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Gergis, Jo??lle L. School of Biological Earth & Environmental Sciences UNSW. "Reconstructing El Nino-southern oscillation." Awarded by:University of New South Wales. School of Biological, Earth and Environmental Sciences, 2006. http://handle.unsw.edu.au/1959.4/24222.
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El Ni??o-Southern Oscillation (ENSO) is the most important coupled ocean-atmospheric phenomenon to cause global climate variability on interannual time scales. Efforts to understand recent, apparently anomalous ENSO behaviour are hampered by the lack of long, high-quality climate records. While instrumental data generally covers the past 150 years, record length is insufficient for the assessment of past changes in the frequency, magnitude, and duration of ENSO. Here, multiproxy networks of high-resolution tree-ring, coral, ice and documentary records derived from eastern and western Pacific ENSO ???centres of action??? are analysed (A.D. 1525-2002). Considerable improvements in ENSO reconstruction are achieved from expanding the use of records from the western Pacific. In particular, ~500 years of a continuous 3,722 year ENSO sensitive tree-ring record from New Zealand is introduced. Although extreme ENSO events are seen throughout a 478-year discrete event analysis, 43% of extreme, 20% of very strong and 28% of all protracted ENSO events occur within the 20th century. Principal component analysis was used to extend instrumental records of the Southern Oscillation Index (SOI) Ni??o 3.4 Sea Surface Temperature (Ni??o 3.4 SST) and a newly developed coupled ocean-atmospheric ENSO index (CEI) by 347 years. Significantly, of the three indices reconstructed here, CEI reconstructions were largely found to be the best predictors of ENSO. The results suggest that ENSO may be more effectively characterised using a coupled ocean-atmosphere index, particularly for December-May periods. Compared to the pre-instrumental period, the late 19th and early 20th centuries indicate a clear trend toward increased ENSO variability over the past 150 years. Significantly, spectral analysis of reconstructed indices reveals a marked change in the frequency and intensity of ENSO beginning ~A.D. 1850, coinciding with the end of the Little Ice Age and the boom in global industrialisation. This suggests that ENSO may operate differently under natural (pre-industrial) and anthropogenically influenced background states. This study asserts that recent ENSO variability appears anomalous in the context of the past five centuries. Given the considerable socio-economic impacts of ENSO events, future investigation into the implications an increasingly anthropogenically-warmed world may have on ENSO is vital.
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Ferrett, Samantha Joanne. "El Nino Southern Oscillation stability under global warming." Thesis, University of Exeter, 2015. http://hdl.handle.net/10871/19362.
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Typically, multi-model ensemble studies show mixed responses of El Nino Southern Oscillation (ENSO) under global warming, so it is currently unknown how, or even if, global warming will impact ENSO and its teleconnections. ENSO is governed by various ocean-atmosphere interactions in the equatorial Pacific, which provide either positive amplifying or negative damping feedbacks and are not always accurate in models. This results in uncertainty in projected ENSO responses. In a flux adjusted HadCM3 perturbed physics ensemble, the Bjerknes' stability index (BJ index), a measure of ENSO stability, has been used to analyse the strength of ENSO feedbacks and their response under the SRES A1B warming scenario with respect to mean climate conditions. Despite mean sea surface temperature biases being minimised by flux adjustment, the important dominant feedbacks, namely the latent heat flux feedback, shortwave flux feedback, the thermocline feedback and the zonal advective feedback are found to be too weak in the ensemble. Common model biases cause weak ocean-atmosphere interactions such as a weak response of ocean currents to wind stress anomalies, a weak thermocline slope response to wind stress anomalies and weak thermodynamic dampings. These biases are linked to overly strong zonal surface ocean currents and convective response biases. Under global warming, a large increase in thermodynamic damping, caused by increasing shortwave damping, is found. This increase is linked to a strong convective response and overrides other feedback responses, resulting in a weakening BJ index in contrast to increasing ENSO amplitude. Positive feedback responses are also found but counteract each other, so have relatively little impact on total ENSO stability. Results here show that common model biases, such as the cold tongue bias, are linked to persistent ENSO feedback biases pointing to areas of improvement in future models. Results also suggest that caution must be exercised when using the BJ index to assess ENSO, as the BJ index is not always representative of ENSO amplitude. This may be caused by non-linearities in ENSO feedbacks which are not accounted for by the linear approximations used in the BJ index, or by ENSO feedbacks not being directly comparable in magnitude, as assumed by the BJ index calculation.
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Thompson, Christopher J. "A linear, stochastic, dynamical model of El Nino/southern oscillation /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/6754.
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Fogt, Ryan Lee. "Investigation of the Southern Annular Mode and the El Nino - Southern Oscillation Interactions." The Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=osu1180462358.
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Manobavan, Manoharadas. "The responses of terrestrial vegetation to El Nino southern oscillation perturbations." Thesis, Kingston University, 2003. http://eprints.kingston.ac.uk/20363/.
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The enhanced warming effect possibly due to anthropogenic green house gas emissions has led to the derangement of global climatic mechanisms (especially at the interannual scale). This has led to the disturbances to the equilibrium of the Earth System and the interconnected self-regulatory processes. Terrestrial vegetation takes an active role in the regulation of the equilibrium of the Earth System by the processes of resistance and resilience. Whilst comprehensive and extensive modelling studies that investigate the effects of climatic change in terrestrial systems have been undertaken, few investigations have focused on the change and evolution in these systems from a holistic geophysiological perspective. In the first part of this thesis, econometric time-series modelling techniques were applied to National Oceanographic and Atmospheric Administration Advanced Very High Resolution Radiometer derived Normalized Difference Vegetation Index data sets in order to evaluate the responses of terrestrial South American vegetation to the interannual El Nifio Southern Oscillation climatic perturbations. Lags between vegetation response and the El Nifio Southern Oscillation perturbations are identified and quantified. The results indicate that the terrestrial vegetation loses its sensitivity to El Nifio Southern Oscillation perturbations in the post 1993 period, leading to the hypothesis that the terrestrial system maybe showing a Gaian behaviour that would enable homeostasis in the system of concern. The null hypothesis of this was tested using a stochastic Auto Regressive Integrative Moving Average model, which further strengthens the argument put forward by the hypothesis. Further comprehensive analysis was performed by using the Hybrid version 4.1, a mechanistical model of vegetation dynamics to test the effects of varying changes in the phase and amplitudes of the El Nino Southern Oscillation on terrestrial vegetation. Simulations of different interannual El Nino Southern Oscillation climatic scenarios under varying trends for increases in atmospheric C02 concentrations confirm the possibility of such a homeostatic property in the terrestrial vegetation system within its geophysiological limits.
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Fan, Yun. "ENSO prediction and predictability in an intermediate coupled model." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390461.
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Peralta-Hernandez, Ana Rosa. "El Nino Southern Oscillation (ENSO) effects on hydro-ecological parameters in central Mexico." Diss., The University of Arizona, 2001. http://hdl.handle.net/10150/298799.
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The impacts of El Nino Southern Oscillation (ENSO) on precipitation, reference evapotranspiration, and vegetation in a three-state region of central Mexico were investigated using daily weather data from 20 weather stations for the years 1970 through 1990, which included 5 El Nino years, 5 La Nina years, and 11 Neutral years. In addition, two years, 1997 (El Nino), and 1998 (La Nina) of 10-day NDVI composites were analyzed during the growing season (May-Oct) along with precipitation and reference evapotranspiration (ETo) over central Mexico. Regional precipitation trends were analyzed using the normalized rainfall departures. The interannual variation of vegetation cover was analyzed using the NDVI on 10-day and monthly bases. The Food and Agricultural Organization (FAO) Penman-Monteith method was used to calculate ETo. The dynamics of the soil water balance in central Mexico was evaluated according to the method proposed by Thornthwaite and Mather. Analyses indicate that driest conditions occurred within the northern part of the region and during neutral ENSO years. Rainfall amounts during El Nino and Neutral years were not statistically different however, La Nina years were about 30% wetter than N and EN years (0.05 level). The correlation coefficient between NDVI and precipitation was 0.79 in 1997, and 0.52 in 1998, in June and July, respectively. Negative correlation was found between NDVI and reference evapotranspiration during the rainy months of July and August. The spatio-temporal variability of NDVI showed that there was significant statistical difference in NDVI between regions, but not between years. Regional soil water balance determinations indicated that conditions were most favorable in the Southern part of the region for crop growth during La Nina years. In general, soil water deficits were reduced by about 50% during the growing season compared to the annual soil water deficits.
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Peskan, Kimberly A. "A statistical assessment of the relationship of the El Nino/Southern Oscillation to Great Lakes water levels." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ62265.pdf.
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Illig, Séréna. "Variabilité basse fréquence de l'Atlantique tropical : rôle de la dynamique océanique équatoriale et influence d'El Nino southern oscillation." Toulouse 3, 2005. https://tel.archives-ouvertes.fr/tel-00260664.
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L'objectif de cette thèse est l'étude de la variabilité interannuelle en Atlantique tropical : nous étudions les rôles des processus couplés liés à la dynamique linéaire et ceux liés à l'influence de la variabilité du Pacifique tropical de type El Niño. Les résultats obtenus suggèrent que la variabilité associée aux propagations d'ondes de Kelvin et de Rossby joue un rôle essentiel dans l'ajustement océanique au forçage par le vent et plus généralement dans les processus couplés océan-atmosphère en Atlantique équatorial. Les résultats de simulations couplées montrent que l'énergie dans la bande de fréquences 1-3 ans est en partie liée aux interactions locales air-mer, tandis que la variabilité associée au Pacifique tropical domine les basses fréquences (3-7 ans). Nos résultats soulignent la complexité du système océan-atmosphère en Atlantique équatorial, dont la prédictibilité dépend fortement de la variabilité du Pacifique tropical et de la variabilité atmosphérique intra-saisonnièreThe objectives of this thesis are to study the coupled interannual variability in the Tropical Atlantic associated to the linear dynamics and the teleconnections with the Tropical Pacific El Niño variability. Our study suggest first that low-frequency wave dynamics (Kelvin and Rossby waves propagation) is to a large extent at work in the Tropical Atlantic, and play a significant part in the ocean-atmosphere mechanisms that can lead to the Atlantic Equatorial mode. The results of coupled experiments show that peak in SST variability in the 1 to 3 year band, as observed in the Equatorial Atlantic, is partly due to the local air-sea interactions, whereas remote ENSO Pacific forcing controls the lower frequency variability (3-7 year). Our results point out the complexity of the Equatorial Atlantic ocean-atmosphere system which predictability depends on the Pacific ENSO conditions and/or the high-frequency atmospheric activity
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Johnson, Scot. "Markov model studies of the El Niño-Southern Oscillation /." Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/15490.
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Fogt, Ryan Lee. "Investigation of the Southern Annular Mode and the El Niño-Southern Oscillation Interactions." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1180462358.
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Sievert, Ulrica. "El Niño Southern Oscillation, Temperature and Precipitation over Central America." Thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-303324.
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This study aims for knowledge about the most important climate features that affect the temperature and precipitation in the continental area of Central America. Systems such as The Caribbean Low Level Jet (CLLJ), The Intertropical Convergence Zone (ITCZ) and The Western Hemisphere Warm Pool (WHWP) components are major contributors to regional climate that strongly interact with the topographical features dividing the Pacific and Caribbean slopes of Central America. Daily data within a 35 year long (1981-2015) time-series of precipitation and temperature for 9 different meteorological stations along both slopes have been investigated to identify their relationship with El Niño Southern Oscillation (ENSO) phases. Missing data were filled in using rellenaf, a routine function developed at the Center for Geophysical Research of the University of Costa Rica. The function estimates data values with principal components and autoregressive methods. Data show that the Pacific slope is mainly characterized by a remarkable contrast between the dry season and the rainy season. The seasonal variations in precipitation are less important for the Caribbean slope. The annual cycle of temperature (for all of the stations) has small differences in amplitude and is rather stable throughout the year, except at the northernmost stations, Belize and Puerto Barrios, where relatively low temperatures dominate the winter months due to cold air intrusions. The low frequency atmospheric mode ENSO, impacts the regional climate and interacts with the earlier mentioned CLLJ, ITCZ and WHWP. Strong ENSO episodes of El Niño and La Niña were compared with anomalies in temperature, precipitation and winds at 925 hPa (mainly focusing on CLLJ). A contribution of negative (positive) anomalies in precipitation was observed during El Niño (La Niña) events for the Pacific slope. This relationship was not present for the Caribbean slope. No connection between the temperature and ENSO could be revealed. It was also shown that CLLJ is stronger (weaker) in February for La Niña (El Niño) and stronger (weaker) in July for El Niño (La Niña) events.I syftet att utöka individuell kunskap om de viktigaste klimatsystemen som påverkar temperatur och nederbörd över den tropiska kontinenten Centralamerika, gjordes en studie. Komponenter såsom den karibiska lågaltituds-jeten (CLLJ The Caribbean Low Level Jet), den intertropiska konvergenszonen (ITCZ The Intertropical Convergence Zone) och västra halvklotets varmvattenspool (WHWP The Western Hemisphere Warm Pool) är huvudsakliga system som påverkar det regionala klimatet och dessa interagerar med topografin. I sin tur delar den upp Centralamerika i Stilla havssidan samt Karibiska sidan, två skiljda regioner ur ett meteorologiskt perspektiv. Dygnsdata, för temperatur och nederbörd inom en tidsperiod av 35 år (1981-2015) för 9 olika meteorologiska stationer, har undersökts för att identifiera mönster kopplat till den södra El Niño-oscillationen (ENSO The El Niño Southern Oscillation). Avsaknad data beräknades med rutinfunktionen rellenaf, som har utvecklats av universitetet i Costa Rica - Centret för geofysisk forskning. Funktionen estimerar datavärden utifrån principiella komponenter -och autoregressiv metod. Från den kompletta datan kunde det identifieras att Stilla havssidan är huvudsakligen kännetecknat av en torrperiod och en regnperiod, medan säsongsvariationerna i nederbörd för Karibiska sidan är mindre. Den årliga temperaturcykeln för hela regionen erhåller små skillnader i amplitud, med andra ord är temperaturen mer eller mindre konstant genom årets gång. Med undantag för de mer nordliga stationerna Belize och Puerto Barrios där lägre temperaturer förekommer under norra halvklotets vintermånader som är orsakat av kallfronter. ENSO är ett lågfrekvent atmosfäriskt system som har påverkan på det regionala klimatet genom att interagera med de tidigare nämna CLLJ, ITCZ and WHWP. De starka faserna El Niño och La Niña observerades och jämfördes med anomalier för temperatur, nederbörd och vindfält på 925 hPa nivå (huvudsakligen fokus på CLLJ). En majoritet av negativa (positiva) anomalier för nederbörd kunde observeras under El Niño (La Niña) fenomen för Stilla havssidan. Dock fanns inte denna relation för den Karibiska sidan. Det fanns heller ingen koppling mellan temperatur och ENSO. Det kunde även ses att CLLJ är starkare (svagare) i februari för la niña (el niño) och starkare (svagare) i juli för el niño (la niña).
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Paul, Nicole Christine. "Variable Recovery of the Massive Coral, Porites Lobata, in Response to El Nino-Southern Oscillation Events at Devil's Crown, Galapagos, Ecuador." NSUWorks, 2012. http://nsuworks.nova.edu/occ_stuetd/93.
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Porites lobata is an important reef building coral in the tropical eastern Pacific and the dominant Porites species in the Galápagos archipelago. Following the 1982-83 El Niño-Southern Oscillation the Galápagos Islands experienced 97-99% coral mortality, leaving many areas throughout the archipelago denuded of corals. Because very few long term assessments have been conducted on the growth and resilience of P. lobata to natural disturbances in the Galápagos Islands (Glynn et al., 2001; Glynn et al., 2009), benthic surveys were performed on a uniquely dense aggregation of P. lobata colonies at Devil’s Crown, Floreana Island between 1993 and 2011. Annual changes in live tissue area were calculated for the majority of the population (n=17) using Coral Point Count with Excel extensions (CPCe 3.6) software to determine growth and recovery trends for this aggregation. Total live tissue area (n=10) increased from 1993 to 2011, however due to high interannual variability this increase was not significant. Within this overall pattern, a general trend of decline was observed in live tissue cover from 1993 to 2000, with increases in tissue area observed from 2000 to 2011. Severe bleaching (85-100%) was observed during the 1998 survey, followed by 42% tissue loss (n=10), coinciding with sea water warming associated with the very strong 1997-1998 El Niño-Southern Oscillation event. Subsequent regrowth of coral tissue was observed during the 2001 survey with continued recovery through 2009. Multiple comparison testing revealed a significant difference between the impacted state (1999) and the recovered state (2009), (p = 0.002, Dunn’s method, n=17), suggesting this aggregation required a period of ten years to recover from this disturbance. During this recovery period the moderately strong 2007-2008 La Niña, with accompanying stressful low temperatures, occurred but did not interrupt tissue regrowth. Warmer than average sea surface temperatures occurred during the warm months from 2008 to 2011, during which time a cool period occurred from 2010 to 2011. While the magnitude and duration of temperature anomalies during warming were not as great as those observed during the 1997-98 ENSO, low temperatures observed during the cool period were similar to those experienced throughout the 2007-08 La Niña. During this time total live tissue cover was reduced by 19% (n=10); however it is unknown whether this was due to warming or the following cool period. Based on results from the 1997-98 El Niño and 2007-08 La Niña, this reduction in live tissue was most likely caused by elevated sea surface temperatures. Data on the growth and resilience of P. lobata populations at Devil’s Crown will be used for conservation and management of this important resource.
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Yocom, Kent Larissa L., Peter Z. Fulé, Peter M. Brown, Julián Cerano-Paredes, Eladio Cornejo-Oviedo, Montaño Citlali Cortés, Stacy A. Drury, et al. "Climate drives fire synchrony but local factors control fire regime change in northern Mexico." WILEY, 2017. http://hdl.handle.net/10150/623223.
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The occurrence of wildfire is influenced by a suite of factors ranging from "top-down" influences (e. g., climate) to "bottom-up" localized influences (e. g., ignitions, fuels, and land use). We carried out the first broad-scale assessment of wildland fire patterns in northern Mexico to assess the relative influence of top-down and bottom-up drivers of fire in a region where frequent fire regimes continued well into the 20th century. Using a network of 67 sites, we assessed (1) fire synchrony and the scales at which synchrony is evident, (2) climate drivers of fire, and (3) asynchrony in fire regime changes. We found high fire synchrony across northern Mexico between 1750 and 2008, with synchrony highest at distances < 400 km. Climate oscillations, especially El Nino-Southern Oscillation, were important drivers of fire synchrony. However, bottom-up factors modified fire occurrence at smaller spatial scales, with variable local influence on the timing of abrupt, unusually long fire-free periods starting between 1887 and 1979 CE. Thirty sites lacked these fire-free periods. In contrast to the neighboring southwestern United States, many ecosystems in northern Mexico maintain frequent fire regimes and intact fire-climate relationships that are useful in understanding climate influences on disturbance across scales of space and time.
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Tangang, Fredolin T. "Forecasting El Niño - Southern Oscillation (ENSO) events, a neural network approach." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq25173.pdf.
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Oliveira, Flavio Natal Mendes de. "Climatologia de bloqueios atmosféricos no hemisfério Sul: observações, simulações do clima do século XX e cenários futuros de mudanças climáticas." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/14/14133/tde-02102011-115448/.
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Este estudo discute uma climatologia de 59 anos (1949-2007) de bloqueios no Hemisfério Sul (SH) usando dados de altura geopotencial em 500-hPa das reanálises do National Center for Environmental Prediction / National Center for Atmospheric Research (NCEP-NCAR). A variabilidade espaço-temporal dos eventos de bloqueio e associações com o El Niño/Oscilação do Sul (ENOS) também foram examinadas. Adicionalmente, os bloqueios foram investigados em dois Modelos de Circulação Geral Acoplados Atmosfera-Oceano de clima (MCGAO) do Intergovernamental Painel for Climate Change (IPCC), o ECHAM5/MPI-OM e o MIROC 3.2. Dois cenários simulados foram analisados: O clima do século XX e o cenário de emissão A1B. Os episódios do ENOS foram identificados usando dois métodos. O primeiro foi o Índice Oceânico Mensal do Niño (ONI) do Climate Prediction Center (CPC-NCEP). O segundo método foi baseado em Funções Empíricas Ortogonais (EOF) e foi aplicado nos MCGAOs. Similarmente, também foi examinado a influencia combinada do ENOS e a Oscilação Antártica (AAO) na ocorrência e características dos bloqueios. O índice diário da AAO foi obtido pelo CPC-NCEP. Os índices convencionais de bloqueios detectam principalmente variações longitudinais. Este trabalho propõe um índice de bloqueio que detecta, além de variações longitudinais também as variações latitudinais dos bloqueios. Cinco setores relevantes de bloqueios foram examinados em detalhes: Indico Sudoeste (SB1), Pacífico Sudoeste (SB2), Pacífico Central (SB3), Pacífico Sudeste (SB4) e Atlântico Sudoeste (SB5). Além disso, foram investigados duas grandes regiões do Pacífico Sul: Pacífico Oeste e Pacífico Leste. Foi encontrado que a escala média típica dos eventos de bloqueio varia entre 1,5 e 2,5 dias. Além disso, a duração dos eventos depende da latitude, com eventos de maior duração observados em latitudes mais altas. Diferenças longitudinais estatisticamente significativas na freqüência do escoamento bloqueado foram observadas entre as fases Quente e Neutra do ENOS desde o outono a primavera. Episódios intensos da fase Quente do ENOS (isto é, moderados a fortes) tendem a modificar o local preferencial de bloqueio, mas não a freqüência. Por outro lado, os episódios fracos da fase Quente do ENOS estiveram associados relativamente com alta freqüência. Os Eventos de bloqueio durante o ENOS+ duram, em média, mais um dia relativamente aos episódios Neutros. Em contraste, a fase Fria do ENOS (ENOS-) caracterizou-se pela redução dos eventos de bloqueio sobre o setor do Pacífico Central, exceto durante os meses do verão austral. Entretanto, nenhuma diferença estatisticamente significativa foi detectada na duração dos eventos. Composições de anomalias de vento em 200-hPa indicam que o enfraquecimento (fortalecimento) do jato polar em torno de 60ºS durante a AAO negativa (positiva) em ambas as fases do ENOS tem uma importância significativa no aumento (redução) dos eventos de bloqueio. Um significativo aumento estatístico dos eventos sobre o setor do Pacífico Sudeste foi observado durante a AAO negativa em ambas as fases do ENOS. Ainda, um aumento (redução) dos eventos foi observado sobre a região do Pacífico Oeste na fase negativa (positiva) da AAO durante o ENOS-. Em contraste, durante o ENOS+ não houve diferenças estatisticamente significativas na distribuição longitudinal dos eventos separado de acordo com as fases opostas da AAO, embora haja um aumento (redução) dos eventos da região do Pacífico Oeste para o Pacífico Leste durante a fase negativa (positiva) da AAO. Os MCGAOs simularam corretamente a amplitude do ciclo anual observado. Também, ambos os MCGAOs simularam melhor a duração e o local preferencial do que freqüência. Nenhum MCGAO simulou adequadamente a freqüência durante a fase Neutra do ENOS. O ECHAM5/MPI-OM (rodada 2) mostra um erro sistemático que levam a uma superestimativa na freqüência de eventos sobre o Pacífico Leste durante as fases Neutra e Fria do ENOS. As diferenças entre as duas versões do MIROC 3.2 indicam que a alta resolução nos modelos melhora o desempenho em simular a freqüência de bloqueios.This study discusses 59-yr climatology (1949-2007) of Southern Hemisphere (SH) blockings using daily 500-hPa geopotential height data from National Center for Environmental Prediction / National Center for Atmospheric Research (NCEP-NCAR reanalysis. The spatiotemporal variability of blocking events and associations with El Nino/Southern Oscillation (ENSO) are examined. Additionally, blockings were examined in two Intergovernmental Panel for Climate Change (IPCC) Coupled General Circulation Models (CGCM), ECHAM5/MPI-OM and MIROC 3.2. Two sets of simulations were examined: the climate of the 20th century and the A1B emission scenario. ENSO episodes were identified using two methods. The first method was the Monthly Oceanic Niño Index (ONI) from the Climate Prediction Center (CPC-NCEP). The second method was based on Empirical Orthogonal Function (EOF) and was applied to identify ENSO episodes in the CGCMs. Similarly, the combined influence of ENSO and the Antarctic Oscillation (AAO) on the occurrence and characteristics of blockings was also examined. The daily AAO index was obtained from CPC/NCEP. Most conventional blocking indices detect longitudinal variations of blockings. In this study we propose a new blocking index that detects longitudinal and latitudinal variations of blockings. The following relevant sectors of blocking occurrence were identified and examined in detail: Southeast Indian (SB1), Southwest Pacific (SB2), Central Pacific (SB3), Southeast Pacific (SB4) and Southwest Atlantic (SB5) oceans. In addition, we investigated two large regions of South Pacific: West Pacific and East Pacific. We found that the typical timescale of a blocking event is about ~1.5 2.5 days. Nonetheless, the duration of events depends on the latitude, with larger durations observed at higher latitudes. Statistically significant differences in the longitude of blockings are observed between Warm (ENSO+) and Neutral ENSO phases from the Austral fall to spring. Moderate to strong Warm ENSO episodes modulate the preferred locations of blockings but do not play a significant role for variations in their frequency. On the other hand, weak ENOS+ episodes were associated with relatively high frequency of blockings. Blocking events during ENSO+ last on average one more day compared to events that occur during Neutral episodes. In contrast, Cold (ENOS-) ENSO episodes are characterized by a decrease of blockings over the Central Pacific sector, except during the Austral summer months. However, no statistically significant differences are detected in the duration. Composites of 200-hPa zonal wind anomalies indicate that the weakening (strengthening) of the polar jet around 60oS during negative (positive) AAO phases in both ENSO phases plays a major role for the relative increase (decrease) of blocking events. A statistically significant increase of events over Southeast Pacific is observed during negative AAO phases in both ENSO phases. Moreover, an increase (decrease) of events is observed over West Pacific region when negative (positive) AAO phases occur during ENSO-. In contrast, during ENSO+ there is no statistically significant difference in the longitudinal distribution of events separated according to opposite AAO phases, although there is an increase (decrease) in the events from West Pacific region to East Pacific during negative (positive) AAO phase. The CGCMs investigated in this study correctly simulated the amplitude of observed annual cycle of geopotential height in the extratropics. Also, both CGCMs show a better performance in simulating the duration and preferred locations of blockings than their frequency. None of these CGCMs simulated well the frequency during Neutral ENSO phase. The ECHAM5/MPI-OM (run2) shows systematic biases in some regions. For instance, this model overestimates the frequency of blockings over East Pacific region during Cold and Neutral ENSO phases. The differences between the two versions of MIROC 3.2 indicate that the increase in resolution improves the performance of the model in simulating the frequency of blockings.
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Begley, Paul. "The El Niño - Southern Oscillation, rainfall and wheat yields in South Africa." Master's thesis, University of Cape Town, 2005. http://hdl.handle.net/11427/19916.
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This thesis assesses the relationships between the El Niño-Southern Oscillation (ENSO), rainfall and South African commercial winter wheat yields from 1974 - 2000. The analysis is through a combination of the Pearson's product moment correlation coefficient and an assessment of the magnitude and consistency of rainfall and wheat anomalies in the year of, and the year following warm (El Niño) and cold (La Niña) ENSO events. The ENSO - rainfall relationship is analysed on timescales from 1 - 24 months and this study finds that there are more unusually dry and unusually wet months during El Niño events than during La Niña episodes (where dry and wet months are <75°/o and over 25~·'0 more than the 1921 - 2000 mean, respectively) and these conditions are consistently found in some rainfall areas during each El Niño or La Niño event; there is marked inter - El Niño and inter La Niña variation in late summer and annual rainfall; and that there has been a significant shift in the timings of maximum rainfall anomalies during El Niño episodes from an earlier investigation. The effects of rainfall on the wheat yield vary spatially, but are most apparent in the Free State where severe droughts have resulted in reduced yields. In the Northern Cape and Western Cape anomalously wet conditions, especially in late summer, coincide with reduced wheat yields. The ENSO - wheat yield relationship is not a simple linear one, and despite yields in the Northern Cape and Western Cape tracking Pacific sea surface temperatures by nearly a year, El Niño and La Niña years are not synonymous With increased or decreased yields in any province. ln fact, maximum and minimum yields in the Free State and Northern Cape are found in the year of, or year following a La Niño event, and consequently the present predictability of wheat yields by ENSO is limited. The relationships between ENSO, rainfall and wheat yield in South Africa is not readily apparent, which may be due to the short (<30 years) data set or mediating factors outside this study such as farm - management strategies or hemispheric variation in the evolution of El Niño and La Niña events.
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Abdolrahimi, Maryam. "The Effect of El Niño Southern Oscillation (ENSO) on World Cereal Production." Thesis, The University of Sydney, 2016. http://hdl.handle.net/2123/15498.
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El Niño Southern Oscillation (ENSO) anomalies are responsible for medium-frequency climate fluctuations across many regions of the world. Not only ENSO induces temperature and precipitation variability in the affected regions, but it is also responsible for larger magnitude weather anomalies, such as droughts, hurricanes, and tsunamis. All these directly impact agricultural production. The overall objective of this research is to determine the relationship between ENSO and world major cereal production. While several studies have addressed the issue, this research contributes to the literature in a number of directions. Firstly, it measures the ENSO effect net of temperature and precipitation. Secondly, it allows for the threshold-like effect of ENSO; that is, El Niño effects are not mirror images of La Niña effects. Thirdly, it incorporates expected price in the regression setting, thus controlling for an important economic variable affecting crop supply. Finally, this study applies the largest possible panel of countries, to analyse the region-specific peculiarities of the ENSO–production relationship, and to best approximate the global production effect of ENSO anomalies. This study uses a combination of extensive climatic and economic datasets spanning the years 1962-2009 to empirically measure the impact of ENSO on wheat, maize and rice production, via a threshold regression framework. The results reveal statistically significant and economically meaningful ENSO impact on cereal production in many regions, with particularly strong effects in Southeast Asian and American countries. Although the expected global effect may camouflage the country-specific effects, the research findings suggest that El Niño shocks are likely to cause on average a reduction in global production of rice and maize. La Niña episodes, on the other hand, are associated with increased global rice and decreased global wheat and maize production. Although consequences of ENSO shocks on a global scale are sporadic, understanding the overall impact of ENSO on major grain production is an important tool for managing global food security. Results of this study provide implications for food policy makers, and help them develop precautionary economic policies that will take advantage of ENSO signals to cope with production shocks and ensure food availability, which is particularly relevant in the developing world.
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Roberts, William Henry Gordon. "An investigation into the causes for the reduction in the variability of the El Niño-Southern Oscillation in the early Holocene in a global climate model /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/10033.
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Gorgues, Thomas. "Modélisation biogéochimique du pacifique équatorial." Paris 6, 2006. http://www.theses.fr/2006PA066468.
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Le Pacifique équatorial est la source océanique la plus importante de CO2 atmosphérique et l’écosystème de cette région module cette source. De ce fait, décrire l’impact de la variabilité du Pacifique équatorial sur la biogéochimie revêt une importance particulière. Le modèle de dynamique océanique et le modèle de biogéochimie marine utilisés dans cette thèse ont montré une sensibilité significative à la prise en compte des détroits indonésiens qui agissent sur la profondeur de la thermocline/nutricline. En tenant compte de ces détroits, nos simulations ont mis en évidence une structuration de l’écosystème par les tourbillons équatoriaux liés aux ondes tropicales d’instabilités. De plus, ces tourbillons affaiblissent en moyenne la concentration de fer à l’équateur, diminuant ainsi la production nouvelle. Les efflorescences simulées de l’année 1998 confirment ce résultat malgré une composition phytoplanctonique inhabituelle confortée par des résultats dérivés d’observations.
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Yiu, Yu Yeung Scott. "El Niño Southern Oscillation teleconnections and their effects on the Amundsen Sea region." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/276236.
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El Niño Southern Oscillation events have global implications both climatologically and socio-economically. One such climatological teleconnection is manifested in the Amundsen Sea region (ASR). The Amundsen sea low (ASL) is the dominant low pressure system located around the ASR and is important to the climate of Western Antarctica. Therefore, it is important to understand the ASL and any phenomena that may affect it. This thesis focuses on the ENSO--ASR teleconnection under El Niño conditions and the mechanism behind it. The ENSO--ASR teleconnection was explored using the UM version 8.4 (HadGEM3) model. Time--slice experiments with various magnitudes of idealised perpetual ENSO events are imposed. Two sets of `switch on' experiments in which tropical Pacific SSTs were ramped up were also carried out to investigate the transient nature of the teleconnection. The seasonality of the ENSO--ASR teleconnection is known from previous studies to be stronger in winter compared to summer. The mechanism behind the seasonality was explored using the time--slice experiments. The seasonality is found to originate from the seasonal differences in the Southern Hemispheric jets. As the subtropical jet is only present in austral winter, Rossby wave source anomalies can only be generated in the mid--latitudes in winter. Furthermore, the propagation of the Rossby waves is not possible in summer due to the strong polar front jet. The lack of the source and propagation in summer explains the weaker ENSO--ASR teleconnection. A flowchart summarising the mechanism was created and then verified by the transient runs. The linearity of the ENSO--ASR teleconnection within El Niño has not been previously investigated. This is mainly due to insufficient reanalysis data available to overcome the high internal variability in the ASR. In this thesis, the linearity of the teleconnection under El Niño is studied using the time--slice runs. The results indicate linearity (within errorbars) for both the summer and winter seasons up to historically maximum El Niños. However, under extreme El Niños (beyond historic records) in winter, the teleconnection is no longer linear. The UPSCALE dataset was used to investigate the effects of horizontal resolution on the simulation of the ASL climatological state and the ENSO--ASR teleconnection. The UPSCALE dataset consists of ensembles of HadGEM3 simulations at three different horizontal resolutions. The high resolution model was found to better simulate the ASL while the low resolution model was found to better simulate the ENSO--ASR teleconnection.
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Wilson, Aaron Benjamin. "Using the NCAR CAM 4 to Confirm SAM’s Modulation of the ENSO Teleconnection to Antarctica and Assess Changes to this Interaction during Various ENSO Flavor Events." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1376919626.
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Leloup, Julie. "Influence du changement climatique sur les caractéristiques d'ENSO par méthodes neuronales." Paris 6, 2006. http://www.theses.fr/2006PA066618.
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Le phénomène El Niño-Southern Oscillation est le mode de variabilité climatique le plus énergétique aux échelles interannuelles. Quelles sont les caractéristiques de cette variabilité et plus particulièrement des événements El Niño/La Niña et comment sont-elles susceptibles d'évoluer en réponse au changement climatique ? À l'aide d'une méthodologie originale, reposant sur l'utilisation des cartes de Kohonen (SOM, Self-Organizing Map) et la température de surface de l'océan Pacifique équatorial, certaines modifications d'ENSO sont identifiées au cours de la période 1950-2002 et la méthode est validée. Dans un second temps, la base de données IPCC (Intergovernmental Panel on Climate Change) est explorée à l'aide de SOM. La variabilité ENSO simulée par les modèles forcés par les conditions climatiques du XXe siècle est validée par les observations. Les événements El Niño/La Niña sont étudiés distinctement et des biais sont mis en évidence. Enfin, un scénario futur est analysé pour proposer des évolutions des caractéristiques identifiées au XXe siècle. Il est montré qu'il n'y a pas de consensus quant à leur devenirEl Niño/Southern Oscillation (ENSO) is the strongest climate perturbation on interannual time scales. What are ENSO characteristics and more specifically El Niño/La Niña events characteristics, and how will they evoluate in response to climate change? Using an original methodology, based on the use of Kohonen maps (SOM, Self-Organizing Maps) and the equatorial Pacific sea surface temperatures, modifications in ENSO are identified during the 1950-2002 period and the method is validated. Then the IPCC (Intergovernmental Panel on Climate Change) is investigated using SOM. The ENSO variability as simulated by models forced by the twentieth century conditions is validated with observations. In particular, El Niño and La Niña events are studied and biases are highlighted. Finally futur scenario is analyzed to propose evolution for those characteristics. Results do not show any consensus
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Hiltunen, Jalle. "Queensland weather patterns during the Australian summer monsoon and the El Niño-Southern Oscillation." Thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-203499.
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The objective of this study is to describe the effects of the El Niño-Southern Oscillation (ENSO) on the weather patterns in Queensland during the Australian summer monsoon. The focus is on the period from October-January when the summer monsoon is governing the weather pattern of Northern Australia. The theory part introduces the reader to the physics of the different phases of ENSO and the Australian summer monsoon. Weather station data of rainfall, minimum and maximum temperature data are investigated statistically. The presented results are an earlier onset of the monsoon season in Queensland during La Niña-events and a stronger monsoon in the sense of more or stronger active periods. Regarding El Niño's effects on the summer monsoon in Queensland no significant results were found. The results show the importance of not looking at the warm and cold phase of ENSO as opposites and agree with what Sarachik (2010) and Sturman & Tapper (1996) states.Målet med studien är att beskriva El Niño-Southern Oscillations (ENSO) effekter på vädret i Queensland under den australiensiska sommarmonsunen. Fokus ligger på perioden oktober-januari då sommarmonsunen styr vädret över norra Australien. Teoridelen syftar till att introducera läsaren till fysiken bakom de olika faserna av ENSO och den australiensiska sommarmonsunen. Data från väderstationer i Queensland av parametrarna nederbörd, minimum och maximum temperatur undersöks statistiskt. Resultaten som presenteras indikerar en tidigare början av monsunsäsongen i Queensland under La Niña-perioder och att monsunen förstärks genom fler eller starkare aktiva perioder. I resultaten sågs ingen eller mycket svag påverkan från El Niño-perioder på monsunen i Queensland. Dessa resultat påvisar vikten av att inte se på den varma och kalla fasen av ENSO som motsatser till varandra och stämmer överens med litteratur av Sarachik (2010) och Sturman & Tapper (1996).
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Boschat, Ghyslaine. "Interannual variability and predictability of the Indian Summer Monsoon : El Niño Southern Oscillation system." Paris 6, 2012. http://www.theses.fr/2012PA066808.
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La Mousson Indienne d’été (ISM) et l’Oscillation Australe El Niño (ENSO) sont parmi les phénomènes climatiques les plus énergétiques et importants de la planète. Bien qu’ils soient localisés dans la région tropicale Indo-Pacifique, ces deux phénomènes peuvent avoir des répercussions climatiques à l'échelle globale via les téléconnections atmosphériques. Cette thèse vise à améliorer notre compréhension et la prévisibilité interannuelle d’ENSO et de l’ISM, en analysant leurs téléconnections grandes échelles, et en déterminant le rôle, dans cette prévisibilité, des modes majeurs de variabilité interannuelle observés dans les régions tropicales et extratropicales de l’Indo-Pacifique. A partir de diagnostiques statistiques d’observations sur les périodes 1950-1976 et 1979-2007, et d’expériences de sensibilité réalisées à l’aide du modèle couplé SINTEX-F, nous montrons l'importance des latitudes tempérées dans la prévisibilité du système ENSO-mousson. Des précurseurs robustes des évènements ENSO et ISM sont identifiés dans les régions du Pacific Nord et de l’Océan Indien Sud pendant l’hiver boréal précédent, apportant ainsi de la prévisibilité plus tôt que leurs traditionnels précurseurs tropicaux. De plus, cette prévisibilité de la mousson d’été est accrue pour les pluies en fin de saison (Août-Septembre). Cette deuxième partie de la saison de mousson se caractérise également par l’émergence de processus couplés océan-atmosphère dans l’Océan Indien, pouvant contrecarrer l’effet d’ENSO sur la mousson. Une amplification de ces rétroactions locales pourrait expliquer l’affaiblissement de la relation ENSO-mousson observé lors des dernières décenniesEl Niño-Southern Oscillation (ENSO) and the Indian Summer Monsoon (ISM) are two of the most energetic and influential climatic phenomena on the planet. Although they originate in the tropical Indo-Pacific region, they can extend their reach well beyond, through atmospheric teleconnnections that can affect patterns of climate variability worldwide. This thesis takes part in a global effort to improve our understanding of the potential predictability of ISM rainfall and ENSO, by exploring the large-scale teleconnections associated with the whole monsoon-ENSO system on interannual timescales, as well as the role played by leading modes of coupled variability, particularly in tropical and extratropical parts of the Indo-Pacific region. Based on statistical diagnoses of observations before and after the 1976-77 climate shift, and numerical experiments with the SINTEX-F coupled model, our results highlight the importance of mid-latitudes in the predictability of the ISM-ENSO system. Indeed, significant and robust precursors are identified in the North Pacific and South Indian Oceans during the previous boreal winter/early spring, and have the potential to predict ISM and ENSO events with longer lead-times than their traditional tropical predictors. Besides, this predictability is stronger for the ‘late’ ISM rainfall during August-September. This second part of the ISM season is also characterized by the occurrence of ocean-atmospheric processes in the Indian Ocean, which compete with the effect of ENSO on the monsoon. The enhancement of these local feedbacks could explain the apparent weakening of the seasonal ENSO-monsoon relationship observed in recent decades
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Hood, L. L., B. E. Soukharev, and J. P. McCormack. "Decadal variability of the tropical stratosphere: Secondary influence of the El Niño–Southern Oscillation." AMER GEOPHYSICAL UNION, 2010. http://hdl.handle.net/10150/623319.
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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.
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Panaou, Toni. "Assessing the Impacts of Climate Change on Streamflow and Reservoir Operation in Central Florida." Scholar Commons, 2018. http://scholarcommons.usf.edu/etd/7211.
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Climate change is a global concern as it may affect many aspects of life, including water supply. A tool used to model climate change’s impacts is called a General Circulation Model (GCM). GCMs project future scenarios including temperature and precipitation, but these are designed at a coarse resolution and require downscaling for employment for regional hydrologic modeling. There is a vast amount of research on downscaling and bias-correcting GCMs data, but it is unknown whether these techniques alter precipitation signals embedded in these models or reproduce climate states that are viable for water resource planning and management. Using the Tampa, Florida region for the case study, the first part of the research investigated 1) whether GCM and the downscaled, bias-corrected data were able to replicate important historical climate states; and 2) if climate state and/or transition probabilities in raw GCMs were preserved or lost in translation in the corrected downscaled data. This has an important implication in understanding the limitations of bias-correction methods and shortcomings of future projection scenarios. Results showed that the GCM, and downscaled and bias-corrected data did a poor job in capturing historical climate states for wet or dry states as well as the variability in precipitation including some extremes associated with El Niño events. Additionally, the corrected products ended up creating different cycles compared to the original GCMs. Since the corrected products did not preserve GCMs historical transition probabilities, more than likely similar types of deviations will occur for “future” predictions and therefore another correction could be applied if desired to reproduce the degree of spatial persistence of atmospheric features and climatic states that are hydrologically important.
Furthermore, understanding the sustainability of water supply systems in a changing climate is required for undertaking adaptation measures. Many water suppliers employ GCMs to examine climate change’s effect on hydrologic variables such as precipitation, but little is known on the propagation of mismatch errors in downscaled products through cascade of hydrologic and systems models. The second study examined how deviations in downscaled GCMs precipitation propagated into streamflow and reservoir simulation models by using key performance metrics. Findings exhibited that simulations better reproduced the resilience metric, but failed to capture reliability, vulnerability and sustainability metrics. Discrepancies were attributed to multiple factors including variances in GCMs precipitation and streamflow cumulative distribution functions, and divergences in serial correlation and system memory.
Finally, the last study examined multiple models, emission scenarios and an ensemble to obtain a range of possible implications on reservation operations for time periods 2030-2053, 2054-2077 and 2077-2100 since the future emission trajectory is uncertain. Currently there are four Representative Concentration Pathways (RCPs) as defined by the IPCC’s fifth Assessment Report which provides time-dependent projections based on different forecasted greenhouse gas emission and land use changes. For this research Representative Concentration Pathways (RCPs) 4.0, 6.0 and 8.5 were examined. Scenarios were evaluated utilizing reliability, resilience, vulnerability and sustainability performance metrics and compared to a historical baseline. Findings exhibited that RCP 4.5, the lower end of emission scenario, improved reservoir reliability and resilience over time. Conversely, RCP 8.5, highest emissions, resulted in a steady decline of all metrics by 2100. Although vulnerability increased by 2100 for all emission scenarios, on average RCP 4.5 was less vulnerable. Investigation of permits and adjustments to capture extreme flows might be necessary to combat climate changes and precipitation inputs along with improvements to atmospheric emissions, which correlated with system recuperation with time.
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Ye, Zhengqing. "Changes in the El Niño-Southern Oscillation under climate regime shift and increased greenhouse gases." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/31187.
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The observed El Niño/Southern Oscillation (ENSO) has shown eastward displacements of the zonal wind stress anomalies and surface heat flux anomalies in the equatorial Pacific during El Niño episodes in the 1981-1995 regime relative to the 1961-1975 regime. Numerical experiments with a modified Zebiak-Cane intermediate complexity coupled model generally reproduced such displacements when the model climatological fields were replaced by the observed and simulated climatologies for the 1981-1995 regime. The later regime climatology resulted in eastward shifts in the ENSO system during El Niño but not La Niña, through the eastward shift of the atmosphere convergence heating rate in the coupled model. The ENSO period and ENSO predictability were also enhanced in the coupled model under the later regime climatology. A similar behavior was found in the Lorenz (1963) 3-component chaos system, i.e. in both the ENSO and Lorenz systems, stronger nonlinearity appears to lengthen the period thereby enhancing the predictability. Using nonlinear principal component analysis, we demonstrated that the leading ENSO mode had changed on a physical basis since the late 1970s. The ENSO modes resembled the destabilized 'ocean basin mode' and 'the recharge-mode' in the pre- and post-1980s regimes, respectively. The surface zonal current acted as an intensifier of ENSO in the earlier regime and played a role in the transition of the ENSO cycle in the later regime. With data from an ensemble of coupled general circulation models in the IPCC-AR4 project, climate under year 2000 greenhouse gas (GHG) level was compared with climate under pre-industrial conditions. In the tropical Pacific, the warming in the mean sea surface temperatures (SST) was found to have an El Niño-like pattern, in agreement with the observed SST data (1900-1999). The models showed that both the equatorial zonal overturning circulation and the shallow meridional overturning circulation weakened under increased GHG forcing. For ENSO, the asymmetry in the SST anomalies between El Niño and La Niña was found to be enhanced under increased GHG, for both the ensemble model data and the observed data. The enhanced asymmetry was mainly caused by the intensified vertical nonlinear dynamic heating. Furthermore, the enhanced GHG simulations showed that the asymmetry between El Niño and La Niña increased in the zonal wind stress anomalies, the equatorial undercurrent anomalies and the shallow meridional overturning circulation anomalies.Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate
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Kingsbury, Joseph D. "Various studies using ¹⁸O distribution within paleoclimatic proxy of past El Niño/southern oscillation disturbances /." Connect to resource, 1998. http://hdl.handle.net/1811/28559.
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Salau, Opeyemi R. S. [Verfasser]. "El Niño, Southern Oscillation during the Holocene and Eemian Warm Periods / Opeyemi R. S. Salau." Kiel : Universitätsbibliothek Kiel, 2012. http://d-nb.info/1024079775/34.
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Xiao, Heng. "A GCM study of El Niño-Southern Oscillation and its relation with the seasonal cycle." Diss., Restricted to subscribing institutions, 2008. http://proquest.umi.com/pqdweb?did=1581421901&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Henke, Lilo Maria Keti. "Long term hydrological change, the El Niño/Southern Oscillation and biomass burning in the tropics." Thesis, University of Exeter, 2016. http://hdl.handle.net/10871/27975.
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Rapidly rising levels of atmospheric greenhouse gases including carbon dioxide and methane since the industrial revolution have drawn scientific attention to the importance of the global carbon cycle to the climate (Cubasch et al., 2013). Tropical peatlands, the majority of which are located in the Indonesian region, are a major source of uncertainty in the carbon cycle as the relationships between carbon accumulation and hydrological changes remain poorly understood (Hergoualc’h & Verchot, 2011, Page et al., 2011). An important driver of carbon emissions in tropical peatlands is fire, which in the Indonesian region is strongly influenced on interannual timescales by the El Niño/Southern Oscillation (ENSO). However, it is not clear how ENSO and fire have varied at decadal to centennial scales over the past two millennia. This thesis explores long term tropical hydrological variability and ENSO-like climate change from palaeorecords and their interactions with fire. Using a wide range of instrumental, proxy and model datasets and a novel reconstruction method, two separate reconstructions of long-term ENSO-like climate change are produced based on precipitation and temperature data. These show no evidence of a difference between the ENSO-like behaviour of precipitation and temperature. There is limited evidence for a difference in long-term ENSO-like state between the Medieval Climate Anomaly and the Little Ice Age. Reconstructions of hydrological variability and biomass burning in the Indonesian region suggest that precipitation and fire have been positively correlated over the past 2,000 years, which is contrary to the modern-day relationship on ENSO timescales. This throws up questions of long-term versus short-term interactions and feedbacks between fire, climate and vegetation. It is likely that anthropogenic activity in the Indonesian region has significantly altered the stability of the fire regime. Further research combining proxy data, climate and fire models, and using more robust statistical analysis is necessary to untangle the natural and anthropogenic driving factors at different time resolutions.
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Johnson, Katelyn M. "Investigating the usage of transpacific ice cores as a proxy for El Niño-Southern Oscillation dynamics." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1343338070.
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Cobb, Kim M. "Coral records of the El Niño-southern oscillation and tropical Pacific climate over the last millennium /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2002. http://wwwlib.umi.com/cr/ucsd/fullcit?p3064467.
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Park, Sungsu. "ENSO-related marine cloud variation and new single column marine boundary layer cloud modeling /." Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/10080.
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Sweeny, Shannon R. "Impact of ENSO on weather conditions at continental United States military bases /." access online version, 1996. http://handle.dtic.mil/100.2/ADA319128.
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Illig, Serena. "Variabilité basse fréquence de l'Atlantique Tropical:Rôle de la dynamique océanique équatoriale et Influence d'El Niño Southern Oscillation." Phd thesis, Université Paul Sabatier - Toulouse III, 2005. http://tel.archives-ouvertes.fr/tel-00260664.
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L'objectif de cette thèse est l'étude de la variabilité interannuelle en Atlantique Tropical: nous étudions les rôles des processus couplés liés à la dynamique linéaire et ceux liés à l'influence de la variabilité du Pacifique Tropical de type El Niño. Les résultats obtenus suggèrent que la variabilité associée aux propagations d'ondes de Kelvin et de Rossby joue un rôle essentiel dans l'ajustement océanique au forçage par le vent et plus généralement dans les processus couplés océan-atmosphère en Atlantique Équatorial. Les résultats de simulations couplées montrent que l'énergie dans la bande de fréquences 1-3 ans est en partie liée aux interactions locales air-mer, tandis que la variabilité associée au Pacifique Tropical domine les basses fréquences (3-7 ans). Nos résultats soulignent la complexité du système océan-atmosphère en Atlantique Équatorial, dont la prédictibilité dépend fortement de la variabilité du Pacifique Tropical et de la variabilité atmosphérique intra-saisonnière.
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Manrique, Paredes Rosa Soledad <1971>. "El Niño southern oscillation and its effect on fog oases along the Peruvian and Chilean coastal deserts." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3436/1/Manrique_Rosa_tesi.pdf.
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Fog oases, locally named Lomas, are distributed in a fragmented way along the
western coast of Chile and Peru (South America) between ~6°S and 30°S following an
altitudinal gradient determined by a fog layer. This fragmentation has been attributed to the
hyper aridity of the desert. However, periodically climatic events influence the ‘normal
seasonality’ of this ecosystem through a higher than average water input that triggers plant
responses (e.g. primary productivity and phenology). The impact of the climatic oscillation
may vary according to the season (wet/dry). This thesis evaluates the potential effect of climate oscillations, such as El Niño Southern Oscillation (ENSO), through the analysis of vegetation of this ecosystem following different approaches:
Chapters two and three show the analysis of fog oasis along the Peruvian and Chilean
deserts. The objectives are: 1) to explain the floristic connection of fog oases analysing their
taxa composition differences and the phylogenetic affinities among them, 2) to explore the
climate variables related to ENSO which likely affect fog production, and the responses of
Lomas vegetation (composition, productivity, distribution) to climate patterns during ENSO
events. Chapters four and five describe a fog-oasis in southern Peru during the 2008-2010
period. The objectives are: 3) to describe and create a new vegetation map of the Lomas
vegetation using remote sensing analysis supported by field survey data, and 4) to identify
the vegetation change during the dry season.
The first part of our results show that: 1) there are three significantly different groups
of Lomas (Northern Peru, Southern Peru, and Chile) with a significant phylogenetic divergence among them. The species composition reveals a latitudinal gradient of plant
assemblages. The species origin, growth-forms typologies, and geographic position also
reinforce the differences among groups. 2) Contradictory results have emerged from studies
of low-cloud anomalies and the fog-collection during El Niño (EN). EN increases water
availability in fog oases when fog should be less frequent due to the reduction of low-clouds
amount and stratocumulus. Because a minor role of fog during EN is expected, it is likely that
measurements of fog-water collection during EN are considering drizzle and fog at the same
time. Although recent studies on fog oases have shown some relationship with the ENSO,
responses of vegetation have been largely based on descriptive data, the absence of large
temporal records limit the establishment of a direct relationship with climatic oscillations.
The second part of the results show that: 3) five different classes of different spectral
values correspond to the main land cover of Lomas using a Vegetation Index (VI). The study
case is characterised by shrubs and trees with variable cover (dense, semi-dense and open). A
secondary area is covered by small shrubs where the dominant tree species is not present. The
cacti area and the old terraces with open vegetation were not identified with the VI.
Agriculture is present in the area. Finally, 4) contrary to the dry season of 2008 and 2009
years, a higher VI was obtained during the dry season of 2010. The VI increased up to three
times their average value, showing a clear spectral signal change, which coincided with the
ENSO event of that period.
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Manrique, Paredes Rosa Soledad <1971>. "El Niño southern oscillation and its effect on fog oases along the Peruvian and Chilean coastal deserts." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3436/.
Full textAbstract:
Fog oases, locally named Lomas, are distributed in a fragmented way along the
western coast of Chile and Peru (South America) between ~6°S and 30°S following an
altitudinal gradient determined by a fog layer. This fragmentation has been attributed to the
hyper aridity of the desert. However, periodically climatic events influence the ‘normal
seasonality’ of this ecosystem through a higher than average water input that triggers plant
responses (e.g. primary productivity and phenology). The impact of the climatic oscillation
may vary according to the season (wet/dry). This thesis evaluates the potential effect of climate oscillations, such as El Niño Southern Oscillation (ENSO), through the analysis of vegetation of this ecosystem following different approaches:
Chapters two and three show the analysis of fog oasis along the Peruvian and Chilean
deserts. The objectives are: 1) to explain the floristic connection of fog oases analysing their
taxa composition differences and the phylogenetic affinities among them, 2) to explore the
climate variables related to ENSO which likely affect fog production, and the responses of
Lomas vegetation (composition, productivity, distribution) to climate patterns during ENSO
events. Chapters four and five describe a fog-oasis in southern Peru during the 2008-2010
period. The objectives are: 3) to describe and create a new vegetation map of the Lomas
vegetation using remote sensing analysis supported by field survey data, and 4) to identify
the vegetation change during the dry season.
The first part of our results show that: 1) there are three significantly different groups
of Lomas (Northern Peru, Southern Peru, and Chile) with a significant phylogenetic divergence among them. The species composition reveals a latitudinal gradient of plant
assemblages. The species origin, growth-forms typologies, and geographic position also
reinforce the differences among groups. 2) Contradictory results have emerged from studies
of low-cloud anomalies and the fog-collection during El Niño (EN). EN increases water
availability in fog oases when fog should be less frequent due to the reduction of low-clouds
amount and stratocumulus. Because a minor role of fog during EN is expected, it is likely that
measurements of fog-water collection during EN are considering drizzle and fog at the same
time. Although recent studies on fog oases have shown some relationship with the ENSO,
responses of vegetation have been largely based on descriptive data, the absence of large
temporal records limit the establishment of a direct relationship with climatic oscillations.
The second part of the results show that: 3) five different classes of different spectral
values correspond to the main land cover of Lomas using a Vegetation Index (VI). The study
case is characterised by shrubs and trees with variable cover (dense, semi-dense and open). A
secondary area is covered by small shrubs where the dominant tree species is not present. The
cacti area and the old terraces with open vegetation were not identified with the VI.
Agriculture is present in the area. Finally, 4) contrary to the dry season of 2008 and 2009
years, a higher VI was obtained during the dry season of 2010. The VI increased up to three
times their average value, showing a clear spectral signal change, which coincided with the
ENSO event of that period.
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Lumper, Randy N. "The relationship between el niño Southern oscillation and levels of paralytic shellfish poisoning present in Washingtons marine waters." Online pdf file accessible through the World Wide Web, 2008. http://archives.evergreen.edu/masterstheses/Accession86-10MES/Lumper_RNMESThesis2008.pdf.
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施錦杯 and Kam-pui Sze. "Effects of the interaction of atmosphere and ocean on humanactivities." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B31254378.
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Sze, Kam-pui. "Effects of the interaction of atmosphere and ocean on human activities /." Hong Kong : University of Hong Kong, 1999. http://sunzi.lib.hku.hk/hkuto/record.jsp?B21301414.
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Malin, Melissa L. "Teleconnection pattern impacts on intra-seasonal climate variability in United States winters." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 244 p, 2009. http://proquest.umi.com/pqdweb?did=1891555391&sid=3&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Thompson, Diane Marie. "Variability and trends in the tropical Pacific and the El Niño-Southern Oscillation inferred from coral and lake archives." Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/311122.
Full textAbstract:
The background state and changes associated with the El Niño-Southern Oscillation (ENSO) in the tropical Pacific Ocean influence climate patterns all over the world. Understanding how the tropical Pacific will be impacted by climate change is therefore critical to accurate regional climate projections. However, sparse historical data coverage and strong natural variability in the basin make it difficult to assess the response of the tropical Pacific to anthropogenic climate change. Further, climate models disagree regarding the response of the basin to continued anthropogenic forcing into the future. Building off of the limited instrumental record, high-resolution records from coral and lake sediment archives can be used to assess the response of the tropical Pacific to past climate changes and to compare and assess climate model projections. In the present study, I use high-resolution coral and lake records from the equatorial Pacific to assess climate model projections and the response of the coupled ocean-atmospheric climate system in the basin (ocean temperature, salinity, winds, precipitation) to natural and anthropogenic forcing. Using a simple model of how climate is recorded by corals, we compare historical climate data and climate model simulations with coral paleoclimate records to assess climate model projections and address uncertainties in the historical data, models and paleoclimate records. We demonstrate that this simple model is able to capture variability and trend observed in the coral records, and show that the both sea surface temperature and salinity contribute to the observed coral trend. However, we find major discrepancies in the observed and climate model simulated trends in the tropical Pacific that may be attributed to uncertainties in model simulated salinity. We then assess 20th-century variability and trends in SST and salinity in the central tropical Pacific using replicated coral δ¹⁸O and Sr/Ca records from the Republic of Kiribati and the central Line Islands. We find that the coral records from these sites display a warming and freshening trend superimposed on strong interannual and low-frequency variability. Further, we demonstrate an apparent strengthening of the E-W SST gradient across the dateline (between 173°E and 160°W) and a slight weakening of the N-S SST gradient due to enhanced warming along the equator and west of the dateline relative to other sites. However, we find no evidence of increased variability in the central Pacific, suggesting that there has not been an increase in central Pacific style ENSO events. Finally, we show that the salinity response to climate change may be very patchy within the basin. Using a new ~90 year coral Mn/Ca record from the central Pacific, we investigate variability and trends in tropical Pacific trade winds. First, we demonstrate a strong association between westerly wind anomalies and coral skeletal Mn/Ca, which recorded all of the major historical El Niño events of the 20th century. In this new long Mn/Ca record, we find a reduction in the amplitude and frequency of Mn/Ca pulses between 1893 and 1982, suggesting a decrease in westerly wind anomalies in the western equatorial Pacific Ocean. Finally, we use a sediment record from Bainbridge Crater Lake, Galápagos Archipelago to assess variability in the eastern tropical Pacific over the past ~6 thousand years. Based on results from long-term monitoring of the lake, we propose a new climate interpretation of the sediment record and find further evidence reduced mid-Holocene ENSO variability and a ramp up of ENSO variability starting around 1775 cal. years BP.
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Cagnazzo, Chiara. "Analyse des facteurs de variabilité de la température dans la stratosphère." Phd thesis, Ecole Polytechnique X, 2004. http://pastel.archives-ouvertes.fr/pastel-00002293.
Full textAbstract:
On sait aujourd'hui que les processus stratosphériques jouent un rôle important dans le système climatique et leur étude est donc de grande importance pour la communauté scientifique. Les changements à long terme observés dans la stratosphère comprennent l'augmentation des gaz à effet de serre, de la vapeur d'eau, la diminution de l'ozone et un refroidissement systématique de cette région de l'atmosphère pendant les deux dernières décennies (1980-2000). Cette recherche est dédiée à la quantification des changements à long terme de la structure thermique et dynamique de la stratosphère et à l'attribution des causes des changements observés, et en particulier l'effet de la diminution de l'ozone stratosphérique. Le travail a été mené pour les vingt dernières années, où des mesures globales de la stratosphère existent; les analyses effectuées ont été ensuite couplées avec des simulations GCM pour quantifier le rôle de la diminution de l'ozone sur les changements à long terme observés. Trois bases de données (températures mensuelles) résultant d'analyses de données satellitaires et/ou de radiosondages ont été considérées : la base TOVS/3I fournit une description de la basse stratosphère à haute résolution spatiale pour une période de 8 ans; la base FUB a une résolution spatiale moins bonne mais est disponible pour une période plus longue; enfin, la base SSU/MSU couvre les vingt dernières années et surtout la totalité de la stratosphère, mais avec une résolution verticale plus faible. Un modèle de régression linéaire multiparamétrique, qui permet de séparer l'effet de la variabilité naturelle de la tendance à long terme, a été utilisé. Dans un premier temps, une analyse détaillée de l'impact des différents facteurs de variabilité de la température stratosphérique été réalisée. Les forçages considérés sont: l'Oscillation Quasi-Biennale (QBO), l'ENSO, la variabilité de 11 ans associée au cycle solaire, et le mode de variabilité extratropicale connu sous le nom d'Oscillation Arctique (AO). Nous montrons tout d'abord que l'amplitude de la réponse de la température à ces forçages peut être du même ordre de grandeur que les tendances calculées. Ensuite, les tendances de la température sont décrites en fonction de l'altitude, de la latitude et de la saison; elles montrent un refroidissement général de la stratosphère, avec une amplitude maximale en moyenne globale dans la haute stratosphère de l'hémisphère nord (de l'ordre de 3 K/décennie); le refroidissement se réduit dans la moyenne stratosphère pour atteindre 1 K/décennie en moyenne globale dans la basse stratosphère (mais avec une structure fortement dépendante de la latitude). L'analyse des températures nous permet aussi de mettre en évidence, de façon indirecte, un affaiblissement de la circulation moyenne de la stratosphère. Pour étudier le rôle de la diminution d'ozone stratosphérique sur les champs dynamiques et thermiques, nous avons enfin considéré deux ensembles de simulations GCM de type « transitoire »; en entrée des simulations, le premier ensemble considère les conditions prévalant avant la diminution de l'ozone, alors que le deuxième inclut les tendances d'ozone observées en moyenne zonale et mensuelle (dite « simulation ozone »). Les tendances de température simulées ont été comparées entre elles. Les résultats indiquent que la diminution de l'ozone stratosphérique est responsable du refroidissement observé à hauteur de 60% dans la haute stratosphère et de 30% dans la basse stratosphère. Si le refroidissement de la haute et moyenne stratosphère est bien reproduit par les simulations ozone, dans la basse stratosphère il est sous-estimé, très probablement à cause de l'effet des tendances de vapeur d'eau, qui n'ont pas été prises en compte dans les simulations. Le refroidissement pendant le printemps Arctique dans la basse stratosphère est observé, mais non complètement reproduit. Enfin, les simulations ozone indiquent une modification dans l'activité des ondes qui se propagent dans la basse stratosphère, observée à travers l'étude de la composante verticale du flux d'Eliassen-Palm.
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Marín, Saul. "The response of precipitation and surface hydrology to tropical macro-climate forcing in Colombia." Access citation, abstract and download form; downloadable file 15.62 Mb, 2004. http://wwwlib.umi.com/dissertations/fullcit/3131688.
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Lee, Song-Weon. "Investigation of techniques for improvement of seasonal streamflow forecasts in the Upper Rio Grande." Texas A&M University, 2004. http://hdl.handle.net/1969.1/2764.
Full textAbstract:
The purpose of this dissertation is to develop and evaluate techniques for improvement of seasonal streamflow forecasts in the Upper Rio Grande (URG) basin in the U.S. Southwest. Three techniques are investigated. The first technique is an investigation of the effects of the El Ni??o/Southern Oscillation (ENSO) on temperature, precipitation, snow water equivalent (SWE), and the resulting streamflow at a monthly time scale, using data from 1952 to 1999 (WY). It was seen that the effects of ENSO on temperature and precipitation were confined to certain months, predominantly at the beginning and end of the winter season, and that the effect of these modulations of temperature and precipitation by ENSO can be seen in the magnitude and time variation of SWE and streamflow.
The second part is a comparison of the use for snowmelt-runoff modeling of the newly available snowcover product based on imagery from the satellite-borne Moderate Resolution Imaging Spectroradiometer (MODIS) with the long-time standard snowcover product from the National Hydrological Remote Sensing Center (NOHRSC). This comparison is made using the Snowmelt Runoff Model (SRM) in two watersheds located inside the URG basin. This comparison is important because the MODIS snowcover product could greatly improve the availability of snowcover information because of its high spatial (500m) and temporal (daily) resolutions and extensive (global) coverage. Based on the results of this comparison, the MODIS snowcover product gives comparable snowcover information compared to that from NOHRSC.
The final part is an investigation of streamflow forecasting using mass-balance models. Two watersheds used in the comparison of MODIS and NOHRSC snowcover products were again used. The parameters of the mass-balance models are obtained in two different ways and streamflow forecasts are made on January 1st, February 1st, March 1st and April 1st. The first means of parameter estimation is to use the parameter values from 1990 to 2001 SRM streamflow simulations and the second means is by optimization. The results of this investigation show that mass-balance models show potential to improve the long-term streamflow forecasts in snowmelt-dominated watersheds if dependable precipitation forecasts can be provided.
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Veettil, Bijeesh Kozhikkodan. "Identificação da influencia do El Niño: oscilação sul e oscilação decenal do Pacífico sobre as geleiras andinas tropicais usando sensoriamento remoto e parâmetros climáticos." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2017. http://hdl.handle.net/10183/153311.
Full textAbstract:
Nas últimas décadas, particularmente desde a década de 1970, testemunhou-se um rápido recuo das geleiras em várias partes dos Andes tropicais. Uma tendência de aquecimento foi observada na região durante o mesmo período, com um hiato recente desde no início de 2010. No entanto, este hiato pode não ser o principal fator a influenciar as observações de aquecimento e recuo das geleiras em altitudes elevadas nos Andes tropicais. Com o surgimento de imagens de alta resolução espacial e espectral, e de modelos digitais de elevação (MDE) de alta resolução, agora é possível compreender as mudanças multitemporais das geleiras, o que era difícil de realizar utilizando as técnicas tradicionais e os dados de baixa resolução. Neste trabalho foram calculadas as variações da linha de neve das geleiras selecionadas ao longo dos Andes tropicais desde o início de 1980. A linha de neve máxima observada durante a estação seca (inverno austral) nos trópicos pode ser considerada como equivalente à linha de equilíbrio que separa a zona de acumulação da zona de ablação. A fim de reduzir o erro na estimativa da linha de neve foram consideradas somente as geleiras com declividades menores que 20o. Dependendo da região estudada e da presença de cobertura de nuvens, foram selecionadas imagens de várias fontes. As imagens da série Landsat (MSS, TM, ETM+ e OLI), EO1 OLI, ASTER e IRS LISS III foram usadas junto com MDE do ASTER GDEM-v2. Três bandas espectrais (TM5 - infravermelho médio, TM4- infravermelho próximo e TM2 - verde) foram utilizadas para calcular a linha de neve durante a estação seca, aplicando limiares adequados para TM4 e TM2. Os conjuntos de dados meteorológicos de várias fontes também foram analisados para observar as mudanças na precipitação, na temperatura e na umidade que influenciam os parâmetros glaciológicos como: o balanço de massa e a linha de equilíbrio. Geleiras representativas nos trópicos internos e trópicos externos foram consideradas separadamente dentro de um novo quadro, que foi baseado na precipitação, umidade e condições de temperatura ao longo da América do Sul. Neste âmbito, os Andes tropicais são classificados em trópicos internos, trópicos externos úmidos do norte, trópicos externos úmidos do sul e os trópicos externos secos. O Vulcão Cotopaxi no Equador (trópicos internos), o Nevado Caullaraju-Pastoruri que é uma geleira na Cordilheira Branca no Peru (trópicos externos úmidos do norte), o Nevado Cololo na Cordilheira Apolobamba na Bolívia (trópicos externos úmidos do sul), o Nevado Coropuna na Cordilheira Ampato no Peru e o Nevado Sajama na Cordilheira Ocidental da Bolívia (trópicos externos secos) são as geleiras representativas de cada grupo consideradas neste estudo. As geleiras tropicais nos trópicos internos, especialmente as situadas perto da Zona de Convergência Intertropicais (ZCIT), são mais vulneráveis a aumentos na temperatura e menos sensíveis a variações na precipitação. Em contraste, as geleiras nos trópicos externos respondem à variabilidade de precipitação muito rapidamente em comparação com a variação de temperatura, particularmente quando se deslocam para as regiões subtropicais. A dependência do balanço de massa sobre as características de sublimação também aumenta a partir dos trópicos internos para os trópicos externos. As condições de aquecimento, com maior umidade, tendem a aumentar a perda de massa por causa do derretimento em vez da sublimação. A elevação da umidade nos trópicos externos pode alterar as geleiras dominadas pela sublimação (nos trópicos externos e subtrópicos) e para as geleiras dominadas por derretimento. Observa-se que as geleiras próximas da ZCIT (trópicos internos e trópicosexternos úmidos do sul) estão recuando mais rapidamente como uma resposta ao aquecimento global, enquanto que as geleiras nos trópicos externos úmidos do norte e trópicos externos secos mostraram recuo relativamente mais lento. Possivelmente isso pode ser devido à ocorrência de fases frias do El Niño - Oscilação Sul (ENOS) conjuntamente com a Oscilação Decenal do Pacífico (ODP). As anomalias observadas nas variáveis meteorológicas seguem os padrões de ODP e as variações anuais de linha de neve seguem eventos de El Niño particularmente na fase ODP quente. No entanto, uma forte correlação entre as variações da linha de neve e dos fenômenos ENOS (e ODP) não está estabelecida. As geleiras do Equador mostram menos retração em resposta à tendência de aquecimento se comparadas às observações feitas por outros pesquisadores na Colômbia e na Venezuela, provavelmente devido à grande altitude das geleiras equatorianas. Em poucas palavras, as geleiras menores e em baixas altitudes nos trópicos internos e trópicos externos úmidos do sul estão desaparecendo mais rapidamente do que outras geleiras nos Andes tropicais. Também se observou neste estudo a existência de uma propriedade direcional no recuo das geleiras, o que não se observou em quaisquer outros estudos recentes. As geleiras nas cordilheiras leste do Peru e da Bolívia, que alimentam muitos rios nos lados leste das cordilheiras orientais, estão recuando do que aquelas geleiras situadas nas encostas ocidentais dos Andes tropicais.Recent decades, particularly since the late 1970s, witnessed a rapid retreat of glaciers in many parts of the tropical Andes. A warming trend is observed in this region during the same period, with a recent hiatus since the early 2010s. However, this hiatus is observed to have not influenced the retreat of high elevation glaciers in the tropical Andes. Due to the emergence of high spatial and spectral resolution images and high quality digital elevation models (DEM), it is now possible to understand the multi-temporal glacier changes compared with the techniques that existed a few decades before. We calculated the snowline variations of selected glaciers along the tropical Andes since the early 1980s. The maximum snowline observed during the dry season (austral winter) in the tropics can be considered as nearly equivalent to the equilibrium line that separates the accumulation zone from the ablation zone. In order to reduce the error in the estimated snowline, glaciers with slopes < 20o only were considered in this research. Depending on the study region and the presence of cloud cover, images from multiple sources were selected. Landsat series (MSS, TM, ETM+, and OLI), EO1 OLI, ASTER, and IRS LISS III images were used along with digital elevation models (DEM) from ASTER GDEM-v2. Three wavebands (TM5 - Middle Infrared, TM4 - Near Infrared, and TM2 - Green) were used to calculate the dry season snowline, after applying suitable threshold values to TM4 and TM2. Meteorological datasets from multiple sources were also analysed to observe the changes in precipitation, temperature, and humidity that influence key glaciological parameters such as the mass balance and the equilibrium line. Representative glaciers in the inner and the outer tropical Andes were considered separately within a new framework, which is based on the precipitation, humidity, and temperature conditions along the South America. In this framework, tropical Andes are classified in to inner tropics, northern wet outer tropics, southern wet outer tropics, and dry outer tropics. Cotopaxi ice-covered volcano, Ecuador (inner tropics), Nevado Caullaraju-Pastoruri Glacier, Cordillera Blanca, Peru (northern wet outer tropics), Nevado Cololo, Cordillera Apolobamba, Bolivia (southern wet outer tropics), and Nevado Coropuna, Cordillera Ampato Peru and Nevado Sajama, Cordillera Occidental, Bolivia (dry outer tropics) are the representative glaciers in each group considered in this study. Inner tropical glaciers, particularly those situated near the January Intertropical Convergence Zone (ITCZ), are more vulnerable to increases in temperature and these glaciers are less sensitive to variations in precipitation. In contrast, outer tropical glaciers respond to precipitation variability very rapidly in comparison with the temperature variability, particularly when moving towards the subtropics. Mass balance dependency on sublimation characteristics also increases from the inner tropics to the outer tropics. Warming conditions with higher humidity tends to enhance mass loss due to melting rather than sublimation. Increased humidity observed in the outer tropics may change the sublimation dominated glaciers in the outer tropics and subtropics to melting dominated ones in the future. It is observed that the glaciers above and near the January ITCZ (inner tropics and southern wet outer tropics) are retreating faster as a response to global warming, whereas the glaciers in the northern wet outer tropics and dry outer tropics show relatively slower retreat. This can be possibly due to the occurrence of cold phases of El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) together. The observed anomalies in the meteorological variables slightly follow PDO patterns and the variations in annual snowlines follows El Niño events, particularly when in phase with warm PDO. However, a strong correlation between snowline variations and ENSO (and PDO) is not established. Mountain glaciers in Ecuador show less retreat in response to the warming trend compared with observations done by other researchers in Colombia and Venezuela, probably due to very high altitude of the Ecuadorean glaciers. In a nutshell, smaller glaciers at lower altitudes in the inner tropics and the southern wet outer tropics are disappearing faster than other glaciers in the tropical Andes. Another observation made in this study is the directional property of glacier retreat, which was not covered in any other recent studies. Those glaciers on the eastern cordilleras of Peru and Bolivia, which feed many rivers on the eastern sides of the eastern cordilleras, are retreating faster than those glaciers situated on the western sides.
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Keenlyside, Noel S. 1974. "Improved modelling of zonal currents and SST in the tropical Pacific." Monash University, Dept. of Mathematics and Statistics, 2001. http://arrow.monash.edu.au/hdl/1959.1/9072.
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Chen, Ying-quei. "Pedictability of ENSO : optimal error growth and forecast skill /." Thesis, Connect to this title online; UW restricted, 1996. http://hdl.handle.net/1773/10023.
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