Abstract In this study, the COADS¡]Comprehensive Ocean-Atmosphere Data Set¡^Long Marine Report Fixed Length Format¡]LMRF¡^ data from 1996 to 2002 are used to investigate the seasonal variations of the sea surface temperature ¡]SST¡^¡Bsea surface wind and sea surface heat flux and their relationship with the 1997/1998 ENSO event in the ocean surrounding Taiwan. It is found that the SST¡Bwind and heat flux variations in this area are mainly annual. In winters when the northeasterly wind prevails , the SST is low and the net heat flux has negative values. In summers the opposite is ture. The SST anomaly (SSTA) of the studied area lags behind that of the NINO 3.4 area for about 10 months. The wind anomaly of the studied area is of the same phase with the Southern Oscillation index. The surface latent heat flux of the studied area lags behind the outgoing longwave radiation anomaly of the NINO 3.4 area for about 4~5 months. Wind speed during the 1997/1998 winter and summer is weaker than that of the climatological value, while the SST is lower in winter and higher in summer. The latent heat flux is lower during the 1997/1998 ENSO episode. It is concluded that the ENSO event significantly affects the wind patterns of this area,and as a result in the SST and heat flux also change. Finally, in the oceans east of Taiwan where Kuroshio traverses through, the latent heat flux is markedly higher than that of other areas due to the higher values of SST and air-sea humidity difference. Both the wind speed and the air-sea humidity difference are important factors affecting the latent heat flux especially during the winters when the SST is lower.

A monthly resolved, 133 year record of coral Sr/Ca variations has been developed from a massive Porites coral that was drilled in the shallow waters of a submerged carbonate platform (Sabine Bank, 15.9°S, 166.14°E) located ~50 km west of Espiritu Santo, Vanuatu. This truly open-ocean site, at which daily measurements of temperature and salinity are available for ~ 6 years, permits the reconstruction of local environmental variability using variations in coral skeletal geochemistry. Coral Sr/Ca-SST variations are well matched to variations in local SST, but bear little relation to changes in local SSS indicating little or no influence of salinity on coral Sr/Ca. The complete coral Sr/Ca-SST time series is characterized by abundant inter-annual variability, a strong trend towards warming (i.e., lower Sr/Ca values) from ~1980-2006. Interannual SSTA variations at Sabine Bank correspond reasonably well to SSTA variations from the central Pacific cool tongue (Niño 3.4 region), indicating that coral Sr/Ca variations record ENSO variability in the region. / text

A decadal variation of tropical lower stratospheric ozone and temperature has previously been identified that correlates positively with the 11 year solar activity cycle. However, the El Niño–Southern Oscillation (ENSO) also influences lower stratospheric ozone and temperature. It is therefore legitimate to ask whether quasi-decadal ENSO variability can contribute to this apparent solar cycle variation, either accidentally because of the short measurement record or physically because solar variability affects ENSO. Here we present multiple regression analyses of available data records to compare differences in results obtained with and without including an ENSO term in the statistical model. In addition, simulations are performed using the NRL NOGAPS-ALPHA GCM for warm/cold ENSO conditions to test for consistency with the ENSO regression results. We find only very minor changes in annual mean solar regression coefficients when an ENSO term is included. However, the observed tropical ENSO response provides useful insights into the origin of the unexpected vertical structure of the tropical solar cycle ozone response. In particular, the ENSO ozone response is negative in the lower stratosphere due to increased upwelling but changes sign, becoming positive in the middle stratosphere (5–10 hPa) due mainly to advective decreases of temperature and NOx, which photochemically increase ozone. A similar mechanism may explain the observed lower stratospheric solar cycle ozone and temperature response and the absence of a significant response in the tropical middle stratosphere.

No description available.

Mechanisms of tropical Pacific climate variability and change are studied in numerical experiments of future anthropogenic global warming (AGW), the Last Glacial Maximum (LGM) 21,000 years ago, and decadal variability (PDV). According to these mechanisms the equatorial Pacific does not become either El Niño- or La Niña-like as the tropics warm up in response to increasing greenhouse gases. Because humidity increases much faster than precipitation as the tropical atmosphere warms up, theory and models anticipate a slowing-down of the Walker circulation in order to keep a balanced flow of water vapor into areas of convection. On long time scales characteristic of climate change, ocean dynamics oppose these changes in the Walker circulation. First, equatorial adjustment theory indicates that changes in the Walker circulation are not amplified via the Bjerknes feedback, as during El Niño or La Niña events. Second, during AGW, the ocean becomes more thermally stratified resulting in enhanced cooling of the equatorial cold tongue opposing the warming there. These ideas can be applied to interpret proxies of the LGM for which El Niño and La Niña analogies have been made. However, the LGM tropics are not an opposite analogue to future AGW because the Walker circulation is also sensitive to changes in the geography of the Maritime continent associated with lower sea level. Models simulate a stronger Walker circulation when the tropics cool in order to compensate for the decrease in moisture due to a cooler/drier atmosphere. However, this response is opposed by a weakening of the ascending branch of the Walker circulation because convection is suppressed over vast areas of the Maritime Continent exposed due to lower sea level. In general, the patterns of warming or cooling for AGW and LGM are not El Niño- or La Niña-like because of the opposing mechanisms presented here. As such, adherence to an ENSO analogy for interpreting tropical Pacific climate change can lead to serious misconceptions. However, proxies of the thermocline tilt can provide unequivocal evidence of changes in the Walker circulation because the pressure gradient associated with the thermocline tilt has to be in balance with the trade winds at all timescales.

Many fields of economics point to technology as the primary vehicle for change. Agencies pushing change often promote technology adoption to achieve their goals. To improve our understanding of how efforts to push new technologies should be focused, two studies are undertaken. The first study defines and tests for universality using meta-regression analysis on 170 analyses of agricultural production technologies. The second study, a case study on an emerging information technology - climate forecasts, examines how the timing of adoption affects the benefits. A factor exhibiting a systematic positive or negative effect on technology adoption is a universal factor. If the impact is the same regardless of location or technology type, the factor is strongly universal. The factor is weakly universal if the impact varies by location or technology type. Education and farm size are found to be weakly positive universal, age is found to be weakly negative universal, and outreach is not found to be a universal factor in the adoption of technology. These results indicate that technology-promoters may want to change their approach and focus on younger, more educated producers with larger farms. In the second study, an international wheat trade model incorporating climate variability is used to simulate different scenarios when wheat producers in the U.S., Canada, and Australia adopt ENSO-based forecasts for use in production decisions. Adoption timing and levels are varied across countries in the different scenarios. The results are highly consistent. Early adopters benefit the most, there is no incentive for more producers to adopt after 60% to 95% have adopted (meaning the adoption ceiling has been reached), and slower adoption corresponds to ceilings closer to 60% than 95%. Examining technology adoption from two angles provides a deeper understanding of the adoption process and aids technology-promoters in achieving their goals. In addition to focusing on younger, more educated producers with larger farms, technology-promoters wanting wide-spread adoption with high benefits need to push constituents to adopt early and fast.

El Niño Southern Oscillation (ENSO) is the most important interannual mode of climate variability in the tropical Pacific affecting the globe through teleconnections. The evolution of ENSO is studied with focus on individual El Nino (EN) events; factors and processes explaining the behaviours of different EN flavours are identified. The comparison to model simulations reveals a number of biases that explain differences in model behaviour. Based on reanalysis data, ENs are divided into Central Pacific (CPEN), Eastern Pacific (EPEN), and Hybrid (HBEN). ENs are found to form a continuous spectrum of events with CPEN and EPEN as its end members depending on: (1) the Western Pacific subsurface potential temperature anomaly (PTA) about 1 year before the EN peak, and (2) the Western to Central Pacific cumulative zonal wind anomaly (ZWA) between the onset and peak of the EN. Using these two parameters, about 70% of the total variance of the maximum EN SSTA can be explained up to 6 months in advance. ZWA describes the potential for triggering Kelvin waves for a given initial West Pacific recharge state as captured by PTA. A cross-validated statistical model is developed to hindcast the 1980-2016 Nov-Dec-Jan (NDJ) mean Niño3.4 SSTA based on the two parameters. The model is comparable to, or even outperforms, many NOAA Climate Prediction Centre's statistical models during the boreal spring predictability barrier. The explained variance between observed and predicted NDJ Niño3.4 SSTA at a lead-time of 8 months is 57% using five years for cross-validation. Predictive skills are lower after 2000 when the mean climate state is more La Niña-like due to stronger equatorial easterly ZWA caused by an intensification of both, Walker and Hadley cell. The ability of climate models to simulate and predict EN is assessed with data from the Climate Model Inter-comparison Project 5 (CMIP5). Most models are able to capture the main features of different EN types. But models struggle to reproduce large intensity ENs as found in observations. This issue can be traced back to a failure to realistically simulate the oceanic recharged state and the subsequent Kelvin waves for intense EN. Causes of EN involve Kelvin waves that are triggered by westerly wind bursts (WWB). From higher temporal resolution of reanalysis data, WWBs above a certain threshold are required to trigger a Kelvin wave. Kelvin waves are triggered in locations of positive Ocean Heat Content (OHC) anomalies. Intensity, longitudinal coverage and duration of a WWB, the strength of the OHC anomaly and gradient influence the amplitude of Kelvin waves as they propagate. Synoptic pattern analysis suggests that most WWBs are caused by cyclones with the combination of an active Madden-Julian Oscillation. The NorESM is able to reproduce many characteristics of observed WWBs, OHC anomalies and their relation to Kelvin waves. However, differences are noticeable for the distribution of synoptic patterns causing WWBs in the model. In future work, climate models can be used to disentangle causes and effects of EN for correlations identified here with the ultimate goal to advance our understanding of ENSO, its variability and future changes.

No description available.

Este estudo teve por finalidade investigar a frequência e intensidade dos Sistemas Frontais (SF) avaliando-os com os episódios ENOS (El Niño Oscilação Sul) para o período da Primavera (SON) de 2000 a 2010 sobre o Estado do Rio Grande do Sul (RS). As análises mostraram que os anos em que se tem a menor ocorrência de SF estão associados principalmente a eventos de La Niña Fraco e Neutralidade. Em contrapartida, um número maior de Sistemas Frontais foi verificado com relação aos episódios de El Niño Moderado e Neutralidade. Especificamente, no que se refere à questão mensal, percebeu-se que no mês de Outubro há uma maior influência dos Sistemas Frontais do que em Setembro e Novembro. Outro fator pertinente e evidenciado deu-se pelas comparações entre o período escolhido (no qual não ocorreram eventos fortes) e os episódios de ENOS Fortes. Notou-se, neste caso, que não ocorreram variações impactantes no número de Sistemas Frontais, embora se tenha o conhecimento dos efeitos e alterações existentes nos padrões de circulação atmosférica devido à atuação dos fenômenos de escala interanual. Ainda, tendo a necessidade de ampliar a gama de entendimento, foi realizada uma abordagem com relação ao comportamento da precipitação em seis sub-regiões do Estado, onde se observou de forma geral, um aumento da precipitação em praticamente todas as áreas do RS, quando comparado com a média Histórica. Com isso, ressaltou-se que os volumes mensais abaixo da média Histórica estão ligados a episódios de Neutralidade. Já a normalidade do regime de precipitação, mostrou-se interligado em média para todas as regiões ao evento de El Niño e por último, as precipitações acima da normal climatológica estão mais presentes em condições de El Niño, mais especificamente de intensidade Moderada. Dentre as sub-regiões analisadas, destacou-se a parte Oeste do Estado por ter apresentado uma maior intensidade nos volumes de precipitação. Outro fator importante analisado foram os valores percentuais das precipitações derivadas dos sistemas frontais. Levando-se em conta a média das avaliações, verificou-se que as sub-regiões Sul e Sudoeste do Rio Grande do Sul são as mais influenciadas pelas passagens dos Sistemas Frontais, enquanto os menores impactos na precipitação podem ser notados nas regiões Central e Norte do Rio Grande do Sul. Além disso, realizou-se um estudo de caso para avaliar o comportamento dos Sistemas Frontais em episódios de ENOS diferentes, nos campos de pressão atmosférica e temperatura do ar. Logo, averigou-se que em um ano de Neutralidade, as passagens de SF sobre o Estado costumam ser mais prolongadas em sua duração de tempo, permanecendo mais dias, com algumas variações significativas nos campos meteorológicos observados. Enquanto para um ano referente à condição de El Niño Moderado, os Sistemas Frontais possuem, na maioria dos casos, uma duração de tempo menor, consequentemente com menores variações na temperatura e pressão. / This study aimed to investigate the frequency and intensity of the frontal systems (FS) evaluating them with respect to the episodes of El Niño – South Oscillation (ENSO) for the spring season (SON) from 2000 to 2010, over the state of Rio Grande do Sul (RS - Brazil). The analysis showed that the years having a smaller incidence of SF are mainly associated to events of weak La Nina and neutrality. In contrast, a larger number of frontal systems were observed with respect to episodes of moderate El Nino and neutrality. Specifically with relation to the monthly aspect, it was noticed that there is a major influence of the frontal systems in October than in September and November. Another inherent and evidenced factor was given by the comparisons between the selected period (with no occurrence of strong events) and the Strong ENSO episodes. In this case it was noticed that there has not occurred impacting variations in the number of frontal systems although the effects and changes of the atmospheric circulation patterns due to the action of the interannual scale phenomena are known. Further, to enlarge the range of understanding, it was made one approach relating to the precipitation behavior in six sub regions of the state where in general it was observed an increase in the precipitation almost in all areas of the RS when compared to the historic average. Thus, the monthly volumes below the historic average are linked to neutral episodes. Otherwise, the normal precipitation regime, on average, was proved to be interconnected for all regions to the event El Niño, and finally the rainfall above the climatology are more common in El Niño conditions, specifically with Moderate intensity. In this manner, considering the analyzed sub regions, the west part of the state has presented a higher intensity of precipitation volumes. Another important factor analyzed were the percentage values of rainfall derived from frontal systems. Taking into account the average of the evaluations, it was found that the South and southwest sub-region of Rio Grande do Sul is the most influenced by passages from the SF, while smaller impacts on precipitation can be noticed in the Central and North regions. In addition, it was realized a case study to evaluate the behavior of frontal systems in different episodes of ENSO, with respect to the fields of atmospheric pressure and air temperature. Thus, it was found that in a year of neutrality, the frontal systems crossings on the state tend to be more prolonged, remaining more days, with some significant variations in the observed meteorological fields. While for a year related to the condition of Moderate El Nino the frontal systems have, in mosta cases, a shorter duration, thus with minor variations in temperature and pressure.

Brazil is the world's sixth largest cocoa producer with 270,000 tonnes of cocoa produced per year. In a world with an increasing demand for chocolate, but with agriculture threatened by climate change, the chocolate industry is worried about a possible shortage of cocoa. Furthermore, growing cocoa is a main cause of deforestation. However, in the state of Bahia, Northeast Brazil, cocoa is grown in traditional agroforests called 'cabrucas' which maintain a forest cover. Cocoa, an understorey crop, is planted under the shade of native Atlantic Forest trees and exotic fruit trees introduced by the farmers. These cabrucas have high conservation value but very low cocoa yield. In my thesis I investigate the factors limiting cocoa yield and how to increase yield in cabrucas. I explore the role of shade trees and the nutrient dynamics in litterfall. Finally, I explore the risk that climate change could represent for cocoa production in the future by looking at the effects of an unexpected drought caused by an El Niño Southern Oscillation (ENSO) event between November 2015 and May 2016. My study is based on data collected in permanent transects in 32 randomly chosen cabruca farms in Barro Preto a municipality of Bahia over a period of three years. I also established littertraps in 10 cocoa farms where I intensively studied nutrient dynamics and cocoa yield per tree over 12 months. My results showed that unproductive trees, low cocoa tree density, high shade cover and high cocoa mortality due to drought were the main factors limiting cocoa yield in cabrucas. Surprisingly, adding fertilisers to the cocoa trees did not increase yield. This suggests that there is no nutrient deficiency in cabrucas. In the farms, I found 69 species of shade trees for an average density of 125 ± 32 trees per hectare. Half of the species of shade trees were Atlantic Forest species of conservation value. The litterfall experiment showed the shade tree species and the quantity of litterfall produced, can affect the number of cocoa pods per tree. In cabrucas, a higher number of cocoa pods was found on cocoa trees under shade trees than under no shade. Finally, I showed that the exceptionally severe ENSO-related drought caused 80% loss in yield and 11% cocoa tree mortality in Barro Preto. Climate models predict an increased frequency of strong ENSO events in the future. Farmers in Bahia are not prepared to face regular drought events. The 2015/16 drought affected the dynamics of cocoa production in Brazil: it accelerated the decrease of extensive wildlife-friendly cocoa production in Bahia whereas it increased the development of cocoa production in intensive low shade plantations in the state of Pará. This suggests that climate change could be a threat to traditional cocoa agroforests in Bahia. Developing wildlife-friendly certification schemes and Payment for Ecosystem Services to internalise the value of forest conservation and to encourage farmers to maintain their shade trees could save cabruca systems from going extinct.