Academic literature on the topic 'Spatial disribution'

Abstract. The problem of boundary conditions for monochromatic Alfvén waves, excited in the magnetosphere by external currents in the ionospheric E-layer, is solved analytically. Waves with large azimuthal wave numbers m»1 are considered. In our calculations, we used a model for the horizontally homogeneous ionosphere with an arbitrary inclination of geomagnetic field lines and a realistic height disribution of Alfvén velocity and conductivity tensor components. A relationship between such Alfvén waves on the upper ionospheric boundary with electromagnetic oscillations on the ground was detected, and the spatial structure of these oscillations determined.

Abstract. Atmospheric inverse modelling has the potential to provide observation-based estimates of greenhouse gas emissions at the country scale, thereby allowing for an independent validation of national emission inventories. Here, we present a regional scale inverse modelling study to quantify the emissions of methane (CH4) from Switzerland, making use of the newly established CarboCount-CH measurement network and a high resolution Lagrangian transport model. Overall we estimate national CH4 emissions to be 196 ± 18 Gg yr−1 for the year 2013 (1σ uncertainty). This result is in close agreement with the recently revised "bottom-up" estimate of 206 ± 33 Gg yr−1 published by the Swiss Federal Office for the Environment as part of the Swiss Greenhouse Gas Inventory (SGHGI). Results from sensitivity inversions using alternative prior emissions, covariance settings, baseline treatments, two different inverse algorithms (Bayesian and extended Kalman Filter), and two different transport models confirms the robustness and independent character of our estimate. According to the latest "bottom-up" inventory the main CH4 source categories in Switzerland are agriculture (78 %), waste handling (15 %) and natural gas distribution and combustion (6 %). The spatial distribution and seasonal variability of our posterior emissions suggest an overestimation of agricultural CH4 emissions by 10 to 20 % in the most recent national inventory, which is likely due to an overestimation of emissions from manure handling. Urban areas do not appear as emission hotspots in our posterior results suggesting that leakages from natural gas disribution are only a minor source of CH4 in Switzerland. This is consistent with rather low emissions of 8.4 Gg yr−1 reported by the SGHGI but inconsistent with the much higher value of 32 Gg yr−1 implied by the EDGARv4.2 inventory for this sector. Increased CH4 emissions (up to 30 % compared to the prior) were deduced for the north-eastern parts of Switzerland. This feature was common to most sensitivity inversions, which rules out an artefact of the transport model and the inversion system. However, it was not possible to assign an unambiguous source process to the region. The observations of the CarboCount-CH network provided invaluable and independent information for the validation of the national bottom-up inventory. Similar systems need to be sustained to provide independent monitoring of future climate agreements.

The processes driving distribution and abundance patterns of highly migratory marine species, such as filter-feeding sharks, remain largely unexplained. The whale shark (Rhincodon typus Smith 1828) is a filter-feeding chondrichthyan that can reach > 18 m in total length, making it the largest extant fish species. Its geographic range has been defined within all tropical and warm temperate waters around the globe. However, even though mitochondrial and microsatellite DNA studies have revealed low genetic differentiation among the three major ocean basins, most studies of the species are focussed on the scale of single aggregations. Our understanding of the species’ ecology is therefore based on only a small proportion of its life stages, such that we cannot yet adequately explain its biology and movement patterns (Chapter I). I present a worldwide conceptual model of possible whale shark migration routes, while suggesting a novel perspective for quantifying the species‘ behaviour and ecology. This model can be used to trim the hypotheses related to whale shark movements and aggregation timings, thereby isolating possible mating and breeding areas that are currently unknown (Chapter II). In the next chapter, I quantify the seasonal suitable habitat availability in the Indian Ocean (ocean basin-scale study) by applying generalised linear, spatial mixed-effects and maximum entropy models to produce maps of whale shark habitat suitability (Chapter III). I then assess the inter-annual variation in known whale shark occurrences to unearth temporal trends in a large area of the Indian Ocean. The results from the Indian Ocean suggest both temporal and spatial variability in the whale sharks occurrence (Chapter IV). Therefore, I applied the same analysis to the Atlantic and Pacific Oceans using similar broad-scale datasets. While the results for the Pacific Ocean were inconclusive with respect to temporal trends, in the Atlantic Ocean I found preliminary evidence for a cyclic regularity in whale shark occurrence (Chapter V). In Chapter VI, I build a model to predict global whale shark habitat suitability for the present, as well as within a climate change scenario for 2070. Finally, Chapter VII provides a general discussion of the work developed within this thesis and presents ideas for future research.
Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2013