Atlantic Multidecadal Oscillation Research Articles

The Weakening of the Stratospheric Polar Vortex and the Subsequent Surface Impacts as Consequences to Arctic Sea Ice Loss

Abstract This study investigates the stratospheric response to Arctic sea ice loss and subsequent near-surface impacts by analyzing 200-member coupled experiments using the Whole Atmosphere Community Climate Model version 6 (WACCM6) with preindustrial, present-day, and future sea ice conditions specified following the protocol of the Polar Amplification Model Intercomparison Project. The stratospheric polar vortex weakens significantly in response to the prescribed sea ice loss, with a larger response to greater ice loss (i.e., future minus preindustrial) than to smaller ice loss (i.e., future minus present-day). Following the weakening of the stratospheric circulation in early boreal winter, the coupled stratosphere–troposphere response to ice loss strengthens in late winter and early spring, projecting onto a negative North Atlantic Oscillation–like pattern in the lower troposphere. To investigate whether the stratospheric response to sea ice loss and subsequent surface impacts depend on the background oceanic state, ensemble members are initialized by a combination of varying phases of Atlantic multidecadal variability (AMV) and interdecadal Pacific variability (IPV). Different AMV and IPV states combined, indeed, can modulate the stratosphere–troposphere responses to sea ice loss, particularly in the North Atlantic sector. Similar experiments with another climate model show that, although strong sea ice forcing also leads to tighter stratosphere–troposphere coupling than weak sea ice forcing, the timing of the response differs from that in WACCM6. Our findings suggest that Arctic sea ice loss can affect the stratospheric circulation and subsequent tropospheric variability on seasonal time scales, but modulation by the background oceanic state and model dependence need to be taken into account. Significance Statement This study uses new-generation climate models to better understand the impacts of Arctic sea ice loss on the surface climate in the midlatitudes, including North America, Europe, and Siberia. We focus on the stratosphere–troposphere pathway, which involves the weakening of stratospheric winds and its downward coupling into the troposphere. Our results show that Arctic sea ice loss can affect the surface climate in the midlatitudes via the stratosphere–troposphere pathway, and highlight the modulations from background mean oceanic states as well as model dependence.

Can the delayed effects of climatic oscillations have a greater influence on global fisheries compared to their immediate effects?

Climatic oscillations affect fish population dynamics, ecological processes, and fishing operations in maritime habitats. This study examined how climatic oscillations affect catch rates for striped, blue, and silver marlins in the Atlantic Ocean. These oscillations are regarded as the primary factor influencing the abundance and accessibility of specific resources utilized by fishers. Logbook data were obtained from Taiwanese large-scale fishing vessels for climatic oscillations during the period 2005-2016. The results indicated that the effect of the Subtropical Indian Ocean Dipole on marlin catch rates did not have a lag, whereas those of the North Atlantic Oscillation, Atlantic Multidecadal Oscillation, Pacific Decadal Oscillation, and Indian Ocean Dipole had various lags. Pearson's correlation analysis was conducted to examine the correlations between atmospheric oscillation indices and marlin catch rates, and wavelet analysis was employed to describe the influences of the most relevant lags. The results indicated that annual atmospheric fluctuations and their lags affected the abundance and catchability of striped, blue, and silver marlins in the study region. This, in turn, may affect the presence of these species in the market and lead to fluctuations in their prices in accordance with supply and demand. Overall, understanding the effects of climatic oscillations on fish species are essential for policymakers and coastal communities seeking to manage marine resources, predict changes in marine ecosystems, and establish appropriate methods for controlling the effects of climate variability.

Deep Atlantic Multidecadal Variability

AbstractInvestigating deep‐sea temperature variability is essential for understanding deep‐sea variability and its profound impacts on climate. The first mode in the Atlantic is referred to as Deep Atlantic Multidecadal Variability (DAMV), characterized by a north‐south dipole pattern in the mid‐high latitudes with a quasi‐period of 20–50 years. The DAMV and Atlantic Multidecadal Variability, despite a statistical discrepancy, may be different responses to ocean heat transport (OHT) driven by the Atlantic Meridional Overturning Circulation (AMOC) at distinct depths separately. The relationship between the DAMV and the AMOC is established, indicating the AMOC is likely to transport surface heat downwards by deep convection and contribute to such dipole pattern in the deep Atlantic. Furthermore, meridional OHT proves the AMOC can explain the DAMV variation as a dynamic driver. These results reinforce the importance of deep‐sea studies concerning the Atlantic climate system.

Downward Mediterranean Cloudiness Beyond Little Ice Age Background Variability

Cloudiness–sea interaction substantially influences Earth’s climate by shaping precipitation patterns and radiative budgets. However, our understanding of long-term variations in land-based cloud cover, spanning over decades, centuries, and more, remains limited. This study presents the most extensive reconstruction to date of the annual total cloud cover fraction across the Mediterranean, spanning 1500–2022 CE. A notable shift occurred after 1818, marked by a surge in multidecadal variability and a sustained decline in cloud cover. This change has been attributed to several factors, including the eruption of Mount Tambora in Indonesia in 1815, intensified solar forcing, and a positive phase of the Atlantic Multidecadal Oscillation. These factors collectively reshaped cloudiness beyond typical background variability. By shedding light on the complex interactions with the climate system, our findings suggest that temperature changes may drive increased cloudiness in the Mediterranean when influenced by cold air masses through advection. This emphasizes the need for a deeper exploration of the impact of clouds on regional atmospheric circulation and climate changes. Ultimately, our enhanced understanding of the relationship between cloudiness and climate change provides valuable insights for climate models. While these models consistently project a decrease in cloudiness over the Mediterranean, our findings can also be helpful in understanding cloud variability in other parts of the globe.

Investigation of Temporal Trends and Spatial Patterns of Extreme Temperatures and Their Relationship to Climate Circulation Indices in Tanzania

This paper examined the spatial and temporal patterns of selected temperature extreme indices using the Mann-Kendall method (MK), the standard t-test, and the Pearson correlation analysis method. The relationship between extreme temperature events and climate circulation indices was analysed in Tanzania between 1983 and 2016 using data from 1961 to 2018. The results uncover a rise in the frequency and intensity of balmy days and nights across Tanzania. It suggests a significant increase in trends and the frequency of mild temperature index days and warm nights. It also indicates an increase in the trends for warm temperature indices (hottest days (TXx), coldest days (TNx), warm days (TX90p), tropical night (TR20), and Warm Spell Duration Indicator (WSDI); and a decrease in cold temperature indices (cold days (TX10p), cold nights (TN10p), cold days (TXn), and Cold Spell Duration Indicator (CSDI); which imply that the lower temperature was gradually decreasing more than in the past. The results further suggest that warm days and nights are significantly correlated with the Tropical Northern Atlantic Index (TNA), the Interdecadal Pacific Oscillation (IPO), the Atlantic Multidecadal Oscillation (AMO), and the El Nino-Southern Oscillation (ENSO). The circulation indices, which were found to be substantially associated with temperature extreme indices, can aid in forecasting, and may potentially serve as a foundation for future studies, particularly in the dynamics and physical mechanisms related to temperature extremes. The results presented in this paper are also vital for developing proper mitigation and adaptation measures to reduce future risks associated with extremely high-temperature events.

PDO and AMO Modulation of the ENSO–Asian Summer Monsoon Teleconnection During the Last Millennium

AbstractObservations show that the teleconnection between the El Niño‐Southern Oscillation (ENSO) and the Asian summer monsoon (ASM) is non‐stationary. However, the underlying mechanisms are poorly understood due to inadequate availability of reliable, long‐term observations. This study uses two state‐of‐the‐art data assimilation‐based reconstructions of last millennium climate to examine changes in the ENSO–ASM teleconnection; we investigate how modes of (multi‐)decadal climate variability (namely, the Pacific Decadal Oscillation, PDO, and the Atlantic Multidecadal Oscillation, AMO) modulate the ENSO–ASM relationship. Our analyses reveal that the PDO exerts a more pronounced impact on ASM variability than the AMO. By comparing different linear regression models, we find that including the PDO in addition to ENSO cycles can improve prediction of the ASM, especially for the Indian summer monsoon. In particular, dry (wet) anomalies caused by El Niño (La Niña) over India become enhanced during the positive (negative) PDO phases due to a compounding effect. However, composite differences in the ENSO–ASM relationship between positive and negative phases of the PDO and AMO are not statistically significant. A significant influence of the PDO/AMO on the ENSO–ASM relationship occurred only over a limited period within the last millennium. By leveraging the long‐term paleoclimate reconstructions, we document and interrogate the non‐stationary nature of the PDO and AMO in modulating the ENSO–ASM relationship.

The Association between climate indexes and tropical cyclones in decadal rainfall in San Ramón, Costa Rica

The decadal variability of precipitation over San Ramón, Costa Rica (SR-CR) and its relationship with the ONI, CLLJ, AMO indexes, and the frequency of tropical cyclones is investigated. Correlation tests are applied between the different indices with eight decades of precipitation in San Ramon. De-cadal precipitation shows that the driest were 1960-69 and 1980-89, and the wettest were 1970-79 and 1990-99. Every twenty years there is a climate change from wet to dry or dry to wet. During El Niño (ONI) events, the Pacific increases sea surface temperature (SST) and precipitation decreases in SR-CR and during La Niña, SST decreases and tends to rain more in SR-CR. Low values of the CLLJ tend to increase the incidence of precipitation in the area. Cyclonic activity has an appreciable influence on rainfall in SR-CR, the first two decades there were one and two cyclones. However, the rest of the decades showed more cyclones per decade, as is the case with 2010-19 with 8 cyclones. The relation-ship between the AMO index and precipitation in San Ramon has a 3-month lag.

Interdecadal change of Tibetan Plateau vortices during the past 4 decades and its possible mechanism

The Tibetan Plateau vortices (TPVs) are mesoscale weather systems active at the near-surface of the Tibetan Plateau (TP), which are one of the major precipitation-producing systems over the TP and its surrounding areas. TPVs mainly occur in the warm season from May to September. In this paper, we investigated the interdecadal change of TPVs in the warm seasons of 1979–2020 with the six widely used reanalysis datasets. A significant change of the TPVs frequency appears around the mid-1990s, associated with less TPVs during 1979–1995 and more TPVs during 1996–2020, which is constant among the multiple reanalysis datasets. The abrupt change of TPVs is caused by a transition of the Atlantic Multi-decadal Oscillation (AMO) from a cold phase to a warm phase in the mid-1990s. The shift of AMO leads to a silk-road pattern-like wave train and a spatially asymmetric change of tropospheric temperature. It modifies the intensity of the subtropical westerly jet and the TP heating, leading to the interdecadal change of TPV activities.

Modulation of the link between the Hadley circulation and the meridional structure of tropical SSTs by the Atlantic multidecadal oscillation

This paper investigates the effects of the Atlantic multidecadal oscillation (AMO) on the relationship between the Hadley circulation (HC) and the different meridional structures of the tropical sea surface temperature (SST). The response of the HC to SSTs shows inconsistent variations between the warm and cold phases of the AMO. The response of the HC to SSTs during the cold phase of the AMO is similar to that seen in the long-term and seasonal cycles. However, during the warm AMO phase, the magnitude of this response is significantly reduced. This significant difference in the response is caused mainly by the weakened response amplitude of the equatorially asymmetric HC and SST. The potential mechanisms associated with this suppression are also investigated, and they relate primarily to differences in the SST meridional anomalies within the Indo-Pacific warm pool (IPWP). During the AMO warm phase, the profile of SST anomalies in the IPWP exhibits characteristics similar to an equatorially symmetric distribution, which weakens the equatorially asymmetric component of the tropical SST and then contributes to the suppression of the response ratio. However, the amplitudes of the insignificant negative SST anomalies in the northern and southern IPWP are similar during the cold AMO phase. This distribution of SST anomalies has a minimal impact on the variation of SST gradients. Therefore, the response ratio during the cold AMO phase is comparable to that observed in the long-term and seasonal cycles. Other atmospheric reanalysis data are used to further confirm these results.

Spatiotemporal Variability in Rainfall Erosivity and Its Teleconnection with Atmospheric Circulation Indices in China

Rainfall erosivity (RE) is a critical factor influencing soil erosion, and soil erosion is closely related to land ecosystem health and long-term sustainable utilization. To ensure regional stable food supply and ecological balance, it is crucial to study the spatiotemporal distribution and influencing factors of RE. This study focuses on China and its three natural regions using daily precipitation data from 611 stations from 1960 to 2020. The study analyses the spatiotemporal changes in RE. Rainfall events were classified as moderate, large, and heavy based on rainfall intensity. The RE contribution from different rainfall levels to the total RE was analyzed, and the key climatic drivers closely linked to RE were identified using random forest. The results demonstrate that (1) on a national scale, RE shows a significant increasing trend, marked by an 81.67 MJ·mm·ha−1·h−1/decade. In the subregions, the Eastern Monsoon Region (EMR) and Qinghai–Tibet Plateau Region (QTR) show a significant increasing trend, with a greater change rate in EMR of 108.54 MJ·mm·ha−1·h−1/decade, and the Northwest Arid Region (NAR) shows a nonsignificant upwards trend. (2) The average RE increases northwest–southeast nationwide, ranging from 60.15 MJ·mm·ha−1·h−1 to 31,418.52 MJ·mm·ha−1·h−1. The RE contribution generated by different rainfall levels to the total RE exhibits spatial variations. The dominant types show that EMR is influenced by heavy RE, NAR is dominated by large RE, and QTR is affected by moderate RE. (3) The REs are associated with teleconnection indices, but the impact of these indices varies in different regions. The Western Hemisphere Warm Pool has the greatest impact on the EMR, while the North Atlantic Oscillation and Atlantic Multidecadal Oscillation are the factors influencing RE in NAR and QTR, respectively. (4) On a national scale, for every 1 mm increase in annual total rainfall, the RE increased by 8.54 MJ·mm·ha−1·h−1, a sensitivity of 8.54 MJ·mm·ha−1·h−1/mm. For the three subregions, there are differences in the sensitivity of RE to changes in annual precipitation. The highest sensitivity is found in EMR, at 8.71 MJ·mm·ha−1·h−1/mm, which is greater than the sensitivity indices in NAR (6.19 MJ·mm·ha−1·h−1/mm) and QTR (3.60 MJ·mm·ha−1·h−1/mm). This study can provide theoretical references for future regional soil erosion prediction and sustainable agricultural development in China.

Inter-decadal shift of spring drought over China around the late 1990s and the possible mechanisms

Based on the Standardized Precipitation-Evapotranspiration Index, this study reveals an inter-decadal shift of spring drought condition in China around the late 1990s, with three significant centers over Southeast China (SEC), the Hetao region (HT), and Northeast China (NEC). Further analysis indicates that potential evapotranspiration (PET) has larger influence on the inter-decadal drought aggravation over HT and SEC than precipitation, while precipitation has a more decisive effect on inter-decadal drought mitigation over NEC than PET. Further analysis suggests that the zonal atmospheric wave train over the Eurasian continent could be responsible for the inter-decadal shift of drought condition over China. The wave train can lead to an anomalous anticyclone around central Asia, which causes significant descending motion over HT and SEC that favors less cloud cover and surface air warming, further resulting in enhanced PET there. Concurrent with the decreased precipitation caused by descending motion and the moisture divergence, the drought in the two regions exhibits inter-decadal aggravation after the late 1990s. Additionally, the anomalous cyclone over Northeast Asia associated with the wave train leads to significant moisture convergence and ascending motion over NEC, resulting in increased precipitation there. The ascending motion also favors more cloud cover and surface air cooling over NEC, thus causing decreased PET there. Therefore, the drought condition over NEC exhibits inter-decadal mitigation after the late 1990s. Further analysis indicates that the Atlantic Multidecadal Oscillation could be an important factor contributing to the inter-decadal shift of drought condition over China by influencing the aforementioned Eurasian wave train.

Extreme waves in the Caribbean Sea: spatial regionalization and long-term analysis

The extreme wave height distribution in the Caribbean Sea is studied using a new method based on the maximum basin-wide aggregate of significant wave height, Hs, values per month. Besides, by means of the Self-Organizing Maps (SOM) technique, we identify coherent geographical regions with similar extreme wave height variability in the Caribbean Sea. Our findings revealed three primary regions: the eastern side with comparatively lower values, the central region with intermediate values, and the western side with the highest extreme wave heights. The study also examines the wind forcing conditions driving the spatial and temporal variability of the extreme waves, highlighting the influence of the low-pressure belt dynamics as well as the role played by the Caribbean Low-Level Jet (CLLJ) index, and the impact of cold fronts and hurricanes on extreme wave heights. Additionally, we explore the relationship between the extreme wave height distribution and climatic indices, such as the Atlantic Multidecadal Oscillation (AMO), the Atlantic Meridional Mode (AMM), the North Atlantic Oscillation (NAO) and the Oceanic Niño (ONI). The results reveal that the spatial distribution of extreme wave heights in the Caribbean Sea is mostly ruled by the influence of the CLLJ, with correlations close to 80%. In addition, significant correlations were observed between the extreme wave heights and the ENSO in the central Caribbean, as well as positive correlations between the extreme wave heights and NAO in the eastern part of the basin, and significant values of correlation with the negative phases of AMO and AMM in the whole basin. We show that, unlike conventional (or broadly used) methods deployed to identify extreme wave height, such as percentile 99th, Hs99, our methodology allows a further assessment of the wind and climate forcing conditions associated with the extreme wave events. Although, we acknowledge that the method here presented has limitations to capture extreme wave height outliers, it has the advantage of being used concomitant with the wind forcing to develop multivariate wave climate analysis at basin scale, and could be extended to a more local scale when studying coastal processes.

Groundwater level reconstruction using long-term climate reanalysis data and deep neural networks

Study regionNorthern Metropolitan France. Study focusAssessing long-term changes in groundwater is crucial for understanding the impacts of climate change on aquifers and for managing water resources.However, long-term groundwater level (GWL) records are often scarce, limiting the understanding of historical trends and variability. In this paper, we present a deep learning approach to reconstruct GWLs up to several decades back in time using recurrent-based neural networks with wavelet pre-processing and climate reanalysis data as inputs. GWLs are reconstructed using two different reanalysis datasets with distinct spatial resolutions (ERA5: 0.25° x 0.25° & ERA20C: 1° x 1°) and monthly time resolution, and the performance of the simulations were evaluated. New insightsLong term GWL timeseries are now available for northern France, corresponding to extended versions of observational timeseries back to early 20th century. All three types of piezometric behaviours could be reconstructed reliably and consistently capture the multi-decadal variability even at coarser resolutions, which is crucial for understanding long-term hydroclimatic trends and cycles. GWLs'multidecadal variability was consistent with the Atlantic multidecadal oscillation. From a synthetic experiment involving a modified long-term observational time series, we highlighted the need for longer training datasets for some low-frequency signals. Nevertheless, our study demonstrated the potential of using DL models together with reanalysis data to extend GWL observations and improve our understanding of groundwater variability and climate interactions.

The observed trend in unusual daily mean temperatures over Germany from 1949 to 2018 and their relationships to major climatic drivers

Unusual events are detected by the statistical changes in ‘extremes’, when extreme anomalies persist through the temporal and spatial interactions of the variable of interest. To identify the occurrences of unusual daily mean temperature events in 3- and 5-day sequences, a statistical method based on an “outlyingness” function is proposed in this study. This function is based on the geometrical position of a point on the multivariate set. To illustrate the methodology, this study uses daily mean temperature records from 18 observation stations across Germany (1949–2018). The findings indicate discernible changes in the frequency of unusual events at the stations, mostly during the boreal winter months between the first and last 35 years of the study period. A wide range of temperature anomaly averages (− 12 °C to + 12 °C) are produced by the interaction of series between warm and cold conditions, which affects the occurrence of disappearing days. While this is happening, the unusual warming is more pronounced on days that emerge from both the 3- and 5-day sequences, with temperature anomaly averages ranging from + 4 to + 12 °C. The Atlantic Multi-Decadal Variability and the Arctic Oscillation/North Atlantic Oscillation, respectively, are both implicated in the unusual surface warming over Germany. The disappearance days of unusual events do not exhibit statistically significant correlations with climatic indices, suggesting a possible anthropogenic effect. The emphasis of this study is on the necessity of determining whether unusual events in daily temperature anomalies across Germany can be attributed to anthropogenic factors.

Two Marine Heatwave (MHW) Variants under a Basinwide MHW Conditioning Mode in the North Pacific and Their Atlantic Associations

Abstract During 2013–16 and 2018–22, marine heatwaves (MHWs) occurred in the North Pacific, exhibiting similar extensive coverage, lengthy duration, and significant intensity but with different warming centers. The warming center of the 2013–16 event was in the Gulf of Alaska (GOA), while the 2018–22 event had warming centers in both the GOA and the coast of Japan (COJ). Our observational analysis indicates that these two events can be considered as two MHW variants induced by a basinwide MHW conditioning mode in the North Pacific. Both variants were driven thermodynamically by atmospheric wave trains propagating from the tropical Pacific to the North Pacific, within the conditioning mode. The origin and propagating path of these wave trains play a crucial role in determining the specific type of MHW variant. When a stronger wave train originates from the tropical central (western) Pacific, it leads to the GOA (COJ) variant. The cross-basin nature of the wave trains enables the two MHW variants to be accompanied by a tripolar pattern of sea surface temperature anomalies in the North Atlantic but with opposite phases. The association of these two MHW variants with the Atlantic Ocean also manifests in the decadal variations of their occurrence. Both variants tend to occur more frequently during the positive phase of the Atlantic multidecadal oscillation but less so during the negative phase. This study underscores the importance of cross-basin associations between the North Pacific and North Atlantic in shaping the dynamics of North Pacific MHWs.

Investigating Atmospheric Responses to and Mechanisms Governing North Atlantic Sea Surface Temperatures over 10-Year Periods

Abstract North Atlantic sea surface temperature (SST) variability plays a critical role in modulating the climate system. However, characterizing patterns of North Atlantic SST variability and diagnosing the associated mechanisms is challenging because they involve coupled atmosphere–ocean interactions with complex spatiotemporal relationships. Here we address these challenges by applying a time-evolving self-organizing map approach to a long preindustrial coupled control simulation and identify a variety of 10-yr spatiotemporal evolutions of winter SST anomalies, including but not limited to those associated with the North Atlantic Oscillation–Atlantic multidecadal variability (NAO–AMV)-like interactions. To assess mechanisms and atmospheric responses associated with various SST spatiotemporal evolutions, composites of atmospheric and oceanic variables associated with these evolutions are investigated. Results show that transient-eddy activities and atmospheric circulation responses exist in almost all the evolutions that are closely correlated to the details of the SST pattern. In terms of the mechanisms responsible for generating various SST evolutions, composites of ocean heat budget terms demonstrate that contributions to upper-ocean temperature tendency from resolved ocean advection and surface heat fluxes rarely oppose each other over 10-yr periods in the subpolar North Atlantic. We further explore the potential for predictability for some of these 10-yr SST evolutions that start with similar states but end with different states. However, we find that these are associated with abrupt changes in atmospheric variability and are unlikely to be predictable. In summary, this study broadly investigates the atmospheric responses to and the mechanisms governing the North Atlantic SST evolutions over 10-yr periods. Significance Statement Climate variability in the North Atlantic Ocean has wide-ranging impacts on global and regional climate. However, the processes involved include interactions between the ocean and atmosphere that vary across both space and time, making it challenging to characterize and predict. Using a novel machine learning approach, this study identifies various time evolutions of North Atlantic sea surface temperature patterns over 10-yr periods. This includes evolutions with similar start states but different trajectories, which have important implications for predictability. Furthermore, we investigate the mechanisms responsible for these evolutions and how different sea surface temperature patterns affect atmospheric circulation through small-scale atmospheric disturbances. These new insights into the complex ocean–atmosphere interactions over time are critical for improving decadal prediction skill.

An interdecadal change in the relationship between May North Atlantic oscillation and early summer precipitation over the Eastern Tibetan Plateau around the late 1990s

Based on the observational and reanalysis datasets, a dipole pattern of the early summer (June) precipitation over the eastern Tibetan Plateau (TP) is identified through empirical orthogonal function. In contrast to previous researches, this paper introduces the May North Atlantic Oscillation (NAO) as a preceding signal and investigates its connection with subsequent early summer precipitation over the eastern TP during 1980–2019, focusing on predictive aspects. Results reveal that the correlation between NAO and primary eastern TP precipitation pattern (Precip_EOF1) has weakened since 2000. During 1980–2000, an equivalent barotropic Silk Road Pattern (SRP) observed across Eurasia triggers southerly wind anomalies over the TP. This, in turn, leads to the northward shift of the water vapor, which favors the ascending motion over the northern TP (NTP) due to water vapor convergence. Additionally, the SRP-related sensible heating also plays a critical role in vertical motion over the eastern TP by enhancing the TP thermal effect. Consequently, these factors contribute to shaping the dipole pattern of eastern TP precipitation. However, the weakened relationship between NAO and Precip_EOF1 during 2001–2019 is attributed to the absence of NAO-related atmospheric circulation over Eurasia. Further analysis suggests that these circulation anomalies arise from the interdecadal variability of the NAO and its phase shift. Moreover, when the influence of sea surface temperature anomalies over the northern North Atlantic is removed, the correlation of Precip_EOF1 with NAO and Atlantic Multidecadal Oscillation (AMO) both become insignificant. This suggests that the NAO-related dipole pattern of eastern TP precipitation is modulated by preceding northern North Atlantic sea surface temperature rather than AMO on the interdecadal timescale.

Does the 11-year solar cycle affect lake and river ice phenology?

Records of ice-on and ice-off dates are available for lakes and rivers across the Northern Hemisphere spanning decades and in some cases centuries. This data provides an opportunity to investigate the climatic processes that may control ice phenology. Previous studies have reported a trend toward shorter ice-covered seasons with global warming, as well as links between ice phenology and several modes of natural climate variability such as the North Atlantic Oscillation, the Pacific-North American Pattern, the El Niño-Southern Oscillation, the Pacific Decadal Oscillation, and the Atlantic Multidecadal Oscillation. The 11-year sunspot cycle has also been proposed as a driver of ice phenology, which is somewhat surprising given that this cycle’s strongest impacts are in the stratosphere. In this study, we use a large data set of lakes and rivers across the Northern Hemisphere to test this potential link. We find little or no connection between the sunspot cycle and either ice-on or ice-off dates. We conclude that while many well-known climate cycles do impact ice phenology, we are able to rule out any strong impact of the solar cycle.

Dendroclimatological study of Sabina saltuaria and Abies faxoniana in the mixed forests of the Qionglai Mountains, eastern Tibetan Plateau

Tree-ring chronologies were developed for Sabina saltuaria and Abies faxoniana in mixed forests in the Qionglai Mountains of the eastern Tibetan Plateau. Climate-growth relationship analysis indicated that the two co-existing species reponded similarly to climate factors, although S. saltuaria was more sensitive than A. faxoniana. The strongest correlation was between S. saltuaria chronology and regional mean temperatures from June to November. Based on this relationship, a regional mean temperature from June to November for the period 1605–2016 was constructed. Reconstruction explained 37.3% of the temperature variance during th period 1961–2016. Six major warm periods and five major cold periods were identified. Spectral analysis detected significant interannual and multi-decadal cycles. Reconstruction also revealed the influence of the Atlantic Multi-decadal Oscillation, confirming its importance on climate change on the eastern Tibetan Plateau.

Responses of the Pacific and Atlantic decadal variabilities under global warming by using CMIP6 models

Decadal variability in the ocean is an important indicator of climate system shifts and has considerable influences on marine ecosystems. We investigate the responses of decadal variability over the global ocean regions using nine CMIP6 models (BCC-CSM2-MR, CESM2-WACCM, CMCC-ESM2, EC-Earth3-Veg-LR, FGOAL-f3-L, INM-CM5-0, MIROC6, MPI-ESM1-2-LR, and NorESM2-MM). Our results show that climate models can capture the Pacific Decadal Oscillation, Tropical Pacific Decadal Variability, South Pacific Decadal Oscillation, and Atlantic Multidecadal Variability under present-day conditions. The ocean decadal variabilities are becoming weaker and their periods are decreasing, especially under the strong global warming scenario. However, there is a discrepancy between the Tropical Pacific Decadal Variability and the other three modes of climate variability. This might be caused by the nearly unchanged atmospheric forcing in the equatorial region, which is decreasing in the higher latitude regions.