of these processes affects experimental design and our ability to predict responses to climate change. Understanding marine biomineralization has many tangible benefits in our changing world, including improvements in conservation and aquaculture and exploitation of natural calcified structure design using biomimicry approaches that are aimed at producing novel biocomposites.last_img read more