Climate Change in Eastern Africa

The climatology of East Africa results from the complex interaction between major global convergence zones with more localized regional feedbacks to the climate system; these in turn are moderated by a diverse land surface characterized by coastal to land transitions, high mountains, and large lakes. The main climatic character of East Africa, and how this varies across the region, takes the form of seasonal variations in rainfall that can fall as one, two, or three rainy seasons, the times and duration of which will be determined by the interplay between major convergence zones with more localized regional feedbacks. One of the key characteristics of East Africa are climatic variations with altitude as climates change along an altitudinal gradient that can extend from hot, dry, “tropical” conditions to cool, wet, temperate conditions and on the highest mountains “polar” climates with permanent ice caps. With this complex and variable climate landscape of the present, as scientists move through time to explore past climatic variability, it is apparent there have been a series of relatively rapid and high-magnitude environmental shifts throughout East Africa, particularly characterized by changing hydrological budgets. How climate change has impacted on ecosystems, and how those ecosystems have responded and interacted with human populations, can be unearthed by drawing on evidence from the sedimentary and archaeological record of the past six thousand years. As East African economies, and the livelihoods of millions of people in the region, have been clearly heavily affected by climate variability in the past, so it is expected that future climate variability will impact on ecosystem functioning and the preparedness of communities for future climate change.

Groundwater, Soil, and Vegetation Interactions at Discrete Riparian Inflow Points (DRIPs) and Implications for Boreal Streams

Hydrological processes at hillslope and catchment scales explain a large part of stream chemistry dynamics through source-transport mechanisms from terrestrial to aquatic ecosystems. Riparian zones play a central role, as they exert a strong influence on the chemical signature of groundwater discharge to streams. Especially important are riparian areas where upslope subsurface flow paths converge, because they connect a large part of the catchment to a narrow section of the stream. Recent research shows that both in terrestrial and aquatic ecosystems, riparian convergence zones fulfill important biogeochemical functions that differ from surrounding riparian zones. Most catchment-scale conceptual frameworks focus on generalized hillslope-riparian-stream transects and do not explicitly consider riparian convergence zones. This study integrates collective work on hydrology, groundwater chemistry, vegetation and soils of discrete riparian inflow points (DRIPs) in a boreal landscape. We show that compared to adjacent riparian forests, DRIPs have groundwater levels that are consistently near the surface, and supply organic-rich water to streams. We suggest that interactions between hydrology, wetland vegetation, and peat soil development that occur in DRIPs leads to their unique groundwater chemistry and runoff dynamics. Stream-based studies show that across flow conditions, groundwater inputs from DRIPs to headwater reaches influence stream temperature, water chemistry and biology. As such, accounting for DRIPs can complement existing hillslope and stream observations, which would allow better representation of chemical and biological interactions associated with convergence of subsurface flow paths in riparian zones.

A Distributed Network for Multimodal Experiential Representation of Concepts

The architecture of the cortical system underlying concept representation is a topic of intense debate. Much evidence supports the claim that concept retrieval selectively engages sensory, motor, and other neural systems involved in the acquisition of the retrieved concept, yet there is also strong evidence for involvement of high-level, supramodal cortical regions. A fundamental question about the organization of this system is whether modality-specific information originating from sensory and motor areas is integrated across multiple ″convergence zones″ or in a single centralized ″hub″. We used representational similarity analysis (RSA) of fMRI data to map brain regions where the similarity structure of neural patterns elicited by large sets of concepts matched the similarity structure predicted by a high-dimensional model of concept representation based on sensory, motor, affective, and other modal aspects of experience. Across two studies involving different sets of concepts, different participants, and different tasks, searchlight RSA revealed a distributed, bihemispheric network engaged in multimodal experiential representation, composed of high-level association cortex in anterior, lateral, and ventral temporal lobe; inferior parietal lobule; posterior cingulate gyrus and precuneus; and medial, dorsal, ventrolateral, and orbital prefrontal cortex. These regions closely resemble networks previously implicated in general semantic and ″default mode″ processing and are known to be high-level hubs for convergence of multimodal processing streams. Supplemented by an exploratory cluster analysis, these results indicate that the concept representation system consists of multiple, hierarchically organized convergence zones supporting multimodal integration of experiential information.

Atmospheric convergence zones stemming from large-scale mixing

Organised cloud bands are important features of tropical and subtropical rainfall. These structures are often regarded as convergence zones, alluding to an association with coherent atmospheric flow. However, the flow kinematics is not usually taken into account in classification methods for this type of event, as large-scale lines are rarely evident in instantaneous diagnostics such as Eulerian convergence. Instead, existing convergence zone definitions rely on heuristic rules of shape, duration and size of cloudiness fields. Here we investigate the role of large-scale turbulence in shaping atmospheric moisture in South America. We employ the finite-time Lyapunov exponent (FTLE), a metric of deformation among neighbouring trajectories, to define convergence zones as attracting Lagrangian coherent structures (LCSs). Attracting LCSs frequent tropical and subtropical South America, with climatologies consistent with the South Atlantic Convergence Zone (SACZ), the South American Low-Level Jet (SALLJ) and the Intertropical Convergence Zone (ITCZ). In regions under the direct influence of the ITCZ and the SACZ, rainfall is significantly positively correlated with large-scale mixing measured by the FTLE. Attracting LCSs in south and southeast Brazil are associated with significant positive rainfall and moisture flux anomalies. Geopotential height composites suggest that the occurrence of attracting LCSs in these regions is related with teleconnection mechanisms such as the Pacific–South Atlantic. We believe that this kinematical approach can be used as an alternative to region-specific convergence zone classification algorithms; it may help advance the understanding of underlying mechanisms of tropical and subtropical rain bands and their role in the hydrological cycle.

Simultaneous determination of layer thicknesses in graded layer materials by ultrasonic non-destructive method

Functionally graded materials (FGMs) are widely applied in aerospace, energy, biology and other fields. Simultaneous determination of the thicknesses of all the graded layers is of great importance in evaluating the quality of an FGM. A model is set up to characterise the ultrasonic waves reflected from an FGM composed of thin layers at normal incidence. The reflection spectrum is derived to simultaneously obtain the thicknesses of the various graded layers. To prove the feasibility of the proposed method, it is applied to measure the layer thicknesses of a prepared Al-Ti bi-layered material specimen without delaminations. An inverse algorithm based on the Gauss-Newton method is introduced to determine the thicknesses by comparing the theoretical and measured reflection spectra. The effects of the frequency bandwidth of the transducer on the thickness convergence zones and the thickness measurement results are investigated. The sensitivity of the proposed method to the thickness parameters is studied. The results indicate that the frequency bandwidth plays an important role in the thickness measurement. The relative thickness errors of the Al layer and the Ti layer in this experiment are –5.28% and +2.77% using 5 MHz and 15 MHz transducers. It is concluded that a combination of reflection spectra and inverse techniques can be employed to simultaneously obtain the graded layer thicknesses.

Climate change and hydrological risk in the Pacific: a Humanitarian Engineering perspective

Pacific Island communities have adapted to floods, droughts and cyclones over many generations. Small and low-lying islands are particularly exposed to natural disasters, and many countries have limited access to water resources. Anthropogenic climate change is expected to further increase these environmental pressures. Any associated engineering response needs to consider the cultural, societal and historical context, and prioritise the agency of local communities to determine their preferred outcomes. It follows that Humanitarian Engineering, a discipline centred around strengths-based and context-appropriate solutions, has an important role to play in climate change adaptation. In this review, the interplay between hydroclimatology, geography and water security in the Pacific Islands is described and projected climate shifts summarised to highlight future adaptation challenges. A key source of uncertainty relates to the dynamics of two convergence zones that largely drive weather patterns. A broad overview of societal factors that present challenges and opportunities for Humanitarian Engineers is given. Finally, actions are recommended to inform climate change adaptation given the scientific uncertainty around hydrologic risks, and outline lessons for best practice Humanitarian Engineering in the Pacific. Enhancing data sharing, building resilience to climate variability and integrating traditional knowledge with convention engineering methods should be key areas of focus.

Evaluation of the ABI/GOES-16 SST Product in the Tropical and Southwestern Atlantic Ocean

Sea surface temperature (SST) is an essential climate variable used for ocean and weather monitoring and forecasting. The NOAA’s next generation geostationary satellite GOES-16 was declared operational at the east position (75°W) in December 2017, carrying onboard an Advanced Baseline Imager (ABI). The hyperspectral ABI sensor now allows SST estimates every 10–15 min at both day and nighttime, with advanced options for cloud screening and water vapor correction. In the present work, we compare the first operational ABI SST product (OSI SAF, 2018) with an in situ match-up database (MDB) across the Tropical and Southwestern Atlantic Ocean, off the Brazilian coast, throughout the year of 2018. The MDB was obtained from two long-term programs, i.e., PIRATA moored buoys (FOLTZ et al., 2016) and PNBoia moored and drifting buoys (MARINHA DO BRASIL, 2017). Separate comparisons were made for each data set, analyzing the uncertainties according to the program (i.e., buoy type and region), satellite SST quality level and influence of diurnal heating. We also compare the ABI product with the OSTIA analysis L4 SST (DONLON et al., 2012) to increment our analyses on the spatio-temporal biases within the study region. The results show that the OSI SAF ABI SST L3C has a mean bias (0.1 °C) and error (RMSE, 0.5 °C) within the GHRSST standards, with an exception being coastal waters off the southeast Brazilian coast (RMSE, 0.65 °C), which are subjected to sharp thermal fronts. The highest biases are for regions/seasons subjected to persistent cloud coverage and high water-vapor content, i.e., the Intertropical and South Atlantic Convergence Zones, as well as highly dynamic frontal zones, i.e., the Brazil Malvinas Confluence Zone, the Subtropical Front and coastal waters. The ABI SST product is suitable for operational use, and applications should explore more deeply the new set of information provided.

Dynamic and Energetic Constraints on the Modality and Position of the Intertropical Convergence Zone in an Aquaplanet

The tropical zonal-mean precipitation distribution varies between having single or double peaks, which are associated with intertropical convergence zones (ITCZs). Here, the effect of this meridional modality on the sensitivity of the ITCZ to hemispherically asymmetric heating is studied using an idealized GCM with parameterized Ekman ocean energy transport (OET). In the idealized GCM, transitions from unimodal to bimodal distributions are driven by equatorial ocean upwelling and cooling, which inhibits equatorial precipitation. For sufficiently strong equatorial cooling, the tropical circulation bifurcates to anti-Hadley circulation in the deep tropics, with a descending branch near the equator and off-equatorial double ITCZs. The intensity and extent of the anti-Hadley circulation is limited by a negative feedback: westerly geostrophic surface wind tendency in its poleward-flowing lower branches balances the easterly stress (and hence equatorial upwelling) required for its maintenance. For weak ocean stratification, which goes along with unimodal or weak bimodal tropical precipitation distribution, OET damps shifts of the tropical precipitation centroid but amplifies shifts of precipitation peaks. For strong ocean stratification, which goes along with pronounced double ITCZs, asymmetric heating leads to relative intensification of the precipitation peak in the warming hemisphere, but negligible meridional shifts. The dynamic feedbacks of the coupled system weaken the gradient of the atmospheric energy transport (AET) near the equator. This suggests that over a wide range of climates, the ITCZ position is proportional to the cubic root of the cross-equatorial AET, as opposed to the commonly used linear relation.

The origin of microplastics of offshore discharge: A review in assessing the relationship between microplastics content and other contaminants

The article reviewed migration, degradation, toxicity, and distribution of microplastics, which was focused on data enumeration of emission samples from countries around the North Pacific Ocean, South Atlantic Ocean, and Circumpolar oceans. Microplastic particles are easily absorbed by animals and spread to the whole food chain, and they have been confirmed to exist in the human body. It was well established that high abundance microplastics were trapped by ocean currents and accumulated in surface and sediment in convergence zones of the five subtropical gyres. While microplastic itself leaches out the toxin in the seawater, synergistic effects between microplastic and other pollutants increase microplastic toxicity for organisms. The monomers of 16 out of 55 plastic polymers were carcinogenic and mutagenic or toxic for reproduction. Additives used in the process are also dangerous polypropylene (PP), and polyethylene (PE) prefer to sorb persistent organic pollutants (POPs) and have an extremely slow rate of desorption, which form synergic effects and increase the toxicity of microplastics (MPs). For other plastic polymers, the sorption and desorption of pollutants by MPs depends on the concentration of POPs, so the toxicity of MPs varies with the content of pollutants. But for some types of MPs and POPs, the concentration of POPs controlled by microplastics also can decrease the lethal toxicity of POPs. Higher concentrations of MPs in the seawater cause larger MPs consumptions of marine organisms, especially in polar regains that have the highest MPs concentrations.