Northern Atlantic Oscillation Research Articles

Changing seasonality of daily and monthly precipitation extremes for the contiguous USA and possible connections with large‐scale climate patterns

AbstractTemporal changes in the seasonality of extreme precipitation, and possible teleconnections between the seasonality of extreme precipitation and large‐scale climate patterns are not well understood. In this study, we investigated temporal changes in seasonality of annual daily maximum (ADM) and monthly maximum (MM) precipitation indices over the period 1951–2014 for 1,108 stations across the contiguous USA. We also examined seasonality of extreme precipitation during negative and positive phases of three major oscillations: the El Niño–Southern Oscillation, the Northern Atlantic Oscillation, and the Pacific Decadal Oscillation. Our results show that many climate regions within the contiguous USA display distinct seasonality for both ADM and MM. Comparison of seasonality between two historical records of equal length, that is, before and after 1981, shows great spatial variability across the contiguous USA. While a spatial coherence of change in the mean date of occurrence of extreme precipitation across a large area is not visible, a cluster of stations showing decrease in strength of seasonality for the recent period is concentrated in the eastern Gulf Coast and coastal sites of Northeast and Northwest regions. Extreme precipitation seasonality during negative and positive phases of three climate indices revealed that large‐scale climate variabilities have a strong influence on the mean date of occurrence of extreme precipitation but generally weak influence on the strength of seasonality in the contiguous USA. Results from our study might be helpful for sustainable water resource management, flood risk mitigation, and prediction of future precipitation seasonality.

Influence of the North American Dipole on ENSO onset as simulated by a coupled ocean–Atmosphere model

The North American Dipole (NAD) is a north–south seesaw pattern of sea level pressure anomalies over the western tropical North Atlantic and northeastern North America. Previous observational studies have demonstrated that the NAD can affect the outbreak of El Niño–Southern Oscillation (ENSO) events. The present study analyzed the NAD–ENSO relationship as simulated by a coupled ocean–atmosphere model—namely, the Flexible Global Ocean–Atmosphere–Land System model, gridpoint version 2 (FGOALS-g2). Results indicated that the model can replicate a distinct dipole comprised of a low over northeastern North America and a high over the western tropical North Atlantic, which is the signature feature of the NAD. Further analysis verified that the winter NAD can initiate the central equatorial Pacific warming in the subsequent winter by effectively forcing an anticyclonic flow and sea surface temperature (SST) warming over the northeastern subtropical Pacific (NESP) during late winter or early spring. In addition, the probability of an El Niño event was increased by a factor of 1.8 in the assimilation experiment with the NAD. By comparison, the winter Northern Atlantic Oscillation had no significant impact on the occurrence of ENSO a year later owing to its failure to induce the SST and surface wind anomalies over the NESP.摘要北美偶极子(NAD)是热带北大西洋西部和北美东北部的南北向海平面气压异常偶极型模态.以往的观测研究表明, NAD可以有效地影响ENSO事件的爆发. 本文利用全球耦合模式FGOALS-g2, 评估了NAD与ENSO的关系. 结果表明, 该模式能较好地重现NAD模态. 进一步的分析验证了冬季NAD可以通过强迫冬末春初副热带东北太平洋上空的反气旋和暖海温的出现, 在随后的冬季触发El Niño事件. 此外, 在同化NAD实验中, 发生El Niño事件的概率增加了将近一倍. 相比之下, NAO未能在副热带东北太平洋上空引起表面风和海温的异常, 因而不能有效地激发次年冬季ENSO事件.

Biogeographic, Atmospheric, and Climatic Factors Influencing Tree Growth in Mediterranean Aleppo Pine Forests

There is a lack of knowledge on how tree species respond to climatic constraints like water shortages and related atmospheric patterns across broad spatial and temporal scales. These assessments are needed to project which populations will better tolerate or respond to global warming across the tree species distribution range. Warmer and drier conditions have been forecasted for the Mediterranean Basin, where Aleppo pine (Pinus halepensis Mill.) is the most widely distributed conifer in dry sites. This species shows plastic growth responses to climate, being particularly sensitive to drought. We evaluated how 32 Aleppo pine forests responded to climate during the second half of the 20th century by using dendrochronology. Climatic constraints of radial growth were inferred by fitting the Vaganov–Shashkin (VS-Lite) growth model to ring-width data from our Aleppo pine forest network. Our findings reported that Aleppo pine growth decreased and showed the highest common coherence among trees in dry, continental sites located in southeastern and eastern inland Spain and Algeria. In contrast, growth increased in wetter sites located in northeastern Spain. Overall, across the Aleppo pine network tree growth was enhanced by prior wet winters and cool and wet springs, whilst warm summers were associated with less growth. The relationships between site ring-width chronologies were higher in nearby forests. This explains why Aleppo pine growth was distinctly linked to indices of atmospheric circulation patterns depending on the geographical location of the forests. The western forests were more influenced by moisture and temperature conditions driven by the Western Mediterranean Oscillation (WeMO) and the Northern Atlantic Oscillation (NAO), the southern forests by the East Atlantic (EA) and the august NAO, while the Balearic, Tunisian and northeastern sites by the Arctic Oscillation (AO) and the Scandinavian pattern (SCA). The climatic constraints for Aleppo pine tree growth and its biogeographical variability were well captured by the VS-Lite model. The model performed better in dry and continental sites, showing strong growth coherence between trees and climatic limitations of growth. Further research using similar broad-scale approaches to climate–growth relationships in drought-prone regions deserves more attention.

Climatic variation in Africa and Europe has combined effects on timing of spring migration in a long-distance migrant Willow Warbler Phylloscopus trochilus.

BackgroundThe arrival of many species of migrant passerine in the European spring has shifted earlier over recent decades, attributed to climate change and rising temperatures in Europe and west Africa. Few studies have shown the effects of climate change in both hemispheres though many long-distance migrants use wintering grounds which span Africa. The migrants’ arrival in Europe thus potentially reflects a combination of the conditions they experience across Africa. We examine if the timing of spring migration of a long-distance migrant, the Willow Warbler, is related to large-scale climate indices across Africa and Europe.MethodsUsing data from daily mistnetting from 1 April to 15 May in 1982–2017 at Bukowo (Poland, Baltic Sea coast), we developed an Annual Anomaly metric (AA, in days) to estimate how early or late Willow Warblers arrive each spring in relation to their multi-year average pattern. The Willow Warblers’ spring passage advanced by 5.4 days over the 36 years. We modelled AA using 14 potential explanatory variables in multiple regression models. The variables were the calendar year and 13 large-scale indices of climate in Africa and Europe averaged over biologically meaningful periods of two to four months during the year before spring migration.ResultsThe best model explained 59% of the variation in AA with seven variables: Northern Atlantic Oscillation (two periods), Indian Ocean Dipole, Southern Oscillation Index, Sahel Precipitation Anomaly, Scandinavian Index and local mean temperatures. The study also confirmed that a long-term trend for Willow Warblers to arrive earlier in spring continued up to 2017.DiscussionOur results suggest that the timing of Willow Warbler spring migration at the Baltic Sea coast is related to a summation of the ecological conditions they had encountered over the previous year during breeding, migration south, wintering in Africa and migration north. We suggest these large-scale climate indices reflect ecological drivers for phenological changes in species with complex migration patterns and discuss the ways in which each of the seven climate indices could be related to spring migration at the Baltic Sea coast.

Cohort antler size signals environmental stress in a moderate climate.

Research in northern latitudes confirms that climate teleconnections exert important influences on ungulate fitness, but studies from regions with milder climates are lacking. We explored the influence of the Pacific Decadal Oscillation (PDO), Northern Atlantic Oscillation (NAO), and El Niño-Southern Oscillation (ENSO) on male, 2.5-year-old white-tailed deer (Odocoileus virginianus) antler and body mass in Mississippi, USA, a region with mild winters and warm, humid summers. Explanatory variables were seasonal averages of each climate index extending back to 3years prior to account for possible maternal and lag effects. Seasonal climate indices from the period of gestation and the first year of life were correlated with deer morphometrics. Reduced antler mass was largely correlated (R2 = 0.52) with PDO values indicating dry conditions during parturition and neonatal development and NAO values indicating warmer than normal winters during gestation and the first year of life. Body mass was less correlated (R2 = 0.16) to climate indices, responding negatively to warmer winter weather during the first winter of life. Climate may promote variable fitness among cohorts through long-term effects on male competition for dominance and breeding access. Because broad-scale climate indices simplify complex weather systems, they may benefit management at larger scales. Although this study compared climate with morphological variables, it is likely that demographic characteristics can likewise be modeled using climate indices. As climate change in this region is projected to include greater variability in summer precipitation, we may see concomitantly greater variability in fitness among cohorts of white-tailed deer.

Solar cycle modulation of the relationship between the boreal spring Northern Atlantic Oscillation and the East and Southeast Asian summer climate

Previous studies have suggested that boreal spring Northern Atlantic Oscillations (NAOs) exert a pronounced influence on the following East Asian summer monsoon (EASM) variability. This study reveals that the relationship between the spring NAO and the following EASM varies with the 11-year solar cycle. The analysis of the time–lag relationship between the NAO in May and the following summer rainfall indicates that during the low solar activity (LS) summers, a more robust relationship is established, with below-normal rainfall anomalies in South China and the Sunda Islands in relation to a positive NAO. In addition, the May NAO-related atmospheric circulation anomalies during boreal summer over East and Southeast Asia may well explain the distinct rainfall difference. The possible mechanism for this solar modulation is attributed to the changes in structure of the spring NAO and associated tripole SST anomalies in the North Atlantic. Specifically, in the LS phase, the North Atlantic tripole SST anomalies associated with the May NAO can strongly develop and persist into the early summer. These SST anomalies tend to induce a remarkable subpolar wave train across the northern Eurasian continent and an enhanced East Asian jet in the summer. Our results indicate that, for the summer climate prediction over East and Southeast Asia, both the spring NAO and the 11-year solar cycle should be considered.

Nonstationary warm spell frequency analysis integrating climate variability and change with application to the Middle East

The Middle East can experience extended wintertime spells of exceptionally hot weather, which can result in prolonged droughts and have major impacts on the already scarce water resources of the region. Recent observational studies point at increasing trends in mean and extreme temperatures in the Middle East, while climate projections seem to indicate that, in a warming weather scenario, the frequency, intensity and duration of warm spells will increase. The nonstationary warm spell frequency analysis approach proposed herein allows considering both climate variability through global climatic oscillations and climate change signals. In this study, statistical distributions with parameters conditional on covariates representing time, to account for temporal trend, and climate indices are used to predict the frequency, duration and intensity of wintertime warm spells in the Middle East. Such models could find a large applicability in various fields of climate research, and in particular in the seasonal prediction of warm spell severity. Based on previous studies linking atmospheric circulation patterns in the Atlantic to extreme temperatures in the Middle East, we use as covariates two classic modes of ‘fast’ and ‘slow’ climatic variability in the Atlantic Ocean (i.e., the Northern Atlantic Oscillation and the Atlantic Multidecadal Oscillation respectively). Results indicate that the use of covariates improves the goodness-of-fit of models for all warm spell characteristics.

Vb Cyclones Synchronized With the Arctic-/North Atlantic Oscillation.

Vb cyclones typically emerge in the Western Mediterranean and propagate to the Northeast into Central Europe. This paper explores the temporal characteristics of Vb cyclone occurrence based on cyclone tracks identified at the atmospheric levels of Z700 and sea level pressure, using JRA‐55 reanalysis data for the period 1959–2015. The risk of Vb occurrence was significantly high in the 1960s and has remained at a lower level since then. Vb cyclones do not occur fully randomly according to a Poisson point process. Eleven well‐separated and distinct clusters as well as 11 hiatus periods are identified, with average occurrence rates of 21.5 and 5.2 yrea−1, respectively. During the event of Vb, the large‐scale atmospheric circulation is changed into a state favoring the development of successive Vb cyclones. Clustering is very prominent in the case of Genoan Vb cyclones in summer as well as those Vb cyclones developing over the Iberian Peninsula or the North African Coast in winter. Superposition of the polar and the subtropical jet stream over the Western Mediterranean is identified as a main feature at the onset of Vb cyclones. Vb cyclone occurrence appears to be synchronized with the Northern Atlantic Oscillation (NAO; at Z500) and Arctic Oscillation (AO; at Z1000). Clusters have occurred when both NAO and AO were negative. This relation applies to Western Mediterranean cyclones not following a Vb track as well, however to a much weaker extent. In contrast, Vb cyclone frequency was particularly low from 1988 to 1997 during a sustained positive phase of both NAO and AO.

Study of sardine (Sardina pilchardus) regime shifts in the Iberian Atlantic shelf waters

AbstractSardine fisheries in the Iberian Atlantic shelf (36°N–44.5°N) show decadal‐scale cycles. In the late 1990s, a positive phase in sardine stock was expected; on the contrary, catches have declined until now. Regime shifts in climatic and oceanographic variables on different scales (as forcing factor) and shifts in sardine stock (as result) have been used with the aim of identifying the physical variables that explain most of the sardine population variance in the region. Circa 1998, when last sardine regime shift was detected, the main patterns of large‐scale atmospheric circulation in the Northern Hemisphere with influence in the study area namely Northern Atlantic Oscillation (NAO) and East Atlantic (EA) pattern changed and coupled in a combination that led to a rise in sea surface temperature and a decline in the coastal upwelling intensity. Several years with a downwelling situation in average in the main spawning and feeding Iberian sardine areas would have affected the stock abundance, averting the return to the projected positive regime. The sardine negative regime shift was detected first in the regions of the study located further north. The regional variable latent heat flux that groups a set of environmental processes related to the ocean–atmosphere heat exchanges and so with the turbulence manages to explain the 72% of sardine recruitment.

Association between the interannual variation in the oceanic environment and catch rates of bigeye tuna (Thunnus obesus) in the Atlantic Ocean

AbstractThe environmental processes associated with variability in the catch rates of bigeye tuna in the Atlantic Ocean are largely unexplored. This study used generalized additive models (GAMs) fitted to Taiwanese longline fishery data from 1990 to 2009 and investigated the association between environmental variables and catch rates to identify the processes influencing bigeye tuna distribution in the Atlantic Ocean. The present findings reveal that the year (temporal factor), latitude and longitude (spatial factors), and major regular longline target species of albacore catches are significant for the standardization of bigeye tuna catch rates in the Atlantic Ocean. The standardized catch rates and distribution of bigeye tuna were found to be related to environmental and climatic variation. The model selection processes showed that the selected GAMs explained 70% of the cumulative deviance in the entire Atlantic Ocean. Regarding environmental factors, the depth of the 20 degree isotherm (D20) substantially contributed to the explained deviance; other important factors were sea surface temperature (SST) and sea surface height deviation (SSHD). The potential fishing grounds were observed with SSTs of 22–28°C, a D20 shallower than 150 m and negative SSHDs in the Atlantic Ocean. The higher predicted catch rates were increased in the positive northern tropical Atlantic and negative North Atlantic Oscillation events with a higher SST and shallow D20, suggesting that climatic oscillations affect the population abundance and distribution of bigeye tuna.

The Little Ice Age was 1.0–1.5 °C cooler than current warm period according to LOD and NAO

We study the yearly values of the length of day (LOD, 1623-2016) and its link to the zonal index (ZI, 1873-2003), the Northern Atlantic oscillation index (NAO, 1659-2000) and the global sea surface temperature (SST, 1850-2016). LOD is herein assumed to be mostly the result of the overall circulations occurring within the ocean-atmospheric system. We find that LOD is negatively correlated with the global SST and with both the integral function of ZI and NAO, which are labeled as IZI and INAO. A first result is that LOD must be driven by a climatic change induced by an external (e.g. solar/astronomical) forcing since internal variability alone would have likely induced a positive correlation among the same variables because of the conservation of the Earth's angular momentum. A second result is that the high correlation among the variables implies that the LOD and INAO records can be adopted as global proxies to reconstruct past climate change. Tentative global SST reconstructions since the 17th century suggest that around 1700, that is during the coolest period of the Little Ice Age (LIA), SST could have been about 1.0-1.5 {\deg}C cooler than the 1950-1980 period. This estimated LIA cooling is greater than what some multiproxy global climate reconstructions suggested, but it is in good agreement with other more recent climate reconstructions including those based on borehole temperature data.

Climatic and atmospheric indices teleconnection impact on the characteristics of frost season in western Iran

Abstract The large-scale variability of atmospheric and ocean circulation patterns cause seasonal climate changes in the Earth. In other words, climate elements are affected by phenomena like El Niño Southern Oscillation (ENSO), El Niño (NINO), and Northern Atlantic Oscillation (NAO). In this study the characteristics of the frost season over a 20-year period (1996–2015) from seven synoptic stations in western Iran were evaluated using support vector machine and random forest regression. Comparing determination coefficients obtained by these models between atmospheric and ocean circulation indices and the characteristics of the frost season showed a positive effect. Thus, the onset and the end of the frost season in this region were highly correlated with the Southern Oscillation Index (SOI) and NAO, respectively. In regions with lower correlations (central areas and some regions of Alvand Mountain), the role of the geographical factors, altitude and topography becomes more pronounced and the impact of the global indices is reduced. Cluster analysis was also conducted to detect patterns and to identify regions according to the effect of the atmospheric and oceanic indices on frost season, and three regions were identified. The largest correlations with global indices (in both models) belonged to the first and third classes, respectively. The results of this study could be applied for planning environmental and agricultural activities.

Inter-annual and decadal changes in teleconnections drive continental-scale synchronization of tree reproduction

Climate teleconnections drive highly variable and synchronous seed production (masting) over large scales. Disentangling the effect of high-frequency (inter-annual variation) from low-frequency (decadal trends) components of climate oscillations will improve our understanding of masting as an ecosystem process. Using century-long observations on masting (the MASTREE database) and data on the Northern Atlantic Oscillation (NAO), we show that in the last 60 years both high-frequency summer and spring NAO, and low-frequency winter NAO components are highly correlated to continent-wide masting in European beech and Norway spruce. Relationships are weaker (non-stationary) in the early twentieth century. This finding improves our understanding on how climate variation affects large-scale synchronization of tree masting. Moreover, it supports the connection between proximate and ultimate causes of masting: indeed, large-scale features of atmospheric circulation coherently drive cues and resources for masting, as well as its evolutionary drivers, such as pollination efficiency, abundance of seed dispersers, and natural disturbance regimes.

Factors affecting cone production in Pinus pinaster Ait.: lack of growth-reproduction trade-offs but significant effects of climate and tree and stand characteristics

Aim of study: Our main goal is to determine the relationship between cone production and radial growth in Pinus pinaster Ait. under different climatic conditions across the Iberian Peninsula.Area of study: Coca Intensive Sampling Plateau, Northern Plateau (Spain).Material and methods: Cone counts were conducted on an intensive monitoring plot in Coca (North-Central Spain) during the years 2000, 2006 and 2007. A ZIP (zero-inflated Poisson) model was adjusted for simultaneously estimating the probability of obtaining crop cones and its amount. The Northern Atlantic Oscillation (NAO) index was used as explanatory variable, together with a wide variety of tree and local stand variables. Climate (as evaluated by NAO), local stand density (here estimated from the six nearest trees), tree size and vigor, competition and growth efficiency significantly influenced both occurrence and intensity of cone production.Main results: ZIP models for predicting reproductive effort seems an adequate tool to predict reproductive responses to climatic fluctuations and the resulting future species distribution in the face of climate change, as well as to identify silviculture actions that would promote reproductive success in naturally-regenerated stands, list and discuss relevant results (including numeric values of experimental results).Research highlights: Climate, stand density and tree conditions (size and vigor, competition and growth efficiency) influence significantly both cone occurrence and intensity of fruiting as shown by a ZIP model. As the climate variables included in the model (based on Northern Atlantic Oscillation, NAO) are general and easily obtained, the proposed model has practical applicability to predicting Pinus pinaster cone production in the Iberian Peninsula.

A tentative study of the relationship between annual δ18O & δD variations of precipitation and atmospheric circulations—A case from Southwest China

In this study, we present the 6-year δ18O and δD records of precipitation from Chongqing, southwest China. Based on these data, the local meteoric water line (LMWL) has been set up as: δD = 8.33δ18O+19.42. It is demonstrated that in El Niño scenarios, more vapor from closer moisture source (Western Pacific) was transported to south China, resulted in heavier stable isotopes of precipitation in southwest China, while in La Niña scenarios, the situations were just on the contrary. In addition, there is a positive correlation between the δ18O of precipitation in southwest China and the Northern Atlantic Oscillation Index (NAOI) when the NAO is in the positive phase (typically in boreal winter-half year). At the interannual timescale, the δ18O of precipitation in southwest China is more negative in strong NAO years than that in weak NAO years. We speculate that the north-south position migration of the westerlies and the route changes of vapor transport are correlated with the δ18O changes of precipitation in southwest China under the climate change scenario around the North Atlantic.

The relationship between wintertime extreme temperature events north of 60°N and large‐scale atmospheric circulations

ABSTRACTThe increased extreme warm and decreased extreme cold temperature events across the Arctic strongly influence the natural environment as well as the societal activities. This study investigates temporal and spatial variability of wintertime extreme high and low temperature events defined by the 95 and 5% percentiles across the Arctic and subarctic regions, respectively (north of 60°N) using data from 238 stations in the Global Summary of the Day for the period 1979–2016. Empirical orthogonal function analyses indicate that the first modes (which account for 30–35% of the total variance) are out‐of‐phase between northern Europe, western and central Russia, and northeastern North America, and that this appears to be related to the Arctic Oscillation (AO) and the Northern Atlantic Oscillation. The second modes explain about 8% of the total variance. During the positive phase of the first and second modes the anomalous northeasterly and northerly winds decrease Arctic extreme high and increase extreme low temperature occurrences; while the anomalous southerly and southwesterly winds have the opposite effect. Symmetric and asymmetric effects of the AO index on extreme temperature events refer to the difference and sum between the composite of its positive and negative phases. The symmetric components of the spatial patterns are similar to those of the first modes. The asymmetric components occur mainly over western and central Russia for extreme high and low temperatures, respectively. In addition the impacts of six other large‐scale climate modes are also explored.

Impact assessment of non-indigenous jellyfish species on the estuarine community dynamic: A model of medusa phase

Non-indigenous jellyfish species (NIJS) Blackforida virginica have recently been introduced to the Guadiana Estuary. A modelling approach was used for the assessment of the species-specific impact on the native community, during the medusa phase. The novel interactions between NIJS and the native community are assessed through biomass variation including hydrodynamic and climatic variables. Sensitivity analysis shows that both native species, as well as NIJS highly depend on the water discharge regime, nutrient contribution and the amount of detritus production. Abiotic factors such as the Northern Atlantic Oscillation, water discharge, nutrient load and detritus production are the most influential factors for the dynamics of the estuarine ecosystem demonstrated by the model. Low water discharge and low nutrient retention rate appear to be the most favourable conditions for B. virginica. The species is a non-selective predator able to integrate into the system effectively and has caused a decrease in the biomass of other organisms in the estuarine ecosystem throughout the summer after dam removal. The B. virginica significant impact can be evaluated only when the jellyfish detritus food pathway is involved. The B. virginica predatory impact potential, as well as food preference, appears to be the most influential factors for the overall biomass variation. On the contrary, winter freshwater pulses reduce the survival rate of jellyfish polyps which results in a decrease of medusa during summer. The model presents a strong ecohydrology movement where the fluctuation of organism biomass strongly depends on the hydrological conditions including the amount of nutrient load.

Transient deformation of karst aquifers due to seasonal and multiyear groundwater variations observed by GPS in southern Apennines (Italy)

AbstractWe present GPS, hydrological, and GRACE (Gravity Recovery and Climate Experiment) observations in southern Apennines (Italy) pointing to a previously unnoticed response of the solid Earth to hydrological processes. Transient patterns in GPS horizontal time series near to large karst aquifers are controlled by seasonal and interannual phases of groundwater recharge/discharge of karst aquifers, modulating the extensional ∼3 mm/yr strain within the tectonically active Apennines. We suggest that transient signals are produced, below the saturation level of the aquifers and above a poorly constrained depth in the shallow crust, by time‐dependent opening of subvertical, fluid‐filled, conductive fractures. We ascribe this process to the immature karstification and intense tectonic fracturing, favoring slow groundwater circulation, and to multiyear variations of the water table elevation, influenced by variable seasonal recharge. The vertical component displays seasonal and multiyear signals more homogeneously distributed in space and closely correlated with estimates of total water storage from GRACE, reflecting the elastic response of the lithosphere to variations of surface water loads. The different sensitivities of vertical and horizontal components to the hydrologically induced deformation processes allow us to spatially and temporally resolve the different phases of the water cycle, from maximum hydrological loading at the surface to maximum hydrostatic pressure beneath karst aquifers. Finally, we suggest that transient deformation signals in the geodetic series of the Apennines are correlated to large‐scale climatic patterns (Northern Atlantic Oscillation) through their influence on precipitation variability and trends at the regional scale.

Variations in annual accumulation recorded in a Laohugou ice core from the northeastern Tibetan Plateau and their relationship with atmospheric circulation

Annual accumulation was reconstructed for a period from 1960 to 2006 using a 21.2-m ice core from the firn basin of Laohugou (LHG) Glacier No. 12 on the northeastern Tibetan Plateau (TP). Significant periodicity of LHG accumulation variations was identified as a quasi-3-year period in accordance with the oscillation of precipitation in the northwestern China, especially the Hexi Corridor. Furthermore, the relationships of LHG accumulation with atmospheric circulation and moisture sources were investigated. LHG accumulation was positively correlated with the 500-hPa geopotential height and pressure in Central Asia, as well as the autumn Northern Atlantic Oscillation, suggesting that the Westerlies may transport moisture to the LHG region and enhance precipitation. In addition, a negative relationship between LHG accumulation and meridional wind indicated that an intense Mongolian cyclone caused by a strong meridional wind in the region could block Arctic air masses from the LHG region. Moisture fluxes and backward air mass trajectories suggested that moisture might originate from Central Asia, Southern and the inland TP. The relationship between LHG accumulation and atmospheric circulation provides an opportunity to reconstruct the history of atmospheric circulation using a deep ice core record.

Atmospheric circulation in northern hemisphere and north atlantic oscillation

Conditions under which statistical connections of interannual changes of repitition duration periods in Northern hemisphere of elementary circulation mechanisms associated to meridional northern and meridional southern groups with variations of North Atlantic oscillation are significant were revealed. It is shown, that the characteristics changes of these connections taking place in modern period can be caused by distribution changes of distribution of sea surface temperatures