Influence Of Atlantic Multidecadal Oscillation Research Articles

Is natural variability really natural? The case of Atlantic Multidecadal Oscillation investigated by a neural network model

Is Atlantic Multidecadal Oscillation a genuine representation of natural variability in the climate system? Or perhaps is it strongly forced by external drivers? In this paper, a data-driven attribution investigation has been performed for the Atlantic Multidecadal Oscillation (AMO) behaviour in the past via a machine learning technique, NN modelling. We clearly see a forced nature of AMO in the last 150 years, with a strong contribution of the forcing coming from anthropogenic sulphates, which induces its typical oscillating behaviour. The following original application of our model to future predictions of the AMO behaviour shows that it shall probably lose its oscillating characteristic features. The only way to recover them is to consider an unrealistic increase in anthropogenic sulphates in the future under a strong mitigation scenario, and possibly a low-power solar regime. Due to the established influence of AMO on climate and meteorological phenomena in several regions of the world, our results can be important to better understand the past and envisage several future scenarios.

Trends in reconstructed monthly, seasonal and annual flows for Irish catchments (1900–2016)

Trends in reconstructed monthly, seasonal and annual flows for Irish catchments (1900–2016)

Influence of Atlantic and Pacific Sea Surface Temperatures on Heat-Related Mortality in the United States.

The frequency and magnitude of extreme summer temperature events in the United States have increased in the past few decades. Long‐term exposure to extreme summer temperatures can be detrimental to human health, due to potential risks of dehydration and thermoregulation strains on the cardiovascular system, which may often lead to heat‐related mortality (HRM). The summer climate of the United States is influenced by variability in Atlantic and Pacific sea surface temperatures, driven in part by Atlantic Multidecadal Oscillation (AMO) and El‐Nino Southern Oscillation (ENSO), respectively. However, the influence of AMO and ENSO on HRM in the United States has not been investigated. Here the longest time series of HRM spanning the past five decades is analyzed in relation with AMO and ENSO. We find that HRM doubled in the early‐1990s, coinciding with the positive phase of the AMO. Furthermore, we note a positive association between the variability in HRM and summer temperatures across all regions of the United States, with the strongest association found over the Southern United States. Therefore, this research suggests that variability in Atlantic and Pacific sea surface temperatures has both a nationwide and regional impact on HRM in the United States. Hence, by understanding variability in sea surface temperatures, the future burden of heat‐attributed emergencies during extreme summer temperature events can be reduced not only for the United States, but also worldwide.

Modulation of the Aleutian–Icelandic low seesaw and its surface impacts by the Atlantic Multidecadal Oscillation

Early studies suggested that the Aleutian–Icelandic low seesaw (AIS) features multidecadal variation. In this study, the multidecadal modulation of the AIS and associated surface climate by the Atlantic Multidecadal Oscillation (AMO) during late winter (February–March) is explored with observational data. It is shown that, in the cold phase of the AMO (AMO|−), a clear AIS is established, while this is not the case in the warm phase of the AMO (AMO|+). The surface climate over Eurasia is significantly influenced by the AMO’s modulation of the Aleutian low (AL). For example, the weak AL in AMO|− displays warmer surface temperatures over the entire Far East and along the Russian Arctic coast and into Northern Europe, but only over the Russian Far East in AMO|+. Similarly, precipitation decreases over central Europe with the weak AL in AMO|−, but decreases over northern Europe and increases over southern Europe in AMO|+. The mechanism underlying the influence of AMO|− on the AIS can be described as follows: AMO|− weakens the upward component of the Eliassen–Palm flux along the polar waveguide by reducing atmospheric blocking occurrence over the Euro–Atlantic sector, and hence drives an enhanced stratospheric polar vortex. With the intensified polar night jet, the wave trains originating over the central North Pacific can propagate horizontally through North America and extend into the North Atlantic, favoring an eastward-extended Pacific–North America–Atlantic pattern, and resulting in a significant AIS at the surface during late winter.

Combined Effect of ENSO-Like and Atlantic Multidecadal Oscillation SSTAs on the Interannual Variability of the East Asian Winter Monsoon

Using long-term observational data and numerical model experiments, this study found that the Atlantic multidecadal oscillation (AMO) affects the influence of ENSO-like sea surface temperature anomalies (SSTAs, which contain the variability of both El Niño–Southern Oscillation and Pacific decadal oscillation) on the interannual change in the East Asian winter monsoon (EAWM). In the observations, the out-of-phase relationship between the variations in ENSO and the EAWM was significantly intensified when the AMO and ENSO-like SSTAs were in phase. Warmer-than-normal winters occurred across East Asia when the ENSO-like SSTAs and AMO were positively in phase, with a significantly weakened Siberian high and anomalous anticyclones over the western North Pacific. The opposite patterns occurred under negative in-phase conditions. In contrast, when the ENSO-like and AMO SSTAs were out of phase, the anomalies related to the EAWM tended to exhibit relatively weaker features. Numerical model experiments confirmed these observational results. When the models were perturbed with warm ENSO-like SSTAs and warm AMO SSTAs, the atmosphere showed a weakened Siberian high, strong anticyclonic anomalies over the Philippine Sea, a weakened East Asian trough, and dominant positive temperature anomalies over East Asia, implying a weaker EAWM. Reverse responses to negative in-phase temperature anomalies were observed. However, the atmospheric signals that responded to the out-of-phase conditions were less robust. This phenomenon may be attributed to the superposition of the interannual variability of the EAWM caused by ENSO-like SSTAs upon the influence of AMO on background Eurasian climate and the Walker circulation response to the heating source provided by the AMO, which induced changes in ENSO-like variability through the surface wind anomalies and modulated the anomalous anticyclone/cyclone over the Philippine Sea in warm–cold ENSO-like events.

Decadal to multi-decadal scale variability of Indian summer monsoon rainfall in the coupled ocean-atmosphere-chemistry climate model SOCOL-MPIOM

The present study is an effort to deepen the understanding of Indian summer monsoon rainfall (ISMR) on decadal to multi-decadal timescales. We use ensemble simulations for the period AD 1600–2000 carried out by the coupled Atmosphere-Ocean-Chemistry-Climate Model (AOCCM) SOCOL-MPIOM. Firstly, the SOCOL-MPIOM is evaluated using observational and reanalyses datasets. The model is able to realistically simulate the ISMR as well as relevant patterns of sea surface temperature and atmospheric circulation. Further, the influence of Atlantic Multi-decadal Oscillation (AMO), Pacific Decadal Oscillation (PDO), and El Niño Southern Oscillation (ENSO) variability on ISMR is realistically simulated. Secondly, we investigate the impact of internal climate variability and external climate forcings on ISMR on decadal to multi-decadal timescales over the past 400 years. The results show that AMO, PDO, and Total Solar Irradiance (TSI) play a considerable role in controlling the wet and dry decades of ISMR. Resembling observational findings most of the dry decades of ISMR occur during a negative phase of AMO and a simultaneous positive phase of PDO. The observational and simulated datasets reveal that on decadal to multi-decadal timescales the ISMR has consistent negative correlation with PDO whereas its correlation with AMO and TSI is not stationary over time.

Atlantic multi-decadal oscillation influence on weather regimes over Europe and the Mediterranean in spring and summer

We analyze the influence of the Atlantic sea surface temperature multi-decadal variability on the day-by-day sequence of large-scale atmospheric circulation patterns (i.e. the “weather regimes”) over the Euro-Atlantic region. In particular, we examine of occurrence of weather regimes from 1871 to present. This analysis is conducted by applying a clustering technique on the daily mean sea level pressure field provided by the 20th Century Reanalysis project, which was successfully applied in other studies focused on the Atlantic Multi-decadal Oscillation (AMO). In spring and summer, results show significant changes in the frequencies of certain weather regimes associated with the phase shifts of the AMO. These changes are consistent with the seasonal surface pressure, precipitation, and temperature anomalies associated with the AMO shifts in Europe.

Evidence of Atlantic Multidecadal Oscillation in the magnetic properties of Alpine lakes during the last 2500 years

We re-analyzed rock-magnetic data of lake sediments from the Alpine region, which were previously recognized as sensitive climate proxy records, in search of decadal climate variability. Different methods of spectral analysis applied to the rock-magnetic data from two independent lake records show the presence of a coherent and statistically significant periodicity with a period of about 50–60years. The frequency-filtered signal of this component co-varies with the instrumental record of the Atlantic Multidecadal Oscillation (AMO) over the last 110years with a negligible phase shift. After having tested and ruled out the possible influence of solar irradiance in the putative AMO frequency band, based on spectral properties, we suggest that a significant influence of AMO in the Alpine region extends back in time for at least two millennia. Comparison of the amplitude of the AMO record with that of the Younger Dryas/Holocene transition suggests that AMO fluctuations played a significant role in pacing the past variability of the Alpine climate.

Estimating the coupling between variations in the atlantic multidecadal oscillation and the El Niño/Southern Oscillation

On the basis of monthly mean data obtained over a period of 1870–2013, relations between the Atlantic Multidecadal Oscillation (AMO) and the El Nino/Southern Oscillation (ENSO) have been studied using the Granger causality analysis and estimates of long-Term effects. A bidirectional relationship has been revealed in the dynamics of these processes; moreover, over the entire period as a whole, the ENSO influence on the AMO was significantly stronger than the AMO influence on the ENSO. However, a more detailed analysis has revealed the variable character of this relationship: the ENSO influence on the AMO was stronger at the beginning of the period under study, while, in recent years, the reverse influence and its increase have become more significant against the background of a decrease in the ENSO influence on the AMO.

Analysis of global and hemispheric temperature records and prognosis

Climate changes are connected to long term variations of global and hemispheric temperatures, which are important for the work out of socio-political strategy for the near future. In the paper the annual temperature time series are modeled by linear multiple regression to identify important climate forcings including external climate factors such as atmospheric CO2 content, volcanic emissions, and the total solar irradiation as well as internal factors such as El Niño-Southern oscillation, Pacific decadal oscillation and Atlantic multidecadal oscillation. Adjusted temperatures were determined by removal of all significant influences except CO2. The adjusted temperatures follow a linear dependence toward the logarithm of the CO2 content, and the coefficient of determination is about 0.91. The evolution of the adjusted temperatures suggests that the warming due to CO2 from the beginning of the studied here time interval in 1900 has never stopped and is going on up to now.The global warming rate deduced from the adjusted temperatures since 1980 is about 0.14±0.02°C/decade. The warming rate reported in the IPCC assessment report 4 based on observed global surface temperature set is about 20% higher, due to the warming by the Atlantic multidecadal oscillation additional to the anthropogenic warming.The predicted temperature evolution based on long time changes of CO2 and the Atlantic multidecadal oscillation index shows that the Northern Hemispheric temperatures are modulated by the Atlantic multidecadal oscillation influence and will not change significantly to about 2040, after that they will increase speedily, just like during the last decades of the past century. The temperatures of the Southern Hemisphere will increase almost linearly and don’t show significant periodic changes due to Atlantic multidecadal oscillation. The concrete warming rates of course are strongly depending on the future atmospheric CO2 content.

Individual and coupled influences of AMO and ENSO on regional precipitation characteristics and extremes

AbstractUnderstanding the influences of Atlantic multidecadal oscillation (AMO) and El Niño southern oscillation (ENSO) on regional precipitation extremes and characteristics in the state of Florida is the focus of this study. Exhaustive evaluations of individual and combined influences of these oscillations using, descriptive indices‐based assessment of statistically significant changes in rainfall characteristics, identification of spatially varying influences of oscillations on dry and wet spell transition states, antecedent precipitation prior to extreme events, intraevent temporal distribution of precipitation and changes in temporal occurrences of extremes including dry/wet cycles are carried out. Rain gage and gridded precipitation data analysis using parametric hypothesis tests confirm statistically significant changes in the precipitation characteristics from one phase to another of each oscillation and also in coupled phases. Spatially nonuniform and uniform influences of AMO and ENSO, respectively, on precipitation are evident. AMO influences vary in peninsular and continental parts of Florida and the warm (cool) phase of AMO contributes to increased precipitation extremes during wet (dry) season. The influence of ENSO is confined to dry season with El Niño (La Niña) contributing to increase (decrease) in extremes and total precipitation. Wetter antecedent conditions preceding daily extremes are dominant in AMO warm phase compared to the cool and are likely to impact design floods in the region. AMO influence on dry season precipitation extremes is noted for ENSO neutral years. The two oscillations in different phases modulate each other with seasonal and spatially varying impacts and implications on flood control and water supply in the region.

Key role of the Atlantic Multidecadal Oscillation in 20th century drought and wet periods over the Great Plains

[1] The Great Plains of North America are susceptible to multi-year droughts, such as the 1930s ‘Dust Bowl’. The droughts have been linked to SST variability in the Pacific and Atlantic basins. This observationally rooted analysis shows the SST influence in multi-year droughts and wet episodes over the Great Plains to be significantly more extensive than previously indicated. The remarkable statistical reconstruction of the major hydroclimate episodes attests to the extent of the SST influence in nature, and facilitated evaluation of the basin contributions. We find the Atlantic SSTs to be especially influential in forcing multi-year droughts; often, more than the Pacific ones. The Atlantic Multidecadal Oscillation (AMO), in particular, contributed the most in two of the four reconstructed episodes (Dust Bowl Spring, 1980s fall wetness), accounting for almost half the precipitation signal in each case. The AMO influence on continental precipitation was provided circulation context from analysis of NOAA's 20th Century Atmospheric Reanalysis. A hypothesis for how the AMO atmospheric circulation anomalies are generated from AMO SSTs is proposed to advance discussion of the influence pathways of the mid-to-high latitude SST anomalies. Our analysis suggests that the La Nina–US Drought paradigm, operative on interannual time scales, has been conferred excessive relevance on decadal time scales in the recent literature.

Multidecadal Climate Variability in Observed and Modeled Surface Temperatures*

AbstractThis study identifies interdecadal natural climate variability in global surface temperatures by subtracting, from the observed temperature evolution, multimodel ensemble mean based on the World Climate Research Programme's (WCRP) Coupled Model Intercomparison Project phase 3 (CMIP3) multimodel dataset. The resulting signal resembles the so-called Atlantic multidecadal oscillation (AMO) and is presumably associated with intrinsic dynamics of the oceanic thermohaline circulation (THC). While certain phases of the oscillation are dominated by the anomalies in the North Atlantic region, other phases are characterized by global teleconnections to the North Pacific Ocean, tropical Atlantic Ocean, as well as the Southern Ocean. In particular, natural variability of sea surface temperature in the Atlantic hurricanes’ main development region has a peak-to-peak amplitude comparable in magnitude to this region’s surface temperature increase over the past century, for all seasons. Evidence suggests that the AMO influence on secular trends in the global-mean surface temperature can arise via direct, regional contribution to the surface temperature evolution, as well as via an indirect route linked to variability of the oceanic uptake of CO2 associated with AMO-related THC changes.

The Atlantic Meridional Mode and hurricane activity

Connections between the Atlantic Meridional Mode (AMM) and seasonal hurricane activity are investigated. The AMM, a dynamical “mode” of variability intrinsic to the tropical coupled ocean‐atmosphere system, is strongly related to seasonal hurricane activity on both decadal and interannual time scales. The connection arises due to the AMM's relationship with a number of local climatic conditions that all cooperate in their influence on hurricane activity. Further analysis indicates that the Atlantic Multi‐decadal Oscillation (AMO) can excite the AMM on decadal time scales. As such, it is suggested that the AMO's influence on seasonal hurricane activity manifests itself through the AMM. This relationship between the AMM, AMO, and seasonal hurricane activity refocuses our understanding of how climate variations relate to seasonal hurricane activity in the Atlantic, and offers an improved framework beyond purely thermodynamic arguments that relates hurricanes to large‐scale climate variations.

Regional relationships between climate and wildfire-burned area in the Interior West, USA

Recent studies have linked the Atlantic Multidecadal Oscillation (AMO) and the Pacific Decadal Oscillation (PDO) with drought occurrence in the interior United States. This study evaluates the influence of AMO and PDO phases on interannual relationships between climate and wildfire-burned area during the 20th century. Palmer's Drought Severity Index (PDSI) is strongly related to burned area at both regional and subregional scales. In the southern Interior West, PDSI is most strongly related to yearly burned area during warm-phase AMO, while for the same period no significant relationships exist between PDSI and burned area in the central Interior West. During cool-phase PDO, interannual climate has little influence on burned area in either the northern or the central Interior West. The opposite is true for the southern Interior West and the eastern slope of the Colorado Rockies using the Southern Oscillation Index and PDSI, respectively. The western slope of the Colorado Rockies is the only climate division or region in which burned area is not related to preceding PDSI. During warm-phase PDO, current PDSI explains 67% of the interannual variance in burned area on the western slope. These regional and temporal differences are most likely governed by variations in fuel dynamics associated with dominant regional and subregional vegetation types.