North Atlantic sea surface temperatures and their relation to the North Atlantic Oscillation during the last 230?years

August Sea Surface Temperatures (aSSTs) based on fossil diatom assemblages are generated with 2?year average resolution from a 230-year-long sediment core (Rapid 21-12B), from the Reykjanes Ridge in the subpolar North Atlantic. The results indicate a warming trend of ~0.5°C of the surface waters at the Reykjanes Ridge for the last 230?years. Superimposed on this warming trend there is a multidecadal to decadal aSST variability of up to 1°C. The interval from the 1770s to the 1830s represents the coldest period, whereas ~1860?C1880 represents the warmest period during the last 230?years. The last 25?years is characterized by a warming trend showing strong decadal aSST variability with several warm years, but also the coldest years since the 1820s. The time of these cold years in the mid-1970s, -1980s and -1990s correspond with the documented great salinity anomalies (GSA) in the North Atlantic suggesting increased fluxes of cold, low-salinity waters from the Arctic during the last decades. The aSST record and the August North Atlantic Oscillation (aNAO) index show similar multidecadal-scale variability indicating a close coupling between the oceanic and atmospheric patterns. The aSST record shows a negative correlation with the aNAO indicating cold aSST during the positive aNAO trend and vice versa. Results suggest that the wind driven variation in volume fluxes of the North Atlantic surface waters could be the major mechanism behind the observed relationship.     

The North Atlantic Oscillation—What Role for the Ocean?

The extent to which the North Atlantic Oscillation (NAO) is influenced by changes in the ocean state is an issue that has attracted much recent attention. Although there have been counter claims, the weight of evidence clearly suggests that forcing by the ocean of year-to-year changes in the NAO is a weak influence by comparison with atmospheric internal variability. The NAO is thus very different in character to the Southern Oscillation (SO), and its predictability—at least on seasonal-to-interannual timescales—is almost certainly much lower.Although weak, the influence of the ocean on the NAO is not negligible. In a previous study we found that wintertime North Atlantic climate, including the NAO, was significantly influenced by a tripole pattern of North Atlantic SST anomalies. Here we report the results of experiments to further elucidate the nature of this influence. We show that the tripole pattern induces a significant response both in the tropical Atlantic and at mid-to-high latitudes. The low latitude response is forced by the low latitude SST anomalies, but the high latitude response is influenced by the extratropical SST anomalies as well as those in the tropics. Furthermore, we find evidence of nonlinear interaction between the influence of the tropical and extratropical SST anomalies. Lastly, we investigate the feedback from the atmosphere onto the SST tripole. We find that the expected negative feedback is significantly modified at low latitudes by the dynamical response of the atmosphere.     

Climatological responses of winter precipitation in Turkey to variability of the North Atlantic Oscillation during the period 1930–2001

Summary Climatological responses of winter (DJFM) precipitation at 78 stations of Turkey to variability of the North Atlantic Oscillation (NAO) were investigated for the period 1930–2001. The analysis was performed with respect to relationships between precipitation and three different NAO indices (NAOIs) and composite precipitation changes corresponding to the extreme phases of the NAOIs, and individual wet conditions and drought events linked to the extreme NAOI events. Main conclusions of the study can be evaluated as follows:(a) The Ponta Delgada–Reykjavik (PD–R) NAOI is superior among the three NAOIs compared, followed by the Lisbon–Stykkisholmur/Reykjavik NAOI, with regards to its ability to control year-to-year variability in winter precipitation series and composite precipitation conditions corresponding to the extreme NAOI phases in Turkey. (b) Variability of winter precipitation at most stations in Turkey is significantly correlated with variability of the three NAOIs. Negative relationships are stronger over the Marmara, the Mediterranean Transition and the Continental Central Anatolia regions, and the Aegean part of the Mediterranean region. (c) Composite precipitation analysis exhibited an apparent opposite anomaly pattern at the majority of stations between the weak and strong phases of the NAOIs. Composite precipitation means corresponding to the weak NAOI phase are explained mostly by wetter than long-term average conditions, whereas composite precipitation responses to the strong NAOI phase mostly produce drier than long-term average conditions. (d) Composite wet (dry) conditions during the weak (strong) phase of the NAOI are significant at about 32% (69%) of 78 stations for the PD–R NAOI, and about 38% (55%) for the L–S(R) NAOI. The dry signals from the strong NAO phases are stronger and show a larger spatial coherence over Turkey. The significant signals are evident in the west, centre and south of the country. (g) Widespread severe droughts in 1943, 1957, 1973, 1974, 1983, 1989, 1990, 1992, 1993 and 1994, and widespread strong wet conditions in 1940–1942, 1956, 1963, 1966, 1969 and 1970 were linked to the extreme high- and low-index events of at least two NAOIs, respectively.     

Impact of the Equatorial Atlantic on the El Ni?o Southern Oscillation

Observations indicate that the Atlantic zonal mode influences El Ni?o Southern Oscillation (ENSO) in the Pacific, as already suggested in previous studies. Here we demonstrate for the first time using partial coupled experiments that the Atlantic zonal mode indeed influences ENSO. The partial coupling experiments are performed by forcing the coupled general circulation model (ECHAM5/MPI-OM) with observed sea surface temperature (SST) in the Tropical Atlantic, but with full air-sea coupling allowed in the Pacific and Indian Ocean. The ensemble mean of a five member simulation reproduces the observational results well. Analysis of observations, reanalysis, and coupled model simulations all indicate the following mechanism: SST anomalies associated with the Atlantic zonal mode affect the Walker Circulation, driving westward wind anomalies over the equatorial Pacific during boreal summer. The wind stress anomalies increase the east-west thermocline slope and enhance the SST gradient across the Pacific; the Bjerknes positive feedback acts to amplify these anomalies favouring the development of a La Ni?a-like anomalies. The same mechanisms act for the cold phase of Atlantic zonal mode, but with opposite sign. In contrast to previous studies, the model shows that the influence on ENSO exists before 1970. Furthermore, no significant influence of the Tropical Atlantic on the Indian Monsoon precipitation is found in observation or model.     

Climate change and the incidence of a forest pest in Mediterranean ecosystems: can the North Atlantic Oscillation be used as a predictor?

Many forest pest species strongly depend on temperature in their population dynamics, so that rising temperatures worldwide as a consequence of climatic change are leading to increased frequencies and intensities of insect-pest outbreaks. In the Mediterranean area, the climatic conditions are strongly linked to the effects of the North Atlantic Oscillation (NAO). The aim of this work is to analyze the dynamics of the pine processionary moth (Thaumetopoea pityocampa), a severe pest of Pinus species in the Circunmediterranean, throughout a region of southern Spain, in relation to NAO indices. We related the percentage of forest plots with high defoliation by pine processionary moth each year with NAO values for the present and the three previous winters, using generalized linear models with a binomial error distribution. The time series is 16-year long, and we performed analyses for the whole database and for the five main pine species separately. We found a consistent relationship between the response variable and the NAO index. The relationship is stronger with pine species living at medium-high altitudes, such as Aleppo (P. halepensis), black (P. nigra), and Scots (Pinus sylvestris) pine, which show the higher defoliation intensities up to 3?years after a negative NAO phase. The results highlight, for the first time, the usefulness of using global drivers in order to understand the dynamics of pest outbreaks at a regional scale, and they open the window to the development of NAO-based predictive models as an early-warning signal of severe pest outbreaks.     

Drought history inferred from tree ring δ 13C and δ 18O in the central Tianshan Mountains of China and linkage with the North Atlantic Oscillation

Annual tree ring δ ¹⁸O and δ ¹³C chronologies from 1790 to 2008 were established using Tianshan spruce (Picea schrenkiana) in the central Tianshan Mountains of northwestern China. Temperature has a positive effect on tree ring δ ¹⁸O and δ ¹³C in the study area, while precipitation and relative humidity have negative effects. The standardized precipitation–evapotranspiration index (SPEI) considered all of these effects and was significantly negatively correlated with tree ring δ ¹⁸O and δ ¹³C. We combined the tree ring δ ¹⁸O and δ ¹³C series to reconstruct the past 192 years of SPEI, which accounted for about 46 % of the total variance of SPEI from 1950 to 2006. The reconstruction showed good spatial agreement with gridded data in Palmer Drought Severity Index and precipitation and an inverse relationship with temperature. Our SPEI reconstruction reveals several wet and dry periods over the past 192 years and has good agreement with other drought records. Wavelet analysis showed quasi-periodic 10-, 20-, 30-, and 70-year fluctuations in the reconstruction. The 10-, 20-, and 30-year periodicities may reflect the potential influence of North Atlantic Oscillation (NAO). Overall, this study indicates that the SPEI is a potential drought index, and the winter NAO affects regional moisture conditions in the long term.     

Sensitivity of the Northern Hemisphere circulation to North Atlantic SSTs in the ARPÈGE Climate AGCM

In order to determine the response of the atmosphere to winter sea surface temperature (SST) anomalies in the North Atlantic area, we carried out ensemble runs of 20 years, forced with constant, perturbed, SST patterns using the climate version of the ARPèGE AGCM, at T42 resolution. A Monte Carlo technique was applied, in such a way that the control experiment, forced with observed climatological temperatures, and the four scenario experiments, forced with perturbed SSTs are equivalent to a length of 20 independent winters. Four anomalous winter North Atlantic sea surface temperature (SST) fields have been constructed by considering the observed SST variability in the main basins, namely the Labrador Sea and the Greenland Sea. Two patterns are of the `seesaw' type, while the two others have same the polarity in both basins. The patterns have been reinforced by a factor of 5–6 compared to presently observed multi-annual anomalies, in order to get SST anomalies which may have occurred during periods of the Little Ice Age. The differences between each of the four winter simulations with perturbed SSTs and the control run are analyzed in terms of tropospheric thickness, mean-sea-level pressure and storm activity. The `seesaw' type patterns give a weaker response in the tropospheric thickness fields than the two others. This is expected from simple considerations. In the mean circulation and synoptic activity, it appears that the Labrador Sea SST is important in determining the atmospheric response. This is probably due to enhanced temperature gradients east of New Foundland which enhances the storm activity. Received: 23 September 1998 / Accepted: 17 November 1999     

Teleconnected influence of North Atlantic sea surface temperature on the El Ni?o onset

Influence of North Atlantic sea surface temperature (SST) anomalies on tropical Pacific SST anomalies is examined. Both summer and winter North Atlantic SST anomalies are negatively related to central-eastern tropical Pacific SST anomalies in the subsequent months varying from 5 to 13?months. In particular, when the North Atlantic is colder than normal in the summer, an El Ni?o event is likely to be initiated in the subsequent spring in the tropical Pacific. Associated with summer cold North Atlantic SST anomalies is an anomalous cyclonic circulation at low-level over the North Atlantic from subsequent October to April. Corresponded to this local response, an SST-induced heating over the North Atlantic produces a teleconnected pattern, similar to the East Atlantic/West Russia teleconnection. The pattern features two anticyclonic circulations near England and Lake Baikal, and two cyclonic circulations over the North Atlantic and near the Caspian Sea. The anticyclonic circulation near Lake Baikal enhances the continent northerlies, and strengthens the East-Asian winter monsoon. These are also associated with an off-equatorial cyclonic circulation in the western Pacific during the subsequent winter and spring, which produces equatorial westerly wind anomalies in the western Pacific. The equatorial westerly wind anomalies in the winter and spring can help initiate a Pacific El Ni?o event following a cold North Atlantic in the summer.     

Comment on “application of the Canadian regional climate model to the Laurentian Great Lakes region: Implementation of a lake model”

Abstract

A recently published slab model formulation of lake thermodynamics (Goyette et al., 2000), including an empirical factor to adjust the incoming heat flux so that the modelled lake surface temperature agrees with observed climatology, leads to a distinct lack of energy conservation. The empirical adjustment conceptually represents an exchange of heat between the mixed‐layer water (the slab that is explicitly simulated in the model) and deeper layers of water. It ensures a realistic temporal progression of temperature in the mixed layer, but the thermodynamic balance of the deeper water is not considered. When the deeper water is considered, it is found that the empirical adjustment accounts for the entire heat input to the deeper water, and on an annual mean basis, it is considerably unbalanced. This reveals a flaw in this model concept and, although not entirely invalidating the model, it needs to be included as a caveat in its use.     

Temperature and precipitation responses to El Niño-Southern Oscillation in a hierarchy of datasets with different levels of observational constraints

Climate Dynamics - El Niño-Southern Oscillation (ENSO) is the dominant mode of climate variability, affecting climate conditions over large areas of the globe. There are, however, substantial...     

How the “best” CMIP5 models project relations of Asian–Pacific Oscillation to circulation backgrounds favorable for tropical cyclone genesis over the western North Pacific

Based on the simulations of 32 models from the Coupled Model Intercomparison Project Phase 5 (CMIP5), the present study assesses their capacity to simulate the relationship of the summer Asian–Pacific Oscillation (APO) with the vertical zonal wind shear, low-level atmospheric vorticity, mid-level humidity, atmospheric divergence in the lower and upper troposphere, and western Pacific subtropical high (WPSH) that are closely associated with the genesis of tropical cyclones over the western North Pacific. The results indicate that five models can simultaneously reproduce the observed pattern with the positive APO phase accompanied by weak vertical zonal wind shear, strengthened vorticity in the lower troposphere, increased mid-level humidity, intensified low-level convergence and high-level divergence, and a northward-located WPSH over the western North Pacific. These five models are further used to project their potential relationship under the RCP8.5 scenario during 2050–2099. Compared to 1950–1999, the relationship between the APO and the vertical zonal wind shear is projected to weaken by both the multi-model ensemble and the individual models. Its linkage to the low-level vorticity, mid-level humidity, atmospheric divergence in the lower and upper troposphere, and the northward–southward movement of the WPSH would also reduce slightly but still be significant. However, the individual models show relatively large differences in projecting the linkage between the APO and the mid-level humidity and low-level divergence.     

How does framing affect policy support for emissions mitigation? Testing the effects of ocean acidification and other carbon emissions frames

Public support for carbon emissions mitigation is crucial to motivate action to address global issues like climate change and ocean acidification (OA). Yet in the public sphere, carbon emissions mitigation policies are typically discussed in the context of climate change and rarely in the context of OA or other global change outcomes. In this paper, we advance research on OA and climate change perceptions and communication, by (i) examining causal beliefs about ocean acidification, and (ii) measuring support for mitigation policies from individuals presented with one of five different policy frames (climate change, global warming, carbon pollution, air pollution, and ocean acidification). Knowledge about OA causes and consequences is more widespread than we anticipated, though still generally low. Somewhat surprisingly, an “air pollution” mitigation frame elicits the highest degree of policy support overall, while “carbon pollution” performs no better than “climate change” or “global warming.” Framing effects are in part contingent on prior knowledge and attitudes, and mediated by concern. Perhaps due to a lack of OA awareness, the OA frame generates the least support overall, although it seems to close the gap in support associated with political orientation: the OA frame increases support among those (few) conservatives who report having heard of OA before the survey. These findings complement previous work on climate change communication and suggest the need for further research into OA as an effective way to engage conservatives in carbon emissions mitigation policy. Potentially even more promising is the air pollution framing.     

Domestic politics and the diffusion of international policy innovations: How does accommodation happen?

What happens to policy innovations after they have been adopted? What factors account for subsequent changes to these policies? These are the research questions guiding this study on the spread of and subsequent changes to limit values for nitrogen oxide emissions from large combustion plants. By comparing the processes of diffusion and follow-up policy changes, we assess whether and how policy innovations translate into policy making. In so doing, we build on the literature on the determinants of policy diffusion and transfer. We employ original data on instances of policy adoption and policy change in 24 Organisation for Economic Co-operation and Development (OECD) countries over a period of thirty years (1976–2005). The data are analysed using semi-parametric event-history models. Our empirical findings show that both international and domestic factors account for the observed variation in our data regarding both first-time adoptions and post-adoption modifications. The results reveal that the subsequent tightening of emission standards faces greater obstacles than their mere diffusion (i.e., policy adoption). While international factors and supranational integration appear to impede the subsequent tightening of existing policies, international peer pressure is a strong predictor of an on-going regulatory commitment. Overall, adoption and accommodation processes seem to follow distinctive patterns, suggesting that a promising strategy in policy innovation research would involve differentiation between the first-time adoption and subsequent modification of policies.