Representing the Indian Ocean Dipole

Purpose. This paper offers an alternative representation of the Indian Ocean Dipole. Instead of the zonal gradient of equatorial sea surface temperature, the new index uses tropical sub-surface temperatures (T100). Methods and Results. The space-time character of the new index is defined by empirical orthogonal function analysis in the domain 20°S–5°N, 35°–120°E. The spatial pattern reflects an inherent zonal dipole with a temporal score that correlates with atmospheric empirical orthogonal function modes that describe the Walker circulation and basin-scale convection. Statistical regressions are conducted in the period 1979–2019 to evaluate the traditional Dipole Mode Index and the new T100 index, and the association with East Africa climate and Pacific Nino3.4 SST. These demonstrate improved performance of the T100 index with ~ 30% higher r2 explained variance. Conclusions. Whereas the old index tracks feedback between equatorial sea surface temperature / zonal wind / surface fluxes, the new index tracks coupling between south Indian Ocean Rossby waves / anticyclonic curl / thermocline oscillations

Three-dimensional lattice-Boltzmann simulations of critical spinodal decomposition in binary immiscible fluids

We use a modified Shan-Chen, noiseless lattice-BGK model for binary immiscible, incompressible, athermal fluids in three dimensions to simulate the coarsening of domains following a deep quench below the spinodal point from a symmetric and homogeneous mixture into a two-phase configuration. We find the average domain size growing with time as $t^\gamma$, where $\gamma$ increases in the range $0.545 < \gamma < 0.717$, consistent with a crossover between diffusive $t^{1/3}$ and hydrodynamic viscous, $t^{1.0}$, behaviour. We find good collapse onto a single scaling function, yet the domain growth exponents differ from others' works' for similar values of the unique characteristic length and time that can be constructed out of the fluid's parameters. This rebuts claims of universality for the dynamical scaling hypothesis. At early times, we also find a crossover from $q^2$ to $q^4$ in the scaled structure function, which disappears when the dynamical scaling reasonably improves at later times. This excludes noise as the cause for a $q^2$ behaviour, as proposed by others. We also observe exponential temporal growth of the structure function during the initial stages of the dynamics and for wavenumbers less than a threshold value.Comment: 45 pages, 18 figures. Accepted for publication in Physical Review

A synthesis of three decades of socio-ecological change in False Bay, South Africa: setting the scene for multidisciplinary research and management

Over the past three decades, marine resource management has shifted conceptually from top-down sectoral approaches towards the more systems-oriented multi-stakeholder frameworks of integrated coastal management and ecosystem-based conservation. However, the successful implementation of such frameworks is commonly hindered by a lack of cross-disciplinary knowledge transfer, especially between natural and social sciences. This review represents a holistic synthesis of three decades of change in the oceanography, biology and human dimension of False Bay, South Africa. The productivity of marine life in this bay and its close vicinity to the steadily growing metropolis of Cape Town have led to its socio-economic significance throughout history. Considerable research has highlighted shifts driven by climate change, human population growth, serial overfishing, and coastal development. Upwelling-inducing winds have increased in the region, leading to cooling and likely to nutrient enrichment of the bay. Subsequently the distributions of key components of the marine ecosystem have shifted eastward, including kelp, rock lobsters, seabirds, pelagic fish, and several alien invasive species. Increasing sea level and exposure to storm surges contribute to coastal erosion of the sandy shorelines in the bay, causing losses in coastal infrastructure and posing risk to coastal developments. Since the 1980s, the human population of Cape Town has doubled, and with it pollution has amplified. Overfishing has led to drastic declines in the catches of numerous commercially and recreationally targeted fish, and illegal fishing is widespread. The tourism value of the bay contributes substantially to the country’s economy, and whale watching, shark-cage diving and water sports have become important sources of revenue. Compliance with fisheries and environmental regulations would benefit from a systems- oriented approach whereby coastal systems are managed holistically, embracing both social and ecological goals. In this context, we synthesize knowledge and provide recommendations for multidisciplinary research and monitoring to achieve a better balance between developmental and environmental agendas

DETERMINATION OF HEALTH IMPACTS IN URBAN REGIONS EXPOSED TO ATMOSPHERIC POLLUTANTS

A simple method for relating urban health responses to ambient air pollution levels is outlined. The methhod requires daily values of concentrations for the most common atmospheric irritant and respiratory complaint statistics from an adjacent medical clinic. The data need to be quality controlled and of sufficient length to be statistically screened using various thresholds. The method is limited in scope, so historical evidence is needed to guide the survey to the relevant time of year and most exposed place. In the example given for Richards Bay - South Africa, health responses achieve maximum variance (27.4%) with respect to peak values of S02 on (he same cdy over a 40 day period in the winter of 1998. The correlation function for various thresholds indicates that 30 ppb is a critical heallh sensitivity level. The economic implications are computed and interpretations address how the results can be used 10 modify town&nbsp;planning efforts.&nbsp

MESOSCALE NUMERICAL MODELS: COST-EFFECTIVE INPUT TO DISPERSION PREDICTION SCHEMES

Dispersion schemes which utilise on-line transport weather data are in increasing use, to predict the concentration distribution of pollutants near an industrial source. In many cases, sharp transitions in plume transport and spread can occur downstream from the source owing to changes in wind directions and mixing properties. These may be observed using costly remote stations or estimated using a mesoscale numerical model. A two dimensional mixed layer numerical model is described and tested for a land-seabreeze scenario in the Cape Town area. Comparisons with previous observational are made. It is suggested that these numerical models be used to interpolate meteorological observations form the source, to the wider area influenced by industrial emissions

Anomalous propagation along the Cape West Coast due to sloping meteorological inversions

VHF television signals along the Cape West Coast are often degraded by fading and/or ghosts. The problem is analyzed from recorded signal strength data and a theory is developed that ducting, caused by a sloping temperature inversion, is the propagation phenomena causing the undesired effects. A meteorological explanation for the effect is given.Articl