Search

The lack of long-term meteorological observations largely hinders a comprehensive assessment of the changes in extreme precipitation in the high-mountainous region of the Yarlung Zanbo (YZ) river basin. In this study, the YZ basin was used as an example to clarify extreme changes based on a newly generated precipitation dataset in Tibetan Plateau (TP) basins with complex terrain and limited observations. Results showed that divergent changes in extreme precipitation were observed in the YZ basin. Extreme precipitation indices showed inconsistent changes in the YZ basin for this period. The duration-based consecutive wet day (CWD) indices (5 days/10 year) showed significant increasing trends, while the other eight indices showed insignificant change. It generally mutated in 1989, which showed increased trends for 1961–1988, but decreased trends for 1989–2020. Mean annual extreme precipitation increased from the upper stream to the downstream sub-basin of the YZ basin, and generally decreased from low altitudes to high altitudes. There were opposite tendencies of extreme precipitation between 1961 and 1988 and 1989–2020 across sub-basins. Extreme precipitation showed decreasing trends for the upper sub-basins of the Lhatse (LZ), Rikaze (RKZ), Lhasa (LS) and region between LZ and Nuxia hydrological station (LZ-NX), with an increasing trend in the region between NX and Pasighat (NX-BXK) for 1961–1988, with the opposite occurring during 1989–2020. The annual change in extreme precipitation was mostly influenced by the Arctic Oscillation (AO), East Asian Summer Monsoon (EASM), Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO) in the YZ basin for 1961–2020. However, the influence of large-scale climatic oscillation on extreme precipitation varied at different sub-basins and periods. We expect these findings will improve our understanding of the extreme precipitation characteristics in the TP basins. [ABSTRACT FROM AUTHOR]

Polar sea surface height observation by radar altimeters requires missions with high-latitude orbit and specific processing to observe the sea-ice-covered region within fractures in the ice. Here, we combine sea surface height estimates from different radar satellites over the ice-free and ice-covered polar oceans to create cross-calibrated along-tracks and gridded products over the Arctic Ocean (2011-2021) and the Southern Ocean (2013-2021). The sea surface height from our regional polar products is in great agreement with tide gauges and bottom pressure recorders at monthly timescales in seasonally to year-round icecovered regions. Thanks to the use of several missions and the mapping strategy, our multi-mission products have a greater resolution than monomission products. Part of the sea level variability of the Arctic Ocean product is related to the Arctic Oscillation atmospheric circulation. At long term, the Arctic altimetry sea level is coherent with in-situ steric height evolution in the Beaufort gyre, and negative sea level trends over the 10-year period are observed in the East Siberian slope region, which may be related to the local freshwater decrease observed by other studies. Our regional polar sea level products are limited by current understanding of the sea-ice lead measurements, and homogenization of these polar products with global sea level products needs to be tackled. [ABSTRACT FROM AUTHOR]

The Arctic Oscillation (AO) has been observed to undergo distinct decadal structural fluctuations that significantly influence regional weather and climate. Understanding the drivers and mechanisms behind the AO's spatial nonstationarity is critical for improving climate predictions related to the AO. We present evidence that the Atlantic Multidecadal Oscillation (AMO) plays a pivotal role in modulating AO's Pacific center in recent decades. The poleward amplified cooling associated with negative AMO enhances the north-south temperature gradient and results the strengthened westerly winds and stratospheric polar vortex (SPV) responses, which reflects more planetary waves from the North Pacific to the North Atlantic. This enhances the atmospheric coupling between these regions and leads to a more pronounced Pacific center within the AO pattern. Numerical simulations from ECHAM5 and 35 CMIP6 models further corroborate the essential role of the AMO. These findings advance our understanding of the mechanisms driving the variability of the AO pattern. [ABSTRACT FROM AUTHOR]

A unified clustering framework based on pattern correlation is used to identify eight blocking regimes over Eurasia and surrounding oceans during the winter months (December–March) of 1948–2021. The regimes are labeled based on their centers of action, which are located over the West Atlantic, Greenland, the East Atlantic, Scandinavia, the Ural Mountains and Siberia, the Okhotsk Sea, the Bering Strait, and the North Pacific. It should be noted that the classification is almost insensitive to the time period but mainly depends on the percentage of different blocking events. The spatial distributions of cold surges differ substantially among these eight regimes. Due mainly to the cold advection downstream of the centers of blocking activities, cold surges can be observed over parts of the Eurasian continent. Possible relationships between the eight blocking regimes and large‐scale modes of climate variability, including the Arctic Oscillation, the North Atlantic Oscillation, and the El Niño‐Southern Oscillation, are explored. Not only contemporary connections but also the predictive value of large‐scale modes is discussed. Plain Language Summary: Atmospheric blocking, an important circulation system in middle and high latitudes, has significant local and upstream/downstream impacts on weather and short‐term climate. Since blockings with diverse occurrence locations affect different regions, it is necessary to classify them by a unified framework. In this study, a clustering method based on pattern correlations is adopted to identify wintertime blocking regimes over Eurasia and surrounding oceans to establish their connections with the corresponding spatial distribution of cold surges. The clustering result is almost insensitive to the time period, which mainly depends on the percentage of blocking events located at different regions. We also examine the large‐scale climate background for each regime to provide a reference for the cold surge forecast over the Eurasian continent. Key Points: Eight wintertime blocking regimes over Eurasia and surrounding oceans are revealed by a clustering methodBlocking activities induce cold surges over parts of the Eurasian continent due to downstream cold advectionThe cluster regimes are almost insensitive to the time period [ABSTRACT FROM AUTHOR]

Persistent positive sea surface temperature anomalies (SSTAs) in the mid‐latitude Northeast Pacific (NEP), also known as "warm blob" or "marine heatwave," have substantial ecological and climate effects. This study delves into the spatiotemporal connection between Arctic Oscillation (AO) and SSTAs in the NEP. First, we conduct the lead‐lag correlation and maximum covariance analyses to disentangle the closest temporal relationship between October AO and wintertime SSTAs in the NEP. Then, we categorize the years in positive AO (pAO) phase into two groups: positive AO with warm anomaly (pAO&Blob) group and positive AO without warm anomaly (pAO&noBlob) group based on the October AO index and wintertime blob index. Results show that the positive phase of AO in October strongly influences the wintertime warm SSTAs in the NEP through local and remote pathways. The local pathway is contingent upon the longitudinal positioning of AO‐related high‐pressure anomaly (i.e., anomalous ridge) in the North Pacific. When easterly anomalies prevail at the southern flank of the anomalous ridge over the NEP, they foster warm SSTAs in the NEP. However, different locations of the high‐pressure anomalies may impede the NEP warming. Remote pathways indicate the teleconnections triggered by AO‐related precipitation increase in Greenland and decrease in East Asia, sustaining the high‐pressure anomaly and promoting the anomalous NEP warming. Hence, this study presents new evidence on polar and mid‐latitude climate connections, which may provide potential predictability for the warm SSTAs in the NEP. Plain Language Summary: Under rapid climate change, long‐lasting warm sea surface temperature anomalies (SSTAs) in the mid‐latitude Northeast Pacific (NEP) have attracted wide attention due to their substantial ecological and climate effects. Arctic Oscillation (AO) is the dominant mode of atmospheric circulation variability in mid‐to‐high latitudes of the Northern Hemisphere. Its positive phase is featured by a low‐pressure center in the Arctic region and high‐pressure centers in the mid‐latitude regions. Our results reveal a robust connection between the positive phase of AO in October and warm SSTAs in the NEP during winter. We identify two primary pathways through which the October AO influences the wintertime sea surface temperature (SST) warming in the NEP. Locally, a high‐pressure anomaly over the NEP is associated with easterly wind anomalies to its southern flank, which diminish oceanic latent heat loss to the atmosphere, thus fostering the SST warming in the NEP. However, other locations of the high‐pressure anomaly related to AO may not be favorable for the warming of the NEP. From a remote view, AO can impact the NEP SST through teleconnections due to increased precipitation in Greenland and decreased precipitation in East Asia, sustaining the high‐pressure anomaly over the NEP and further bolstering the NEP warming. Key Points: Temporally, Arctic Oscillation (AO) in October is closely linked to wintertime sea surface temperature (SST) anomalies in the mid‐latitude Northeast Pacific (NEP)The AO‐related anomalous ridge located over the NEP is favorable for the warming of SST locallyRemotely, enhanced rainfall in Greenland and decreased rainfall near East Asia sustain the anomalous ridge over the NEP via teleconnection [ABSTRACT FROM AUTHOR]

We demonstrate a 1-year lagged extratropical response to the El Niño-Southern Oscillation (ENSO) in observational analyses and climate models. The response maps onto the Arctic Oscillation and is strongest in the North Atlantic, where it resembles the North Atlantic Oscillation (NAO). Unexpectedly, these 1-year lagged teleconnections are at least as strong as the better-known simultaneous winter connections. However, the 1-year lagged response is opposite in sign to the simultaneous response such that 1 year later, El Niño is followed by a positive NAO, whereas La Niña is followed by a negative NAO. The lagged response may also interfere with simultaneous ENSO teleconnections. We show here that these effects are unlikely to be caused by residual aliasing of ENSO cycles; rather, slowly migrating atmospheric angular momentum anomalies explain both the sign and the timing of the extratropical response. Our results have implications for understanding ENSO teleconnections, explaining observed extratropical climate variability and interpreting seasonal to inter annual climate predictions. [ABSTRACT FROM AUTHOR]

The Northern Annular Mode (NAM) is traditionally defined as the leading empirical orthogonal function (EOF) of mean sea‐level pressure (MSLP) anomalies during winter. Previous studies have shown that the Pacific centre‐of‐action of the NAM is typically more amplified in models than in reanalysis. Here, we analyse the NAM in hindcasts from nine seasonal prediction models over 1993/1994–2016/2017. In all the models, the Pacific centre‐of‐action is much larger than in reanalysis over that period, during which the NAM and the North Atlantic Oscillation (NAO) are almost indistinguishable. As a result, the NAM in the models is correlated with Aleutian Low variability around four times more strongly than in reanalysis. We show that this discrepancy can be explained primarily by the amplitude of Aleutian Low variability, which is on average 17% higher in models than in reanalysis, with a secondary effect from a stronger correlation between the Aleutian Low and NAO. When the NAM is computed using zonally averaged MSLP, the Aleutian Low amplitude does not influence the pattern directly. Instead, the amplitude of the Pacific centre‐of‐action is governed primarily by the correlation between the Aleutian Low and NAO, reducing the apparent Pacific biases in models. While the two methods yield almost identical results in reanalysis, the large Aleutian Low biases result in differences when applied to model data. Modifying the MSLP statistically to alter the Aleutian Low amplitude reveals that the spatial pattern of the traditionally defined NAM is highly sensitive to Aleutian Low variability, even without modifying the correlation between the Aleutian Low and NAO. Hence, the NAM in models may not be as biased as the traditional method would suggest. We therefore conclude that the traditional EOF method is unsuitable for defining the NAM in the presence of highly amplified Aleutian Low variability, and encourage the use of the zonal‐mean method. [ABSTRACT FROM AUTHOR]

This study is an additional investigation of stratosphere–troposphere coupling based on the recent stratospheric winter descriptions in five distinct modes: January, February, Double, Dynamical, and Radiative. These modes, established in a previous study, categorize the main stratospheric winter typologies modulated by the timing of important sudden stratospheric warmings (SSWs) and final stratospheric warmings (FSWs). The novelty of this research is to investigate the Northern Annular Mode, mean sea level pressure (MSLP) anomalies in the Ural and Aleutian regions, and the decomposition of Eliassen–Palm flux into wavenumbers 1 and 2 within each mode. The results show that the January and Double modes exhibit similar pre-warming surface signals, characterized by Ural blocking and Aleutian trough events preceding weak polar vortex events. The January mode displays a positive MSLP anomaly of +395 hPa (−191 hPa) in the Ural (Aleutian) region in December, while the Double mode shows +311 hPa (−89 hPa) in November. These modes are primarily wave-1 driven, generating tropospheric responses via negative Arctic Oscillation patterns. Conversely, the February and Dynamical modes show opposite signals, with Aleutian blocking and Ural trough events preceding strong polar vortex events. In December, the February mode exhibits MSLP anomalies of +119 hPa (Aleutian) and −180 hPa (Ural), while the Dynamical mode shows +77 hPa and −184 hPa, respectively. These modes, along with important SSWs in February and dynamical FSWs, are driven by both wave-1 and wave-2 and do not significantly impact the troposphere. The Radiative mode's occurrence is strongly related to the Aleutian blocking presence. These findings confirm that SSW timing is influenced by specific dynamical forcing related to surface precursors and underscore its importance in subsequent tropospheric responses. This study establishes a connection between early winter tropospheric conditions and upcoming stratospheric states, potentially improving seasonal forecasts in the northern hemisphere. [ABSTRACT FROM AUTHOR]

The Indian Central Himalaya Region (ICHR), the northern topographic front of the Indian summer monsoon (ISM), is an ideal location to study topography-climate interactions because two weather systems—the ISM and mid-latitude westerlies (MLW)—create distinct eco-climatic regimes from tundra (north) to tropical (south). The region's paleoclimatic studies show considerable climatic variations since the late Pleistocene. We evaluated 29 paleoclimatic records from the region and synthesized the results semi-quantitatively using the weighted palaeoclimate index (WApCI) to better understand the important climatic events and their driving mechanisms. According to the WApCI, the region has at least six enhanced monsoonal periods and eight drier spells during the past 34 ka. The cold-dry climatic events, such as the last glacial maxima (LGM), Younger Dryas (YD), 8.2 ka, and 4.2 ka, are associated with northern-hemisphere (NH) climate dynamics and propagated via MLWs. While, the warmer phases are dictated by the insolation-driven ISM dynamics. The WApCI's reconstructed rainfall anomaly aligns with paleoclimatic-model experiments for dynamically generated Paleoclimate Modeling Intercomparison Projects (PMIP3/PMIP4) rainfall for chosen time-slices (last-millenium, historical, mid-Holocene, and LGM). Finally, the Granger causality test determines the temporal relationship between the climatic drivers/forcing indices and primary meteorological parameters. The results showed that summer and post-monsoon precipitation is primarily influenced by total solar irradiation, winter precipitation is driven by a complex mix of variables, and pre-monsoon precipitation is driven by the Arctic oscillation. Based on the facts, we hypothesize that past climate variability demonstrates a complex interplay of local and hemisphere teleconnections in ICHR's climate dynamics. [ABSTRACT FROM AUTHOR]

This study investigates the effect of internal variability and external forcing on the interdecadal variations of winter East Asian averaged surface air temperature (EASAT) during the past millennium (i.e., 850 − 1850) based on the Community Earth System Model–Last Millennium Ensemble simulations. The simulated winter EASAT exhibits periods of 10 − 40 and 80 − 90 years, which are consistent with the reconstructions. Internal variability explains 76% of the interdecadal EASAT variations, in which the Arctic Oscillation (AO) plays a vital role. The positive AO phase-related Rossby waves at northern mid-latitudes feature enhanced equatorward propagation in the middle–upper troposphere and reduced upward propagation into the stratosphere. The decreased wave amplitudes at northern mid-latitudes denote the weakened Siberian high, Aleutian low, and East Asian trough, enhancing the warm horizontal temperature advection in the lower troposphere and downward longwave flux at the surface. Thus, the positive AO phase favors warmer-than-normal EASAT, and vice versa. In comparison, external forcing, especially volcanic forcing, mainly affects the EASAT variations at 40 and 80 − 90 years and plays a secondary role. [ABSTRACT FROM AUTHOR]

East Asia is a major source of dust accounting for 20% of the global dust emission. Work on reconstructing past changes in dust transport in East Asia is complicated by difficulties in distinguishing local sedimentation from aerial material and lack of suitable material for age determination. Here, we address these issues and present a new dust proxy record from Lake Motosu, located on the Pacific side of Japan. The record is anchored by a high‐quality tephra and radiocarbon chronology. Because Lake Motosu is situated in a quartz‐free basaltic volcanic province, all quartz deposited in the lake is likely to be aerially sourced, and variations in quartz content should reflect past changes in dust transport. Our new record detects a low dust deposition event from 3.0 to 2.0 ka. This event corresponds to elevated sea surface temperature in the Sea of Japan and climate conditions similar to a negative phase of the Arctic Oscillation, indicating an association with the weakened Westerlies and with less frequent dust storms in the source region. The increase in spatial resolution of past dust transport reconstructions will further improve our understanding of the mechanism related to dust emission from East Asia. Plain Language Summary: One potential proxy for understanding past changes in atmospheric conditions is aeolian dust. The climate variability links between non‐contiguous geographic regions and strong constraints on geological ages are required to better contribute to the understanding of dust transport. Here, the dust deposition history of the past 8,000 years at Lake Motosu was obtained by quantitative X‐ray diffraction analysis to determine the amount of quartz in the sediments. There is no local source of quartz to Lake Motosu, so we consider that quartz is transported to the lake in the atmosphere. The amount of dust deposition to the Lake Motosu has persistently decreased between 3 and 2 thousand ago. This sustained decrease in dust deposition may be caused by conditions similar to a negative phase of the Arctic Oscillation. This interpretation is consistent with other proxy records from East Asia. Key Points: Dust deposition history of the past 8 kyr at Lake Motosu was obtained by quantifying quartz amount by X‐ray diffraction analysisReduced amounts of dust accumulation are recognized between 3 and 2 ka, suggesting the Westerlies were away from Lake MotosuClimate conditions similar to a negative phase of the Arctic Oscillation may be the cause of the sustained decrease in dust deposition [ABSTRACT FROM AUTHOR]

The influence of northern polar vortex in the stratosphere (SPV) in December‐January on Asia's surface air temperature (SAT) in February has been examined using reanalysis data sets and a barotropic model. An out‐of‐phase interannual linkage between the SPV in December‐January and SAT in February during 1979–2022 has been observed, that is, a strong (weak) SPV corresponds to a cooling (warming) over Asia. Approximately 25% of the SAT over Asia in February can be explained by the SPV in December‐January. This relationship between the SPV and SAT is independent of the Arctic Oscillation. The influence of the SPV on SAT over Asia cannot be solely explained by radiative processes, but is instead related to circulation anomalies in the troposphere. A stronger SPV tends to result in negative geopotential height anomalies with cyclonic circulation over Asia. The SPV‐related geopotential height over Asia is accompanied by a weakened teleconnection pattern between the North Atlantic and Asia, with three centers from the northeastern Atlantic‐eastern Europe‐Asia, and fewer stationary waves propagated from North Atlantic into Asia. These anomalous circulation patterns and anomalous northerly wind over Central Asia in February are beneficial to the colder air transportation from the higher latitudes to Asia, facilitating a surface cooling over Asia. Our results shed light on the interannual linkage between SPV and SAT over Asia, suggesting that the SPV in December‐January could be considered as a new predicator of SAT in February over Asia. Plain Language Summary: Scientists and the public have become increasingly aware of the significant influences of the stratosphere on tropospheric weather and climate. While numerous studies have focused on the crucial roles of stratospheric anomalies in shaping surface air temperature (SAT) anomalies over Europe and North America, relatively little attention has been given to understanding the potential impacts of stratospheric polar vortex over Arctic (SPV) on SAT over Asia. In this study, we found a robust and out‐of‐phase linkage between the SPV in December‐January and SAT in February over Asia during 1979–2022. A stronger SPV tends to induce an anomalous cyclonic circulation characterized by negative geopotential height, facilitating the transport of colder air from higher latitudes to Asia, thereby contributing a cooling effect on the surface. Our findings suggest that the December‐January SPV can serve as a predictor for SAT in February over Asia. Key Points: A strong (weak) SPV in December‐January tends to result in a cooling (warming) over Asia in February on interannual timescalesThe out‐of‐phase linkage between December‐January SPV and February surface air temperature (SAT) is independent of AO in FebruaryThe influence of SPV on Asia SAT is related to the tropospheric circulation anomalies via dynamic process, rather than radiative process [ABSTRACT FROM AUTHOR]

The results of an analysis of long-term trends and interannual variations of the NO2 content in the atmosphere according to measurements with the Ozone Monitoring Instrument (OMI) aboard the EOS Aura satellite in 2004–2020 are compared to the results of a similar analysis of the NO2 content derived from independent spectrometric twilight NO2 measurements by zenith-scattered solar radiation at stations of the Network for the Detection of Atmospheric Composition Change (NDACC). According to both data, seasonally dependent estimates of linear NO2 trends and variations of the NO2 content under the influence of an 11-year cycle of solar activity and large-scale circulation factors such as the Arctic and Antarctic Oscillations, variations in ocean surface temperature in the Niño 3.4 zone, and the quasi-biennial oscillation in zonal wind in the equatorial stratosphere have been obtained. In general, a good qualitative and, in some cases, quantitative correspondence between estimates of interannual variations of NO2 has been obtained. For interannual variations of stratospheric NO2, the correspondence between estimates based on satellite and ground-based data on average for all stations is not bad, but the correspondence between trend estimates is noticeably worse. The best correspondence between the analysis results has been obtained for the Zvenigorod station. For stratospheric NO2, it was noted in 80–90% of cases, and the correspondence for tropospheric NO2 is practically 100%. [ABSTRACT FROM AUTHOR]

The atmospheric circulation significantly influences the snowpack over mid-high-latitude Eurasia. This study examines the characteristics of the leading subseasonal variability mode of boreal winter sea level pressure (SLP) with 20-80-day period and its relationship with snowpack over mid-high-latitude Eurasia, using the fifth generation of European Center for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA5) data and different snowpack datasets. The SLP leading mode, characterized by a monopole pattern with a strong surface anomalous high centered near the Ural Mountains, exhibits a barotropic structure and extends from the surface to the tropopause. Above SLP and geopotential height anomalies propagate southeastward from the Barents-Kara Sea to East Asia. This leading SLP mode contributes to surface air temperature (SAT) and snowfall circulation anomalies over mid-high-latitude Eurasia. The latter two both directly influence on snowpack anomalies in situ. Over high latitude region, snowfall circulation anomaly is the dominant factor to control the snow depth anomaly. Over middle latitude region, both SAT and snowfall circulation anomalies lead to the snowpack anomaly. Furthermore, the response of snow depth to the leading subseaonal SLP mode occurs 2–5 days earlier than the response of snow cover to the same mode over middle latitude region. In addition, it is suggested that the Arctic Oscillation (AO), East Atlantic/West Russia (EAWR) and Polar/Eurasia (PEU) pattern may contribute to the development of the leading SLP mode and subsequently influence snowpack anomalies. [ABSTRACT FROM AUTHOR]

Arctic and Eurasian wintertime temperature displays a north-south dipole distribution, characterized by a marked inter-decadal reversal between 1988–2003 and 2003–2016. This study unveils the roles of winter Arctic Oscillation (AO) characterized by opposite sea level pressure anomalies between the Arctic and mid-latitude regions such as North Pacific and North Atlantic, and Barents sea ice in driving this reversal. Specifically, in the negative phase of warm Arctic-cold Eurasian (WACE–) (positive phase of warm Arctic-cold Eurasian, WACE+), Arctic exhibits a cyclonic (an anticyclonic) anomaly while central Eurasia experiences an anticyclonic (a cyclonic) anomaly, which is attributed to the subtropical and subpolar wave trains over Eurasia under the modulation of positive (negative) AO. Moreover, more (less) Barents sea ice decreases (increases) the upward net heat flux, which tends to cool (heat) the lower-level atmosphere and triggers circulation anomalies resembling the positive (negative) Polar-Eurasian teleconnection, intensifying the cyclonic (anticyclonic) anomaly over Arctic and anticyclonic (cyclonic) anomaly over central Eurasia, favouring the weakening (strengthening) of Ural ridge and East Asian trough. Zonal (Meridional) circulations tend to be established and unfavorable (favorable) for the exchange of warm and cold air between middle-high latitudes, ultimately promoting the WACE– (WACE+) pattern. [ABSTRACT FROM AUTHOR]

Cold surges represent one of the most hazardous weather events impacting the Yellow and Bohai Seas. The current limited comprehension of their wind impacts motivated the present study. The investigation delved into the spatial and temporal features of high winds during cold surges from 1960 to 2021, scrutinizing trends in interannual and monthly variations, as well as their relevance with large-scale climate patterns. The results revealed an overall declining trend in wind impacts at an annual rate of ∼ 8%. The decline was primarily attributed to the reduction in high wind duration and was irrelevant to alterations in wind speed. Spatial analysis revealed a distinct bimodal pattern, with a short-lived but enhanced center in Liaodong Bay and a longer-lasting albeit less intense center in the central Yellow Sea. Monthly variabilities were characterized by the formation, intensification, and dissipation of this bimodal pattern. Wind impacts showed a tendency to decrease substantially during late autumn and to slightly increase in the spring season. Furthermore, empirical orthogonal function (EOF) analysis revealed modes of variation in high winds, with the primary modes closely linked to the intensity of the Siberian High (SH) and East Asian Winter Monsoon (EAWM). Increased incidence of cold surges and stronger high wind impacts were associated with SH + and EAWM+. Additionally, cold surge frequency and associated high winds showed moderate but statistically significant relevance to the Arctic Oscillation (AO), with more frequent and intensified wind impacts observed during AO-. Marginal influence from the El Niño-Southern Oscillation (ENSO) was also noted, with a positive (negative) ENSO phase corresponding to less (more) frequent cold surges but more (less) intense high wind impacts. [ABSTRACT FROM AUTHOR]

A Stratospheric Northern Annular Mode (SNAM) phase-based composite analysis reveals that continental Cold Air Outbreaks (CAOs) can occur during both positive and negative SNAM events. CAOs tend to occur over Asia, characterized by a meridional-dipole surface temperature anomaly pattern (cold midlatitudes and warm high-latitudes) when the SNAM index is decreasing or the stratospheric polar vortex is weakening, but over North America and Europe with a meridionally-homogeneous pattern when the SNAM index is increasing or the stratospheric polar vortex is strengthening. While the decreasing SNAM is dominated by a stronger stratospheric poleward warm branch (WB-ST) of the isentropic meridional mass circulation and vice versa, the CAOs always follow a stronger tropospheric poleward warm branch (WB-TR) and an equatorward cold branch (CB) of the isentropic meridional mass circulation. The correspondence between the stronger/weaker WB-ST and stronger/weaker WB-TR&CB during majority of SNAM phases (referred to as stratosphere-troposphere coupling regimes) is responsible for the CAOs in Asia. During the remaining phases (stratosphere-troposphere decoupling regimes), in accompany with a weaker/stronger WB-ST, the WB-TR&CB are stronger/weaker and relates to the CAOs occurred in North America and Europe. The coupling regimes when the stratospheric polar vortex is weakening/strengthening are mainly attributed to the E-P flux convergence/divergence from the middle troposphere to the lower stratosphere, the larger wave amplitude throughout the column, and anomalous tropospheric wave flux mainly in the Asia in subpolar latitudes. The decoupling regimes, however, are mainly related to the anomalous westward-tilting of waves and the wave flux reflection toward the North America or Europe. [ABSTRACT FROM AUTHOR]

To quantify the relative contributions of Arctic sea ice and unforced atmospheric internal variability to the "warm Arctic, cold East Asia" (WACE) teleconnection, this study analyses three sets of large-ensemble simulations carried out by the Norwegian Earth System Model with a coupled atmosphere–land surface model, forced by seasonal sea ice conditions from preindustrial, present-day, and future periods. Each ensemble member within the same set uses the same forcing but with small perturbations to the atmospheric initial state. Hence, the difference between the present-day (or future) ensemble mean and the preindustrial ensemble mean provides the ice-loss-induced response, while the difference of the individual members within the present-day (or future) set is the effect of atmospheric internal variability. Results indicate that both present-day and future sea ice loss can force a negative phase of the Arctic Oscillation with a WACE pattern in winter. The magnitude of ice-induced Arctic warming is over four (ten) times larger than the ice-induced East Asian cooling in the present-day (future) experiment; the latter having a magnitude that is about 30% of the observed cooling. Sea ice loss contributes about 60% (80%) to the Arctic winter warming in the present-day (future) experiment. Atmospheric internal variability can also induce a WACE pattern with comparable magnitudes between the Arctic and East Asia. Ice-loss-induced East Asian cooling can easily be masked by atmospheric internal variability effects because random atmospheric internal variability may induce a larger magnitude warming. The observed WACE pattern occurs as a result of both Arctic sea ice loss and atmospheric internal variability, with the former dominating Arctic warming and the latter dominating East Asian cooling. [ABSTRACT FROM AUTHOR]

Tornado outbreaks (TOs) are highly dangerous meteorological phenomena common in the United States and have limited known relationships with climate variability. Many of the challenges in understanding TOs result from a lack of formal TO quantification (both in definition and impact). Here, we present a TO definition based on a spatially cohesive and distinct region of tornado activity and present a TO intensity index using tornado characteristics within the TO region. In developing this index, we present a support vector regression-based detrending methodology to remove the secular trends within tornado reporting. The resulting TO definition suggests a decline in TO activity of roughly 1 TO per 4–5 years, with a similar decline in TO intensity. In addition, the relationship between this new quantification of TOs and common North American interannual and monthly climate variability indices is explored, namely the El Niño Southern Oscillation, the North Atlantic Oscillation, the Arctic Oscillation, and the Pacific North American Oscillation. In general, the links between these teleconnections and TO frequency and intensity were minimal (and sometimes in opposition when comparing TO frequency and intensity), but interesting patterns emerged that may offer an initial pathway to exploring longer-term TO predictability. [ABSTRACT FROM AUTHOR]

In December 2022, the United States (US) experienced an extreme cold event. Its duration was 5 days, and it ranked third in intensity (−9.16 °C) during the period from 1979 to 2022. During the Early Stage (12–16 December), the surface air temperature (SAT) anomaly peaked at 2.98 °C. In the Development Stage (17–21 December), cold air moved towards North America (NA). This event reached its peak during the Outbreak Stage (22–26 December), with a minimum SAT anomaly of −9.16 °C. Concurrently, high pressure occurred in Alaska and the Archipelago region, while low-pressure centers occurred in the US. The U-component of wind (U-wind) was in a negative anomaly in the northern part of NA. The negative anomaly of the V-component of wind (V-wind) moved southward. These atmospheric structural changes facilitated the southward movement of cold air from the Arctic to NA. Furthermore, a positive (negative) U-wind anomaly was observed to obstruct (promote) the southward progression of cold air to NA. A linear regression analysis indicated that a negative Arctic Oscillation (AO) correlated with the accumulation of cold air in the Arctic, while a positive Arctic High led to the transport of cold air to NA. In an empirical orthogonal function (EOF) analysis, EOF1 (16.3%) was characterized by a warm Arctic and cold northern part of NA pattern, reflecting the cold air from the Arctic region moving southward into NA, while EOF2 (14.4%) depicted a cold Arctic and cold NA pattern, characterizing the outbreak of cold events in the US. In January 2024, the US experienced another extreme cold event. Its maximum intensity was −9.50 °C, and its duration was 8 days. The course of the two cold events was very similar. [ABSTRACT FROM AUTHOR]

The Arctic has experienced greatly decreased sea ice and increased ocean temperatures in recent decades but there is a paucity of biological time‐series data allowing assessment of resulting temporal variation in the region's marine ecosystems. Seabirds, as highly mobile and highly visible, upper trophic‐level predators, can be valuable monitors of modifications in marine ecosystems, especially for regions lacking commercial fisheries or regular oceanographic sampling. Since 1975, we have studied annually an Arctic Alaskan colony of Mandt's black guillemot (Cepphus grylle mandtii), an ice‐obligate diving seabird, specializing on Arctic cod (Boreogadus saida), the primary forage fish of the ice‐associated cryopelagic ecosystem. Using multi‐state capture–mark–recapture models, matrix population models, and perturbation analysis, we quantified the environmental and demographic drivers of population change from 1980 to 2019 for the individually marked population. The colony increased rapidly, from <20 to >200 breeding pairs from 1975 to 1990 in response to increased availability of nesting cavities, before experiencing intermittent declines to <50 pairs in 2021. Immigration and apparent survival were the primary demographic parameters affecting population growth with sea ice extent in late summer and fall the primary environmental driver. The initial growth occurred during a period of primarily negative winter Arctic Oscillations (WAO) and extensive summer sea ice. The decline began when an extremely positive WAO in 1989/1990 initiated changes in atmospheric and oceanographic circulation causing major reductions in summer sea ice throughout the region. The three‐decade decline in the population saw plateaus or minor growth with increasing frequency of negative WAOs and increasing declines following two previously identified "tipping points" in sea ice loss. Breeding success at the study colony declined with decreased availability of Arctic cod due to sea ice loss and increasing sea surface temperature and is presumed to have occurred at the source colonies for immigrants where similar oceanographic changes were occurring. Quasi‐extinction of the colony (reduction to <25 pairs) is predicted within the next two decades. The sensitivity of Mandt's black guillemot to multi‐decadal changes in the Arctic's cryopelagic ecosystem makes it an excellent sentinel species for the region with its recent collapse having dire implications for the Arctic Ocean's constituent species. [ABSTRACT FROM AUTHOR]

Copyright of Plateau Meteorology is the property of Plateau Meteorology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Fram Strait is one of the main gateways for fresh water leaving the Arctic Ocean toward the deep‐water formation regions of the North Atlantic. Monitoring transport through Fram Strait is important to quantify the impact of Arctic amplification on the hydrography in lower latitudes. We update existing time series from the moorings in the western Fram Strait and investigate the monthly and interannual variability of the liquid freshwater transport (FWT, reference salinity 34.9), volume transport and freshwater content between 2003 and 2020. We examine composites and correlations of sea‐level pressure (SLP) reanalysis, and remote‐sensing dynamic‐ocean topography (DOT) in the Arctic Ocean. We identify two remote forcing mechanisms of FWT: (a) North Pole convergence freshens the region north of Fram Strait 13–24 months before high FWT events. (b) Beaufort Gyre weakening allows spreading of fresh water to the margins of the Arctic Basin zero to 9 months before high FWT events. In addition a third mechanism occurs locally, (b) Fram Strait northerly winds confine freshwater to the Greenland shelf and drive stronger southward FWT. Additionally, we find a decreasing trend in the total volume transport, concurrent with weakening northerly winds and reducing north‐south DOT gradient across the strait. We also examined correlations between the Fram Strait time series and the Arctic Oscillation and Arctic Ocean Oscillation. Both are found to correlate positively with the total volume transport, while the Arctic Oscillation correlates negatively with FWT with 1‐year lag. Plain Language Summary: The East Greenland Current brings fresh water from the central Arctic Ocean to lower latitudes. The exported fresh water affects stratification, and can contribute to variations of the global meridional overturning circulation. In Fram Strait, between Greenland and Svalbard, the properties of this current have been systematically monitored using moored instruments. We present updated time series of freshwater transport from the moorings in the Fram Strait, and analyze their variability between 2003 and 2020. We identify three mechanisms that contribute to high freshwater transport in the Strait. (a) 13–24 months before, clockwise wind anomalies in the Eurasian Arctic drive converging current anomalies and freshen the area preconditioning fresh outflow events. (b) 0–9 months before, anticlockwise wind anomalies in the Canadian Arctic drive diverging current anomalies directing fresh water to the periphery and Fram Strait. (c) Northerly winds over the strait drive southward transport instantly. We find additionally that total volume transport in the Fram Strait decreases in relation to weakening northerlies that could be a result of a warming Greenland. Key Points: Fram Strait local northerly winds force instant southward volume and freshwater transportArctic Ocean large‐scale wind variability forces two distinguished lagged responses of freshwater content and transport in Fram StraitBetween 2004 and 2019 freshwater transport shows no trend but total volume transport of the East Greenland Current decreases by ∼0.1 SV/year [ABSTRACT FROM AUTHOR]

The co-occurrence of multiple hazards can either exacerbate or mitigate risks. The interrelationships between multiple hazards greatly depend on the spatiotemporal scale and can be difficult to detect from large to local scales. In this paper, we identified coastal regions worldwide where the leading tropical (El Niño-Southern Oscillation, ENSO) and polar (Arctic Oscillation, AO; Southern Annular Mode, SAM) modes of climate variability simultaneously modify the seasonal conditions of multiple hazards, including the near-surface wind speed and swell and wind-sea wave powers. We classified the results at the national and municipal levels, with a focus on multiple hazards simultaneously occurring in space and time. The results revealed that the ENSO modulates multiple hazards, affecting approximately 40% of coastal countries, while the polar annular modes affect approximately 30% of coastal countries. The ENSO induced a greater diversity of multiple hazards, with Asian countries (e.g., Indonesia experienced increases of + 2% in wind and + 7% in swell) and countries in the Americas (e.g., Peru exhibited increases of + 1.5% in wind and + 6% in wind-sea) the most notably affected. The SAM imposed a greater influence on swells in the eastern countries of ocean basins (+ 2.5% in Chile) than in other countries, while the influence of the AO was greater in Norway and the UK (+ 12% for wind-sea and 8% for swell). Low-lying islands exhibited notable variations in pairwise hazards between phases and seasons. Our results could facilitate the interpretation of multihazard interactions and pave the way for a wide range of potential implementations of different coastal industries. [ABSTRACT FROM AUTHOR]

The Chinese Loess Plateau (CLP) in northern China is home to one of the most prominent loess records in the world, reflecting past eolian dust activity in East Asia. However, their interpretation is hampered by ambiguity in the origin of loess‐forming dust and an incomplete understanding of the circulation forcing dust accumulation. In this study, we used a novel modeling approach combining a dust emission model FLEXDUST with simulated back trajectories from FLEXPART to trace the dust back to where it was emitted. Over 21 years (1999–2019), we modeled back trajectories for fine (∼2 μm) and super‐coarse (∼20 μm) dust particles at six CLP sites during the peak dust storm season from March to May. FLEXPART source‐receptor relationships are combined with the dust emission inventory from FLEXDUST to create site‐dependent high‐resolution maps of the source contribution of deposited dust. The nearby dust emission areas were found to be the main source of dust to the CLP. Dust deposition across the CLP was found to predominantly occur via wet removal, with also some super‐coarse dust from distant emission regions being wet deposited following high‐level tropospheric transport. The high topography located on the downwind side of the emission area plays an essential role in forcing the emitted super‐coarse dust upward. On an interannual scale, the phase of the Arctic Oscillation in the preceding winter was found to have a strong association with the spring deposition rate on the CLP, while the strength of the East Asian Winter Monsoon was less influential. Plain Language Summary: The dust deposits on the Chinese Loess Plateau (CLP) in northern China provide an extensive record of changes in past dust activity in East Asia. In this work, we combine an atmosphere transport model with a dust emission model to trace the dust backward to where it was emitted. Choosing six locations at the CLP where we traced the dust back to emissions over a 21‐year period during the most active dust months from March until May, for which we investigated how different parts of the CLP were influenced by the different dust emission areas, transport mechanisms, and wind patterns. We find that dust is mainly brought from the emission areas located near the CLP, and that dust from far‐away emission areas in Central Asia has the potential to reach the CLP in smaller amounts. Furthermore, our results show that wet removal of dust by precipitation is important for dust deposition on the CLP, a mechanism that is often overlooked when explaining variations in past dust activity. On a year‐to‐year basis the dust deposition rate over the CLP was found to be connected to the high‐latitude northern hemisphere's climate oscillation (Arctic Oscillation) rather than the regional East Asian winter monsoon. Key Points: The source contribution of emitted dust aerosols to the Chinese Loess Plateau (CLP) is mapped using backward trajectory modelingDistant dust emission regions in Central Asia have a non‐negligible impact on the CLP, with wet deposited dust showing a clearer connectionStrong dust deposition years over the CLP are associated with the negative phase of the Arctic Oscillation [ABSTRACT FROM AUTHOR]

The Pacific Decadal Oscillation (PDO), the dominant pattern of sea surface temperature anomalies in the North Pacific basin, is an important low-frequency climate phenomenon. Leveraging data spanning from 1871 to 2010, we employed machine learning models to predict the PDO based on variations in several climatic indices: the Niño3.4, North Pacific index (NPI), sea surface height (SSH), and thermocline depth over the Kuroshio–Oyashio Extension (KOE) region (SSH_KOE and Ther_KOE), as well as the Arctic Oscillation (AO) and Atlantic Multi-decadal Oscillation (AMO). A comparative analysis of the temporal and spatial performance of six machine learning models was conducted, revealing that the Gated Recurrent Unit model demonstrated superior predictive capabilities compared to its counterparts, through the temporal and spatial analysis. To better understand the inner workings of the machine learning models, SHapley Additive exPlanations (SHAP) was adopted to present the drivers behind the model's predictions and dynamics for modeling the PDO. Our findings indicated that the Niño3.4, North Pacific index, and SSH_KOE were the three most pivotal features in predicting the PDO. Furthermore, our analysis also revealed that the Niño3.4, AMO, and Ther_KOE indices were positively associated with the PDO, whereas the NPI, SSH_KOE, and AO indices exhibited negative correlations. [ABSTRACT FROM AUTHOR]

The Arctic, Antarctica and the Tibetan Plateau in the high mountains of Asia are called the Earth's three poles and have exhibited the most intense warming worldwide in recent decades. The Arctic Oscillation (AO), Antarctic Oscillation (AAO) and South Asia High (SAH) are the most influential and stable large-scale systems affecting the three poles. The global carbon neutrality targets (1.5 °C/2°C), which promote sustainable development, and the future evolution of these large-scale systems will have implications for global climate projections at the three poles. In this study, our evaluation revealed the satisfactory performance of the multi-initial-value ensemble mean of the Community Earth System Model (CESM) in capturing the observed AO, AAO and SAH patterns. Based on the simulations derived from the CESM Low Warming Experiment, the warming in the three poles will be significantly greater than the global mean when the global warming reaches 1.5 °C/2°C. Under the 1.5 °C global warming level (GWL), a stronger center of action over the North Atlantic will lead to an enhanced influence of the AO on the surface air temperature (SAT) in northern Europe. However, all of the centers of action for the AO and its remote influence on the SAT in the Northern Hemisphere will be weaker when global warming reaches 2 °C. For the AAO, the pair of centers of action in the southern pole and Southern Ocean will weaken under the 1.5 °C scenario, leading to a stronger influence of the AAO on the SAT in the Antarctic Peninsula and a weaker effect in East Antarctica and its surrounding seas. In contrast, the eastward movement of the centers of action over the Southern Ocean under the 2 °C scenario will weaken the teleconnection between the AAO and summer SAT across the Antarctic. During the 21st century, over the third pole, the SAH will move southeastward with significantly increased interannual variability. The change in the SAH at the 1.5 °C GWL will contribute to a warmer summer and less precipitation in Northeast China. Under the 2 °C scenario, the greater movement and strengthening of the SAH will lead to more precipitation and cooler summers in the Yangtze River. Our results suggest that the AO/AAO/SAH are related to the regional climate in a carbon-neutral world. This study has important implications for decadal climate predictions in a future 1.5 °C/2°C warmer world, offering insights into the associated climate risks across the three poles. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Natural Hazards & Environment (JNHE) / Doğal Afetler ve Çevre Dergisi (DACD) is the property of Artvin Coruh University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Gobi Desert (GD) is one of the major global dust sources, where dust events are frequent. Based on satellite observations, we compiled extreme dust events (EDEs) over the GD during spring since 2000. Among all 43 extreme events, EDEs on 4–10 April 2001 (EDE 2001) and 14–19 March 2021 (EDE 2021) are the most pronounced, due to the longest duration and the most intense strength, while the generation mechanisms underlying these two EDEs are different. EDE 2001 is associated with extreme westerlies, which are caused by an abnormal low-pressure due to the extreme Eurasian teleconnection (EU). However, EDE 2021 is attributable to extreme droughts, which are caused by an abnormal high-pressure due to the extreme Arctic Oscillation (AO) and West Pacific teleconnection (WP). Moreover, the trends in EU, AO, and WP combined with the analysis of all EDEs indicate a shift in the dominant factor of EDEs over the GD from extreme winds to extreme droughts. Therefore, regional droughts should be given more importance in future EDE forecasts. [ABSTRACT FROM AUTHOR]

Many previous studies have examined the influence of Arctic sea ice on the weather/climate of the Northern Hemisphere. However, the precursor signals of Arctic sea ice regarding East Asian winter low temperatures, which are important for climate prediction, have received little attention. This study identified an out‐of‐phase relationship between the autumn sea ice area of the Kara Sea (SICK) and subsequent winter minimum temperature in Northeast China (NEC) during 1979–2019, that is, diminished SICK facilitates cooling anomalies at NEC. Further results showed that the Arctic Oscillation (AO) acts as a bridge in the linkage between the autumn SICK and minimum temperature in NEC. Diminished autumn SICK leads to a weakened polar vortex in both the troposphere and the stratosphere in the subsequent winter through vertical propagation of planetary waves, contributing to a negative phase of the AO. Accordingly, the SICK is followed by anomalous Rossby wave train that originates from Mediterranean Sea and propagates eastward to Northeast Asia. Thus, the SICK has substantially influences on the Mongolia cyclone and minimum temperature in NEC by modulation of the AO. Moreover, the shrinking SICK could lead to the upper‐level decelerated westerly anomalies at East Asia through altering the equator‐to‐pole temperature gradient and induce negative minimum temperature anomalies at NEC. The results of this study have importance regarding the prediction of low temperature anomalies over NEC. [ABSTRACT FROM AUTHOR]

The Arctic Beaufort Gyre plays a critical role in climate and marine ecosystems. This study investigates the response of the liquid freshwater in the Beaufort Gyre to various wind perturbations using numerical simulations. A new diagnostic called "freshwater renewal" is introduced, which quantifies the amount of freshwater that has entered the Beaufort Gyre since a specific point in time. The findings reveal that the process of freshwater renewal is persistently efficient in the Beaufort Gyre region, occurring irrespective of the gyre's status. The spatial distribution of freshwater renewal varies, influenced by factors such as wind forcing and gyre circulation patterns. Cyclonic wind perturbation associated with a negative Beaufort high sea level pressure anomaly triggers freshwater release from the Beaufort Gyre, with freshwater export and renewal dependent on wind-perturbation locations and time scales. While some released Beaufort Gyre freshwater exits the Arctic Ocean through the Davis and Fram Straits, a considerable portion could remain within the Arctic Ocean for many years under specific conditions. Wind perturbation associated with the positive Arctic Oscillation enhances the Arctic export of Beaufort Gyre freshwater, mainly through the Fram Strait. The Arctic export of total freshwater and the Arctic export of the portion originating from the Beaufort Gyre have different time scales and magnitudes. Hence, it is essential to collectively examine different freshwater components in order to assess the role of Arctic export in the climate system. [ABSTRACT FROM AUTHOR]

Ensemble forecasts have been shown to better predict observed Atlantic climate variability than that of their own ensemble members. This phenomenon—termed the signal‐to‐noise paradox—is found to be widespread across models, timescales, and climate variables, and has wide implications. The signal‐to‐noise paradox can be interpreted as forecasts underestimating the amplitude of predictable signals on seasonal‐to‐decadal timescales. The cause of this remains unknown. Here, we examine sea level pressure variability from a very large multi‐model ensemble of uninitialized atmosphere‐only simulations, focusing on boreal winter. To assess signal‐to‐noise errors, the ratio of predictable components (RPC) is examined globally, as well as for regional climate indices: the North Atlantic Oscillation, Arctic Oscillation, Southern Annular Mode, and an Arctic index. Our analyses reveal significant correlations between the multi‐model ensemble‐mean and observations over large portions of the globe, particularly the tropics, North Atlantic, and North Pacific. However, RPC values greater than one are apparent over many extratropical regions and in all four climate indices. Higher‐resolution models produce greater observation‐model correlations and greater RPC values than lower‐resolution models in all four climate indices. We find that signal‐to‐noise errors emerge more clearly at higher resolution, but the amplitudes of predictable signals do not increase with resolution, at least across the range of resolutions considered here. Our results suggest that free‐running atmospheric models underestimate predictable signals in the absence of sea surface temperature biases, implying that signal‐to‐noise errors originate in the atmosphere or in ocean–atmosphere coupling. [ABSTRACT FROM AUTHOR]

Polar sea surface height observation by radar altimeters requires missions with high-latitude orbit and specific processing to observe the sea-ice-covered region within fractures in the ice. Here, we combine sea surface height estimates from different radar satellites over the ice-free and ice-covered polar oceans to create cross-calibrated along-tracks and gridded products over the Arctic Ocean (2011–2021) and the Southern Ocean (2013–2021). The sea surface height from our regional polar products is in great agreement with tide gauges and bottom pressure recorders at monthly timescales in seasonally to year-round ice-covered regions. Thanks to the use of several missions and the mapping strategy, our multi-mission products have a greater resolution than mono-mission products. Part of the sea level variability of the Arctic Ocean product is related to the Arctic Oscillation atmospheric circulation. At long term, the Arctic altimetry sea level is coherent with in-situ steric height evolution in the Beaufort gyre, and negative sea level trends over the 10-year period are observed in the East Siberian slope region, which may be related to the local freshwater decrease observed by other studies. Our regional polar sea level products are limited by current understanding of the sea-ice lead measurements, and homogenization of these polar products with global sea level products needs to be tackled.

In this paper, the authors quantitatively investigated the joint impact of the Arctic Oscillation (AO) and El Niño‐Southern Oscillation (ENSO) on vegetation net primary productivity (NPP) over Indo‐Myanmar in boreal winter from 1981 to 2018, and found that there is a significant in‐phase variation between them. When the warm ENSO co‐occurs with the positive AO, the NPP in more than 80% of the grids in the study region significantly increases by approximately 24 gC m−2. For the cold ENSO plus the negative AO, the regionally averaged NPP anomalies are approximately −10 gC m−2, and the local minimum is as low as −60 gC m−2. The combination of AO and ENSO can explain approximately 36% of the total variance of NPP in Indo‐Myanmar. The AO/ENSO linkages to the NPP are very likely due to regional precipitation anomalies through atmospheric circulation. In association with the positive (negative) AO, the Rossby wave, propagating eastward along the subtropical jet stream, brings an anomalous cyclone (anticyclone) over Indo‐Myanmar. This enhances (weakens) Indo‐Myanmar Trough, and resulting in more (less) regional precipitation. During the warm (cold) ENSO, through the Gill‐type response, an anomalous high (low)‐pressure appears in the lower and middle troposphere over Philippine‐South China Sea. The Walker circulation is also weaker (stronger) than normal. These are conducive to anomalous southerly (northerly) winds in Indochina. As a result, in the warm ENSO plus positive AO winters, the mean precipitation anomaly in Indo‐Myanmar increased by 27% as averaged for five data sets. In contrast, when the cold ENSO co‐occurs with negative AO, the precipitation is significantly reduced where the largest anomaly exceeds 100 mm in the ERA5. The precipitation changes are consistent with the local NPP anomalies, whereas the temperature does not seem to be a dominant limiting factor. Plain Language Summary: Vegetation is closely dependent on regional climatic conditions such as temperature and precipitation, whereas these meteorological elements are sensitive to large‐scale climate factors. Therefore, it is necessary to explore the vegetation drivers and underlying physical mechanisms. In this research, we focused on investigating the joint impact of the Arctic Oscillation (AO) and El Niño‐Southern Oscillation (ENSO) on vegetation net primary productivity (NPP) over Indo‐Myanmar in boreal winter from 1981 to 2018, the results show that the combination of AO and ENSO can explain approximately 36% of the total variance in regional NPP. The AO/ENSO linkages to the NPP are very likely due to regional precipitation anomalies through atmospheric circulation. In association with the positive (negative) AO, an eastward Rossby wave propagating along the subtropical jet stream brings an anomalous cyclone (anticyclone) over Indo‐Myanmar. During the warm (cold) ENSO, a southerly (northerly) wind anomaly prevails over Indochina via the Gill‐type response and weaker (stronger) Walker circulation than normal. As a result, when the warm (cold) ENSO co‐occurs with the positive (negative) AO winters, Indo‐Myanmar could experience more (less) precipitation than normal, which can lead to more NPP here. Key Points: There is a significant and robust in‐phase variation between the Arctic Oscillation (AO)/El Niño‐Southern Oscillation (ENSO) and net primary productivity (NPP) over Indo‐Myanmar in boreal winterThe combination of AO and ENSO can explain 36% of the total variance in NPPPrecipitation plays a critical bridge in teleconnection between AO/ENSO and local NPP and explains nearly 40% of the total variance in NPP [ABSTRACT FROM AUTHOR]

Based on the JRA-55 reanalysis data, the persistent downward impacts of the weak stratospheric polar vortex (WPV) events are examined. The WPV events with persistent tropospheric impacts are selected and classified into two groups according to whether there is a phase switch of the surface Arctic Oscillation (AO) around the onset day of the cases. The results suggested a one-month longer duration of the tropospheric impacts for the cases with preexisting negative AO anomalies in the troposphere (i.e., the −AO-pre-WPV events), than the cases with a phase switch of the surface AO from positive to negative (i.e., the +AO-pre-WPV events). The connections between the precursory surface AO anomalies and the following downward propagation are found to be closely related to the different events background state of the two types of events. A strong signal of the east quasi-biennial oscillation (QBO) at 30 hPa is observed during the −AO-pre-WPV events, which induces an anomalous poleward propagation of the planetary waves and convergence anomalies of the wave flux in the lower stratosphere. This slow-changing QBO signal exerts continuous wave forcing in the polar region of the lower stratosphere during the −AO-pre-WPV events and delays the recovery of the polar vortex, leading to the long-persistent tropospheric impacts. Moreover, after the background state of each independent case is removed, the preexisting negative surface AO for the −AO-pre-WPV events also disappears. However, the downward propagation during the +AO-pre-WPV events has not been affected with the events background removed, probably because the QBO signal is quite weak. The results reveal the possible role of the precursory surface AO and the background QBO on the downward propagation of the WPV events, which may offer useful information for the subseasonal prediction. [ABSTRACT FROM AUTHOR]

Studies have shown that the springtime Arctic Oscillation (AO) has a strong influence on the subsequent Indian Ocean Dipole (IOD) and El Niño-Southern Oscillation (ENSO). Nevertheless, not every AO is followed by IOD and ENSO. This study divides the spring AO into three types: followed by both IOD and ENSO (AO-Both), followed by ENSO only (AO-ENSO), and followed by IOD only (AO-IOD). In the AO-Both type, the Pacific component of the AO, which is characterized by a dipole pattern, induces sea surface temperature (SST) anomalies in the subtropical North Pacific that extend southward to the tropical Pacific via a wind-evaporation-SST (WES) feedback. The generated tropical SST anomalies influence subsequent ENSO via tropical air-sea interaction and impact autumn IOD via modulation of the tropical Walker circulation. In the AO-ENSO type, the Pacific component of the AO is featured by a mono-pole anomaly pattern with a center over the mid-latitude northeast Pacific. The northeast Pacific atmospheric anomalies propagate southward and lead to surface zonal wind anomalies in the tropical central Pacific via the WES feedback that influence subsequent ENSO via tropical air-sea interaction. In the AO-IOD type, the Pacific component of the AO is weak. Spring AO-related atmospheric heating anomalies over the North Atlantic excite a wave train extending from the North Atlantic to the western Pacific. The associated low-level wind anomalies induce SST anomalies around the Maritime Continent, which play a crucial role in influencing subsequent IOD. This study suggests that the spatial pattern of the AO plays a critical role in determining its impact on tropical climate variability. [ABSTRACT FROM AUTHOR]

This study reveals a strong relationship between the North Pacific Meridional Mode (PMM) in boreal spring and the Indian Ocean Dipole (IOD) in following autumn. A positive spring PMM tends to be followed by a positive IOD and vice versa. The mechanism for the influence of the PMM on the IOD is then investigated. Positive spring PMM-related cyclonic and SST warming anomalies over the subtropical North Pacific propagate southward to the equatorial central Pacific in the following summer via wind-evaporation-SST feedback. SST warming and enhanced atmospheric heating in summer in the equatorial central Pacific induce an anomalous Walker circulation with ascending anomalies over the tropical central Pacific and descending anomalies over the Maritime Continent. The descending anomalies over the Maritime Continent result in southeasterly wind anomalies off the west coast of Sumatra, which lead to cold SST anomalies in the southeastern tropical Indian Ocean via modulating surface heat flux and upwelling of cold water. The associated increase in zonal SST gradient in the tropical Indian Ocean leads to low-level easterly wind anomalies and contributes to warm SST anomalies in the western tropical Indian Ocean via oceanic dynamic process. The warm and cold SST anomalies in the tropical western and southeastern Indian Ocean further develop to an IOD event in the following autumn via a positive air-sea interaction. The above process for the PMM influence on IOD can be simulated in the long historical simulations of coupled climate models. This study suggests that the spring PMM is a potential precursor for the occurrence of IOD event in the following autumn. [ABSTRACT FROM AUTHOR]

This study assesses the variability of coastal extreme sea levels globally by utilizing nearly three decades of along-track, multi-mission satellite altimetry data. An altimetry-based global coastal database of the non-tidal residual sea level component has been produced. The climate variability of extremes is modeled through a parametric, non-stationary statistical model. This model captures intra-annual, inter-annual and long-term variations in non-tidal residual return levels. Comparisons with tide gauge data demonstrate the ability of altimetry data to capture the variability of coastal extreme sea levels. Our findings reveal a greater complexity in the monthly variability patterns of non-tidal residual extremes in tropical latitudes, often exhibiting multiple storm periods, contrasting with coasts in extratropical latitudes, which are mostly controlled by a winter–summer pattern. This study also highlights the significant influence of established climate circulation patterns on sea level extremes. The positive phase of the Arctic Oscillation pattern leads to increases of over 25% in non-tidal residual return levels in Northwestern Europe with respect to a neutral phase. Furthermore, return levels in the western coast of Central America could be 50% higher during El Niño compared to La Niña. Our results show a robust increasing trend in non-tidal residual return levels along most global coastlines. A comparative analysis shows that variations during the 1995–2020 period were primarily driven by intra-annual variations. [ABSTRACT FROM AUTHOR]

Recently, a connection between the quasi‐biennial oscillation (QBO) and the Madden–Julian oscillation (MJO) was found in observations. The boreal winter seasonal mean amplitude of the daily MJO is anticorrelated with the QBO winds measured at 50 hPa. We investigate whether this relationship is captured in reforecasts of past winters in a seasonal prediction system, and find the ensemble mean response does not show this association, with essentially zero correlation. By repeated subsampling of the ensemble reforecast data, we also show that the observed correlation is very unlikely to arise merely as the result of sampling in the relatively short observational record. Instead, we conclude that the reforecasts genuinely cannot capture the observed QBO–MJO seasonal relationship. We also consider the boreal winter seasonal mean response of tropical convection to the QBO and its influence on the subtropics. We find that the reforecasts are able to capture the stationary pattern found in the observed outgoing long‐wave radiation (OLR) over the tropical west Pacific in response to the QBO. We also find that the associated upper tropospheric divergence in observations interacts with the west Pacific subtropical jet to produce atmospheric Rossby wave patterns that propagate across the midlatitude Pacific Ocean. These extratropical waves have the potential to interfere with the climatological waves in midlatitudes, modifying the strength of the midlatitude annular mode through interactions with the extratropical stratosphere. However, the observed influence on wavenumber 1 is not captured by the reforecasts, suggesting a weak extratropical influence and a partial explanation for the weaker‐than‐observed QBO teleconnection to the Arctic Oscillation and North Atlantic Oscillation. [ABSTRACT FROM AUTHOR]

Using the ERA‐5 reanalysis datasets, NCEP/NCAR sea ice concentration (SIC) and observed winter surface wind speed (WSWS) in northwest China during 1979–2020, this study examined the regime shift of the leading mode of observed WSWS in northwest China and investigated its possible link with the winter Barents–Kara Sea (BKS) SIC. The leading mode of observed WSWS in northwest China showed negative anomalies in southern and northeastern Xinjiang, Gansu, western and northern Shaanxi Provinces, and positive anomalies in northwestern and middle Xinjiang, Qinghai and Ningxia Provinces. The signs of WSWS in the leading mode is generally opposite to their trends during 1979–2020. Leading principal component (PC1) of observed WSWS in northwest China underwent an obvious decreasing regime shift in 2003/04, as well as the winter BKS SIC. There are significant correlations between PC1 and BKS SIC on both interdecadal and interannual timescales. Decadal decrease of BKS SIC is accompanied with a positive phase of Scandinavia pattern (SP) with positive anomalies of 500‐hPa geopotential height over subtropical North Atlantic, Arctic‐Ural region and southern Asia, and negative anomalies over northern North Atlantic‐West Europe and Siberia regions. BKS SIC and SP significantly influenced the Northern China Wind Index (NCWI) at 200 hPa on interdecadal timescale, which was related to the PC1 on both interdecadal and interannual timescales after removing the signal of Arctic Oscillation. Meridional configuration of Siberian cyclonic anomaly and southern Asian anticyclonic anomaly associated with the winter BKS SIC could enhance the intensity of NCWI, which favoured the increase of observed WSWS in northwest China and thereby may contribute to the regime shift in 2003/04 of the leading mode. However, there were still some stations showing decreasing regime shift, which mainly located at the region of steeping terrain. These decreasing changes of WSWS may be related to circumfluence effect of terrain, urbanization and local microclimate, and these reasons still need further detailed study. [ABSTRACT FROM AUTHOR]

Observations show predictive skill of the minimum sea ice extent (Min SIE) from late winter anomalous offshore ice drift along the Eurasian coastline, leading to local ice thickness anomalies at the onset of the melt season—a signal then amplified by the ice–albedo feedback. We assess whether the observed seasonal predictability of September sea ice extent (Sept SIE) from Fram Strait Ice Area Export (FSIAE; a proxy for Eurasian coastal divergence) is present in global climate model (GCM) large ensembles, namely the CESM2-LE, GISS-E2.1-G, FLOR-LE, CNRM-CM6-1, and CanESM5. All models show distinct periods where winter FSIAE anomalies are negatively correlated with the May sea ice thickness (May SIT) anomalies along the Eurasian coastline, and the following Sept Arctic SIE, as in observations. Counterintuitively, several models show occasional periods where winter FSIAE anomalies are positively correlated with the following Sept SIE anomalies when the mean ice thickness is large, or late in the simulation when the sea ice is thin, and/or when internal variability increases. More important, periods with weak correlation between winter FSIAE and the following Sept SIE dominate, suggesting that summer melt processes generally dominate over late-winter preconditioning and May SIT anomalies. In general, we find that the coupling between the winter FSIAE and ice thickness anomalies along the Eurasian coastline at the onset of the melt season is a ubiquitous feature of GCMs and that the relationship with the following Sept SIE is dependent on the mean Arctic sea ice thickness. [ABSTRACT FROM AUTHOR]

The objective of this study was to reconstruct the last century's climatic oscillations in the Arctic region around the Fram Strait using high-resolution analysis of foraminiferal assemblages as proxies for surface and deep-water mass properties. In this area, warm Atlantic water masses are advected to the Arctic Ocean through the West Spitsbergen Current, representing the northernmost tip of the Global Thermohaline Circulation. The interaction between the cold Arctic and the warm Atlantic water masses significantly influences the entire foraminiferal community. Planktic species such as Neogloboquadrina pachyderma and Turborotalita quinqueloba are respectively used as indicators of cold Arctic water and warm Atlantic water masses. Among the main benthic species, Cibicidoides wuellerstorfi, Epistominella exigua, and Oridorsalis tener stand out, serving as proxies for the bottom water mass current velocity and paleoproductivity. The paleoenvironmental reconstruction obtained with the foraminiferal assemblages, together with data from satellite monitoring of the sea ice extent and the long-term record of the annual temperature of the West Spitsbergen Current measured over the last 50 years, support the evidence of a progressively rising heat influx into the Arctic Ocean due to an increasing Atlantic water inflow, forcing the consequent decay of the sea ice extent. [ABSTRACT FROM AUTHOR]

Traveling quasi-5-day oscillations (Q5DOs) with different wavenumbers are independently observed in the mesosphere and the lower thermosphere during many recent sudden stratospheric warming (SSW) events, but their common activities during SSWs are still unclear. Based on the geopotential height data measured by the Aura/Microwave Limb Sounder (MLS) from August 2004 to March 2021, we statistically investigate the characteristics of the Q5DOs during eight Arctic major SSW events. The amplitudes of the Q5DOs are obtained by a new fitting method, which inhibits the effect of rapid changes in stationary planetary waves during SSWs. Our results reveal a robust feature that Q5DOs were enhanced during all interested SSW events. Our analysis indicates that eastward and westward propagating Q5DOs can be simultaneously enhanced during SSWs. Additionally, the wavenumbers of the enhanced Q5DOs are found to be associated with the geometry of polar vortices. Extremely strong westward Q5DOs with wavenumber 2 are consistently observed during split-type major SSWs. [ABSTRACT FROM AUTHOR]

In this study, cold waves (CW) were set and classified in different severity levels by applying standardized index (Z score) of minimum temperature (MT) in the period of 1951–2019, and also, the frequency of monthly, annual and decadal occurrence of CW was calculated and analyzed. The results showed that there was a decreasing linear trend in distribution of temporal changes of CW. The probability for annual occurrence of CW (which annually reaches 42 times or less) was 99%, and the probability of its occurrence for more than 42 waves was 1%. The trend analysis of time series component represented a significant reduction in the cold waves frequency (CWF) in the study area. Also the results of the trend analysis for the severity levels of occurrence of different cold waves showed that despite the significant reduction in the CWF, none of the classes had a significant trend except the reducing trend of annual cold waves frequency (ACWF). Investigating the decadal condition of CWF displays an increased incidence of CW from 70 s and stepwise reduction in the CWF from the 1981 to 2010, and consequently, the general trend of decadal occurrence of CW was decreasing. The twenty-first-century prediction of the CWF shows the CWF will decrease significantly compared to the long-term average of the twentieth century. The results obtained from the correlation and Morlet wavelet analysis (MWA) between the levels of CW severities with Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) teleconnections indicated that the correlation between CWF is in-phase, positive and incremental. [ABSTRACT FROM AUTHOR]

This study focuses on the interannual variability of winter mean surface air temperature (SAT) and subseasonal SAT reversal in North China, which have profound impacts on national life and economic activities. The analysis explores the temporal and spatial distribution characteristics of these variations and their relationship with the Eurasian Zonal Circulation (EZ). The findings reveal distinct interdecadal changes in North China's winter mean SAT, along with a general subseasonal reversal of cold and warm conditions. In comparison to the North Atlantic oscillation/Arctic Oscillation, the EZ has a more significant influence on the interannual variability of winter and subseasonal reversals. Strong EZ years are associated with the weakening of the Siberian High and the Ural Blocking High, causing the East Asian Trough to move eastward, which leads to the retention of cold air from the north and increased SAT in North China. Conversely, weak EZ years exhibit opposite circulation patterns. The winter mean EZ is influenced by preceding autumn Arctic sea ice concentrations (SIC). Reduced autumn SIC results in decreased heat flux and reduced eddy energy, leading to substantial attenuation of the winter storm track across Scandinavia and Western Asia. This attenuation, mediated through the interaction between eddies and mean flow, triggers a slowdown of Eurasian zonal circulation and intensification of the Siberian High. These conditions favor a positive phase of the winter Scandinavia pattern, facilitating the transport of cold Arctic air into North China. Likewise, subseasonal reversals in SIC influence corresponding alterations in the EZ. Plain Language Summary: The winter surface air temperatures (SAT) in North China exhibit notable interdecadal variations and distinct intra‐seasonal changes. These intra‐seasonal variations lead to subseasonal reversals, where early winter may be unusually warm, followed by later winter turning unusually cold, or vice versa. These subseasonal SAT fluctuations are influenced by atmospheric circulation anomalies. In this study, we investigate the spatial and temporal patterns of the mean winter SAT and subseasonal SAT reversals in North China, focusing on their interannual variability. We emphasize the significant impact of anomalous zonal circulation over the middle and high latitudes in Eurasia and explore the relative influence of the Arctic as a boundary forcing factor in circulation anomalies. Key Points: The winter surface air temperature (SAT) and subseasonal SAT reversal in North China have noteworthy interannual variationsThe Eurasian Zonal Circulation (EZ) strongly influences winter SAT and subseasonal reversal variabilityThe physical mechanisms linking autumn Arctic sea ice concentrations to EZ is examined [ABSTRACT FROM AUTHOR]

Snow is the most important component of the Arctic climatic and hydrological system and is directly vulnerable to climate change. In recent decades, observations have indicated significant decreases in the Arctic snow cover and snowfall rate, whereas water discharge from circumpolar Arctic river basins into the Arctic Ocean has increased. To evaluate the contribution, not well quantified, of snow to the river discharge increase, we conducted sensitivity simulations with surface air temperature and precipitation as climatic treatment variables, combining a land surface model and a distributed discharge model. Variables were treated assuming higher climate variations in the Arctic cold season in 1979–2018. The surface and subsurface runoffs simulated by the land surface model were set as inflows in the discharge model to estimate river discharge. Snowmelt mostly converted to surface runoff, accounting for 73.6% of the anomalous surface runoff increase and inducing the simulated peak discharge in spring and early summer. This relationship was enhanced by the winter precipitation increase. Snow loss induced by higher air temperature contributed to the decrease in the peak and annual discharges, but caused the peak discharge to occur earlier. Additionally, warmer temperature increased the proportion of rainfall in the partitioning of precipitation, causing more subsurface runoff, particularly in autumn and winter. These results provide a first separate evaluation of factors influencing Arctic water discharge, including seasonal hydrographs, and illustrate the influence of climate warming-induced snowfall and rainfall variations on the circumpolar Arctic river discharge. [ABSTRACT FROM AUTHOR]

In recent decades, winter Arctic sea-ice concentration (SIC) has experienced a most prominent decline over Barents-Kara Seas (BKS). However, what regulates the time scale and spatial structure of the SIC variability over the Eurasian Arctic is unclear. Here, we find that the SIC variability over the Eurasian Arctic exhibits two major modes: decadal dipole mode with antiphase variation between the BKS and East Greenland (EG), and interannual monopole mode with in-phase variation between the BKS and EG. This decadal mode mainly results from interdecadal changes in ocean heat transports (OHTs) through Barents Sea Opening (BSO) and EG, lagging the Atlantic Multidecadal Oscillation by 7–16 years. The positive SIC dipole mode with a decrease over the BKS and an increase over the EG is also tied to the negative Arctic Oscillation comprised of Ural blocking and the negative North Atlantic Oscillation (NAO). However, the SIC loss of the interannual monopole mode mainly stems from the positive Arctic dipole comprised of Ural blocking and positive NAO through interannual changes in the BSO OHT and atmospheric moisture or heat transport. We further highlight that interannual atmospheric transports and BSO OHT associated with the Arctic dipole contribute to ~66% and ~34% of the interannual variability of the Eurasian Arctic SIC during 1960-2017, respectively. On decadal timescales, the relative contributions of atmospheric transports associated with Arctic Oscillation and OHT to the Eurasian Arctic SIC variability are ~19% and ~81%, respectively. Especially, the contribution of decadal atmospheric transports is significantly intensified during 2000–2017. [ABSTRACT FROM AUTHOR]

The synoptic cold surge is a weather event that frequently occurs in the Northern Hemisphere, often causing severe damage accompanied with intense winds and precipitation. It is reported that the Arctic Oscillation and the North Atlantic Oscillation can affect the cold surge. However, on interacting with tropical circulation, the cold surge potentially links to the Antarctic sea‐ice loss with influence extending to Tropics. Therefore, this research aims to investigate the potential link between Antarctic sea‐ice loss and Northern Hemisphere cold surges and corresponding wind–precipitation compound events. To study this link, twin numerical experiments using a physically based atmosphere model with a prescribed 30% Antarctic sea‐ice loss scenario were used. The results show that the cold surge occurs more frequently in most regions of the world, except for central North America and central Eurasia. In Europe, the cold surges occur closer to the lower latitudes in the Antarctic sea‐ice loss scenario. Additionally, the Antarctic sea‐ice loss can result in intensified wind and precipitation extremes within compound events. The intensified precipitation extremes are caused by increased moisture transportation by tropical easterlies and higher local temperature after the cold surge occurrence, providing more moisture available for precipitation in East Asia and East North America, respectively. Overall, the results of the numerical experiments provide evidence that Antarctic sea‐ice loss influences cold surges in Northern Hemisphere through atmospheric teleconnections. It is important to continue investigating the link between Antarctic sea‐ice loss and weather events like cold surges, as this research can help improve our understanding of the impacts of polar climate change on lower latitudes. [ABSTRACT FROM AUTHOR]