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Using fifth-generation ECMWF Atmospheric Reanalysis (ERA-5) we investigate the topical changes in global teleconnection with seasonal precipitation dynamics in the backdrop of climate change particularly for the recent 20 years (L20:2002 to 2021) with respect to the previous 20 years (F20: 1982–2001). It unveils a considerable decrease in both monsoon and pre-monsoon precipitation over the Northwest Himalaya (NWH) in the Indian region and a decline in winter precipitation over the Tibetan Plateau (TP). Statistically robust K-S test shows notable changes (5% significance level) in the regional distribution of the atmospheric parameters in parts of the High Mountain Asia (HMA) region in recent decades (L20). Further, a weakening of the North Atlantic Oscillation (NAO) and El-Nino Southern Oscillation (ENSO) influence on precipitation pattern is noted in the L20 (2002–2021) compared to the F20 (1982–2001) years over parts of the HMA region. A regional heterogeneity is perceptible among different parts of HMA i.e. NWH in the Indian region and the TP. The NWH precipitation shows a diametrically opposite relation with the NAO index for winter precipitation in L20 (correlation coefficient R= -0.18, sample size: 240) compared to a positive correlation in F20 (correlation coefficient R = 0.15, sample size: 240) which is significant at 5% significance level. The plausible reasons for such a diametrical change in the relationship during winter are addressed by examining the changing signature of the subtropical jet stream and its relationship with NAO and ENSO. Sea surface temperature shows cooling of the tropical Pacific and the resulting weakening in El-Nino signatures in recent years. Our results point to the noteworthy changes in the atmospheric circulation pattern over the HMA region in recent decades which is attributed to the alteration in the global teleconnection patterns and subsequent their association with the precipitation distribution over the HMA region. This study would be useful for an improved understanding of the precipitation dynamics over the HMA region and global teleconnections in the future. [ABSTRACT FROM AUTHOR]

Identified for the first time in Norway, windblown yellowish-brown dust in Folldal, east-central southern Norway, fulfils physical and geochemical criteria for sensu stricto loess, including a high carbonate content. Two extant and one relict marl pond located on low-carbonate rocks are investigated. An allochthonous origin for the marl ponds is suggested and explained by the deposition of suspended clastic carbonate as loess by aeolian processes. The scattered geographical distribution of loess and the need for a calcareous source area suggest a W-SW provenance from a relict valley sandur/existing flood plain in upper Grimsdalen. The mean grain size (~22.4 µm) of the aeolian silt is in the finer range of average loess, explained by the up to 25–30 km long transport and approximately 250–300 m airborne uphill move from the suggested source area to the marl ponds. Based on age-depth modelling using 9 AMS radiocarbon dates, loess deposition occurred from ca. 10,390 to 9780 cal. yr BP (610 years). Two prominent periods of loess accumulation occurred from ca. 10,390 to 10,190 (200 years) and ca. 10,020–9950 (70 years) cal. yr BP. Loess deposition results from W-SW wintertime winds in a dry to semi-arid climate. In southern Norway, W-SW winds in winter are associated with a positive mode of the North Atlantic Oscillation (NAO). From source to deposition, the response time to erode, transport and accumulate loess is suggested to be seasonal to 1 year. An immediate increase in organic production followed loess deposition as early initiation of a warmer and wetter Holocene climatic optimum. [ABSTRACT FROM AUTHOR]

In deserts and dry areas, sudden changes in temperature cause strong winds and as a result cause the phenomenon of dust. The purpose of this research is to investigate the relationship between the occurrence of dust storms and the North Atlantic Oscillation (NAO) index at selected stations in the west and southwest of Iran (Abadan, Bostan, Ilam, Dehloran, Kermanshah and Sarpol-E-Zahab). For this purpose, we used the codes of days with dust storms, horizontal visibility of less than 1 km, data related to index values (NAO) during the statistical period 1987-2022, and satellite data including dust optical depth index (AOD) obtained from the productions of the gauges of 2000-2017 MISR and 2002-2022 MODIS periods. The results of the correlation coefficients showed that there is a relatively strong inverse relationship between the NAO index in the negative phase and a weak direct relationship with dust in the positive phase, and between 51% and 70% of the dust occurrences were simultaneous with the positive phase. The graph of changes in the time series of the indices in the two negative and positive phases showed that the value of the AOD index increased from west to southwest, which is evident in the Abadan station. According to the index produced by the MISR sensor in the years 2011 and 2015 in the positive phase and in the year 2008 in the negative phase, the peak of dust storm activity in all stations and its lowest value are related to the Sarpol-E-Zahab and Kermanshah stations in the years 2002 and 2004, respectively. According to the Deep Blue index obtained from the MODIS sensor, the positive phase of 2022 and the negative phase of 2009 can be separated as the peak of dust storms. The results of the Wind rose and HYSPLIT models showed that the direction of dust storms entering Abadan, Bostan and Ilam stations was from the northwest and southwest and in Dehlorn, Kermanshah, and Sarpol-E-Zahab from the west, and the storms with external origin in these stations were influenced more by the countries of Iraq, Syria and Saudi Arabia. [ABSTRACT FROM AUTHOR]

The North Atlantic Oscillation (NAO) is a dominant atmospheric variability in the Northern Hemisphere that has a substantial impact on weather and climate on various time scales. Here, we investigate the role of energy conversion terms day‐by‐day during the NAO life cycle. The relative timing and contribution of the energy conversion terms are quantified by projecting the terms onto the eddy total energy, eddy kinetic energy (EKE), and eddy available potential energy (EAPE) patterns associated with the NAO. The results show a remarkable phase dependence in the growth and maintenance mechanisms. For positive NAOs, the initial growth is driven by the barotropic interactions between the eddies propagating over North America. This suggests that a non‐local growth mechanism plays an important role in the initiation of positive NAOs. In contrast, it is the baroclinic processes that initiate negative NAOs. The conversion of the mean APE into the EAPE and then into the EKE, processes which include eddy heat fluxes and vertical motions, results in the relatively local growth of negative NAOs. During the mature phase, the largest source of energy is the conversion of the mean APE into EAPE. Part of this is converted to EKE, making a substantial contribution to the maintenance of the EKE. This process is particularly important for negative NAOs. [ABSTRACT FROM AUTHOR]

The North Atlantic Oscillation (NAO) is the most recognized and leading mode of atmospheric variability observed over the Atlantic sector of the Northern Hemisphere, and its impacts on weather and climate over the North Atlantic and Eurasia via large-scale teleconnections have been extensively studied. Here we use a multidata synthesis approach to analyze surface and tropospheric variables from multiple long-term observational and reanalysis datasets to identify the NAO's footprint on interannual temperature variability over the vast but least-studied Sahara Desert during December–January–February–March for the satellite era (1979–2022) and century-long periods. Our results present evidence for a solid teleconnection pattern in surface and tropospheric temperatures associated with the NAO over the Sahara and document some major spatial–temporal and vertical characteristics of this pattern. It is found that the Saharan temperature anomalies are negatively correlated with the NAO index and this correlation is very strong, consistent, and statistically significant between different periods and across different datasets. The teleconnection is closely linked to large-scale circulation anomalies throughout the troposphere over the North Atlantic–Sahara sector, where the anomalous horizontal wind components and geopotential height exhibit opposite changes in sign with altitude from the lower to upper troposphere. During the negative NAO− (positive NAO+) phase, above-normal (below-normal) temperatures over the Sahara could be mainly explained by three major processes: (1) advection of climatological warm and moist (cold and dry) air over the North Atlantic (northern higher latitudes) by the anomalous southwesterly (northeasterly) flow in the lower troposphere; (2) advection of anomalous North Atlantic warm (cold) air by the climatological strong westerlies in the middle and upper troposphere; and (3) strengthened (weakened) vertical mixing in the atmospheric boundary layer. These results suggest that the NAO plays an important role in modulating the interannual temperature variability over the Sahara, and that this NAO footprint is mostly realized through horizontal temperature advection and vertical heat transfer by turbulent mixing. [ABSTRACT FROM AUTHOR]

High‐latitude winter warming was observed following strong tropical volcanism, which has long been believed to be due to the volcanic‐induced positive North Atlantic Oscillation (NAO) phase. However, recent works argue that this warming is caused by El Niño–Southern Oscillation (ENSO) variability instead of volcanoes. Moreover, some studies further argue that El Niño and volcanoes work together to produce this post‐volcanic NAO winter warming. To better understand these arguments on post‐volcanic high‐latitude winter warming, we conducted ENSO‐preconditioned volcanic experiments. Our simulations strongly suggest that the post‐eruption Eurasian winter warming is caused by a post‐eruption positive NAO phase and not by coexisting ENSO‐preconditioned variability. Additionally, we find that the El Niño‐preconditioned volcanic eruption enhances the El Niño phase; however, the neutral and La Niña‐preconditioned eruptions do not lead to an ENSO–like response. These findings are helpful to better understand volcanic‐induced circulation impacts and have important implications for the interpretation of model results and post‐volcanic prediction. Plain Language Summary: The El Niño–Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) linkage to volcanism and associated post‐volcanic high‐latitude winter warming is a topic of great interest. However, the origin of this post‐volcanic winter warming is still controversial. Therefore, to resolve the controversies related to post‐volcanic ENSO and NAO variability and high‐latitude winter warming, we conducted a set of ENSO‐preconditioned volcanic experiments using a coupled atmosphere‐ocean model. The model simulations demonstrate that the post‐eruption high‐latitude Eurasian winter warming is mainly related to the post‐eruption positive NAO phase with no linkage to post‐volcanic ENSO variability. Moreover, the strong tropical volcanism initialized with the El Niño state enhances the El Niño phase, while the Neutral and La Niña initialized simulations do not lead to ENSO–like variability. These results strongly suggest that the high‐latitude post‐eruption Eurasian winter warming is caused by NAO pressure changes during volcanism, and not due to strengthened ENSO responses to volcanism. Key Points: Volcano‐El Niño–Southern Oscillation (ENSO) sensitivity experiments are conducted to better understand the source of post‐eruption northern hemisphere high‐latitude winter warmingWe found that the post‐eruption Eurasian winter warming is caused by volcanic‐induced positive North Atlantic Oscillation (NAO)‐phase and not by ENSO teleconnectionCoexistence of El Niño with volcanism is not essential to produce volcanic‐induced positive NAO and associated winter warming [ABSTRACT FROM AUTHOR]

Severe storm flooding poses a major hazard to the coasts of north-western Europe. However, the longterm recurrence patterns of extreme coastal flooding and their governing factors are poorly understood. Therefore, high-resolution sedimentary records of past North Atlantic storm flooding are required. This multi-proxy study reconstructs storm-induced overwash processes from coastal lake sediments on the Shetland Islands using grain-size and geochemical data, and the re-analysis of historical data. The chronostratigraphy is based on Bayesian age-depth modelling using accelerator mass spectrometry 14C and 137Cs data. A high XRF-based Si/Ti ratio and the unimodal grain-size distribution link the sand layers to the beach and thus storm-induced overwash events. Periods with more frequent storm flooding occurred 980-1050, 1150-1300, 1450-1550, 1820-1900 and 1950-2000 CE, which is largely consistent with a positive North Atlantic Oscillation mode. The Little Ice Age (1400-1850 CE) shows a gap of major sand layers suggesting a southward shift of storm tracks and a seasonal variance with more storm floods in spring and autumn. Warmer phases shifted winter storm tracks towards the north-east Atlantic, indicating a possible trend for future storm-track changes and increased storm flooding in the northern North Sea region. [ABSTRACT FROM AUTHOR]

Background: This study is an attempt to analyze the correlation of the impact of the North Atlantic Oscillation (NAO)and Southern Oscillation Index (SOI) on the climate of Iraq. Method: This has been conducted based on the highest and lowest recorded values of the mentioned oscillations. The values of temperature and rain for the stations of Mosul, Baghdad, Rutba, Basrah and for a major climatic cycle from 1950-2018 were also relied upon. On the statistical analytical approach to find the correlation relationship between the studied oscillations and depending on the Pearson Correlation Coefficient. Results: The results brought to light that there is a strong and statistically significant correlation between the oscillations. The time series of oscillations were also analyzed during the fall season, due to the absence of a single effect of oscillations on the studied elements. Therefore, the analysis of the simultaneous behavior of oscillations on the climatic elements during the autumn was relied upon. In the meantime, four cases of simultaneous behavior for selected years of the study were found, recording the highest oscillations' values. Such four cases were compared with the values of the elements for those years. Conclusion: It became clear from the four cases that there are two cases that show a regular behavior of the influence, as it became clear when the poles are NAO +, SOI - and vice versa that the climatic elements are affected more clearly with the oscillation's indicators and that the climate of Iraq has become more affected by the oscillations. [ABSTRACT FROM AUTHOR]

Extratropical cyclones are critical weather systems that affect large-scale weather and climate changes at mid-high latitudes. However, prior research shows that there are still great difficulties in predicting extratropical cyclones for occurrence, frequency, and position. In this study, mean sea level pressure (MSLP) data from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA5) are used to calculate the variance statistics of the MSLP to reveal extratropical cyclone activity (ECA). Based on the analysis of the change characteristics of ECA in the Northern Hemisphere, the intrinsic link between ECA in the Northern Hemisphere and Arctic sea ice is explored. The results show that the maximum ECA mainly occurs in winter over the mid-high latitudes in the Northern Hemisphere. The maximum ECA changes in the North Pacific and the North Atlantic, which are the largest variations in the Northern Hemisphere, are independent of each other, and their mechanisms may be different. Furthermore, MSLP is a significant physical variable that affects ECA. The North Atlantic Oscillation (NAO) and North Pacific Index (NPI) are significant indices that impact ECA in the North Atlantic and North Pacific, respectively. The innovation of this paper is to explore the relationship between the activity of extratropical cyclones in the Northern Hemisphere and the abnormal changes in Arctic sea ice for the first time. The mechanism is that the abnormal changes in summer-autumn and winter Arctic sea ice lead to the phase transition of the NPI and NAO, respectively, and then cause the occurrence of ECA in the North Pacific and North Atlantic, respectively. Arctic sea ice plays a crucial role in the ECA in the Northern Hemisphere by influencing the polar vortex and westerly jets. This is the first exploration of ECAs in the Northern Hemisphere using Arctic sea ice, which can provide some references for the in-depth study and prediction of ECAs in the Northern Hemisphere. [ABSTRACT FROM AUTHOR]

As important atmospheric circulation patterns in Northern Hemisphere (NH), the North Atlantic Oscillation (NAO) and the Western Pacific teleconnection (WP) affect the winter climate in Eurasia. In order to explore the combined effects of NAO and WP on East Asian (EA) temperature, the NAO and WP indices are divided into four phases from 1980–2021: the positive NAO and WP phase (NAO+/WP+), the negative NAO and WP phase (NAO−/WP−), the positive NAO and negative WP phase (NAO+/WP−), the negative NAO and positive WP phase (NAO−/WP+). In the phase of NAO+/WP+, the low geopotential height (GH) stays in north of EA at 50°–80°N; the surface air temperature anomaly (SATA) is 0.8–1 °C lower than Southern Asian. In the phase of NAO−/WP−, the center of high temperature and GH locate in the northeast of EA; the cold air spreads to Southern Asia, causing the SATA decreases 1–1.5 °C. In the phase of NAO+/WP−, the high GH belt is formed at 55°–80°N. Meanwhile, the center of high SATA locates in the north of Asia that increases 0.8–1.1 °C. The cold airflow causes temperature dropping 0.5–1 °C in the south of EA. The SATA improves 0.5–1.5 °C in south of EA in the phase of NAO−/WP+. The belt of high GH is formed at 25°–50°N, and blocks the cold air which from Siberia. The NAO and WP generate two warped plate pressure structures in NH, and affect the temperature by different pressure configurations. NAO and WP form different GH, and GH acts to block and push airflow by affecting the air pressure, then causes the temperature to be different from the north and south of EA. Finally, the multiple linear regression result shows that NAO and WP are weakened by each other such as the phase of NAO+/WP+ and NAO−/WP−. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive study of winter temperatures in Norway and northern Sweden, covering a period of 50 to 70 years. The analysis utilizes Singular Spectrum Analysis (SSA) to investigate temperature trends at six selected locations. The results demonstrate an overall long-term rise in temperatures, which can be attributed to global warming. However, when investigating variations in highest, lowest, and average temperatures for December, January, and February, 50% of the cases exhibit a significant decrease in recent years, indicating colder winters, especially in December. The study also explores the variations in Atlantic Meridional Overturning Circulation (AMOC) variations as a crucial climate factor over the last 15 years, estimating a possible 20% decrease/slowdown within the first half of the 21st century. Subsequently, the study investigates potential similarities between winter AMOC and winter temperatures in the mid to high latitudes over the chosen locations. Additionally, the study examines another important climatic index, the North Atlantic Oscillation (NAO), and explores possible similarities between the winter NAO index and winter temperatures. The findings reveal a moderate observed lagged correlation for AMOC-smoothed temperatures, particularly in December, along the coastal areas of Norway. Conversely, a stronger lagged correlation is observed between the winter NAO index and temperatures in northwest Sweden and coastal areas of Norway. Thus, NAO may influence both AMOC and winter temperatures (NAO drives both AMOC and temperatures). Furthermore, the paper investigates the impact of colder winters, whether caused by AMOC, NAO, or other factors like winds or sea ice changes, on electrical power and energy systems, highlighting potential challenges such as reduced electricity generation, increased electricity consumption, and the vulnerability of power grids to winter storms. The study concludes by emphasizing the importance of enhancing the knowledge of electrical engineering researchers regarding important climate indices, AMOC and NAO, the possible associations between them and winter temperatures, and addressing the challenges posed by the likelihood of colder winters in power systems. [ABSTRACT FROM AUTHOR]

Biomass burning (BB) has a significant influence on the Arctic environment. Here, we determined the atmospheric levels of BB‐specific tracer compounds such as levoglucosan (Lev), galactosan (Gan), and mannosan (Man) in Arctic aerosols during 2010–2018. The average concentrations of Lev during the study period ranged between 0.43 and 4.15 ng m−3. Both Lev/Man (0–30) and Man/Gan (0–3) ratios further suggested their origin from softwood/hardwood burning. The North Atlantic Oscillation (NAO) was the main driver of the Lev variability during the study period and Lev could be advected to Arctic air during the NAO was in a positive phase. Based upon the levels of Lev, black carbon (BC) generated from BB was estimated, and the corresponding radiative forcing was then calculated by Santa Barbara DISORT Atmospheric Radiative Transfer. BC has a potential warming effect in the atmosphere (+4.28 W/m2) while shows a cooling effect on the surface, which is equivalent to a large volcanic eruption (−3 W/m2). Since climate change is expected to intensify BB around the Arctic, such BC aerosols should be considered in future climate model projections. Plain Language Summary: In this study, long‐term observation of levoglucosan in Arctic aerosols was performed to demonstrate its spatial distribution, sources, interannual variability and drivers, and implication on radiative forcing. An overall increasing trend of levoglucosan during 2010–2018 was observed and the ratios of Lev to its isomers suggested the dominate biomass types of softwood/hardwood. The major factor driving interannual variability of levoglucosan was found to be the atmospheric circulation (North Atlantic Oscillation). Further estimation of the radiative forcing of BB‐derived black carbon revealed its potential effect on Arctic climate. These results provide scientific basis for evaluating influence of biomass burning on the Arctic climate, especially when climate change is expected to increasing wildfires. Key Points: The levoglucosan (Lev) concentration showed an increasing trend from 2010 to 2018 over the Arctic OceanDiagnostic ratios of anhydrosugar indicated that softwood and hardwood dominate biomass burningThe concentration variability of Lev may be affected by the North Atlantic Oscillation [ABSTRACT FROM AUTHOR]

Changes in the wind speed of the Iraqi-Kurdistan region are associated with many types of teleconnection patterns. Daily wind speed datasets for eight meteorological stations in the Iraqi-Kurdistan region were gathered from Sulaymaniya, Penjwen, Hallabja, Kalar, Erbil, Sallahadin, Zakho, and Duhok weather stations. spectral comparability between the daily wind speed of the eight sites and prominent atmospheric indices was implemented for the North Atlantic Oscillation (NAO), Southern Oscillation (SO), Mediterranean Oscillation (MO), and Arctic Oscillation (AO), using the multi-taper method (MTM) for spectral analysis to find the source of the wind speed cycle of the cites for the study area. It was found that the common cycles for the eight stations are 2.22, 2.5, 3.33, 3.7, 4.35, 5.56, 7.14, 10, and 14.29 cycles. It is obvious that there are common cycles between each of the NAO, SO, MO, and AO indices and the cycles of daily wind speed of the eight stations. The results of this study will allow us to understand the relation between the regional daily wind speeds patterns fluctuations and the global teleconnection patterns and also to forecast the behavior of daily regional wind speed.

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Monthly climate data of days with clear and cloudy skies at 38 stations (1991–2017) and daily visual observations of total cloud amounts (TCA) available at six principal stations (1992–2017) were used to investigate regional, subregional, and temporal characteristics of cloudiness in Serbia. Annual, seasonal, and monthly means were used in the analysis. Results showed differences due to influences from topography, predominant synoptic situations, and possible teleconnection with the North Atlantic Oscillation (NAO). According to our criteria, the annual number of cloudy‐sky days (~80–120) was higher than that of selected clear‐sky days (~50–90), except for 3 years of prevailing anticyclonic circulations. A maximum cloudiness frequency was in winter (December), while a minimum frequency was in summer (August). TCA variability was the highest in an area of complex orography. Southeast Serbia was characterized by the smallest daily temporal variation of TCA based on 7, 14, and 21 h observations as well as by a high number of clear‐sky days during all seasons, while the western mountainous part was much cloudier. From October to January, morning TCA was higher than afternoon TCA, ranging from 70% (January) to 78% (December). Statistically significant positive trends in the number of cloudy‐sky days were found for three stations. A statistically significant moderate positive/negative correlation coefficient was found between the monthly cumulative frequencies of clear‐sky/cloudy‐sky days and the NAO for the winter seasons, respectively. During the 18 winters with the negative NAO index (i.e., frequent westerly warm and moist advection), there were approximately six times more cloudy‐sky days (588) than clear‐sky days (88). [ABSTRACT FROM AUTHOR]

North-central Ukraine is vulnerable to temperature increases and precipitation pattern changes associated with climate change. With water management becoming increasingly important, information on current water sources and moisture recycling is critically needed. Isotope ratios of oxygen (δ18O) and hydrogen (δ2H) in precipitation are sensitive to these variables and allow comparisons across the region. The δ2H and δ18O values from collected precipitation in Kyiv and Cherkasy in 2020 and published 3H data for Kyiv from the year 2000 show an influence of the North Atlantic Oscillation (NAO) and provide information about processes affecting precipitation along the storm trajectory. The δ18O values also show a correlation with temperature, indicating that precipitation patterns may be affected by the rising temperatures in the region, as predicted by recent regional studies using Representative Concentration Pathway scenarios and the global climate model GFDL-ESM2M. When compared to backtracked storm trajectory and NAO data, clear relationships emerged between water isotope ratios, storm paths, and likely moisture recycling. Overall, δ2H, δ18O, 3H, and backtracked storm trajectory data provide more regional and local information on water vapour processes, improving climate-change-driven precipitation forecasts in Ukraine. [ABSTRACT FROM AUTHOR]

Recent research has linked the climate variability associated with ocean-atmosphere teleconnections to impacts rippling throughout environmental, economic, and social systems. This research reviews recent literature through 2021 in which we identify linkages among the major modes of climate variability, in the form of ocean-atmosphere teleconnections, and the impacts to temperature and precipitation of the South-Central United States (SCUSA), consisting of Arkansas, Louisiana, New Mexico, Oklahoma, and Texas. The SCUSA is an important areal focus for this analysis because it straddles the ecotone between humid and arid climates in the United States and has a growing population, diverse ecosystems, robust agricultural and other economic sectors including the potential for substantial wind and solar energy generation. Whereas a need exists to understand atmospheric variability due to the cascading impacts through ecological and social systems, our understanding is complicated by the positioning of the SCUSA between subtropical and extratropical circulation features and the influence of the Pacific and Atlantic Oceans, and the adjacent Gulf of Mexico. The Southern Oscillation (SO), Pacific-North American (PNA) pattern, North Atlantic Oscillation (NAO) and the related Arctic Oscillation (AO), Atlantic Multidecadal Oscillation/Atlantic Multidecadal Variability (AMO/AMV), and Pacific Decadal Oscillation/Pacific Decadal Variability (PDO/PDV) have been shown to be important modulators of temperature and precipitation variables at the monthly, seasonal, and interannual scales, and the intraseasonal Madden-Julian Oscillation (MJO) in the SCUSA. By reviewing these teleconnection impacts in the region alongside updated seasonal correlation maps, this research provides more accessible and comparable results for interdisciplinary use on climate impacts beyond the atmospheric-environmental sciences.

:Drought has been a major natural disaster for mankind since ancient times. Even today, with the development of science and technology, the disastrous consequences caused by droughts are still everywhere. In this paper, the evolution characteristics of the drought and its correlation with circulation in Henan Province from 1970 to 2019 are analyzed by using the methods of standardized precipitation evapotrans- piration index (SPEI), Mann Kendall test and cross wavelet analysis. The results show that based on SPEI value, the climate in Henan Province has gradually become arid in recent 50 years. In terms of spatial variation, the drought in spring, summer and winter is significant in the northwest and relatively humid in the southeast. From the circulation correlation, the North Atlantic Oscillation (NAO), Arctic Oscillation (AO) and Southern Oscillation (SOI) have a strong correlation with droughts in spring, summer and autumn in Henan Province, and the Pacific Decadal Oscillation (PDO) and SOI have a strong inter-annual correlation with droughts in Henan Province. [ABSTRACT FROM AUTHOR]

We examine the influence of the solar cycle on the North Atlantic Oscillation (NAO) on its pathway from the upper stratosphere to the surface by applying lagged regression analyses to recent observations, historical observations covering 194 years, and an Earth system model simulation covering 165 years. The propagation of the solar signal can well be explained by a top‐down mechanism, but one that was strongly affected by air‐sea coupling. The solar signal first appears in the subtropical upper stratosphere as a temperature signal. The associated zonal wind signal then propagates downward to the surface in response to stratospheric variability known as the Polar‐night Jet Oscillation. The NAO signal tends to appear in February during years of peak solar activity. The solar signal is further modulated such that positive NAO signals tend to appear earlier in winter with increasing years after peak solar activity associated with the appearance of the NAO‐related SST signal. There are also 50‐year scale fluctuations and amplitude modulations of the solar‐NAO signal, but the tendency of increasing NAO amplitude with increasing NAO‐related SST amplitude suggests a strong influence of decadal ocean dynamics on these modulations. Key Points: Propagation of the solar signal can be explained by a top‐down mechanism modulated by air‐sea couplingSolar‐related North Atlantic Oscillation (NAO) signal tends to peak in February of solar maximum years but shows a 50‐year scale drift with lagged amplitudes of ∼2 yearsA positive NAO signal tended to appear earlier in winter as the years since peak solar activity increased [ABSTRACT FROM AUTHOR]

With the role of surface winds in the generation of ocean waves, secondary microseisms induced by ocean wave‐wave interactions represent a unique interconnection between the solid Earth, the ocean and global atmospheric circulation patterns. In this study, temporal changes in the ocean generated seismic wavefield in Northeast Atlantic are monitored offshore West of Ireland using ocean bottom seismometers located on top of a thick sedimentary basin. Comparisons with numerical seismic simulations and ocean wave model hindcast data suggest those variations are correlated with changing patterns in ocean wave‐wave interactions closely linked to secondary microseism generation areas. Here we show how those changes, accentuated by the specific structure of the Irish offshore margin, reveal the signature of the North Atlantic Oscillation (NAO) in the Earth's background seismic wavefield. In the North Atlantic, secondary microseism sources likely fluctuate with the changing storm track in response to variations in the NAO. Plain Language Summary: Ocean waves continuously generate seismic waves at the seafloor that are observed all over the world. In this study, we show how such vibrations recorded at the seafloor offshore West of Ireland are sensitive to long term weather and climate fluctuations in the Northeast Atlantic. Combining ocean wave and seismic simulation models with observations, we show that the North Atlantic Oscillation (NAO) climate index is hidden in the seismic records. Key Points: Fluctuating secondary microseism sources in the Northeast Atlantic highlight the variability of the NAO climate index through timeAmbient seismic noise recorded at key locations on the seafloor exhibits detailed sensitivity to global atmospheric circulation patternsTemporal changes in the modal excitation of secondary microseism Rayleigh waves reveal changing patterns in local ocean wave‐wave interactions [ABSTRACT FROM AUTHOR]

Comparison of EAM reconstructions with other paleoclimatic proxies. [Display omitted] • On a centennial timescale, the EASM was negatively correlated with EAWM. • On a centennial timescale, the relationship between the EASM and EAWM was mainly influenced by solar radiation. • The sustained negative correlation between the EASM and EAWM during the periods of 5.1–4.3 ka BP and 2.0–0.6 ka BP was modulated by the strong NAO. Sediments in the muddy areas of marginal seas of East China can serve as natural archives of global climate and environmental changes. Studies of these sediments can offer valuable insights for paleoclimate changes. This study examined S04-2, a core located in the central of the inner-shelf muddy area of the East China Sea, to reveal the evolutionary history since 12 ka BP and investigate the relationship between the East Asian Winter Monsoon (EAWM) and East Asian Summer Monsoon (EASM). On a centennial timescale, the EASM was negatively correlated with EAWM and this relationship is mainly influenced by solar radiation, wherein increases or weakening of solar radiation led to a negative or positive correlation between the EASM and EAWM. Additionally, it was observed that the sustained negative correlation during the periods of 5.1–4.3 ka BP and 2.0–0.6 ka BP was modulated by the strong North Atlantic Oscillation (NAO), resulting in periods of heightened social sensitivity in ancient China during 2.0–0.6 ka BP. [ABSTRACT FROM AUTHOR]

The influence of Arctic stratospheric ozone (ASO) in March on precipitation in eastern China during the boreal spring has been investigated by using observations, reanalysis datasets, and historical simulations from CMIP6. Results show a robust in-phase relationship between March ASO and precipitation in eastern China in April and May on interannual timescale during 1980–2020, with the strongest positive correlation in April in the Yangtze River Basin (YRB) and in May in South China (SC). A (an) decrease (increase) of ASO tends to result in a (an) decrease (increase) in precipitation by a combination of factors, including a lack (sufficiency) of water vapor, vigorous downward (upward) motion, and a negative (positive) North Atlantic-Ural Mountain-East Asia (NAULEA)-like wave train. The shift in the strongest positive correlation center of ASO and precipitation from April at the YRB to May at the SC is closely linked to the shift in the most pronounced center of upward movement from April to May. Additionally, anomalies in the North Atlantic Oscillation (NAO) in April play an important role in connecting ASO to precipitation in eastern China. A decrease of March ASO tends to result in a positive phase of NAO, which triggers a negative NAULEA-like wave train along with a strengthened East Asian jet stream. The modification of local circulation results in a decrease in precipitation in eastern China. This study suggests that the March ASO can serve as a potential predictor for precipitation forecasts in eastern China during the boreal spring. • A robust in-phase link between the March Arctic stratospheric ozone (ASO) and precipitation in China in April and May. • ASO loss leads to decreased precipitation by enhanced downward motion and a negative NAULEA wave train. • ASO-related NAO anomalies in April play a critical role in connecting ASO to precipitation in eastern China. [ABSTRACT FROM AUTHOR]

The North Atlantic sea surface temperature exhibits fluctuations on the multidecadal time scale, a phenomenon known as the Atlantic Multidecadal Oscillation (AMO). This letter demonstrates that the multidecadal fluctuations of the wintertime North Atlantic Oscillation (NAO) are tied to the AMO, with an opposite-signed relationship between the polarities of the AMO and the NAO. Our statistical analyses suggest that the AMO signal precedes the NAO by 10-15 years with an interesting predictability window for decadal forecasting. The AMO footprint is also detected in the multidecadal variability of the intraseasonal weather regimes of the North Atlantic sector. This observational evidence is robust over the entire 20th century and it is supported by numerical experiments with an atmospheric global climate model. The simulations suggest that the AMO-related SST anomalies induce the atmospheric anomalies by shifting the atmospheric baroclinic zone over the North Atlantic basin. As in observations, the positive phase of the AMO results in more frequent negative NAO - and blocking episodes in winter that promote the occurrence of cold extreme temperatures over the eastern United States and Europe. Thus, it is plausible that the AMO plays a role in the recent resurgence of severe winter weather in these regions and that wintertime cold extremes will be promoted as long as the AMO remains positive. © 2014 IOP Publishing Ltd.

The complexity and spatio–temporal scale of populations' dynamics influence how populations respond to large‐scale ecological pressures. Detecting and attributing synchrony (i.e. temporally coincident fluctuations in populations' parameters) is key as synchronous populations can become more vulnerable to stochastic events that can affect the viability of harvest and have profound consequences to community structure. Here, we aimed to estimate the level of synchrony in fish growth within and among species across 1 million km2 and identify the environmental drivers contributing to synchronous population fluctuations. We developed otolith increment‐based growth chronologies for two deep‐sea scorpaenid fishes (Helicolenus dactylopterus and Pontinus kuhlii) from geographically and bathymetrically disjunct populations in the northeast Atlantic (one species in three locations; two species with different depth preferences). We used hierarchical models to partition variation in growth within and between populations attributing it to intrinsic (age, species, population) and extrinsic (environmental variables) drivers. We assessed synchrony in growth variation within and among species and identified common change points in population specific growth patterns. We documented time‐variant synchrony in growth variation of geographically and bathymetrically segregated deep‐sea fish populations, lasting 25 and 18 years, respectively. The observed synchrony was likely driven by shared environmental forcing (Moran effect) as large‐scale climate indices (East Atlantic pattern and North Atlantic Oscillation) were important environmental drivers of overall growth variation while the onset of synchrony in growth variation was likely related to marine regime shifts occurring in a wide area of the northeast Atlantic that affected the entire ecosystem. However, our capacity to extrapolate growth information across species and locations was dependent on the timing and magnitude of environmental change. Developing a better understanding of the mechanisms driving growth synchrony is key to ensure sustainable management of populations in habitats that are fragile and highly sensible to environmental change, such as the deep‐sea. [ABSTRACT FROM AUTHOR]

The characteristics of the wintertime Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) and their impacts on climate variability over the Northern Hemisphere are important metrics for evaluating a climate system model. Observational analyses reveal that the horizontal and vertical structures in the AO and NAO exhibit a meridional dipole and a large-scale barotropic pattern between the Arctic and mid-latitudes. Historical model simulations from the Energy Exascale Earth System Model (E3SM-HIST) are used to identify how well it captures these major climate modes. It is found that the simulated AO and NAO modes have spatial structures similar to the observed features. In addition, the observed frequency bands in the AO and NAO-related time variability are captured well in the E3SM-HIST simulation. Associated with the positive phase in wintertime AO and NAO, zonal flow and warm advection in mid-latitude continents are enhanced, along with stronger cold flow from enhanced northerly winds over high latitudes. These features are linked to the atmospheric circulation pattern reflected by lower SLP anomalies over the Arctic and higher SLP anomalies over the mid‐latitudes. In E3SM-HIST, these spatial associations and main structural features are analogous to those in observations. In the time-height evolution related to winter AO and NAO modes, it can also be seen that the simulations reproduce the downward propagating patterns in observations. Nevertheless, the vertical structures associated with AO and NAO in E3SM-HIST exhibit substantial biases in the lower stratosphere. The cause of these stratospheric biases is investigated using the strength of climatological stratospheric polar vortex (SPV) and wave activity fluxes. The results herein suggest that E3SM-HIST has a reasonable skill in reproducing the observed characteristics related to the winter AO and NAO, although there exist systematic biases in the associated climate variability. [ABSTRACT FROM AUTHOR]

Clouds shape weather and climate by regulating the latent and radiative heating in the atmosphere. Recent work has demonstrated the importance of cloud‐radiative effects (CRE) for the mean circulation of the extratropical atmosphere and its response to global warming. In contrast, little research has been done regarding the impact of CRE on internal variability. Here, we study how clouds and the North Atlantic Oscillation (NAO) couple on synoptic time‐scales during Northern Hemisphere winter via CRE within the atmosphere (ACRE). A regression analysis based on 5‐day mean data from CloudSat/CALIPSO, CERES and GERB satellite observations and ERA‐Interim short‐term forecast data reveals a robust dipole of high‐level and low‐level cloud‐incidence anomalies during a positive NAO, with increased high‐level cloud incidence along the storm track (near 45°N) and the subpolar Atlantic, and decreased high‐level cloud incidence poleward and equatorward of this track. Opposite changes occur for low‐level cloud incidence. The cloud anomalies lead to an anomalous column‐mean heating from ACRE over the region of the Iceland low, and to a cooling over the region of the Azores high. To quantify the impact of the ACRE anomalies on the NAO, and to thereby test the hypothesis of a cloud‐radiative feedback on the NAO persistence, we apply the surface pressure tendency equation for ERA‐Interim short‐term forecast data. The NAO‐generated ACRE anomalies amplify the NAO‐related surface pressure anomalies over the Azores high but have no area‐averaged impact on the Iceland low. In contrast, diabatic processes as a whole, including latent heating and clear‐sky radiation, strongly amplify the NAO‐related surface pressure anomalies over both the Azores high and the Iceland low, and their impact is much more spatially coherent. This suggests that, while atmospheric cloud‐radiative effects lead to an increase in NAO persistence on synoptic time‐scales, their impact is relatively minor and much smaller than other diabatic processes. [ABSTRACT FROM AUTHOR]

The Caspian Sea level (CSL) has undergone variations of more than 3 m during the past century with important implications for the life of coastal people, economy and the ecosystem. The origin of these variations as well as future changes in the Caspian water budget are still a matter of debate. Here, the major modes of North Atlantic winter climate variability and atmospheric teleconnections that have a potential effect on the hydroclimate of the Caspian catchment region are examined. The skill of the Community Earth System Model (CESM1.2.2) regarding the simulation of the modern climatology in the Caspian region and the major North Atlantic modes are analysed using different atmospheric grid resolutions and setups of the atmospheric component, the Community Atmosphere Model (CAM4 and CAM5). CESM1.2.2 with CAM5 atmosphere physics and 1° atmospheric grid resolution shows reasonable skill in simulating the regional Caspian basin climatology and the winter North Atlantic Oscillation (NAO). Using this model version, a weakly positive (r =.2) statistically significant (p <.05) correlation between the catchment winter water budget (precipitation minus evaporation, P‐E, integrated over the catchment area) and the NAO is found for the historical period 1850–2000. Climate projections of the 21st century under the Representative Concentration Pathways RCP4.5 and RCP8.5 show that the NAO remains the leading mode of winter variability with a dominant influence on the climate in the Caspian catchment region. Under the RCP4.5 scenario the correlation between the winter NAO and winter P‐E over the Caspian catchment region increases (r =.5, p <.05). For RCP8.5, however, this correlation disappears due to a north–south dipole pattern with a positive P‐E anomaly over the northern and a negative anomaly over the southern parts of the Caspian catchment region, cancelling out an effect on the total Caspian water budget. Nevertheless, due to increasing annual evaporation over the Caspian Sea in the warming climate, the model predicts an additional CSL decrease of about 9 and 18 m between 2020 and 2100 for the RCP4.5 and RCP8.5 scenarios, respectively. Even though the model tends to overestimate the total evaporation due to a too large Caspian Sea surface area, these values are larger than previous projections of CSL decline. [ABSTRACT FROM AUTHOR]

The thermodynamic structure of the North Atlantic Oscillation (NAO), in terms of the pattern of the winter‐mean potential temperature (PT) anomaly in the troposphere, is a crucial indicator of regional climate variations and can be influenced by synoptic‐scale eddy heat (EH) fluxes. The role and mechanism of EH feedback in modulating the winter‐mean thermodynamic structure of the NAO are investigated. We show that the low‐frequency NAO‐related flow can barotropically regulate EH flux and give rise to an EH transport that is down‐gradient (up‐gradient) of the NAO‐related PT anomalies, thus creating negative (positive) EH feedback on PT anomalies in the middle‐lower (upper) troposphere. Using eddy structure decomposition, we calculated the two primary terms of anomalous EH flux: the BA term is the product of basic eddy velocity and anomalous eddy PT, and the AB term is the product of anomalous eddy velocity and basic eddy PT. The meridional BA EH flux is caused by the meridional shift of eddy PT structure under NAO. It is a major contributor of the anomalous EH flux and forcing, which weaken NAO‐related PT anomalies. The zonal AB EH flux is smaller in magnitude and is induced by the zonal slant of the eddy streamfunction structure in the negative NAO phase. It creates EH feedback upstream of the NAO flow. In addition, the positive NAO phase has a negatively stronger EH feedback than the negative phase; this is related to the higher persistence of the anomalous PT pattern under negative NAO. Key Points: The low‐frequency NAO flow can clearly regulate the eddy heat flux in the whole troposphereThe meridional shifting of eddy potential temperature structure is primarily responsible for generating the eddy heat feedback onto NAOThe positive NAO phase has a negatively stronger eddy heat feedback than the negative phase [ABSTRACT FROM AUTHOR]

Increased use of solar photovoltaic electricity requires a better understanding of the impact of large-scale atmospheric teleconnections on incident short wave (SW) solar radiation. Our focus is on the relationship between winter (December to February) SW radiation in northwest Europe and the dominant Euro-Atlantic atmospheric teleconnection patterns using multiple multidecadal observational and gridded reanalysis datasets, with a focus on the islands of Ireland and Britain. Our study reveals that the previously reported west--east seesaw in the correlation pattern between the winter North Atlantic Oscillation (NAO) index and winter SW radiation across the United Kingdom is complex, involving several zonal changes in the sign of the NAO--SW correlations (multiple seesaws). By comparison with the NAO, the east Atlantic pattern exerts only a weak control on winter SW radiation across the United Kingdom and Ireland, although in the western part of the Iberian Peninsula and adjacent Atlantic Ocean significant positive correlations occur. High values of the Scandinavian pattern index result in higher than average winter SW radiation in much of northern Europe, although it is evident that some regions (e.g. northeast England, east Scotland and the adjacent North Sea area) exhibit the opposite behaviour. Inter-seasonal variations in the dominant atmospheric flow and moisture transport directions, steered by large-scale atmospheric pressure patterns, combined with orographic uplift and rainout effects on the windward side of hills and mountains are interpreted to be the physical drivers of the observed zonal variations and correlation sign reversals between winter SW anomalies and the NAO index. [ABSTRACT FROM AUTHOR]

Atmospheric-oceanic circulations (teleconnections) have an important influence on regional climate. In Great Britain, the North Atlantic Oscillation (NAO) has long been understood as the leading mode of climate variability, and its phase and magnitude have been found to influence regional rainfall in previous research. The East Atlantic Pattern (EA) is also increasingly recognised as being a secondary influence on European climate. In this study we use high resolution gridded rainfall and Standardised Precipitation Index (SPI) time series data for Great Britain to map the monthly rainfall signatures of the NAO and EA over the period January 1950–December 2015. Our analyses show that the influence of the two teleconnections varies in space and time with distinctive monthly signatures observed in both average rainfall/SPI-1 values and incidences of wet/dry extremes. In the winter months the NAO has a strong influence on rainfall and extremes in the north-western regions. Meanwhile, in the southern and central regions stronger EA-rainfall relationships are present. In the summer months opposing positive/negative phases of the NAO and EA result in stronger wet/dry signatures which are more spatially consistent. Our findings suggest that both the NAO and EA have a prominent influence on regional rainfall distribution and volume in Great Britain, which in turn has implications for the use of teleconnection forecasts in water management decision making. We conclude that accounting for both NAO and EA influences will lead to an enhanced understanding of both historic and future spatial distribution of monthly precipitation.

The northern North Atlantic Ocean and its adjacent shelf seas, are influenced by several large-scale physical processes which can be described by various climate indices. Although the signal of these indices on the upper ocean has been investigated, the potential effects on vulnerable benthic ecosystems remains unknown. In this study, we examine the relationship between pertinent climate indices and bottom conditions across the northern North Atlantic region for the first time. Changes are assessed using a composite approach over a 50 year period. We use an objectively-analyzed observational dataset to investigate changes in bottom salinity and potential temperature, and output from a high-resolution ocean model to examine changes in bottom kinetic energy. Statistically significant, and spatially coherent, changes in bottom potential temperature and salinity are seen for the North Atlantic Oscillation (NAO), Atlantic Meridional Overturning Circulation (AMOC), Atlantic Multi-decadal Oscillation (AMO), and Subpolar Gyre (SPG); with statistically significant changes in bottom kinetic energy seen in the subpolar boundary currents for the NAO and AMOC. As the climate indices have multi-annual timescales, changes in bottom conditions may persist for several years exposing sessile benthic ecosystems to sustained changes. Variations in baseline conditions will also alter the likelihood of extreme events such as marine heatwaves, and will modify any longer-term trends. A thorough understanding of natural variability and its effect on benthic conditions is thus essential for the evaluation of future scenarios and management frameworks.

Based on the viewpoint that the North Atlantic Oscillation (NAO) has an intrinsic timescale of approximate two weeks and can be treated as an initial value problem, targeted observations for improving the prediction of the onset of NAO events are investigated by using the conditional nonlinear optimal perturbation (CNOP) method with a quasigeostrophic model. The results show that flow-dependent sensitive areas for the prediction of NAO onset are mainly located over North Atlantic and its upstream regions. Targeted observations over the main sensitive areas could improve NAO onset prediction in most cases (approximately 75%) due to reduced errors in anomalous eddy vorticity forcing (EVF) projection in the typical NAO mode. Moreover, a flow-independent sensitive area is determined based on the winter climatological flow, which is located over North America and its adjacent ocean. The NAO onset prediction can also be improved by targeted observations over the flow-independent sensitive area, but the skill improvement is somewhat lower than that derived from observations over the flow-dependent sensitive area. The above results indicate that targeted observations over sensitive areas identified by the CNOP method can help to improve the onset prediction of NAO events. [ABSTRACT FROM AUTHOR]

The Tien Shan is the largest independent latitudinal mountain ranges in Eurasia, but due to a lack of long‐term instrumental data, knowledge of past temperature variability in the Tien Shan is limited. In this paper, a maximum latewood density (MXD) chronology of Schrenk spruce (Picea schrenkiana) was constructed from the Tien Shan, Central Asia. Correlation analyses indicate that the MXD variations of spruce trees in the Tien Shan are mainly limited by summer temperature variations. The July–August mean temperature was reconstructed for the Tien Shan back to 1615 CE. The temperature reconstruction explained 42.9% of the instrumental variance (1930–2005). This reconstruction successfully captured the past temperature variabilities in the Tien Shan and enabled visualization of the cool climate before 1850s and the climatic warming after the 1850s. Agreement among the temperature series of the Tien Shan and regional temperature records based on MXDs from Eurasia suggested that our reconstruction had good reliability, captured some warm/cold periods, and first principal component of these MXD records showed that there are strong large‐scale temperature forcings in Eurasia. Our study also showed that there is a linkage between temperature changes in Central Asia and the atmospheric circulations of the middle‐high latitude westerly region and the sea surface temperatures of both the Pacific Ocean and the Atlantic Ocean. The positive correlations among the principal component time series of regional temperature reconstructions based on MXDs and Northern Hemisphere temperature reconstructions revealed that the MXD chronologies from Central Asia have the potential for developing large‐scale temperature reconstruction. Key Points: Tree rings provide a summer temperature record of the Tien Shan since 1656 CEThere was reasonable agreement between our temperature reconstruction and cold and warm periods previously estimated using MXDs from EurasiaTree ring record shows some close relationships with climate forcings, included volcanic eruptions and summer North Atlantic Oscillation [ABSTRACT FROM AUTHOR]

This paper investigated the variability of freshwater discharge (Q) in the Dez River Basin in Iran and its possible links to the North Atlantic Oscillation (NAO) and El Nino Southern Oscillation (ENSO). Nonparametric statistical tests were applied to analyze fluctuations of discharge and teleconnection indexes. The results indicated statistically significant monotonic decreases of the discharge and peak flow (p-value <0.05) across most of the subbasins. Furthermore, a downward step change was detected in discharge time series around the mid-1990s from 14.7% to 43.3% with respect to long-term values. Similarly, almost concurrent shifts detected in the Oceanic Nino Index (ONI) (from þ0.254 to -0.416 in 1998) and the NAO (from +0.196 to -0.155 in 1995) that suggest changing conditions toward more cold phases of ENSO and negative phases of NAO coincided with discharge and monthly peak flow depletion. Comparing the amount of discharges during different phases showed that Q (El Niño) > Q (neutral) > (La Nina) and Q (NAO+) > Q (NAO-) . Furthermore, the Mann-Whitney U test verified statistically significant differences (p-value <0.05) between flows pertaining to different phases of both ENSO and NAO. Correlations between discharge and teleconnection indexes indicated that discharge is apparently affected by teleconnections considering the lag time. [ABSTRACT FROM AUTHOR]

The interaction between the atmosphere, specifically the North Atlantic Oscillation, and the North Atlantic Ocean circulation on subdecadal time scale is analyzed in a subset of models participating in the Coupled Model Intercomparison Project phase 5. From preindustrial control runs of at least 500‐year length, we derive anomaly patterns in the atmospheric and ocean circulation and of air‐sea heat exchange. All models simulate a distinct dipolar oceanic overturning anomaly at the subdecadal time scale, with centers at 30°N and 55°N. The dipolar overturning anomaly goes along with marked anomalies in the North Atlantic sea surface temperature and gyre circulation. Lag‐regression analyses demonstrate, with relatively small ensemble spread, how the atmosphere and the ocean circulation interact. The dipolar anomalies in the overturning are forced by North Atlantic Oscillation‐related wind stress curl anomalies. Anomalous surface heat fluxes in concert with anomalous vertical motions drive a meridional dipolar heat content anomaly in the upper ocean, and it is this dipolar heat content anomaly which carries the coupled system from one phase of the subdecadal cycle to the other by reversing the tendencies in the overturning circulation. The coupled subdecadal variability derived from the Coupled Model Intercomparison Project phase 5 models is characterized by three elements: a wind‐driven part steering the dipolar overturning anomaly, surface heat flux anomalies that support a heat buildup in the subpolar gyre region, and the heat storage memory which is instrumental in the phase reversal of the North Atlantic Oscillation. Plain Language Summary: The climate variability of the North Atlantic region is largely determined by interactions between atmosphere and ocean. The North Atlantic Oscillation in the atmosphere and variations in the oceanic meridional heat transport are key phenomena in the Atlantic sector and responsible for large fractions of variability. In the ocean, the meridional heat transport is closely related to the Atlantic meridional overturning circulation, and to the subtropical and subpolar gyres. We derive the interaction between the atmosphere and ocean, on the subdecadal time scale in a subset of 12 climate models. Here we find a distinct dipolar overturning anomaly with centers at 30°N and 55°N and a period between six and eight years. Marked anomalies in North Atlantic sea surface temperature and gyre circulation go along with the dipolar overturning variability. Anomalous wind fields in concert with anomalous vertical motions in the ocean changes the heat content pushed the coupled system from one North Atlantic Oscillation phase to the other. The subdecadal variability is characterized by three elements: a wind‐driven part steering the overturning, surface heat flux anomalies supporting an oceanic heat buildup, and the heat storage memory which is instrumental in the phase reversal of the North Atlantic Oscillation. Key Points: We investigate the subdecadal interaction between the NAO, and the North Atlantic Ocean circulation in a subset of CMIP5 modelsA distinct dipolar oceanic overturning anomaly goes along with anomalies in the North Atlantic sea surface temperature and gyre circulationAnomalous surface heat fluxes in concert with anomalous vertical motions drive a meridional dipolar heat content anomaly in the upper ocean [ABSTRACT FROM AUTHOR]

Using multichannel singular spectrum analysis (MSSA) we decomposed climatic time series into principal components, and compared them with Earth rotation parameters. The global warming trends were initially subtracted. Similar quasi 60 and 20 year periodic oscillations have been found in the global mean Earth temperature anomaly (HadCRUT4) and global mean sea level (GMSL). Similar cycles were also found in Earth rotation variation. Over the last 160 years multi-decadal change of Earth's rotation velocity is correlated with the 60-year temperature anomaly, and Chandler wobble envelope reproduces the form of the 60-year oscillation noticed in GMSL. The quasi 20-year oscillation observed in GMSL is correlated with the Chandler wobble excitation. So, we assume that Earth's rotation and climate indexes are connected. Despite of all the clues hinting this connection, no sound conclusion can be done as far as ocean circulation modelling is not able to correctly catch angular momentum of the oscillatory modes.

This work addresses the relationship between major dynamical forcings and variability in NO _2 column measurements. The dominating impact in Northern Southeast Asia is due to El Niño-Southern Oscillation (ENSO); in Indonesia, Northern Australia and South America is due to Indian Ocean Dipole (IOD); and in Southern China Land and Sea, Populated Northern China, Siberia, Northern and Arctic Eurasia, Central and Southern Africa, and Western US and Canada is due to North Atlantic Oscillation (NAO). That NO _2 pollution in Indonesia is modulated by IOD contradicts previous work claiming that the emissions in Indonesia are a function of El Niño impacting upon Aerosol Optical Depth and Fire Radiative Power. Simultaneous impacts of concurrent and lagged forcings are derived using multi-linear regression, demonstrating ENSO impacts future NO _2 variability, enhancing NO _2 emissions 7–88 weeks in the future, while IOD and NAO in some cases increase the emissions from or the duration of the future burning season as measured by NO _2 . This impact will also extend to co-emitted aerosols and heat, which may impact the climate. In all cases, lagged forcings exhibit more impact than concurrent forcings, hinting at non-linearity coupling with soil moisture, water table, and other dynamical effects. The regression model formed demonstrates that dynamical forcings are responsible for over 45% of the NO _2 emissions variability in most non-urban areas and over 30% in urban China and sub-arctic regions. These results demonstrate the significance of climate forcing on short-lived air pollutants.

This study investigates the influence of atmospheric initial conditions on winter seasonal forecasts of the North Atlantic Oscillation (NAO). Hindcast (or reforecast) experiments – which differ only in their initial conditions – are performed over the period 1960–2009, using prescribed sea surface temperature (SST) and sea‐ice boundary conditions. The first experiment ("ERA‐40/Int IC") is initialized using the ERA‐40 and ERA‐Interim reanalysis datasets, which assimilate upper‐air, satellite and surface observations; the second experiment ("ERA‐20C IC") is initialized using the ERA‐20C reanalysis dataset, which assimilates only surface observations. The ensemble mean NAO skill is largest in ERA‐40/Int IC (r = 0.54), which is initialized with the superior reanalysis data. Moreover, ERA‐20C IC did not exhibit significantly more NAO hindcast skill (r = 0.38) than in a third experiment, which was initialized with incorrect (shuffled) initial conditions. The ERA‐40/Interim and ERA‐20C initial conditions differ substantially in the tropical stratosphere, where the quasi‐biennial oscillation (QBO) of zonal winds is not present in ERA‐20C. The QBO hindcasts are highly skilful in ERA‐40/Int IC – albeit with a somewhat weaker equatorial zonal wind amplitude in the lower stratosphere – but are incorrect in ERA‐20C IC, indicating that the QBO is responsible for the additional NAO hindcast skill; this is despite the model exhibiting a relatively weak teleconnection between the QBO and NAO. The influence of the QBO is further demonstrated by regressing out the QBO influence from each of the hindcast experiments, after which the difference in NAO hindcast skill between the experiments is negligible. Whilst ERA‐40/Int IC demonstrates a more skilful NAO hindcast, it appears to have a relatively weak predictable signal; this is the so‐called "signal‐to‐noise paradox" identified in previous studies. Diagnostically amplifying the (weak) QBO–NAO teleconnection increases the ensemble‐mean NAO signal with negligible impact on the NAO hindcast skill, after which the signal‐to‐noise problem seemingly disappears. (a) shows the ratio‐of‐predictable‐components (RPC) for the NAO in the ERA‐40/Int IC, ERA‐20C IC, Correct SST‐only and Correct IC‐only hindcast experiments. Also shown in unfilled blue bars are RPC values for the post‐processed ERA‐40/Int IC hindcast experiment, where the QBO influence on the NAO in each ensemble member has been amplified (or reduced) by various factors. (b) shows the ensemble mean NAO correlation in the same ensemble hindcast experiments. [ABSTRACT FROM AUTHOR]