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Author: Erik T. Swenson Publisher: ISBN: Category : Climatic changes Languages : en Pages : 0
Book Description
The boreal winter extratropical response to tropical heating associated with a significant El Niño Southern Oscillation (ENSO) event has been understood primarily in terms of a seasonal average. However, the development and variability of the response forced by a highly sub-seasonally variable atmospheric forcing is still unclear. Significant modes of sub-seasonal tropical convective variability exist that have well documented transient impacts on the extratropics, e.g. the Madden-Julian Oscillation (MJO). Does sub-seasonal tropical convective variability impact the seasonal mean extratropical response? If so, what matters for the response: short-lived strong events or more persistent moderate events? Does sub-seasonal convective variability have implications for predictability during El Niño? Using the Community Atmospheric Model v. 4.0 (CAM4) of the National Center for Atmospheric Research, the response to ENSO is simulated using large ensembles of seasonal integrations forced with observed SST from multiple El Niño events. We decompose the diabatic heating rate (Q) across the tropical Indo-Pacific in terms of temporal and intra-ensemble variability. We then repeat the simulations by prescribing subsets of Q in an effort to diagnose the impact of sub-seasonal and intra-ensemble Q variability. Neglecting sub-seasonal Q variability has a systematic impact on the response, generally extending the Pacific jet and deepening upper-level heights across the North Pacific. A local enhancement is simulated in tropical upper-level divergence, likely related to the vertical redistribution of Q resulting from averaging together vertical profiles associated with moderate and deep convection. Persistence may also play a role. When prescribing nearly all Q variability (for frequencies greater than one day), we find that Q-circulation coupling is locally unimportant, i.e. the temporal evolution, mean, and variance of upper-level divergence from a coupled control simulation are reproducible. However, interestingly the amplification of the extratropical response to El Niño is still simulated. It follows that these differences are attributed to the neglect of tropical-extratropical two-way coupling. This is the primary finding of the study and suggests that the extratropical response to a significant El Niño event is not simply a forced response to tropical heating. Regarding the variability of the response to El Niño, we find a robust relationship in the seasonal mean ensemble spread, linking Q variations in the west/central tropical Pacific and extratropical fluctuations projecting onto the Arctic Oscillation (AO). This mode accounts for about a third of the ensemble spread (in 200 hPa geopotential height). Previous studies have revealed a similar relationship in observed interannual variability and have simulated the tropically forced component. In CAM4, this relationship in the ensemble spread is only evident during El Niño and is the dominant contributor to the enhanced ensemble spread simulated during El Niño, acting to lower predictability of the response. Extratropical forcing of the tropics is important for this mode, as prescribing Q variability weakens the relationship and cannot reproduce the enhancement in spread. We find that this relationship emerges as residue of a low frequency sub-seasonal tropical-extratropical coupled mode for which a significant extratropical influence is evident. Over the Pacific, coherent interaction is simulated between evolving persistent planetary waves and convectively coupled waves bearing a resemblance to equatorial Kelvin waves or MJO-like behavior. We hypothesize that the two-way tropical-extratropical interaction for this mode acts to weaken the extratropical response to El Niño.
Author: Erik T. Swenson Publisher: ISBN: Category : Climatic changes Languages : en Pages : 0
Book Description
The boreal winter extratropical response to tropical heating associated with a significant El Niño Southern Oscillation (ENSO) event has been understood primarily in terms of a seasonal average. However, the development and variability of the response forced by a highly sub-seasonally variable atmospheric forcing is still unclear. Significant modes of sub-seasonal tropical convective variability exist that have well documented transient impacts on the extratropics, e.g. the Madden-Julian Oscillation (MJO). Does sub-seasonal tropical convective variability impact the seasonal mean extratropical response? If so, what matters for the response: short-lived strong events or more persistent moderate events? Does sub-seasonal convective variability have implications for predictability during El Niño? Using the Community Atmospheric Model v. 4.0 (CAM4) of the National Center for Atmospheric Research, the response to ENSO is simulated using large ensembles of seasonal integrations forced with observed SST from multiple El Niño events. We decompose the diabatic heating rate (Q) across the tropical Indo-Pacific in terms of temporal and intra-ensemble variability. We then repeat the simulations by prescribing subsets of Q in an effort to diagnose the impact of sub-seasonal and intra-ensemble Q variability. Neglecting sub-seasonal Q variability has a systematic impact on the response, generally extending the Pacific jet and deepening upper-level heights across the North Pacific. A local enhancement is simulated in tropical upper-level divergence, likely related to the vertical redistribution of Q resulting from averaging together vertical profiles associated with moderate and deep convection. Persistence may also play a role. When prescribing nearly all Q variability (for frequencies greater than one day), we find that Q-circulation coupling is locally unimportant, i.e. the temporal evolution, mean, and variance of upper-level divergence from a coupled control simulation are reproducible. However, interestingly the amplification of the extratropical response to El Niño is still simulated. It follows that these differences are attributed to the neglect of tropical-extratropical two-way coupling. This is the primary finding of the study and suggests that the extratropical response to a significant El Niño event is not simply a forced response to tropical heating. Regarding the variability of the response to El Niño, we find a robust relationship in the seasonal mean ensemble spread, linking Q variations in the west/central tropical Pacific and extratropical fluctuations projecting onto the Arctic Oscillation (AO). This mode accounts for about a third of the ensemble spread (in 200 hPa geopotential height). Previous studies have revealed a similar relationship in observed interannual variability and have simulated the tropically forced component. In CAM4, this relationship in the ensemble spread is only evident during El Niño and is the dominant contributor to the enhanced ensemble spread simulated during El Niño, acting to lower predictability of the response. Extratropical forcing of the tropics is important for this mode, as prescribing Q variability weakens the relationship and cannot reproduce the enhancement in spread. We find that this relationship emerges as residue of a low frequency sub-seasonal tropical-extratropical coupled mode for which a significant extratropical influence is evident. Over the Pacific, coherent interaction is simulated between evolving persistent planetary waves and convectively coupled waves bearing a resemblance to equatorial Kelvin waves or MJO-like behavior. We hypothesize that the two-way tropical-extratropical interaction for this mode acts to weaken the extratropical response to El Niño.
Author: National Research Council Publisher: National Academies Press ISBN: 0309161347 Category : Science Languages : en Pages : 193
Book Description
More accurate forecasts of climate conditions over time periods of weeks to a few years could help people plan agricultural activities, mitigate drought, and manage energy resources, amongst other activities; however, current forecast systems have limited ability on these time- scales. Models for such climate forecasts must take into account complex interactions among the ocean, atmosphere, and land surface. Such processes can be difficult to represent realistically. To improve the quality of forecasts, this book makes recommendations about the development of the tools used in forecasting and about specific research goals for improving understanding of sources of predictability. To improve the accessibility of these forecasts to decision-makers and researchers, this book also suggests best practices to improve how forecasts are made and disseminated.
Author: William K.-M. Lau Publisher: Springer Science & Business Media ISBN: 3642139140 Category : Science Languages : en Pages : 642
Book Description
Improving the reliability of long-range forecasts of natural disasters, such as severe weather, droughts and floods, in North America, South America, Africa and the Asian/Australasian monsoon regions is of vital importance to the livelihood of millions of people who are affected by these events. In recent years the significance of major short-term climatic variability, and events such as the El Nino/Southern Oscillation in the Pacific, with its worldwide effect on rainfall patterns, has been all to clearly demonstrated. Understanding and predicting the intra-seasonal variability (ISV) of the ocean and atmosphere is crucial to improving long range environmental forecasts and the reliability of climate change projects through climate models. In the second edition of this classic book on the subject, the authors have updated the original chapters, where appropriate, and added a new chapter that includes short subjects representing substantial new development in ISV research since the publication of the first edition.
Author: Andrew Robertson Publisher: Elsevier ISBN: 012811715X Category : Science Languages : en Pages : 588
Book Description
The Gap Between Weather and Climate Forecasting: Sub-seasonal to Seasonal Prediction is an ideal reference for researchers and practitioners across the range of disciplines involved in the science, modeling, forecasting and application of this new frontier in sub-seasonal to seasonal (S2S) prediction. It provides an accessible, yet rigorous, introduction to the scientific principles and sources of predictability through the unique challenges of numerical simulation and forecasting with state-of-science modeling codes and supercomputers. Additional coverage includes the prospects for developing applications to trigger early action decisions to lessen weather catastrophes, minimize costly damage, and optimize operator decisions. The book consists of a set of contributed chapters solicited from experts and leaders in the fields of S2S predictability science, numerical modeling, operational forecasting, and developing application sectors. The introduction and conclusion, written by the co-editors, provides historical perspective, unique synthesis and prospects, and emerging opportunities in this exciting, complex and interdisciplinary field. Contains contributed chapters from leaders and experts in sub-seasonal to seasonal science, forecasting and applications Provides a one-stop shop for graduate students, academic and applied researchers, and practitioners in an emerging and interdisciplinary field Offers a synthesis of the state of S2S science through the use of concrete examples, enabling potential users of S2S forecasts to quickly grasp the potential for application in their own decision-making Includes a broad set of topics, illustrated with graphic examples, that highlight interdisciplinary linkages
Author: Henry F. Diaz Publisher: Cambridge University Press ISBN: 9780521621380 Category : Nature Languages : en Pages : 518
Book Description
The El Niño/Southern Oscillation (ENSO) phenomenon is a recurrent feature of the climate in tropical regions. In this volume leading experts summarize information gained over the past decade concerning diverse aspects of ENSO, which have led to marked improvements in our ability to forecast its development months or seasons in advance. This volume compares ENSO's modern morphology and variability with its recent historic and prehistoric behaviour. It expands and updates Diaz and Markgraf's earlier volume El Niño: Historical and Paleoclimatic Aspects of the Southern Oscillation (1992, Cambridge University Press). The volume will be of importance to a broad range of scientists in meteorology, oceanography, hydrology, geosciences, ecology, public health, emergency management response and mitigation, and decision-making. It will also be used as a supplementary textbook and reference source in graduate courses in environmental studies.
Author: Michael J. McPhaden Publisher: John Wiley & Sons ISBN: 1119548128 Category : Science Languages : en Pages : 528
Book Description
Comprehensive and up-to-date information on Earth’s most dominant year-to-year climate variation The El Niño Southern Oscillation (ENSO) in the Pacific Ocean has major worldwide social and economic consequences through its global scale effects on atmospheric and oceanic circulation, marine and terrestrial ecosystems, and other natural systems. Ongoing climate change is projected to significantly alter ENSO's dynamics and impacts. El Niño Southern Oscillation in a Changing Climate presents the latest theories, models, and observations, and explores the challenges of forecasting ENSO as the climate continues to change. Volume highlights include: Historical background on ENSO and its societal consequences Review of key El Niño (ENSO warm phase) and La Niña (ENSO cold phase) characteristics Mathematical description of the underlying physical processes that generate ENSO variations Conceptual framework for understanding ENSO changes on decadal and longer time scales, including the response to greenhouse gas forcing ENSO impacts on extreme ocean, weather, and climate events, including tropical cyclones, and how ENSO affects fisheries and the global carbon cycle Advances in modeling, paleo-reconstructions, and operational climate forecasting Future projections of ENSO and its impacts Factors influencing ENSO events, such as inter-basin climate interactions and volcanic eruptions The American Geophysical Union promotes discovery in Earth and space science for the benefit of humanity. Its publications disseminate scientific knowledge and provide resources for researchers, students, and professionals. Find out more about this book from this Q&A with the editors.
Author: Feiyu Lu Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Tropical variability (e.g. El Niño-Southern Oscillation or ENSO) and climatology (e.g. asymmetric Inter-Tropical Convergence Zone or ITCZ) were initially thought to be determined mostly by local forcing and ocean-atmosphere interaction in the tropics. Since late 20th century, numerous studies have showed that extratropical forcing could affect, or even largely determine some aspects of the tropical climate. Due to the coupled nature of the climate system, the challenge of determining and further quantifying the causality of extratropical forcing on the tropical climate remains to be further explored. This dissertation studies the extratropical influence on the tropical climate, including both variability and climatology, using the Regional Coupled Data Assimilation (RCDA) method in a coupled general circulation model (CGCM). The RCDA method limits the data assimilation to the desired model components (e.g. atmosphere) and regions (e.g. the extratropics) and studies the ensemble-mean model response (e.g. tropical response to "observed" extratropical atmospheric variability). First, perfect-model RCDA experiments demonstrate significant control of extratropical atmospheric forcing on ENSO variability in the CGCM. When atmospheric "observations" are assimilated only poleward of 20° in both hemispheres, most ENSO events in the "observation" are reproduced. Experiments with single-hemisphere assimilation show that the forced ENSO variability is contributed roughly equally and independently by the Southern and Northern Hemisphere extratropical atmosphere. Robust precursors are found in both the extratropical atmosphere over southeastern Pacific and equatorial Pacific thermocline, consistent with previous studies. However, neither precursor alone is sufficient to trigger ENSO onset, therefore neither alone could serve as a reliable predictor. Then, RCDA experiments with real world reanalysis data show extratropical impact on both tropical climatology and variability in the CGCM. The model's double-ITCZ bias is improved systematically when SST, air temperature and wind are corrected toward real world data from the extratropics into the tropics progressively. Coupled dynamics, as well as atmospheric and oceanic processes, play important roles in this extratropical-to-tropical teleconnection. Certain historical ENSO events are also reproduced by assimilating extratropical atmospheric observations. Analysis of the real world RCDA experiments confirms the effects of the precursors found in the perfect-model experiments, while also points to the impact of model bias on ENSO variability
Author: Daeho Jin Publisher: ISBN: Category : El Niño Current Languages : en Pages : 0
Book Description
The impact of tropical remote forcing on the extratropics is examined with ideal El Niño-Southern Oscillation (ENSO) forcing in the tropical Pacific. A set of numerical experiments are described in which perfectly periodic ENSO is prescribed in the tropical Pacific as a lower boundary condition, and a slab mixed layer ocean model is coupled to an Atmospheric General Circulation Model (AGCM) in all other ocean basins. First, the role of subtropical air-sea coupling is investigated by changing the tropical Pacific forcing region, i.e., narrow (10[degrees]S-10[degrees]N) vs. broad (20[degrees]S-20[degrees]N) forcing region. When the tropical Pacific is prescribed to be only the climatological annual cycle, different SST in the subtropics results. This, in turn, leads to different atmospheric motions, and consequently affects the adjacent extratropical atmosphere. The effect is limited to the Pacific basin only. When the tropical Pacific includes ENSO, meridionally broad structure of SST forcing intensifies the meridional atmospheric circulation in the North Pacific basin, and, hence, the extratropical response to ENSO increases. Secondly, the relationship between remote ENSO forcing and seasonality is examined. Here we compare the response to perfectly periodic ENSO forcing that peaks in boreal summer versus boreal winter. The results indicate that the maximum extratropical response to the ENSO is determined by the local seasonality rather than the temporal phase of ENSO. When the peak of ENSO is in boreal summer, the surface heat flux in the North Pacific is maximized in the boreal winter, six months earlier than the peak of ENSO. At the same time, the evolution of SST in the South Pacific is very similar to that of the observed North Pacific. The tropical atmosphere linearly responds to the prescribed SST forcing, but the atmospheric bridge connecting the deep tropics to the extratropics occurs in specific seasons. Lastly, we examined how the extratropical response to ENSO varies depending on the period of ENSO. Ideally periodic two, four, and six year ENSO period experiments were performed. When the ENSO responses mature in the North Pacific, the composite patterns are similar among experiments, but the variance is sensitive to the ENSO periodicity. The extratropical response to ENSO is damped by local air-sea interaction. This local damping has a time-scale that is considerable longer than one year. Hence, the high frequency ENSO, in which the time-scale between successive ENSO events is shorter than the local damping process, results in increased variances of the ENSO forced pattern. In addition, the La Niña forced pattern persists longer than the El Niño forced pattern.
Author: Carlos R. Mechoso Publisher: Cambridge University Press ISBN: 1108492703 Category : Science Languages : en Pages : 359
Book Description
A comprehensive review of interactions between the climates of different ocean basins and their key contributions to global climate variability and change. Providing essential theory and discussing outstanding examples as well as impacts on monsoons, it a useful resource for graduate students and researchers in the atmospheric and ocean sciences.
Author: Erik T. Swenson
Author: Erik T. Swenson
Author: National Research Council
Author: William K.-M. Lau
Author: Andrew Robertson
Author: Henry F. Diaz
Author: K. M. Lau
Author: Michael J. McPhaden
Author: Feiyu Lu
Author: Daeho Jin
Author: Carlos R. Mechoso