Summer North Atlantic Oscillation Research Articles

Long-term relationships between summer clouds and aerosols over mid-high latitudes of the Northern Hemisphere

While the short-term relationship between clouds and aerosols is well known, no adequate data is available to verify the longer-term, annual to decadal, relationship. It is important to quantify the aerosol–cloud interaction (ACI) for mitigating uncertainty in climate prediction. Here the long-term ACI over the mid-to-high latitudes of the Northern Hemisphere was analyzed by using seasonally-resolved ion fluxes reconstructed from a southeastern Greenland ice core (SE-Dome ice core) as aerosol proxies, and satellite-based summer cloud amount between 1982 and 2014. As a result, SO42− flux in the ice core shows significant positive correlation with total cloud amounts (CCT\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${CC}_{T}$$\\end{document}) and cloud droplet concentration (Nd\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${N}_{d}$$\\end{document}) in the summer over the southeastern Greenland Sea, implying that the sulfate aerosols may contribute to the variability of CCT\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${CC}_{T}$$\\end{document} via microphysical cloud processes. Significant positive correlations are persistent even under the constrained conditions when cloud formation factors such as relative humidity, air temperature at cloud height, and summer North Atlantic Oscillation are limited within ± 1σ variability. Hence sulfate aerosols should control the interannual variability of summer CCT\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${CC}_{T}$$\\end{document} In terms of decadal changes, CCT\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${CC}_{T}$$\\end{document} was approximately 3–5% higher in the 1960s–1970s than in the 1990s–2000s, which can be explained by changes in the, SO42-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{{\ ext{SO}}}_{4}}^{2-}$$\\end{document} flux preserved in the SE-Dome ice core.

A regional attentive empirical orthogonal function analysis: An application to North Atlantic Oscillation

AbstractEmpirical orthogonal function (EOF) analysis is widely adopted for identifying spatial patterns in regular latitude‐longitude gridded geographical data. However, a standard EOF analysis could underestimate variances from low latitudes due to the increasing grid cell areas when moving toward the equator. A broadly adopted compensating approach is the area‐weighted EOF, where the grid data are multiplied by a factor proportional to the grid area, thereby forcing each datum to represent identical areas. In this article, we revisit the area‐weighting scheme and discuss its potential drawbacks. In particular, we show that along with compensating the unequal areas, another unaddressed issue is which region of the data is more relevant to our focused problem. We propose a regional attentive EOF (RA‐EOF) method, which resolves area‐compensation and region selection simultaneously. We conduct case studies of the North Atlantic Oscillation (NAO) analysis and perform RA‐EOF to the sea level pressure variability in the North Atlantic sector. Experiments show that our method evidently detects the NAO pattern in the leading mode of sea level pressure variability and suggests the southwestward movement of the southern action centre of NAO during the summers. Our findings clarify the ambiguity about the summer NAO in previous studies. The proposed methodology provides a potent instrument for discerning the spatial distribution and analysing the temporal variability of atmospheric teleconnections and oscillations, particularly in cases characterized by weak signal strength.

Evaluation of Summer Non‐Uniform Multidecadal Temperature Variations Over Eurasia in CMIP6 Models

AbstractThe summer surface air temperatures (SAT) over Eurasia exhibit a non‐uniform multidecadal pattern since the 1990s, with amplified warming over Europe–West Asia (EWA) and Northeast Asia (NEA) but weak warming over Central Asia. However, current climate models may inadequately capture this regional pattern. In this study, we evaluated the performance of 44 coupled models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) in simulating the decadal variability of Eurasian temperatures. Results show that all the CMIP6 models generally reproduce the largest SAT trends from 1985 to 2020 over EWA and NEA. However, the models fail to capture the non‐uniform warming pattern and the SAT magnitudes are underestimated in most CMIP6 models. We compare “good” and “poor” ensemble, which represent the best and worst simulations of the non‐uniform warming, in order to understand the inter‐model spread. The BMME models capture the teleconnection wave trains from northwest Europe to East Asia, and the associated summer North Atlantic Oscillation like circulation changes. In contrast, the WMME models fail to reproduce such teleconnections. The contrast between the BMME and WMME simulations give a measure of confidence that the non‐uniform warming pattern over Eurasia is tightly coupled with the upper‐tropospheric wave‐like pattern over Eurasia. If such atmospheric circulation changes cannot be reproduced, the non‐uniform warming pattern over Eurasia will not be captured. Our results suggest a fundamental pattern of atmospheric circulation changes that determine the non‐uniform warming variations in model simulations.

Skilful predictions of the Summer North Atlantic Oscillation

The Summer North Atlantic Oscillation is the primary mode of atmospheric variability in the North Atlantic region and has a significant influence on regional European, North American and Asian summer climate. However, current dynamical seasonal prediction systems show no significant Summer North Atlantic Oscillation prediction skill, leaving society ill-prepared for extreme summers. Here we show an unexpected role for the stratosphere in driving the Summer North Atlantic Oscillation in both observations and climate prediction systems. The anomalous strength of the lower stratosphere polar vortex in late spring is found to propagate downwards and influence the Summer North Atlantic Oscillation. Windows of opportunity are identified for useful levels of Summer North Atlantic Oscillation prediction skill, both in the 50% of years when the late spring polar vortex is anomalously strong/weak and possibly earlier if a sudden stratospheric warming event occurs in late winter. However, we show that model dynamical signals are spuriously weak, requiring large ensembles to obtain robust signals and we identify a summer ‘signal-to-noise paradox’ as found in winter atmospheric circulation Our results open possibilities for a range of new summer climate services, including for agriculture, water management and health sectors.

Asthma incidence can be influenced by climate change in Italy: findings from the GEIRD study—a climatological and epidemiological assessment

An association between climatic conditions and asthma incidence has been widely assumed. However, it is unclear whether climatic variations have a fingerprint on asthma dynamics over long time intervals. The aim of this study is to detect a possible correlation of the Summer North Atlantic Oscillation (S-NAO) index and the self-calibrated palmer drought severity index (scPDSI) with asthma incidence over the period from 1957 to 2006 in Italy. To this aim, an analysis of non-stationary and non-linear signals was performed on the time series of the Italian databases on respiratory health (ISAYA and GEIRD) including 36,255 individuals overall, S-NAO, and scPDSI indices to search for characteristic periodicities. The ISAYA (Italian Study on Asthma in Young Adults) and GEIRD (Gene Environment Interactions in Respiratory Diseases) studies collected information on respiratory health in general population samples, born between 1925 and 1989 and aged 20–84 years at the time of the interview, from 13 Italian centres. We found that annual asthma total incidence shared the same periodicity throughout the 1957–2006 time interval. Asthma incidence turned out to be correlated with the dynamics of the scPDSI, modulated by the S-NAO, sharing the same averaged 6 year-periodicity. Since climate patterns appear to influence asthma incidence, future studies aimed at elucidating the complex relationships between climate and asthma incidence are warranted.

Long-term warming and interannual variability contributions’ to marine heatwaves in the Mediterranean

In the past 40 years, marine heatwaves (MHWs) have experienced a worldwide increase in duration, intensity, frequency and spatial extent. This trend has been particularly evident in the Mediterranean, where exceptional events were observed during the summers of 2022, 2018 and 2003. This study proposes a twofold analysis of MHWs in the Mediterranean, focusing on their statistical characteristics and physical causes. A satellite dataset is utilized to analyze MHWs via an index, called activity, which aggregates the occurrence, duration, intensity and spatial extent of events. Our results show that the trend toward more active summers for MHWs is strongest in the western Mediterranean basin and long-term warming is the main driver in the whole Mediterranean basin. We also show that in the western and Adriatic Mediterranean region, the increase of SST variability contributes about a third to the MHW activity long-term trend whereas in the central, eastern and Aegean basins, the variability of SST mostly acts to diminish this trend. Through principal component analysis (PCA) of MHW activity, we found that the three most severe summer MHW events in the Mediterranean occur at the same location where the overall trend is highest. Interannual variability increased MHW activity in 2022 around the Balearic Sea, in 2018 in the eastern basins and in 2003 in the central basins. A joint PCA revealed that the long-term trend in MHW activity co-varies with a positive geopotential height anomaly over the Mediterranean, which is consistent with the generation of atmospheric-driven MHWs and which, at the North Atlantic scale, resembles the positive phase of the summer East Atlantic. The additional interannual variability contribution to these three severe summers was associated with western warming and projected onto the positive phase of the summer North Atlantic Oscillation. The increase in MHW over the last 40 years is also associated in the western, central and Adriatic regions with increased downward short-wave radiation and in the eastern Mediterranean with decreased upward long-wave radiation. Increased upward latent heat flux partly compensated for the MHW long-term increase over the whole Mediterranean basin. The interannual variability of MHW activity is related in the western, central and Adriatic basins to increased downward sensible and decreased upward latent heat flux possibly due to warm and humid air intrusion.

Introduction

Introduction

Weakening of the Silk Road Pattern in August after the Mid-1990s

Abstract This study identified that the Silk Road pattern (SRP), which is a teleconnection pattern along the Asian upper-tropospheric westerly jet, becomes significantly weakened in August after the mid-1990s. The SRP in August dominates the upper-tropospheric meridional wind variability over the Eurasian continent before the mid-1990s but does not afterward. Further results suggested that the summer North Atlantic Oscillation (SNAO) and the South Asian rainfall play a role in inducing this decadal weakening of SRP. Before the mid-1990s, the SNAO is stronger and its southern pole is located over northwestern Europe but is weakened and its southern pole shifts southwestward afterward, resulting in the decadal weakening of its contribution to the SRP. In addition, the relationship between the SRP and South Asian rainfall is substantially weakened after the mid-1990s, which also contributes to the weakening of SRP.

The extremely hot and dry 2018 summer in central and northern Europe from a multi-faceted weather and climate perspective

Abstract. The summer of 2018 was an extraordinary season in climatological terms for northern and central Europe, bringing simultaneous, widespread, and concurrent heat and drought extremes in large parts of the continent with extensive impacts on agriculture, forests, water supply, and the socio-economic sector. Here, we present a comprehensive, multi-faceted analysis of the 2018 extreme summer in terms of heat and drought in central and northern Europe, with a particular focus on Germany. The heatwave first affected Scandinavia in mid-July and shifted towards central Europe in late July, while Iberia was primarily affected in early August. The atmospheric circulation was characterized by strongly positive blocking anomalies over Europe, in combination with a positive summer North Atlantic Oscillation and a double jet stream configuration before the initiation of the heatwave. In terms of possible precursors common to previous European heatwaves, the Eurasian double-jet structure and a tripolar sea surface temperature anomaly over the North Atlantic were already identified in spring. While in the early stages over Scandinavia the air masses at mid and upper levels were often of a remote, maritime origin, at later stages over Iberia the air masses primarily had a local-to-regional origin. The drought affected Germany the most, starting with warmer than average conditions in spring, associated with enhanced latent heat release that initiated a severe depletion of soil moisture. During summer, a continued precipitation deficit exacerbated the problem, leading to hydrological and agricultural drought. A probabilistic attribution assessment of the heatwave in Germany showed that such events of prolonged heat have become more likely due to anthropogenic global warming. Regarding future projections, an extreme summer such as that of 2018 is expected to occur every 2 out of 3 years in Europe in a +1.5 ∘C warmer world and virtually every single year in a +2 ∘C warmer world. With such large-scale and impactful extreme events becoming more frequent and intense under anthropogenic climate change, comprehensive and multi-faceted studies like the one presented here quantify the multitude of their effects and provide valuable information as a basis for adaptation and mitigation strategies.

The synergistic effect of the summer NAO and northwest pacific SST on extreme heat events in the central–eastern China

Extreme heat events happen frequently in East Asia, and may cause great damage to the ecosystem and society. The synergistic effect of the summer positive North Atlantic Oscillation (pNAO) and positive northwest Pacific (pNWP) sea surface temperature anomaly (SSTA) on the interannual variability of the extreme heat events in the central–eastern China (CEC) is investigated in this study. The two factors act synergistically in strengthening the extreme heat events in the CEC via a series of atmospheric bridges, and the CEC is likely to experience a hotter summer when both the summer pNAO and pNWP SSTA occur. The pNWP SSTA increases the strength of pNAO via the eastward propagating Rossby wave from the western Pacific. The enhanced pNAO induces a stronger eastward Rossby wave propagation across the Eurasian continent, and leads to a strong anomalous anticyclone over the CEC. The significantly increased atmosphere thickness increases the air temperature of the layer, and favors the extreme heat events in the CEC. Besides, the pNWP SSTA also has adjacent effect on the atmospheric circulation over the CEC, which could lead to a positive geopotential height anomaly. Therefore, the summer pNAO and pNWP SSTA act synergistically in influencing the atmospheric circulation over the CEC, and thereby significantly increase the extreme heat events in the CEC.

Taylor expansion of the correlation metric for an individual forecast evaluation and its application to East Asian sub-seasonal forecasts

This study develops a skill evaluation metric for an individual forecast by applying a Taylor expansion to the commonly-used temporal correlation skill. In contrast to other individual forecast evaluation metrics, which depend on the amplitude of forecasted and observed anomalies, the so-called “association strength (AS) skill” is less affected by the anomaly amplitude and mainly depends on the degree of similarity between the forecasted and the observed values. Based on this newly developed index, the forecast skill is evaluated for an individual case, then, a group is categorized with respect to the AS skill. The cases with the highest AS skill exhibit the highest correlation skill than any group randomly selected, indicating that the AS skill is a powerful metric to evaluate the non-dimensionalized forecast skill. This strategy is adopted for the subseasonal East Asian summer precipitation forecasts produced by the UK Met Office’s ensemble Global Seasonal forecast system version 5 (GloSea5). In the group with the highest AS skill of the East Asian summer precipitation index (i.e., highest AS cases), the geopotential height anomalies showed quasi-stationary Rossby waves from the North Atlantic to East Asia. The spatial distribution of the dominant subseasonal anomalies for cases with the highest AS is distinct from the cases or groups with the lowest AS skill. Furthermore, the dominant pattern with the highest AS is not solely explained by any well-known typical subseasonal climate patterns, such as the Madden–Julian Oscillation, circumglobal teleconnection pattern, Pacific-Japan pattern, or the Summer North Atlantic Oscillation. This implies that the excitation of well-known climate patterns only partly contributes to increasing the mid-latitude climate predictability in the GloSea5.

Combined impact of summer NAO and northern Russian shortwave cloud radiative effect on Eurasian atmospheric circulation

Based on ERA-Interim and CERES_SYN1deg Ed4.1 datasets, the combined influence of summer North Atlantic Oscillation (SNAO) and positive shortwave cloud radiative effect (SWCRE) events in northern Russia on Eurasian atmospheric circulation is investigated at the intraseasonal scale. The impact of the SNAO on the position of the North Atlantic storm track is modified combined with the Ural anticyclone anomaly contributed by positive northern Russian SWCRE anomalies, which could affect the summer stationary wave pattern. During positive northern Russian SWCRE events under SNAO+, the upstream wave train enhanced by the southward Ural anticyclone anomaly is easily trapped by the northward South Asian jets, thus propagating to low latitudes and causing extreme heat events in East Asia. Under SNAO-, the wave train propagates in the British–Baikal Corridor pattern along polar front jet towards the Far East, slowing down the dramatic melting of sea ice in the Laptev and East Siberian seas. Summer positive SWCRE events in northern Russian act as a bridge by promoting the emergence of the Ural anticyclone anomaly, influencing extreme weather in East Asia and Arctic sea ice variability.

The Summertime Circulation Types over Eurasia and Their Connections with the North Atlantic Oscillation Modulated by North Atlantic SST

ERA5 monthly averaged reanalysis data during 1979–2020 are used to analyze the anomalous characteristics of summertime circulation types over Eurasia and their connections with the North Atlantic Oscillation (NAO) modulated by North Atlantic sea surface temperature (SST). A circulation index (CI) is defined to describe the anomalous characteristics of summertime circulation types over the Eurasian mid-high latitude and classify the anomalous circulation into a double-ridge type (DR-type) and double-trough type (DT-type). The results show that these anomalous circulation types are closely related to the variation of the western Pacific subtropical high (WPSH), East Asian subtropical jet (EASJ), South Asia high (SAH) and summer precipitation anomalies in China. There is a significant negative correlation between summer NAO and circulation types over Eurasia. The positive CI is favorable for the southward movement of the EASJ and two positive height anomalies over the Ural Mountains and the Sea of Okhotsk, respectively. Accompanied by moisture convergence and a strong ascending motion over the middle and lower reaches of the Yangtze River Valley (MLYRV), the summer rainfall will be above normal. These patterns are reversed in positive NAO-index years. The connection between the NAO and circulation types over Eurasia is modulated by a tri-pole SST anomaly pattern over the North Atlantic, which may induce the NAO-like atmospheric circulation and strengthen the impacts of the NAO on Eurasian circulation types. A wave train from the North Atlantic to East Asia, which is aroused by the tri-pole SST anomaly pattern, is the potential mechanism for linking summer NAO and circulation types over Eurasia.

The Physical Processes Dominating the Impact of the Summer North Atlantic Oscillation on the Eastern Tibetan Plateau Summer Rainfall

Abstract The summer North Atlantic Oscillation (SNAO), an important climate signal in regulating the interannual variability of Tibetan Plateau (TP) summer rainfall, is closely related to a meridional precipitation dipole pattern between the southeastern and northeastern TP. In this study, based on diagnoses of observations and multiple realizations of the CESM2 historical simulation, we find that there are fundamental differences between the formation processes dominating the SNAO-related summer rainfall anomaly in the southeastern and northeastern TP. An atmospheric moisture budget analysis reveals that the anomalous vertical (horizontal) moisture advection makes the largest contribution to the southeastern (northeastern) TP summer rainfall anomaly. During the negative phase of SNAO, the increased precipitation in the southeastern TP is related to the anomalous ascending flows, which are driven by two processes according to the moist static energy budget. The first is the southward shift of the subtropical westerly jet stream, which produces positive anomalous zonal advection of the climatological moist enthalpy in the upper-middle troposphere over the southeastern TP. The second is related to the enhanced transport of anomalous warm moist air to the south of TP, which produces positive anomalous meridional advection of anomalous moist enthalpy into the lower troposphere over the southeastern TP under the control of climatological monsoonal meridional circulations. This positive moist enthalpy advection enhances the atmospheric moist static energy and facilitate enhanced local convection. For the northeastern TP, the decreased precipitation is dominated by negative anomalous horizontal moisture advections due to the SNAO-induced equivalent-barotropic anomalous cyclone near the eastern edge of the TP.

Maximum July-August temperatures for the middle of the southern Tien Shan inferred from tree-ring latewood maximum densities.

Long-term temperature reconstructions are urgently needed to prolong meteorological climatic data, which are too short to evaluate the anthropogenic effect on climate change since the Industrial Revolution. The maximum latewood chronology (MXD) of Picea schrenkiana in the middle of the southern Tien Shan was established, and it showed a strong correlation with the mean maximum temperature of the current July to August (TmaxJA), with r = 0.773 (p < 0.001, 1959-2016), which implies that a high temperature in the late growing season could increase the cell wall thickness and lead to high latewood density. Then, the TmaxJA of the middle of the southern Tien Shan was reconstructed over the period of 1720-2018. Three MXD chronologies from Kyrgyzstan significantly correlated with our TmaxJA reconstruction at the interannual scale, and they also showed similar variations on decadal scales. None of these MXD series showed a warming trend in the past century, which was also found in several MXD series from different regions of the world. Spatial correlation analysis revealed that our TmaxJA reconstruction showed significant correlations with that in eastern Asia, southern Europe, and north-western Africa, forming a teleconnection called the Silk Road Pattern. However, moving correlation analysis between our TmaxJA reconstruction and Hokkaido temperature series indicated that this teleconnection was unstable in the past 3 centuries. The volcanic eruptions from the mid-high latitudes in the Northern Hemisphere showed a stronger cooling effect than those from the Southern Hemisphere and the low latitudes of the Northern Hemisphere. The summer North Atlantic Oscillation was also shown to affect the temperature in the Tien Shan to a certain extent.

The Relationship between the North Atlantic Oscillation and the Silk Road Pattern in Summer

Abstract The Silk Road pattern (SRP), which is the leading mode of upper-tropospheric meridional wind anomalies over midlatitude Eurasia, has been widely used to explain the impacts of the summer North Atlantic Oscillation (SNAO) on East Asian climate. However, the relationship between the SNAO and SRP has not been fully elaborated yet. This study classifies the SNAO into two categories according to whether it is closely associated with the SRP or not: the strongly linked category and weakly linked category, on the interannual time scale. The SNAO of the strongly linked category features a concentrated and significant southern pole over the northwestern Europe, and corresponding significant negative (positive) precipitation and upper-tropospheric wind convergence (divergence) anomalies over the northwestern Europe. The wind convergence (divergence) anomalies directly induce the positive (negative) planetary vortex stretching anomalies, which contribute overwhelmingly to positive (negative) Rossby wave source anomalies of the northwestern Europe. These Rossby wave source anomalies, acting as disturbances, further inspire circulation anomalies of surrounding regions, including meridional wind anomalies over the Caspian Sea, which are crucial for the SRP formation. As a result, the downstream SRP is triggered. All these essential features responsible for a strong SNAO–SRP linkage are weak for the weakly linked category. The SNAO–SRP correspondence on the interdecadal time scale is also discussed, and generally similar results are found. Results suggest the importance of shapes for the SNAO southern pole (including the location, the space extent, and the intensity) in determining whether the SNAO can closely link the SRP. Therefore, the shape of the SNAO southern pole should be involved in the discussion of the SNAO’s remote impacts.

Interannual Relationship between Summer North Atlantic Oscillation and Subsequent November Precipitation Anomalies over Yunnan in Southwest China

Interannual Relationship between Summer North Atlantic Oscillation and Subsequent November Precipitation Anomalies over Yunnan in Southwest China

Characteristics of the Greenland Ice Sheet Mass Variations Revealed by GRACE/GRACE Follow-On Gravimetry

As a major contributor to global mean sea-level rise, the Greenland ice sheet (GrIS) and the patterns of its mass change have attracted wide attention. Based on Gravity Recovery and Climate Experiment (GRACE)/GRACE Follow-On (GRACE-FO) gravimetry data, we computed monthly non-cumulative mass change time series of the GrIS, which agree with those from the mass budget method confirming the reliability of GRACE-FO-derived mass change. Over the GrIS, mass was mainly gained in winter, followed by spring. It primarily lost mass in summer, with the percentage of summer mass loss versus the corresponding annual mass loss ranging from 61% to 96%. We report that spring mass loss has become more frequent since 2015, and autumn mass gain occurred more frequently after 2014. By separating mass gain from mass loss at the annual timescale, we find that both the mass gain and mass loss showed a slightly increasing trend during 2003–2020, which might be a response to the ongoing Arctic warming. Summer mass variations highly correlated with the summer North Atlantic Oscillation index are dominated by temperature-associated precipitation and meltwater runoff. This study suggests that long-term observations would be necessary to better understand patterns of the GrIS mass variations in future.

Linking maize yields in Veneto Italy, to large-scale atmospheric variability, circulation regimes and weather types

AbstractThis paper describes the relationships between large-scale modes of climate variability and its related weather types with the fluctuations in the yield of maize crops in Veneto, Italy. The teleconnections analysed in this work are the winter North Atlantic Oscillation (NAO) and the summer North Atlantic Oscillation (SNAO); the West African monsoon (WAM) and the Intertropical Front (ITF). Despite that these indices are not rigorously linked to one another, they result in being considerably related to atmospheric circulation regimes and associated weather types. They have an impact on temperature and precipitation patterns in Italy and on yields of maize crops in Veneto, a region located in northeast Italy. Yields are strongly affected by large-scale temperate and tropical variability directly through three main circulation regimes. Troughing weather regimes that produced below average temperatures depress yields over the entire Veneto region, as does the zonal regime that affects rainfall. Results confirm the relevance of large-scale modes and associated weather regimes and types on maize crop yields fluctuations in Veneto.

Impact of the North Atlantic and the Indian Ocean on the summer hydroclimate over East Central Asia: A case study in the central Tianshan Mountains

Observations have shown that the hydroclimatic variations in East Central Asia (ECA) are a result of the interaction of high-, middle- and low-latitude atmospheric circulation systems. This study aims to explore the potential mechanisms of hydroclimate variability in ECA over a longer timescale than in previous studies. Based on tree-ring stable oxygen isotope (δ 18 O), we reconstructed the May–July relative humidity variations in the central Tianshan Mountains from 1661 to 2016, which can represent the dry/wet variations over a large region of ECA. The reconstruction revealed several dry periods that occurred in 1674–1691, 1705–1740, 1750–1770, 1806–1826, the 1940s, and 1960–1980. The reconstructed relative humidity presented an obvious upward trajectory from the 18th to the early 20th century and humidification characteristics in the mid- to late 1980s. The summer North Atlantic Oscillation (SNAO) had a nonlinear impact on the hydroclimate of ECA by modulating the position of the subtropical westerly jet stream (SWJS). Positive sea surface temperature anomalies in the tropical Indian Ocean (TIO), which may enhance the cross-equatorial jet, transport additional water vapour into ECA, and the South Asian summer monsoon (SASM) provides favourable circulation conditions for water vapour transport. Summer hydroclimatic variations in ECA are jointly affected by the North Atlantic and the TIO. The impact of the TIO on the hydroclimate in ECA cannot be ignored. • Summer relative humidity in ECA was reconstructed by tree-ring δ 18 O during the past three centuries. • Summer hydroclimatic variations in ECA were jointly affected by the North Atlantic and the Indian Ocean. • The negative phase of the SNAO favours the transport of southerly water vapour to ECA through the SWJS. • Summer hydroclimatic variations in ECA correspond well with the climate variability of tropical Indian Ocean.