Response of the tropical convergence zones to extratropical thermal forcing

Paleoclimatic data, 20th century observations and numerical simulations have all suggested the capability of the extratropics to trigger global teleconnection patterns and drive changes in the distant tropical regions mediated through atmospheric and ocean processes. The emerging general picture is that the Inter Tropical Convergence Zone (ITCZ) tends to shift toward the warmer hemisphere at the same time that the atmospheric energy transport is modified to favour the transport of energy to the colder hemisphere. Apart from paleo and 20th century climate implications, the extratropical to tropical teleconnection problem has also been related with the future climate as the projected pattern of temperature change for the 21st century presents an interhemispheric asymmetry with the strongest warming projected to occur over the Northern Hemisphere (NH) high latitudes. This thesis aims to shed further light into the sensitivity of the tropical climate to an extratropical thermal forcing via a series of numerical simulations performed with an Atmospheric General Circulation Model (AGCM) coupled to either a low or a medium complexity ocean model, using realistic surface boundary conditions in all the cases. The behaviour of two convergence zones, the ITCZ and the South Atlantic Convergence Zone (SACZ), is the main focus of the work. The relative roles of the atmosphere, sea surface temperature (SST), land surface temperature (LST), hemispheric component of the forcing and tropical ocean dynamics are investigated and physical mechanisms mediating in the extratropical to tropical teleconnection are proposed and tested. In simulations in which the AGCM is coupled to slab ocean and land models we find that if the tropical SSTs are not allowed to change in response to the extratropical forcing then the ITCZ response strongly weakens although it is not negligible in particular over the Atlantic Ocean and Africa. If, in addition to the tropical SST constraint, the LST over Africa is prevented to change the ITCZ response to the remote signal completely vanishes. Therefore, our results indicate that the ITCZ response to the extratropical forcing is not possible just trough purely atmospheric processes, but needs the involvement of either the tropical SST or the LST. The clear-sky longwave radiation feedback is highlighted as the main physical mechanism operating behind the land-based extratropical to tropical communication. Regarding the SACZ, we present numerical evidence that indicates that it can be affected by an extratropical thermal forcing with a behaviour that does not replicate the ITCZ response of shifting toward the warmer hemisphere. In fact, we find that when the NH (Southern Hemisphere, SH) extratropics warm (cool), the SACZ experiences a significant weakening associated, mostly, to the NH component of the forcing. Our results indicate that 75% of the SACZ signal in response to the forcing is linked to the development of a secondary tropical convergence zone in the Atlantic Ocean around 20°N-30ºN, which depends on the tropical SST response. The remaining 25% of the signal can be explained through the development of a Walker-type of circulation between western tropical Africa and the SACZ, being this mechanism associated with the African LST reaction to the remote forcing. To assess the role of the tropical ocean dynamics we analyse and compare simulations in which the AGCM is coupled either to a slab ocean model or to a combination of a Reduced Gravity Ocean model in the tropics and a slab model elsewhere. The inclusion of tropical ocean dynamics enables changes in the equatorial Pacific SST seasonal cycle, whose response to a NH (SH) high latitude warming (cooling) consists of a significant strengthening in the eastern portion of the basin. The annual mean response, however, is weaker than the signal the extratropical forcing would generate if only thermodynamic coupling was allowed, thus suggesting that tropical ocean dynamics tends to oppose the extratropical forcing in the mean. We further find that under an extratropical forcing the activity of the El Niño-Southern Oscillation weakens, which is consistent with a strengthening of the seasonal cycle through the previously proposed frequency entrainment mechanismDatos paleoclimáticos, observaciones del siglo XX y simulaciones numéricas sugieren que los extratrópicos tienen la capacidad para desencadenar patrones de teleconexión globales y forzar cambios en las regiones tropicales, a través de de procesos atmosféricos y oceánicos. La imagen general que surge es que la Zona de Convergencia Inter Tropical (ZCIT) tiende a desplazarse hacia el hemisferio más cálido mientras que el transporte de energía atmosférico se modifica para favorecer la transferencia energética hacia el hemisferio más frío. Además de implicaciones paleoclimáticas y para el clima del siglo XX, el problema de la teleconexión desde los extratrópicos hacia los trópicos ha sido también relacionado con el clima futuro, dado que el patrón proyectado de cambio de temperatura para el sigo XXI presenta una marcada asimetría interhemisférica con un calentamiento acentuado en las latitudes altas del Hemisferio Norte (HN). El objetivo de esta tesis es profundizar en el estudio de la sensibilidad del clima tropical a un forzante térmico extratropical mediante una serie de simulaciones numéricas realizadas con un modelo de circulación general de la atmósfera (MCGA) acoplado a modelos oceánicos de complejidad baja o media y utilizando, en todos los casos, condiciones de borde realistas. El comportamiento de dos zonas de convergencia, la ZCIT y la Zona de Convergencia del Atlántico Sur (ZCAS), es el foco principal del trabajo. Los roles relativos de la atmósfera, la temperatura de superficie del mar (TSM), la temperatura de superficie continental (TSC), la componente hemisférica del forzante y la dinámica de los océanos tropicales son investigados al mismo tiempo que mecanismos físicos que median en la teleconexión son propuestos y testeados. En simulaciones en las que el MCGA se acopla a modelos tipo slab para océanos y continentes encontramos que si no se permite que la TSM tropical reaccione al forzante extratropical entonces la respuesta de la ZCIT se debilita notablemente pero sigue siendo significativa, en particular, sobre el océano Atlántico y África. Si, además de la restriction a la TSM tropical, no se permite que la TSC sobre África cambie entonces la respuesta de la ZCIT se desvanece completamente. Por lo tanto, nuestros resultados indican que la respuesta de la ZCIT a un forzante extratropical no es posible a través de procesos puramente atmosféricos, sino que necesita del involucramiento de o bien la TSM o bien la TSC tropical. Encontramos que la retroalimentación de radiación de onda 5 larga en cielo claro es el principal mecanismo físico operando detrás de la comunicación extratrópicos-trópicos a través del continente africano. En cuanto a la ZCAS, presentamos evidencia numérica que indica que puede ser afectada por un forzante térmico extratropical con un comportamiento que no replica la respuesta de la ZCIT de desplazarse hacia el hemisferio más cálido. De hecho, encontramos que cuando los extratrópicos del HN (Hemisferio Sur, HS) se calientan (enfrían) la ZCAS experimenta un debilitamiento significativo asociado, mayoritariamente, a la componente del forzante localizada en el HN. Nuestros resultados muestran que el 75% de la señal de la ZCAS en respuesta al forzante está asociado al desarrollo de una zona de convergencia tropical secundaria en el océano Atlántico entre 20°N y 30°N, la cual es dependiente de la respuesta de la TSM tropical. El 25% restante de la señal puede ser explicado mediante el desarrollo de una circulación del tipo de Walker entre el oeste de África tropical y la ZCAS, estando este mecanismo asociado a la reacción de la TSC africana al forzante remoto. Para evaluar el rol de la dinámica oceánica tropical analizamos y comparamos simulaciones en las que el MCGA se acopla o bien a un modelo slab oceánico o bien a una combinación de un modelo de gravedad reducida en los trópicos y un modelo slab en el resto de los puntos oceánicos. La inclusión de la dinámica oceánica tropical permite que se produzcan cambios en el ciclo estacional de la TSM del Pacífico ecuatorial, cuya respuesta a un calentamiento (enfriamiento) en latitudes altas del HN (HS) consiste en una intensificación significativa en la porción este de la cuenca. Sin embargo, la respuesta en términos de promedios anuales es más débil que la que el forzante generaría si únicamente una acople termodinámico estuviese permitido sugiriendo, por ende, que la dinámica oceánica tropical tiende a oponerse al forzante extratropical en promedio. Por otro lado, también encontramos que bajo la influencia de un forzante extratropical la actividad del fenómeno El Niño-Oscilación Sur se debilita, lo cual es consistente con la intensificación del ciclo estacional a través del ya propuesto mecanismo de arrastre de frecuencias

Accounting for the Ocean Economy Using the System of National Accounts

The increasing importance to measure the ocean economy cannot be discounted. A number of countries attempted to measure the ocean economy based on their needs and perceptions. At this point, however, there is no agreed scope and coverage of the ocean economy nor is there an agreed operational definition of the variables needed for its measurement. Moreover, there is no internationally endorsed framework that will guide and lead to comparable estimates across countries or regions. Utilizing the 2008 System of National Accounts (SNA) as a framework, this paper endeavors to estimate the contribution of the ocean economy in the Philippines using the present Philippine System of National Accounts (PSNA) and taking into consideration the agreement in the Inception Workshop on the Blue Economy Assessment held last 28-30 July 2015 in Manila on the initial list of sectors relevant to the ocean economy. The current PSNA has adopted the 2008 SNA in May 2011 and has incorporated estimates of the “unorganized sector”, which is an approximation of the informal sector in the Philippine economy. The paper also explores the possibility of utilizing the System of Environmental Economic Accounting (SEEA) and the Experimental Ecosystem Approach being done in the Philippines to complement the existing national accounts estimates. Key words and Phrases: ocean economy, system of national accounts, industrial classification, unorganized sector, environmental accounting, ecosystem

Response of the Asian Summer Monsoons to a High-latitude Thermal Forcing: Mechanisms and Nonlinearities

This study investigates mechanisms and nonlinearities in the response of the Asian Summer Monsoons (ASM) to high-latitude thermal forcings of different amplitudes. Using a suite of runs carried out with an intermediate-complexity atmospheric general circulation model, we find that the imposed forcings produce a strong precipitation response over the eastern ASM but a rather weak response over the southern ASM. The forcing also causes a precipitation dipole with wet conditions over the eastern Tibetan Plateau (TP) and dry conditions over the Bay of Bengal (BoB) and southeast Asia. A moderate increase of precipitation along the southern margin of the TP is also produced. Simulations designed to isolate the causal mechanisms show that thermodynamic interactions involving the tropical surface oceans are far less important than the water-vapour feedback for the transmission of information from the high-latitudes to the ASM. Additionally, we assess the nonlinearity of the ASM precipitation response to the forcing amplitude using a novel application of the empirical orthogonal function method. The response can be decomposed in two overlapping patterns. The first pattern represents a precipitation dipole with wet conditions over the eastern TP and dry conditions over BoB, which linearly increases with forcing amplitude becoming quasi-stationary for large forcing amplitudes (i.e. amplitudes leading to Arctic temperature anomalies larger than 10 degrees C). The second pattern is associated with increased precipitation over the southeastern TP and is nonlinearly dependent on forcing, being most important for intermediate forcing amplitudes (i.e. amplitudes leading to Arctic temperature anomalies between 5 and 10 degrees C)

Sensitivity of the tropical climate to an interhemispheric thermal gradient: the role of tropical ocean dynamics

This study aims to determine the role of the tropical ocean dynamics in the response of the climate to extratropical thermal forcing. We analyse and compare the outcomes of coupling an atmospheric general circulation model (AGCM) with two ocean models of different complexity. In the first configuration the AGCM is coupled with a slab ocean model while in the second a reduced gravity ocean (RGO) model is additionally coupled in the tropical region. We find that the imposition of extratropical thermal forcing (warming in the Northern Hemisphere and cooling in the Southern Hemisphere with zero global mean) produces, in terms of annual means, a weaker response when the RGO is coupled, thus indicating that the tropical ocean dynamics oppose the incoming remote signal. On the other hand, while the slab ocean coupling does not produce significant changes to the equatorial Pacific sea surface temperature (SST) seasonal cycle, the RGO configuration generates strong warming in the central-eastern basin from April to August balanced by cooling during the rest of the year, strengthening the seasonal cycle in the eastern portion of the basin. We hypothesize that such changes are possible via the dynamical effect that zonal wind stress has on the thermocline depth. We also find that the imposed extratropical pattern affects El Ninõ-Southern Oscillation, weakening its amplitude and low-frequency behaviour

Constraining two climate field reconstruction methodologies over the North Atlantic realm using pseudo-proxy experiments

This study presents pseudo-proxy experiments to quantify the reconstruction skill of two climate field reconstruction methodologies for a marine proxy network subject to age uncertainties. The BARCAST methodology (Bayesian Algorithm for Reconstructing Climate Anomalies in Space and Time) is tested for sea surface temperature (SST) reconstruction for the first time over the northern North Atlantic region, and compared with a classic analogue reconstruction methodology. The reconstruction experiments are performed at annual and decadal resolution. We implement chronological uncertainties inherent to marine proxies as a novelty, using a simulated age-model ensemble covering the past millennium. Our experiments comprise different scenarios for the input data network, with the noise levels added to the target variable extending from ideal to realistic. Results show that both methodologies are able to reconstruct the Summer mean SST skillfully when the proxy network is considered absolutely dated, but the skill of the analogue method is superior to BARCAST. Only the analogue method provides skillful correlations with the true target variable in the case of a realistic noisy and age-uncertain proxy network. The spatiotemporal properties of the input target data are partly contrasting with the BARCAST model formulations, resulting in an inferior reconstruction ensemble that is similar to a white-noise stochastic process in time. The analogue method is also successful in reconstructing decadal temperatures, while BARCAST fails. The results contribute to constraining uncertainties in CFR for ocean dynamics which are highly important for climate across the globe

The reuse of waste heaps from extraction sites: An architectural methodology

This research was funded by the FCT-Funda??o para a Ci?ncia e a Tecnologia, under grant number SFRH/BD/133777/2017. The first author thanks the FCT-Funda??o para a Ci?ncia e a Tecnologia, under grant number SFRH/BD/133777/2017. The work of J. C. Kullberg was supported by national funds from Fundac?o para a Ci?ncia e a Tecnologia (FCT) through the research unit UID/GEO/04035/2013 (GeoBioTec).Nowadays, the rehabilitation of quarries is a widespread practice. It stems from the most significant environmental concern in the management of non-renewable resources. However, reusing quarry waste in the process of regeneration represents the aspect less prevalent. This procedure results from the non-commercialized material, accumulated in huge piles of waste, that constitute invasive elements of the landscape. Because of the intense industrial activity, the wastes further contribute to the degradation of the sites. The result of the waste abandonment could be reversed if this discarded material is considered as a product in the landscape requalification process. Mixing theoretical concepts with practical examples, this article proposes an application methodology to reuse the waste material in the landscape and architectural domains. This new contribution highlights the importance of considering scrap accumulations as an integral part of the architectural project, filling the existing gap in both architectural and theoretical domains. There is not any similar schematization in the literature and the idea of dealing with the mounds of wastes has been only slightly approached until now. The reached outcomes are demonstrative of the possibility of working with the waste heaps in architecture, creating a solid basis for further investigations not documented yet.publishersversionpublishe

Quarries: From abandoned to renewed places

This research was funded by FCT—Fundação para a Ciência e a Tecnologia, grant number SFRH/BD/133777/2017.Numerous industrial pits are discarded after their exploitation in every part of the world. Humanity both transforms the original morphology of the landscape, due to industrial activity in the territory, and, at the same time, rejects this "new" situation. This is to the detriment of the landscape, which is witness to this transfiguration, degradation, and abandonment. What is the future of these impersonal and empty areas? In this article, we present a general survey concerning the notion of quarry reuse to highlight the importance of this current and common problem. Our work approached the topic through a combination of the main concepts and a description of selected cases of study of quarry reconversions, sensitive to the environmental issues, climate changes, and sustainability. According to this premise, the research also provides an innovative matrix of schemes to classify the existing fundamental methods of recovery. For this effect, the investigation was proposed to be an instrument to improve the knowledge in the scientific and theoretical sectors, flanking the practical understanding, which has already started to move in this direction of reconversion, as the paper shows.publishersversionpublishe

Constraining two climate field reconstruction methodologies over the North Atlantic realm using pseudo-proxy experiments

This study presents pseudo-proxy experiments to quantify the reconstruction skill of two climate field reconstruction methodologies for a marine proxy network subject to age uncertainties. The BARCAST methodology (Bayesian Algorithm for Reconstructing Climate Anomalies in Space and Time) is tested for sea surface temperature (SST) reconstruction for the first time over the northern North Atlantic region, and compared with a classic analogue reconstruction methodology. The reconstruction experiments are performed at annual and decadal resolution. We implement chronological uncertainties inherent to marine proxies as a novelty, using a simulated age-model ensemble covering the past millennium. Our experiments comprise different scenarios for the input data network, with the noise levels added to the target variable extending from ideal to realistic. Results show that both methodologies are able to reconstruct the Summer mean SST skillfully when the proxy network is considered absolutely dated, but the skill of the analogue method is superior to BARCAST. Only the analogue method provides skillful correlations with the true target variable in the case of a realistic noisy and age-uncertain proxy network. The spatiotemporal properties of the input target data are partly contrasting with the BARCAST model formulations, resulting in an inferior reconstruction ensemble that is similar to a white-noise stochastic process in time. The analogue method is also successful in reconstructing decadal temperatures, while BARCAST fails. The results contribute to constraining uncertainties in CFR for ocean dynamics which are highly important for climate across the globe

Constraining two climate field reconstruction methodologies over the North Atlantic realm using pseudo-proxy experiments

This study presents pseudo-proxy experiments to quantify the reconstruction skill of two climate field reconstruction methodologies for a marine proxy network subject to age uncertainties. The BARCAST methodology (Bayesian Algorithm for Reconstructing Climate Anomalies in Space and Time) is tested for sea surface temperature (SST) reconstruction for the first time over the northern North Atlantic region, and compared with a classic analogue reconstruction methodology. The reconstruction experiments are performed at annual and decadal resolution. We implement chronological uncertainties inherent to marine proxies as a novelty, using a simulated age-model ensemble covering the past millennium. Our experiments comprise different scenarios for the input data network, with the noise levels added to the target variable extending from ideal to realistic. Results show that both methodologies are able to reconstruct the Summer mean SST skillfully when the proxy network is considered absolutely dated, but the skill of the analogue method is superior to BARCAST. Only the analogue method provides skillful correlations with the true target variable in the case of a realistic noisy and age-uncertain proxy network. The spatiotemporal properties of the input target data are partly contrasting with the BARCAST model formulations, resulting in an inferior reconstruction ensemble that is similar to a white-noise stochastic process in time. The analogue method is also successful in reconstructing decadal temperatures, while BARCAST fails. The results contribute to constraining uncertainties in CFR for ocean dynamics which are highly important for climate across the globe