Interdecadal Climate Variability Research Articles

Identifying a Damped Oscillatory Thermohaline Mode in a General Circulation Model Using an Adjoint Model

A damped oscillatory mode of the thermohaline circulation (THC), which may play a role in interdecadal climate variability, is identified in a global primitive equation model. This analysis is done under mixed boundary conditions using an adjoint of the primitive equation model. The linearized versus nonlinear stability behavior of the model is studied by comparing the adjoint analysis to runs of the fully nonlinear model. It is shown that a steady-state solution obtained under larger amplitude freshwater surface forcing (and hence with a weaker North Atlantic overturning) is unstable, while a steadystate solution with stronger THC is stable. In a certain intermediate parameter regime it is found that the full nonlinear model state may be unstable, while the linearized analysis indicates that the model state is stable. It is proposed that this may be because either the instability mechanism at this intermediate regime is nonlinear or, while the model is linearly stable at this regime, it allows for temporary growth of small perturbations due to the non-normal nature of the problem. A clear signal of variations is not found in the amplitude of the horizontal gyre circulation, possibly indicating that the gyre effect that was found in THC oscillations in some previous studies may not be essential for the existence of the THC oscillation. The long timescale of the oscillation in the present model also seems to indicate that the gyre effect may not be a main active participant in the thermohaline oscillation mechanism.

Interdecadal climate variability and regime‐scale shifts in Pacific North America

A transect of climate sensitive tree ring‐width chronologies from coastal western North America provides a useful proxy index of North Pacific ocean‐atmosphere variability since 1600 AD. Here we use this high‐resolution record to identify intervals of an enhanced interdecadal climate signal in the North Pacific, and to assess the timing and magnitude of abrupt shifts in this system. In the context of this record, the step‐like climate shift that occurred in 1976–1977 is not a unique event, with similar events having occurred frequently during the past 400 years. Furthermore, most of the pre‐instrumental portion of this record is characterized by pronounced interdecadal variability, while the secular portion is more strongly interannual in nature. If the 1976–1977 event marks a return to this mode of variability there may be significant consequences for natural resources management in the North Pacific Sector.

Reviews

The Geographical JournalVolume 166, Issue 3 p. 267-281 Reviews First published: 05 July 2005 https://doi.org/10.1111/j.1475-4959.2000.tb00026.xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat Abstract Borneo: Jewel in a Jade Rainbow. By David and Sue Fielding. People, Land and Time: an historical introduction to the relations between landscape, culture and environment. Edited by Peter Atkins, Ian Simmons and Brian Roberts. Solid Waste Management: Critical Issues for Developing Countries. Edited by Eltzabeth Thomas-Hope. Ecoregions: the Ecosystem Geography of the Oceans and Continents. By Robert C. Bailey. Ecohydrological response modelling: predicting plant species’ response to changes in site conditions(in English with Dutch summary). By A.C.D. Ertsen. Agrarian Reform in Theory and Practice: a study of the lake Titicaca region of Bolivia. By Jane Benton. Debt and Adjustment: Social and Environmental Consequences in Jamaica. By Patricia Lundy. Swidden Farming and Fallow Vegetation in Northern Thailand. By Dietrich Schmidt-Voct. Sustainability: Life Chances and Livelihoods. Edited by Michael Redclift. Tropical Pacific Island Environments. By Christopher S. Lobban and Maria Schefter. Beyond El Niiio: decadal and inter-decadal climate variability. Edited by Antonio Navarra. Public Purpose or Private Benefit? The Politics of Energy Conservation. By Gill Owen. Sudan's Predicament: Civil War, Displacement and Ecological Degradation. Edited by Girma Kebbede. Shock-Shift in an Enlarged Europe: The geography of socio-economic change in East-Central Europe after 1989. Edited by F.W. Carter and W. Maik. Miombo Ecology and Management: an introduction. By E.M. Chidumayo. Weather and Climate (CD Rom). By Harald Frater. The Bankruptcy of Economics: Ecology, Economics and the Sustainability of the Earth. By Joseph Wayne Smith, Graham Lyons and Gary Sauer-Thompson Edited by David Harper and Tony Brown. Precision Agriculture: Spatial and temporal variability of environmental quality (Ciba Foundation Symposium 210). Edited by John V. Lake, Gregory R. Bock and Jamie A. Goode. The Road to Egdon Heath: the Aesthetics of the Great in Nature. By Richard Bevis. Secure From Rash Assault: Sustaining the Victorian Environment. By J. Winter. Coastal defence and Earth Science conservation. Edited by Janet Hooke. Human Geography Today. Edited by Doreen Massey, John Allen and Philip Sarre. Volume166, Issue3September 2000Pages 267-281 RelatedInformation

Climate change and vector-borne diseases: a regional analysis.

Current evidence suggests that inter-annual and inter-decadal climate variability have a direct influence on the epidemiology of vector-borne diseases. This evidence has been assessed at the continental level in order to determine the possible consequences of the expected future climate change. By 2100 it is estimated that average global temperatures will have risen by 1.0-3.5 degrees C, increasing the likelihood of many vector-borne diseases in new areas. The greatest effect of climate change on transmission is likely to be observed at the extremes of the range of temperatures at which transmission occurs. For many diseases these lie in the range 14-18 degrees C at the lower end and about 35-40 degrees C at the upper end. Malaria and dengue fever are among the most important vector-borne diseases in the tropics and subtropics; Lyme disease is the most common vector-borne disease in the USA and Europe. Encephalitis is also becoming a public health concern. Health risks due to climatic changes will differ between countries that have developed health infrastructures and those that do not. Human settlement patterns in the different regions will influence disease trends. While 70% of the population in South America is urbanized, the proportion in sub-Saharan Africa is less than 45%. Climatic anomalies associated with the El Niño-Southern Oscillation phenomenon and resulting in drought and floods are expected to increase in frequency and intensity. They have been linked to outbreaks of malaria in Africa, Asia and South America. Climate change has far-reaching consequences and touches on all life-support systems. It is therefore a factor that should be placed high among those that affect human health and survival.

Enhancement of Interdecadal Climate Variability in the Sahel by Vegetation Interaction.

The role of naturally varying vegetation in influencing the climate variability in the West African Sahel is explored in a coupled atmosphere-land-vegetation model. The Sahel rainfall variability is influenced by sea-surface temperature variations in the oceans. Land-surface feedback is found to increase this variability both on interannual and interdecadal time scales. Interactive vegetation enhances the interdecadal variation substantially but can reduce year-to-year variability because of a phase lag introduced by the relatively slow vegetation adjustment time. Variations in vegetation accompany the changes in rainfall, in particular the multidecadal drying trend from the 1950s to the 1980s.

Decadal climate variability in a coupled atmosphere‐ocean climate model of moderate complexity

In this study we determined characteristic temporal modes of atmospheric variability at the decadal and interdecadal timescales. This was done on the basis of 1000 year long integrations of a global coupled atmosphere‐ocean climate model of moderate complexity including the troposphere, stratosphere, and mesosphere. The applied model resolves explicitely the basic features of the large‐scale long‐term atmospheric and oceanic variables. The synoptic‐scale processes are described in terms of autocorrelation and crosscorrelation functions. The paper includes an extended description and validation of the model as well as the results of analyses of two 1000 year long model integrations. One model run has been performed with the fully coupled model of the atmosphere‐ocean system. The performed time‐frequency analyses of atmospheric fields reveal strong decadal and interdecadal modes with periods of about 9, 18, and 30 years. To quantify the influence of the ocean on atmospheric variations an additional run with seasonally varying prescribed sea surface temperatures has been carried out, which is characterized by strong decadal modes with periods of about 9 years. The comparison of both runs suggests that decadal variability can be understood as an inherent atmospheric mode due to the nonlinear dynamics of the large‐scale atmospheric circulation patterns whereas interdecadal climate variability has to be regarded as coupled atmosphere‐ocean modes.

Analytical Prototypes for Ocean–Atmosphere Interaction at Midlatitudes. Part II: Mechanisms for Coupled Gyre Modes*

A simple midlatitude coupled model for idealized ocean basins is used to investigate processes of ocean‐ atmosphere interaction and its role in interdecadal climate variability at midlatitudes. The ocean model consists of a linearized quasigeostrophic upper ocean layer and a sea surface temperature (SST) equation for an embedded surface mixed layer. The atmospheric response to the ocean is through wind stress and heat flux feedbacks associated with SST. Eigenvalue analysis of both coupled and uncoupled models presented here complements previous work on the stochastically forced system. Comparison of the eigenspectrum of coupled and uncoupled cases shows that coupling creates an oscillatory interdecadal mode whose properties are distinct from any other mode in the system. This mode exists whether the atmospheric feedbacks are weak or strong, and is stable even in the strong feedback case. The weak decay rate makes it possible for the mode to be maintained by atmospheric stochastic forcing. Analytic approximations to the dispersion relation show how the spatial structure of the atmospheric feedback tends to select a large-scale spatial pattern for this eigenmode. The oscillation involves westward Rossby wave propagation in the ocean with the atmosphere carrying information back eastward into the interior of the basin in response to SST anomalies produced by advection. SST modes are also found, which purely decay in most cases due to both local and nonlocal negative heat flux feedbacks. A case with large positive heat flux feedback can produce a purely growing SST mode but does not greatly impact the interdecadal mode.

Recent abatement of easterly winds in the northern Adriatic

Easterly winds from the northern Adriatic contribute, together with atmospheric depressions, and the often decisive southerly winds from the southern and middle Adriatic, to produce damaging sea surges in the Gulf of Venice. A new statistical analysis of 3-hourly wind records from Trieste for the period 1951–1996, has shown a clear decline in the frequency and strength of Bora and other easterlies. This abatement is not accompanied by a strengthening of winds from other directions, but by more frequent calm situations (from 26% of total observations in the 1950s, to 44% during the last 10 years, and even to over 60% during the early 1980s). Similar (although weaker) declining trends for the easterlies have been recorded at other stations in the northern Adriatic (Ronchi, Venice). An inspection of previously published data from Trieste suggests that such trends may have been going on, possibly with minor fluctuations, since at least the beginning of regular instrumental records, in the late 1860s. Such changes in wind pattern, which have favourable effects on the frequency of coastal flooding, may be due, at least in part, to interdecadal climate variability. However, the persistence of certain trends suggests a climatic shift, with, in particular, less-frequent situations, with strong atmospheric pressure gradients between highs in central/eastern Europe and lows in southern Italy or in the Adriatic area. Such situations may be a consequence of recent global warming and of less-frequent drifts of polar cold air towards middle latitudes. Copyright © 1999 Royal Meteorological Society

Analytical Prototypes for Ocean–Atmosphere Interaction at Midlatitudes. Part I: Coupled Feedbacks as a Sea Surface Temperature Dependent Stochastic Process*

Effects of ocean‐atmosphere feedback processes and large-scale atmospheric stochastic forcing on the interdecadal climate variability in the North Atlantic and North Pacific Oceans are examined in a simple midlatitude ocean‐atmosphere model. In the ocean, the authors consider a linearized perturbation system with quasigeostrophic shallow-water ocean dynamics and a sea surface temperature (SST) equation for a surface mixed layer. The atmosphere is represented as stochastic wind stress and heat flux forcing. This includes a noise component that depends on SST, as well as an additive component that is independent of SST. Coupling is represented by the SST dependent stochastic process, in which SST influences the probability density function of the atmospheric noise both in shifting the mean and affecting the variance. It thus includes a multiplicative noise component. The model results in both oceans indicate that large-scale additive atmospheric stochastic forcing alone (the uncoupled case) can give coherent spatial patterns in the ocean and sometimes even a weak power spectral peak at interdecadal periods. Coupling due to the SST dependent stochastic process can produce a more distinct power-spectral peak relative to the uncoupled ocean. Moreover, the time and spatial scales of the interdecadal mode are insensitive to the standard deviation of the multiplicative noise. Thus a deterministic feedback limit can be used to simplify the coupled model for further investigation of the physical mechanisms of the interdecadal mode. In both uncoupled and coupled cases, the period of the interdecadal oscillation is determined by the zonal length scale of atmospheric wind stress and oceanic Rossby wave dynamics. The atmospheric spatial pattern sets the length scale of large-scale wave motion in the ocean. This wave propagates to the west due to oceanic Rossby wave dynamics and is dissipated at the western boundary. However, in the coupled case, the SST anomalies generated by geostrophic current can feed back to the atmosphere, which in turn brings some information back to the east and reexcites oceanic waves there. Although the magnitude of the feedback of SST on the atmosphere is much smaller than atmospheric internal variability, its effects are significant.

Mesozooplankton in the eastern and western subarctic Pacific: community structure, seasonal life histories, and interannual variability

The zooplankton community of the subarctic Pacific is relatively simple, and contains a similar set of major species in all deep water areas of the subarctic Pacific. Their role in the food web varies considerably between coastal and offshore locations. In the oceanic gyres, microzooplankton and other mesozooplankton taxa replace phytoplankton as the primary food source for the dominant mesozooplankton species. Micronekton and larger zooplankton probably replace pelagic fish as major direct predators. Productivity and upper ocean biomass concentrations are intensely seasonal, in part because of seasonality of the physical environment and food supply, but also because of life history patterns involving seasonal vertical migrations (400–2000 m range) and winter dormancy. During the spring–summer season of upper ocean growth, small scale horizontal and vertical patchiness is intense. This can create local zones of high prey availability for predators such as planktivorous fish, birds, and marine mammals. On average, the cores of the subarctic gyres have lower biomass and productivity than the margins of the gyres. There is also some evidence that the Western Gyre is more productive than the Alaska Gyre, but more research is needed to confirm whether this east–west gradient is permanent. There is increasing evidence that the pattern of zooplankton productivity is changing over time, probably in response to interdecadal ocean climate variability. These changes include 2–3 fold shifts in total biomass, 30–60 day shifts in seasonal timing, and 10–25% changes in average body length.

Hunter receives 1998”1999 AGU Congressional Science Fellowship

David E. Hunter was selected by the Committee on Public Affairs (COPA) to receive the Congressional Science Fellowship at its Spring Committee Meeting.David is currently a U.S. Department of Energy (DoE) Global Change Fellow at the Scripps Institution of Oceanography. His dissertation, under Professor Christopher Charles, has focused on the interannual to interdecadal climate variability in the western Indian Ocean. By measuring oxygen isotopes in Seychelles corals, he created a 150‐year, monthly resolution record of climate. This record yielded a history of interaction between the monsoon and the El Niño/Southern Oscillation and is providing key insights into the decadal variability in the tropics.

Effects of interdecadal climate variability on the oceanic ecosystems of the NE Pacific

A major reorganization of the North‐east Pacific biota transpired following a climatic `regime shift' in the mid 1970s. In this paper, we characterize the effects of interdecadal climate forcing on the oceanic ecosystems of the NE Pacific Ocean. We consider the concept of scale in terms of both time and space within the North Pacific ecosystem and develop a conceptual model to illustrate how climate variability is linked to ecosystem change. Next we describe a number of recent studies relating climate to marine ecosystem dynamics in the NE Pacific Ocean. These studies have focused on most major components of marine ecosystems – primary and secondary producers, forage species, and several levels of predators. They have been undertaken at different time and space scales. However, taken together, they reveal a more coherent picture of how decadal‐scale climate forcing may affect the large oceanic ecosystems of the NE Pacific. Finally, we synthesize the insight gained from interpreting these studies. Several general conclusions can be drawn. 1 There are large‐scale, low‐frequency, and sometimes very rapid changes in the distribution of atmospheric pressure over the North Pacific which are, in turn, reflected in ocean properties and circulation. 2 Oceanic ecosystems respond on similar time and space scales to variations in physical conditions. 3 Linkages between the atmosphere/ocean physics and biological responses are often different across time and space scales. 4 While the cases presented here demonstrate oceanic ecosystem response to climate forcing, they provide only hints of the mechanisms of interaction. 5 A model whereby ecosystem response to specified climate variation can be successfully predicted will be difficult to achieve because of scale mismatches and nonlinearities in the atmosphere–ocean–biosphere system.

Evaluation of the European daily precipitation characteristics from the atmospheric model intercomparison project

Evaluating the daily precipitation performance of general circulation models at a regional scale is beset with two (related) difficulties: (i) ensuring an adequate network of observed daily station data across a region; and (ii) establishing 'true' areal means of daily precipitation from these station data to ensure a like-with-like comparison. These two difficulties have generally restricted past evaluations of daily model precipitation to individual grid boxes and to comparisons of model grid-box data with observed sub-grid-box scale data. In this paper we exploit a dataset of several dozen daily station time series in western Europe using a recently published method for estimating 'true' areal mean daily precipitation to evaluate the daily precipitation performance in this region of 12 atmospheric general circulation model simulations undertaken as part of the Atmospheric Model Intercomparison Project. We examine four quantities derived from the simulated daily precipitation: seasonal mean precipitation, daily standard deviation, the frequency of raindays and the mean precipitation intensity of those raindays. We show that simulated winter precipitation tends to be too great, falls on too many-days, but is generally less intense than that observed. In summer, model results are more variable with some model simulations yielding statistics quite similar to those observed. Although there is some uncertainty in these evaluation statistics owing to the effect of inter-decadal climate variability, there is a weak suggestion of improved performance with increased spatial resolution. Any systematic effect in model performance due to different convective parameterisation schemes is obscured by other confounding factors.

On the role of ocean‐atmosphere interaction in midlatitude interdecadal variability

A simple midlatitude ocean‐atmosphere model is used to investigate possible roles of coupled feedback in interdecadal climate variability over the North Atlantic and North Pacific oceans. Stochastic forcing by atmospheric internal variability maintains variance in both uncoupled and coupled cases. Coupling contributes to creating an interdecadal mode with distinct spatial pattern and preferred time scale, seen as a broad spectral peak. A near‐analytic solution for the coupled interdecadal mode suggests that the most important parameter in determining the period is the zonal length scale of the atmospheric wind stress feedback over the region. Subject to this scale, the period is then determined by oceanic Rossby wave dynamics, which tends to give westward propagation in subsurface fields. The dipolar sea surface temperature (SST) anomalies are generated primarily by the advection of climatological SST by geostrophic current. Although the magnitude of the feedback of SST to atmospheric response is much smaller than atmospheric internal variability, its effects are significant.

Interdecadal variations in global climate and earth rotation rate

A science plan for future 15 a, 'A Study of Climate Variability and Predictability'(CLIVAR), was published by WMO in 1996. As the plan treated interdecadal climatic variability as a sub-plan, it showed that this problem is very important. By the implementation of 'Tropical Ocean and Global Atmosphere' (TOGA) 10-a plan during 1985—1994, the interdecadal variability that occurred in ENSO (El Nino/Southern Oscillation) ocean-atmosphere interaction has been found. This variability made the traditional ENSO prediction pattern useless in

A Theory of Interdecadal Climate Variability of the North Pacific Ocean–Atmosphere System*

Abstract A linear coupled model for the atmosphere–upper-ocean system is proposed to highlight the mechanisms of decadal to interdecadal climate variability in the North Pacific. In this model, wind stress anomalies over the North Pacific are related to anomalies in the meridional temperature gradient of the upper ocean. The latter depends upon air–sea thermodynamical feedbacks and meridional heat transport by upper-ocean currents. Slow adjustment of the oceanic gyre circulation to the change in wind stress is accomplished by the forced baroclinic oceanic Rossby waves, which carry out the meridional heat transport. Uncoupled ocean dynamic adjustment can produce a weak decadal to interdecadal peak in the power spectrum of the meridional transport under temporal white noise wind stress forcing with organized spatial structure. Coupled dynamics produce a basin-scale interdecadal oscillatory mode. This mode arises from the dynamic coupling and the memory of the system, residing in the slow gyre circulation ad...

Linear versus Self-Sustained Interdecadal Thermohaline Variability in a Coupled Box Model

Recent studies of decadal/interdecadal climate variability suggested two main classes of mechanisms: selfsustained (supercritical) oscillations due to the internal nonlinearity of the ocean and linear (subcritical) thermohaline oscillations driven by stochastic atmospheric forcing. The authors use a coupled ocean‐atmosphere meridional box model to carefully examine these two alternatives. It is shown that a weakly nonlinear relation between the north‐south density gradient in the ocean and the meridional ocean transport can lead to selfsustained oscillations. A nonlinear relation between the SST and the air‐sea heat flux can also lead to selfsustained oscillations, although indications are given that the air‐sea heat flux depends linearly on the SST for a wide range of SST perturbations. It is thus concluded that, if interdecadal climate variability is due to selfsustained oscillations, the necessary nonlinearity must be related to internal ocean dynamics rather than to the air‐sea interaction or to nonlinear atmospheric dynamics. The box model results are used to discuss a simple criterion, based on the probability distribution function of the meridional circulation time series, for differentiating between self-sustained and linear variability. This criterion could not rule out either the linear or nonlinear hypotheses for the thermohaline variability in the GFDL coupled general circulation model run of Delworth, Manabe, and Stouffer. This may indicate that the variability in the coupled general circulation model is near critical.

Correction to “Evidence for interannual and interdecadal climate variability in the South Atlantic”

Correction to “Evidence for interannual and interdecadal climate variability in the South Atlantic”

Evidence for interannual and interdecadal climate variability in the South Atlantic

A singular value decomposition (SVD) analysis is used to determine the coupled modes of variability of monthly sea surface temperature (SST) and sea level pressure (SLP) data from the South Atlantic region, for the period 1953–1992. We find that the three leading SVD modes respectively account for 63%, 20% and 6% of the total square covariance. The first mode represents an approximately 15‐year period oscillation in the strength of the subtropical anticyclone, accompanied by fluctuations of a north‐south dipole structure in the SST. It appears to be linked to the global‐scale interdecadal (15‐year) joint mode in SST and SLP recently studied by Mann and Park. The second mode is characterized by east‐west displacements of the anticyclone center, in association with strong 6 to 7‐year period fluctuations of SST off the coast of Africa. The third mode is characterized by north‐south displacements of the anticyclone and 4‐year period fluctuations in the SST in a broad band across the central South Atlantic. This mode is strongly correlated with ENSO.

Interdecadal climate variability in the subpolar North Atlantic

The statistical relationships between various components of the subpolar North Atlantic air-sea-ice climate system are reexamined in order to investigate potential processes involved in interdecadal climate variability. It is found that sea surface temperature anomalies concentrated in the Labrador Sea region have a strong impact upon atmospheric sea level pressure anomalies over Greenland, which in turn influence the transport of freshwater and ice anomalies out of the Arctic Ocean, via Fram Strait. These freshwater and ice anomalies are advected around the subpolar gyre into the Labrador Sea affecting convection and the formation of Labrador Sea Water. This has an impact upon the transport of North Atlantic Current water into the subpolar gyre and thus, also upon sea surface temperatures in the region. An interdecadal negative feedback loop is therefore proposed as an internal source of climate variability within the subpolar North Atlantic. Through the lags associated with the correlations between different climatic components, observed horizontal advection time scales, and the use of Boolean delay equation models, the time scale for one cycle of this feedback loop is determined to have a period of about 21 years.