Atlantic Sea Surface Temperature Research Articles

Recent autumn sea ice loss in the eastern Arctic enhanced by summer Asian-Pacific Oscillation

Recent rapid Arctic sea ice loss was documented as combined results from anthropogenic forcing and climate system internal variability. However, the role of internal variability is not well understood. Here, we propose that the Asian-Pacific Oscillation (APO), an intrinsic atmospheric mode featuring out-of-phase variations in upper-tropospheric temperatures between Asia and the North Pacific, is one driver for autumn sea ice variability in the eastern Arctic. The positive summer APO favors warming of the mid-latitude North Atlantic sea surface temperatures. This warming persists to autumn and in turn triggers strong anticyclonic anomalies over the Barents-Kara-Laptev Seas and weak lower-tropospheric cyclonic anomalies over the East Siberian Sea, enhancing moisture transport into the eastern Arctic. Such changes consequently increase lower-tropospheric humidity, downwelling longwave radiation, and surface air temperature in the eastern Arctic, thereby melting sea ice. Hence, a recent tendency of the summer APO towards the positive phase accelerates autumn sea ice loss in the eastern Arctic.

Reversal of Projected European Summer Precipitation Decline in a Stabilizing Climate

AbstractPrecipitation projections in transient climate change scenarios have been extensively studied over multiple climate model generations. Although these simulations have also been used to make projections at specific Global Warming Levels (GWLs), dedicated simulations are more appropriate to study changes in a stabilizing climate. Here, we analyze precipitation projections in six multi‐century experiments with fixed atmospheric concentrations of greenhouse gases, conducted with the UK Earth System Model and which span a range of GWLs between 1.5 and 5°C of warming. Regions are identified where the sign of precipitation trends in high‐emission transient projections is reversed in the stabilization experiments. For example, stabilization reverses a summertime precipitation decline across Europe. This precipitation recovery occurs concurrently with changes in the pattern of Atlantic sea surface temperature trends due to a slow recovery of the Atlantic Meridional Overturning Circulation in the stabilization experiments, along with changes in humidity and atmospheric circulation.

Connections between low- and high- frequency variabilities of stratospheric northern annular mode and Arctic ozone depletion

Previous studies have demonstrated a dynamical linkage between the ozone and stratospheric polar vortex strength, but only a few have mentioned the persistence of the anomalous vortex. This study uses the complete ensemble empirical mode decomposition with adaptive noise to decompose the winter stratospheric northern annular mode (NAM) variabilities into relatively low frequencies (>4 months) and high frequencies (<2 months) (denoted as NAML and NAMH) and investigates their relationship with the Arctic ozone concentration in March. A closer relationship is found between the Arctic ozone and the NAML, i.e. a persistently strong stratospheric polar vortex in winter (especially February–March) is more critical than a short-lasting extremely strong vortex in contributing to Arctic ozone depletion. We find that a negative NAMH or major stratospheric sudden warming event in early winter could be a precursor for the anomalous depletion of Arctic ozone in March. The NAML changes are further related to the warm North Pacific sea surface temperature (SST) anomalies and ‘central-type’ El Niño-like or La Niña-like SST anomalies in early winter months, as well as cold North Atlantic SST anomalies and higher sea ice concentration in the Barents–Kara Sea from late-autumn to early-spring.

Combined Effects of Multiple Forcing Factors on Extreme Summer Multivariate Compound Heatwaves Over Western Europe

AbstractThe Multivariate compound heatwaves (MCHWs) present a significant risk to human health and ecological diversity, which attract widespread attention from researchers and society. The intensity and variability of summer MCHWs over Western Europe (WE) (MCHWs_WE) have substantially increased over the last two decades. The growing chance of such events is likely related to human activity‐induced climate change. However, the possible contributions from multiple atmospheric boundary forcing remain unclear. This study investigates the combined effects of North Atlantic sea surface temperature (SST), Tibetan Plateau (TP) snow cover (SC), and Arctic sea ice (SIC) on the variability of extreme summer MCHWs_WE. Observational analysis shows that an intensified anticyclonic system prevailing over WE, one of the centers of an atmospheric wave train dominating the North Atlantic‐Europe sector and persists from late spring to summer, is the essential system contributing to the extreme MCHWs_WE. Spring North Atlantic SST anomalies in the form of a dipole pattern persist from spring to summer and contribute to the summer extreme MCHWs_WE by exciting a downward propagating Rossby wave train pattern. Additionally, excessive late spring SC over the western TP and SIC over the Arctic, which are stimulated by the North Atlantic anomalous SST‐related wave train, can intensify the MCHWs_WE‐related anticyclonic system through vertical circulation and wave energy transport. The study further quantifies the relative contributions of the aforementioned factors. The findings of this study could potentially offer valuable insights for improving the prediction skill of summer extreme MCHWs_WE.

Enhanced influence of tropical Atlantic Sea surface temperature anomalies on east Asian summer monsoon since the late 1970s

Enhanced influence of tropical Atlantic Sea surface temperature anomalies on east Asian summer monsoon since the late 1970s

Hydroclimate Changes Based on Testate Amoebae in the Greater Khingan Mountains’ Peatland (NE China) during the Last Millennium

The driving force of climate change in the monsoon margin is complex, making it a key area for regional and global climate change research. Palaeohydrological studies in the monsoon margin have increased the resolution of research in the long term, transitioning from qualitative to quantitative studies to comprehend climate change processes, patterns, and mechanisms. Testate amoebae (TA) in peat sediments are used as a proxy indicator organism for quantitative reconstruction of palaeohydrology. Thus, their community changes are directly related to precipitation, and widely used to reconstruct the patterns of summer precipitation globally. We investigated TA species and reconstructed palaeohydrological changes in the Greater Khingan Mountains’ Hongtu (HT) peatland, located in the East Asian Summer Monsoon (EASM) margin. The result showed that the most abundant TA species were Assulina muscorum (12.4 ± 5.0%) and Nebela tincta (8.9 ± 4.9%) in the HT peat core. The increase in dry indicator species (e.g., A. muscorum and Alabasta militaris) indicated a drying pattern in the HT peatland since 150 cal yr BP. Principal component analysis (PCA) explained 47.6% of the variation in the selected TA assemblages. During 400 to 250 cal yr BP, PCA axis 1 scores ranged from 0.2 to −1.3 (reflecting a drier climate), associating with the Little Ice Age. The paleohydrology of the northern part of the Greater Khingan Mountains was mainly controlled by the EASM, which was associated with changes in North Atlantic Sea surface temperature and solar radiative forcing. The apparent drying pattern may be the result of the gradual intensification of anthropogenic activities and the increase in EASM intensity.

Flash Drought in the South of Yangtze River and the Potential Impact of North Atlantic Sea Surface Temperature

AbstractFlash droughts (FDs), a type of drought with rapid onset, occurred in growing season have damaging impacts on crops, ecosystem and hence livelihoods. However, the associated physical mechanism were not well understood, which prohibits a skillful early warning. Based on the reanalysis data for 1961–2022, we diagnosed the characteristics, antecedent meteorological conditions and large‐scale atmospheric circulation of FDs over the region south of Yangtze River (SYR), a hotspot region of FDs. The FDs tend to occur during the periods before (i.e., from April to mid‐June) and after (i.e., early July–September) Meiyu season (B‐Meiyu and A‐Meiyu periods). Large precipitation deficits and rapid elevated temperature caused by anomalous subsidence and moisture divergence are responsible for the onset of FDs during the two periods. The North Atlantic tripole‐like sea surface temperature anomaly (SSTA) modes have potential impact on the anomalous circulations via modulating Rossby wave trains, but with different locations among the two periods. During B‐Meiyu period, the SSTA mode is characterized by positive SSTA over subtropical North Atlantic and negative SSTAs over the tropical and mid‐latitude ocean, triggering a “+ − + − + −” circulation pattern over North Atlantic–Eurasia, which reinforces the East Asian trough (EAT). Anomalous northeasterly winds dominate the SYR suppressing moisture transport from the tropics. The SSTA mode locates farther to the north during A‐Meiyu period, inducing a “+ − + − +” wave train over mid‐latitude North Atlantic‐Eurasia, leading to the strengthening of the western Pacific subtropical high. The high‐pressure anomalies control the SYR, resulting in anomalous subsidence and hence negative precipitation anomalies.

The Important Role of Reduced Moisture Supplies from the Monsoon Region in the Formation of Spring and Summer Droughts over Northeast China

Abstract Anomalies in atmospheric moisture transport are critical for drought formation, with East Asian monsoon anomalies identified as the primary driver of droughts in East Asia. However, the drought mechanism for the border region between monsoon and nonmonsoon land areas remains unclear due to complex interactions between latitudinal circulation patterns. Using a Lagrangian framework, we quantify moisture supply (MS) during spring and summer drought events within the border region, specifically Northeast China (NEC). Our results reveal that decreased MS from monsoon land areas is more crucial than nonmonsoon land areas and local areas for NEC droughts, with the local water recycling playing a more substantial role in summer than in spring. On average, summer droughts are 4 times more intense than spring droughts. Contributions to MS deficits from monsoon land areas, nonmonsoon land areas, and local areas during spring (summer) droughts are 43.2% (43.8%), 25.1% (19.2%), and 22% (33.8%), respectively. The weakened atmospheric circulation from source regions to NEC contributes to over 80% of MS deficits during droughts. Atmospheric wave trains triggered by North Atlantic sea surface temperature anomalies (SSTA) gradients, along with the weakening of the East Asian subtropical westerly jet in spring and a positive phase of the polar–Eurasian teleconnection in summer, contribute to spring and summer droughts, respectively. A sustained, record-breaking positive SSTA along the western European coast from the spring to summer excited a wave train, and resulted in the extreme 2017 spring–summer drought. These findings provide valuable insights into the drought mechanism within the interaction zone of circulation systems from different latitudes. Significance Statement The complex interactions between atmospheric circulation patterns at different latitudes have led to an insufficient understanding of the mechanisms causing extreme drought in the border region between the monsoon and nonmonsoon land areas. This study aims to investigate the drought mechanisms in the border region from the perspective of moisture tracking. Results indicate a moisture supply deficit from the monsoon region contributes the most (approximately half) to droughts, although the majority of air parcels reaching this region originate from the nonmonsoon region. The weakening of circulation contributes to more than 80% of the moisture supply deficit during droughts, far exceeding the impact of reduced evaporation from the moisture source regions. These findings are conducive to understanding the mechanisms of extreme drought.

Sea surface temperature driven modulation of decadal co-variability in mean and extreme precipitation

This study investigates the role that sea surface temperature (SST) variability plays in modulating the relationship between decadal-scale mean precipitation and monthly-scale extreme precipitation using the Australian Community Climate and Earth System Simulator Earth System model (ACCESS ESM1.5) climate model. The model large ensemble successfully reproduces the observed strong co-variability between monthly mean rainfall and wet extreme rainfall, defined as monthly rainfall totals above the 95th percentile. Removing SST variability in the ACCESS ESM1.5 model significantly weakens the co-variability between mean and wet extremes over most of the globe, showing that SSTs play a key role in modulating this co-variability. The study identifies Pacific and Atlantic SST patterns as the main drivers of the decadal scale co-variability in mean and extreme wet precipitation. On the other hand, observations and model results show that co-variability between mean and dry extremes is generally weaker than for wet extremes, with highly regional signals. Model experiments also show that SST variability plays a weaker role in modulating the co-variability between the mean precipitation and dry extremes as compared to wet extremes. These results suggest that stochastic atmospheric variability plays a stronger role in generating dry precipitation extremes compared SST forcing.

Exploring covariabilities of the high-summer subtropical upper-level pressure systems in the Northern Hemisphere

The Northern Hemisphere subtropical upper-tropospheric pressure systems, i.e., South Asian high (SAH), mid-Pacific Trough (MPT), and mid-Atlantic Trough (MAT), play key roles in regulating the Eurasian–Pacific–North American climate, but their covariabilities and drivers remain unclear. Here, we reveal two seesaw-like teleconnections between MPT and western SAH (WSAH) and between MPT and MAT during the boreal high summer, respectively, and explore their associations with the tropical Pacific and Atlantic sea surface temperature (SST) anomalies. The MPT-WSAH teleconnection, featured by coherent variations between WSAH and MPT, is coupled with enhanced western Pacific subtropical high and Asian mid-latitude low in the low-level troposphere. In contrast, the MPT-MAT teleconnection features an out-of-phase relationship between MPT and MAT, which is associated with westward expanded western Pacific subtropical high but weakened North Atlantic subtropical high. Both two teleconnections are closely linked to Pacific SST anomalies. However, the former is mainly driven by the hybrid La Niña in the tropical Pacific, where cold SST anomalies spreading eastward since preceding winter. Whereas the latter corresponds to the central Pacific La Niña since late-spring mainly driven by preceding successive SST warming in the tropical North Atlantic. Above conclusions are further confirmed by the simulated results from the numerical experiments, which are performed using the US National Center for Atmospheric Research global Community Atmosphere Model version 4.

Causal oceanic feedbacks onto the winter NAO

Of the climate variability patterns that influence the weather in the North Atlantic region in winter, the North Atlantic Oscillation (NAO) is the most dominant. The effects of the NAO span from cold air outbreaks to unseasonably warm conditions and unusual precipitation, with significant impacts on human activities and ecosystems. While a connection between the NAO and antecedent sea surface temperature (SST) conditions has been recognised for decades, the precise causal interaction between the ocean and the atmosphere remains enigmatic. In this study we uncover a robust statistical relationship between North Atlantic SSTs in November and the NAO throughout the subsequent winter in the extended ERA5 reanalysis back to 1940. We apply a well-established causal inference technique called mediation analysis, commonly used in social science and now adopted in climate research. This analysis highlights the roles of low-level baroclinicity, latent heat fluxes, and latent heat release in mediating the effect of November SSTs on the NAO in January and February. It is important to recognise that these mediators are interrelated. Moreover, our analysis reveals bidirectional relationships, where the NAO reciprocally mediates the effects of the November SSTs on these variables. This is evidence of a complex web of feedback mechanisms which collectively contribute to the response of the winter NAO to late autumn/early winter SSTs.

The Tropical Atlantic's Asymmetric Impact on the El Niño‐Southern Oscillation

AbstractUsing observations and Atlantic forced coupled model simulations, we show evidence for an asymmetry in the link between beginning of year tropical Atlantic sea surface temperature anomalies (SSTAs) and end of the year El Niño‐Southern Oscillation events. We find a greater tendency for warm Atlantic SSTAs to lead to a La Niña than for cold anomalies to lead to El Niño. The model experiments showed that the Atlantic had a greater chance to force the tropical Pacific if the Pacific was initially in a neutral state. In the model, a warm Atlantic from March–May was able to produce an atmospheric response leading to easterly wind anomalies in the western Pacific. This in turn induces a subsurface oceanic response, leading to La Niña at the end of the year. The atmospheric response does not occur for a cold Atlantic, leading to no impacts in the Pacific.

Diatom-based inferences of environmental changes from an alpine lake on the southeast edge of the Tibetan plateau over the last 4000 years

To better understand how global and regional-scale climate has changed, high-resolution records for environmental changes are still needed in southwestern (SW) China during the Late Holocene epoch. This study presents a well-dated high-resolution diatom analysis from a 1.66-m-long sediment core taken from Lake Cuogeda (CGD) on the southeast (SE) edge of the Tibetan Plateau to document environmental changes over the past ∼4000 years. Diatom and other geochemical proxies show that, from 3850 to 3430 cal yr BP (before present, 0 BP=1950 AD, 1900 to 1480 BC), the environment of Lake CGD is acidic, oligotrophic, and enriched with humic acids. And the lake ice cover duration is short during this period. During 3430–1550 cal yr BP (1480 BC-400 AD), Lake CGD has less humic acid and a relatively high pH environment. The ice cover duration is longer, and the temperature drops during this period. Our multi-indicator recorded two environment fluctuations at ∼2800 cal yr BP (850 BC) and 2210–1950 cal yr BP (260 BC-0 AD). From 1550 to 3.6 cal yr BP (400–1946 AD), the lake ecosystem changed to a higher pH condition and had a prolonged freezing time. From 3.6 cal yr BP (1946 AD) to the present, Lake CGD’s water was acidic, with an environment of shorter duration of ice cover and stronger lake water turbulence. Comparisons between the CGD records and other climate reconstructions underscore the relevance of the CGD record for regional and global environments. Comparisons indicate that the environment evolution pattern of SW China during the Late Holocene was greatly affected by solar radiation and North Atlantic sea surface temperature.

Regime change in northwest Atlantic sea surface temperatures revealed using a quantile approach

Trends in sea surface temperatures (SST) of the US Northeast Continental Shelf and the adjacent Slope Sea were analyzed using a quantile approach. SST through the period 1982–2021 were analyzed for change in annual mean and range. In addition, the mean of each 25% quantile of the data by year was calculated. Using the full time series, the climatological SSTs at each quantile was determined, which in turn were used with the annual data to determine the number of days temperature fell within the limits of each climatological quantile. The time series of the data parameters were summarized by grid location and for a series of representative index areas. The index areas were analyzed for evidence of change points or regime shifts using the STARS (Sequential T-test Analysis of Regime Shifts) algorithm. The widely reported SST warming in this region was reinforced with our analysis; our findings also revealed new aspects of the change of thermal conditions in important ways. Mean annual temperature trended at approximately 0.36 °C per decade; however, warm quantile SSTs increased by more than 1.25 °C per decade in the Slope Sea, representing a five degree increase over the study period. The change point analysis suggested the change in thermal regime began as early as 2005 or 2007 with the study region fully enveloped by regime change by 2012. A previously identified change point in 1999 appears to be related to the duration of warming as opposed to SST levels. Mean SST alone does not capture the nature of high temperature exposure for living marine species in the study area; these regions may be experiencing a month or more of stressfully higher SST. The thermal effects derived using the quantile approach suggest different types of thermal exposures compared to heat wave analyses, especially related to cumulative exposure.

Comparison of climate time series – Part 5: Multivariate annual cycles

Abstract. This paper develops a method for determining whether two vector time series originate from a common stochastic process. The stochastic process considered incorporates both serial correlations and multivariate annual cycles. Specifically, the process is modeled as a vector autoregressive model with periodic forcing, referred to as a VARX model (where X stands for exogenous variables). The hypothesis that two VARX models share the same parameters is tested using the likelihood ratio method. The resulting test can be further decomposed into a series of tests to assess whether disparities in the VARX models stem from differences in noise parameters, autoregressive parameters, or annual cycle parameters. A comprehensive procedure for compressing discrepancies between VARX models into a minimal number of components is developed based on discriminant analysis. Using this method, the realism of climate model simulations of monthly mean North Atlantic sea surface temperatures is assessed. As expected, different simulations from the same climate model cannot be distinguished stochastically. Similarly, observations from different periods cannot be distinguished. However, every climate model differs stochastically from observations. Furthermore, each climate model differs stochastically from every other model, except when they originate from the same center. In essence, each climate model possesses a distinct fingerprint that sets it apart stochastically from both observations and models developed by other research centers. The primary factor contributing to these differences is the difference in annual cycles. The difference in annual cycles is often dominated by a single component, which can be extracted and illustrated using discriminant analysis.

New insights into the biennial-to-multidecadal variability of the water level fluctuation in Lake Titicaca in the 20th century

The water disponibility of Lake Titicaca is important for local ecosystems, domestic water, industry, fishing, agriculture, and tourism in Peru and Bolivia. However, the water level variability in Lake Titicaca (LTWL) still needs to be understood. The fluctuations of LTWL during the 1921–2018 period are investigated using continuous wavelet techniques on high- and low-pass filters of monthly time series, ERA-20C reanalysis, sea surface temperature (SST), and water level. We also built multiple linear regression (MLR) models based on SST indices to identify the main drivers of the LTWL variability. LTWL features annual (12 months), biennial (22–28 months), interannual (80–108 months), decadal (12.75–14.06 years), interdecadal (24.83–26.50 years), and multidecadal (30–65 years) signals. The high- and low-frequency components of the LTWL are triggered by the humidity transport from the lowland toward the Lake Titicaca basin, although different forcings could cause it. The biennial band is associated with SST anomalies over the southeastern tropical Atlantic Ocean that strengthen the Bolivian High-Nordeste Low system. The interannual band is associated with the southern South Atlantic SST anomalies, which modulate the position of the Bolivian High. According to the MLR models, the decadal and interdecadal components of the LTWL can be explained by the linear combination of the decadal and interdecadal variability of the Pacific and Atlantic SST anomalies (r &amp;gt; 0.83, p &amp;lt; 0.05). In contrast, the multidecadal component of the LTWL is driven by the multidecadal component of the North Atlantic SST anomalies (AMO) and the southern South Atlantic SST anomalies. Moreover, the monthly time series of LTWL exhibits four breakpoints. The signs of the first four trends follow the change of phases of the multidecadal component of LTWL, while the fifth trend is zero attributable to the diminished amplitude of the interdecadal component of LTWL.

Process-Informed Subsampling Improves Subseasonal Rainfall Forecasts in Central America.

Subseasonal rainfall forecast skill is critical to support preparedness for hydrometeorological extremes. We assess how a process-informed evaluation, which subsamples forecasting model members based on their ability to represent potential predictors of rainfall, can improve monthly rainfall forecasts within Central America in the following month, using Costa Rica and Guatemala as test cases. We generate a constrained ensemble mean by subsampling 130 members from five dynamic forecasting models in the C3S multimodel ensemble based on their representation of both (a) zonal wind direction and (b) Pacific and Atlantic sea surface temperatures (SSTs), at the time of initialization. Our results show in multiple months and locations increased mean squared error skill by 0.4 and improved detection rates of rainfall extremes. This method is transferrable to other regions driven by slowly-changing processes. Process-informed subsampling is successful because it identifies members that fail to represent the entire rainfall distribution when wind/SST error increases.

Record-Breaking Rainfall in the Northern Amazon in Spring 2022 Tied to the Pacific and Atlantic Sea Surface Temperatures

In the boreal spring of 2022, a record-breaking rainfall event occurred in the northern Amazon basin, causing major economic and property damage. Using observational datasets and sensitivity tests from the linear baroclinic model, this study shows that the combined effect of the Pacific and Atlantic sea surface temperatures (SSTs) contributed to this extreme rainfall event. Negative (positive) SST anomalies in the tropical southeastern Pacific (tropical South Atlantic) favored anomalous westerlies (southeasterlies) from the tropical eastern Pacific (southwestern Atlantic) to the northern Amazon basin, which led to enhanced convergence of water vapor and positive rainfall anomalies in the northern Amazon basin. Our study offers insight into the combined effects of the Pacific and Atlantic SSTs in driving extreme rainfall event in the Amazon basin.

Possible impact of North Atlantic sea surface temperature on decadal variability of dust activity in Gobi Desert

Semiarid to arid regions located in north of China are known as one of the largest sources of dust aerosols in the globe. Previous studies demonstrated direct and indirect effects of atmospheric dust loading on climate. The surface and meteorological properties are known to be affecting dust entrainment process. In this study, we found decadal variations of dust occurrence in Gobi Desert with the period of ∼24 years, utilizing the data acquired at the surface meteorological stations. An analysis of reanalysis datasets shows significant correlations between February North Atlantic Sea Surface Temperature (NASST) and precipitation in Gobi Desert and Mongolia in the following summer, causing a decadal variation of dust event frequency in the subsequent spring over the region. Strong time-lagged correlation is shown to be linked to an atmospheric wave train pattern that initiated from the NASST region, affecting large-scale circulation, ultimately causing surface drought over Gobi Desert.

Uncertainty on Atlantic Niño Variability Projections

AbstractSources of uncertainty (i.e., internal variability, model and scenario) in Atlantic Niño variability projections were quantified in 49 models participating in the Coupled Model Intercomparison Phases 5 (CMIP5) and 6 (CMIP6). By the end of the twenty‐first century, the ensemble mean change in Atlantic Niño variability is −0.07 ± 0.10˚C, with 80% of CMIP models projecting a decrease, and representing a 16% reduction relative to the 1981–2005 ensemble mean. Models' projections depict a large spread, with variability changes ranging from 0.23˚C to −0.50˚C. Internal variability is the main source of uncertainty until 2045 but model uncertainty dominates thereafter, eventually explaining up to 80% of the total uncertainty. The scenario uncertainty remains low (&lt;1%) throughout the twenty‐first century. The total uncertainty on Atlantic Niño variability projections is not improved when considering only CMIP models with a realistic zonal equatorial Atlantic sea surface temperature gradient.