A numerical ocean circulation model of the Norwegian and Greenland Seas

The dynamics and thermodynamics of the Norwegian and Greenland Seas are investigated using a three-dimensional primitive equation ocean circulation model. The horizontal resolution of the model is 1° in the zonal direction and 0.5° in the meridional direction. The vertical structure is described by 15 levels. The model is driven by both annual mean and seasonally varying wind and thermohaline forcing. The connections of the Norwegian and Greenland Seas with the North Atlantic and Arctic Ocean are modelled with an open boundary condition. The simulated currents are in reasonable agreement with the observed circulation

Buoyancy driven rotating boundary currents

The structure of boundary currents formed from intermediately dense water introduced into a rotating, stably stratified, two-layer environment is investigated in a series of laboratory experiments, performed for Froude numbers ranging from 0.01 to 1. The thickness and streamwise velocity profiles in quasi-steady currents are measured using a pH activated tracer (thymol blue) and found to compare favorably to simplified analytic solutions and numerical models. Currents flowing along sloping boundaries in a stratified background exhibit robust stability at all experimental Froude numbers. Such stability is in sharp contrast to the unequivocal instability of such currents flowing against vertical boundaries, or of currents flowing along slopes in a uniform background. The presence of a variety of wave mechanisms in the ambient medium might account for the slower and wider observed structures and the stability of the currents, by effecting the damping of disturbances through wave radiation.Comment: 9 pages with 2 figures to appear in Ann NYAS "Long range effects in physics and astrophysics

On the origin and pathway of the saline inflow to the Nordic Seas: insights from models

The behaviours of three high-resolution ocean circulation models of the North Atlantic, differing chiefly in their description of the vertical coordinate, are investigated in order to elucidate the routes and mechanisms by which saline water masses of southern origin provide inflows to the Nordic Seas. An existing hypothesis is that Mediterranean Overflow Water (MOW) is carried polewards in an eastern boundary undercurrent, and provides a deep source for these inflows. This study, however, provides an alternative view that the inflows are derived from shallow sources, and are comprised of water masses of western origin, carried by branches of the North Atlantic Current (NAC), and also more saline Eastern North Atlantic Water (ENAW), transported northwards from the Bay of Biscay region via a ‘Shelf Edge Current’ (SEC) flowing around the continental margins. In two of the models, the MOW flows northwards, but reaches only as far as the Porcupine Bank (53°N). In third model, the MOW also invades the Rockall Trough (extending to 60°N). However, none of the models allows the MOW to flow northwards into the Nordic Seas. Instead, they all support the hypothesis of there being shallow pathways, and that the saline inflows to the Nordic Seas result from NAC-derived and ENAW water masses, which meet and partially mix in the Rockall Trough. Volume and salinity transports into the southern Rockall Trough via the SEC are, in the various models, between 25 and 100% of those imported by the NAC, and are also a similarly significant proportion (20–75%) of the transports into the Nordic Seas. Moreover, the highest salinities are carried northwards by the SEC (these being between 0.13 and 0.19 psu more saline at the southern entrance to the Trough than those in the NAC-derived waters). This reveals for the first time the importance of the SEC in carrying saline water masses through the RockallTrough and into the Nordic Seas. Furthermore, the high salinities found on density surfaces appropriate to the MOW in the Nordic Seas are shown to result from the wintertime mixing of the saline near-surface waters advected northwards by the SEC/NAC system. Throughout, we have attempted to demonstrate the extent to which the models agree or disagree with interpretations derived from observations, so that the study also contributes to an ongoing community effort to assess the realism of our current generation of ocean models

Southern Ocean bottom water characteristics in CMIP5 models

Southern Ocean deep water properties and formation processes in climate models are indicative of their capability to simulate future climate, heat and carbon uptake, and sea level rise. Southern Ocean temperature and density averaged over 1986–2005 from 15 CMIP5 (Coupled Model Intercomparison Project Phase 5) climate models are compared with an observed climatology, focusing on bottom water. Bottom properties are reasonably accurate for half the models. Ten models create dense water on the Antarctic shelf, but it mixes with lighter water and is not exported as bottom water as in reality. Instead, most models create deep water by open ocean deep convection, a process occurring rarely in reality. Models with extensive deep convection are those with strong seasonality in sea ice. Optimum bottom properties occur in models with deep convection in the Weddell and Ross Gyres. Bottom Water formation processes are poorly represented in ocean models and are a key challenge for improving climate predictions

Social structures in the regular combat arms units of the British Army : a model

An original model is presented for describing, analysing, and predicting soldiers’ behaviour in current regular combat arms units in the British Army. It was derived, using social anthropological techniques, during participant observation by a serving British Army officer, and provides more coherent insights than other models of unit life. Its central principle, created for this study, is a plurality of >social structures’. These >social structures’ are separate bodies of ideas, rules and conventions of behaviour which inform groups of people or individuals how to organise and conduct themselves vis-à-vis each other. One >social structure’ operates at any single moment, according to context. Such an approach has not previously been applied to British Soldiers. The model’s top level (low resolution), comprises: the formal command structure, consisting in the unit organisation, the apparatus of rank and discipline, and the framework of official accountability; the informal structure, comprising the conventions of behaviour in the absence of formal constraints; the functional structure, concerning >soldierly’ activity, attitudes, and expectations; and the loyalty/identity structure, encompassing the conventions involved in embracing and expressing membership of the formal hierarchy of groups within and above the unit. Lower levels provide higher resolution, including a typology of informal relationships which encompasses different degrees of closeness and differences or equality in rank. The model’s rigour is established by testing its sensitivity at high resolution to the different conditions of life in historical British armies. The top level, however, and the typology of informal relationships, are found potentially to provide a unifying framework for historical analysis of unit life in the British Army throughout its history. The model’s ability to illuminate current issues in the Army is demonstrated by its application to leadership training for officer cadets and the integration of women into regular combat arms units.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The Dynamics of Viral Marketing

We present an analysis of a person-to-person recommendation network, consisting of 4 million people who made 16 million recommendations on half a million products. We observe the propagation of recommendations and the cascade sizes, which we explain by a simple stochastic model. We analyze how user behavior varies within user communities defined by a recommendation network. Product purchases follow a 'long tail' where a significant share of purchases belongs to rarely sold items. We establish how the recommendation network grows over time and how effective it is from the viewpoint of the sender and receiver of the recommendations. While on average recommendations are not very effective at inducing purchases and do not spread very far, we present a model that successfully identifies communities, product and pricing categories for which viral marketing seems to be very effective

Why name generators with a fixed number of alters may be a pragmatic option for personal network analysis

Social network analysis (SNA) has grown exponentially in recent years, giving rise to methodological innovations in different scientific disciplines. In psychology, SNA has been incorporated into studies of individual personality differences and has generated novel areas, such as network psychometrics and network interventions. In community psychology, a recent review examined the use of network analysis in American Journal of Community Psychology publications (Neal & Neal, American Journal of Community Psychology , 2017, 60, 279). Based on their study, the authors advise researchers to avoid using the fixed-choice name generator when possible, as one of the five methodological recommendations proposed. In this essay, I explain how the recent increase of name generators with a fixed number of alters when studying personal networks is originally linked to an interest in describing structural properties. Second, I analyze the pragmatic contributions of this method: establishing a limit of alters a priori can entail advantages in terms of standardization and comparability of personal networks. Finally, to contextualize the methodological debate, I argue that personal networks represent the diversity of contexts in which the individual participates and are naturally integrated into community surveys