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This study investigates the relationship between sea surface temperature (SST) anomalies in the subtropical Atlantic Ocean, as represented by the Southern Atlantic subtropical dipole (SASD), and SST anomalies in the tropical Pacific Ocean, identified by the El Niño‐Southern Oscillation (ENSO). Contrary to the previously held notion of a weak relationship between SASD and ENSO as suggested by earlier literature, our analysis reveals a substantial inverse correlation between the two. This correlation exhibits significant multi‐decadal variability, which has notably intensified over the most recent two decades compared with the preceding two decades. This intensification in the SASD–ENSO inverse correlation may be attributed to the shift in ENSO regime from predominance of eastern Pacific El Niño to central Pacific El Niño events around the turn of the century. This transition triggers wavetrains that propagate along different paths, consequently influencing the South Atlantic subtropical high and inducing alterations in anomalous SST patterns in the subtropical Atlantic Ocean. These findings advance our comprehension of the interactions between South Atlantic and Pacific SST variations, which strongly influence rainfall patterns, particularly in South America and southern Africa. Understanding such teleconnection holds promise for improving sub‐seasonal to seasonal precipitation predictions in these regions. [ABSTRACT FROM AUTHOR]

This study investigates the relationship between sea surface temperature (SST) in the subtropical Atlantic Ocean, as represented by the Southern Atlantic Subtropical Dipole (SASD), and SST in the tropical Pacific Ocean, identified by the El Niño-Southern Oscillation (ENSO). Our analysis reveals a significant inverse correlation between the SASD and Niño indices over a century, with multi-decadal variability that contradicts weak simultaneous correlations previously reported in the literature. The study also highlights a strengthening of their inverse correlations in the most recent two decades compared to the preceding two decades, which can be attributed to the shift in ENSO regime from more frequent eastern Pacific El Niño to central Pacific El Niño around the turn of the century. This shift helps set the stage for changes in convective activity in the critical region (20° S–40° S, 180°–140° W) of the central South Pacific Ocean, triggering wavetrains that propagate along different paths and ultimately contributing to different southern Atlantic subtropical high (SASH) and changes in anomalous SST patterns in the subtropical Atlantic Ocean. These findings advance our understanding of the interactions between South Atlantic and Pacific SST variations, which strongly influence rainfall patterns particularly in South America and southern Africa and may improve sub-seasonal to seasonal precipitation predictions in these regions. [ABSTRACT FROM AUTHOR]

Both the Southern Annular Mode (SAM) and El Niño–Southern Oscillation (ENSO) are critical factors contributing to Antarctic sea ice variability on interannual time scales. However, their joint effects on sea ice are complex and remain unclear for each austral season. In this study, satellite sea ice concentration (SIC) observations and atmospheric reanalysis data are utilized to assess the impacts of combined SAM and ENSO on seasonal Antarctic sea ice changes. The joint SAM–ENSO impacts on southern high latitudes are principally controlled by the strength and position of the wave activity and associated atmospheric circulation anomalies affected by their interactions. In-phase events (La Niña/positive SAM and El Niño/negative SAM) are characterized with an SIC dipole located in the Weddell/Bellingshausen Seas and Amundsen/Ross Seas, while out-of-phase events (El Niño/positive SAM and La Niña/negative SAM) experience significant SIC anomalies in the Indian Ocean and western Pacific Ocean. Sea ice budget analyses are conducted to separate the dynamic and thermodynamic contributions inducing the sea ice intensification anomalies. The results show that in-phase intensification anomalies also display a pattern similar to the SIC dipole and are mainly driven by the direct thermodynamic forcing at the ice edge and thermodynamic responses to meridional sea ice drift in the inner pack, especially in autumn and winter. Dynamic processes caused by zonal sea ice drift also play an important role during out-of-phase conditions in addition to the same mechanisms during in-phase conditions. [ABSTRACT FROM AUTHOR]

The Antarctic sea ice variability has been linked to tropical sea surface temperature. However, little is known as to whether and how the Indian Ocean Basin Mode (IOBM) influences Antarctic sea ice changes. We revealed the existence of a teleconnection between the IOMB and Antarctic sea ice anomalies, which is much stronger in austral spring and autumn than summer and winter. In particular, under the positive phase of the IOBM, significant positive sea ice anomalies occur in the Bellingshausen and northern Weddell Seas, in contrast to negative anomalies in the Amundsen Sea, the southern Atlantic Ocean, and the coastal seas off Dronning Maud Land. This teleconnection is established by planetary wavetrains excited over the tropical Indian Ocean and the tropical Pacific Ocean and is modulated by El Niño‐Southern Oscillation. The IOBM‐related Antarctic sea ice anomalies are largely consistent with those of the anomalous surface air temperature and wind fields associated with the IOBM. Plain Language Summary: The variability of sea surface temperature in the tropical Indian Ocean is dominated by two modes, the Indian Ocean Dipole (IOD) and the Indian Ocean Basin Mode (IOBM). While previous studies have linked IOD to Antarctic sea ice changes, little is known about whether and how IOBM may affect seasonal Antarctic sea ice. Using 40‐year (1979–2018) observational and reanalysis data, we found that there exists a significant teleconnection between the IOBM and the Antarctic sea ice anomalies in austral autumn and spring, and that this remote connection can be largely explained by anomalous atmospheric circulations. Key Points: A teleconnection exists between the Antarctic sea ice anomalies and the sea‐surface‐temperature anomaly known as the Indian Ocean Basin Mode (IOBM)The IOBM and Antarctic sea ice connection varies spatially and seasonally, is stronger in autumn and spring, and is modulated by El Niño‐Southern Oscillation (ENSO)Removing the ENSO modulation, the extent of sea ice concentration anomalies shrinks a lot, and the source of the wavetrain moves westward [ABSTRACT FROM AUTHOR]

The relationship of the tropical Indo‐Pacific upper ocean heat content (HC) and the South China Sea (SCS) summer monsoon (SCSSM) onset during 1980–2020 was investigated. It was found that when HC anomalies in the preceding winter–spring are positive (negative) in the eastern Indian–western Pacific Ocean or negative (positive) in the southwestern Indian Ocean and eastern Pacific Ocean, SCSSM onset is usually early (late). Empirical orthogonal function (EOF) analysis suggested that the primary EOF modes of HC anomaly in both tropical Pacific and Indian Oceans are associated with El Niño–Southern Oscillation (ENSO). It is through modulating the westerly over the north Indian Ocean–SCS and the western north Pacific subtropical high (WNPSH) via the Walker circulation over the Indo‐Pacific basin, monsoon circulation in the Indian Ocean that the ENSO related Indo‐Pacific HC variation connects with the SCSSM onset. Both the second EOF modes for the tropical Pacific and Indian Ocean also show significant correlations with the SCSSM onset. The former related vertical motion over the SCS–far northwestern Pacific can influence the WNPSH and convection, thus occurrence of the SCSSM. The latter represents the intrinsic Indian Ocean HC variability; the air temperature variation associated with it can modulate the atmospheric circulation in the Indian Ocean–SCS through thermal wind balance, and thus the SCSSM onset by acting on the westerly over the SCS and the WNPSH. A western Pacific index and an Indian Ocean dipole index were defined to represent the leading HC modes in the tropical Pacific and Indian Ocean, respectively. A binary linear regression model was constructed using these two indices to improve SCSSM onset prediction. [ABSTRACT FROM AUTHOR]

We used 35-year (1979-2013) hourly rainfall data from the North American Land Data Assimilation System (NLDAS-2) to examine the relationships of the symmetric and asymmetric components of two types of El Niño-Southern Oscillation (ENSO) (El Niño and El Niño Modoki) episodes with occurrences of extreme precipitation events across the United States. During the cold season, the symmetric impacts of El Niño and El Niño Modoki are more significant than during the warm season. The asymmetric components associated with El Niño during the two seasons are comparable, while the asymmetric components associated with El Niño Modoki during the warm season are more significant than those during the cold season. The connections between the symmetric and asymmetric components of the two types of ENSO and extreme precipitation occurrences are related to atmospheric moisture convergence patterns that tend to occur in response to the anomalous large-scale atmospheric circulations during the ENSO episodes. [ABSTRACT FROM AUTHOR]

ABSTRACT The inter-annual variability of southerly low-level jets ( SLLJs) over North America during the warm (April-September) and cool (October-March) seasons is investigated. SLLJ occurrences over a 31-year period (1979-2009) were identified from the North American Regional Reanalysis ( NARR) vertical wind profiles. The first empirical orthogonal function ( EOF) modes of the SLLJ frequency during the warm and cool seasons account for about 30 and 20% of the total variance, respectively. Both modes can be interpreted as a strengthening or weakening of the core area of SLLJ anomalies. The principal component ( PC) time series display significant positive trends, suggesting an increase in SLLJ activity during both seasons on inter-decadal time scales and are significantly correlated to the summertime Pacific Decadal Oscillation ( PDO) and Atlantic Multidecadal Oscillation ( AMO) for the warm season and the wintertime PDO, AMO and El Niño Modoki for the cool season. The second modes account for about 20 and 15% of the total variance for the warm and cool seasons, respectively, and are interpreted as primarily a subseasonal latitudinal shift in SLLJ activity between the central Great Plains and the western Gulf of Mexico and southern Texas during the warm season and a longitudinal shift between the western Gulf of Mexico and the Caribbean during the cool season. The second mode appears to be significantly correlated to El Niño Modoki for the warm season and to Niño 3.4 for the cool season. [ABSTRACT FROM AUTHOR]

Irregular oscillations of Equatorial Pacific sea surface temperatures known as El Niño-Southern Oscillation (ENSO) has been shown to affect air pollution in China by altering atmospheric circulations. In this study, we use hourly PM2.5 data from nearly 1500 monitoring stations across entire China to further explore the connection between ENSO and China's haze pollution by comparing PM2.5 concentrations for the two most recent ENSO events, the 2015–2016 El Niño and the 2017–2018 La Niña. The PM2.5 concentrations show significant differences between the two events and the differences are larger in winter and smaller in summer. In summer, the PM2.5 concentrations are higher across China during El Niño. However in winter, higher concentrations are found at most stations in northern China during El Niño, but at majority of stations in southern China during La Niña. Spring and autumn show a transitional pattern between summer and winter. Dividing the country into nine regions with similar geographical conditions, the relationship between the monthly PM2.5 concentration anomalies and the Niño3.4 indices, as revealed by linear regression, is generally positive at stations in North, Northeast and the northern parts of Central and East China, but generally negative in South, Southwest and the southern parts of Central and East China. No difference is found in the oscillation periods of the PM2.5 concentrations between the two events, except that the seasonal and intra-seasonal oscillatory signals appear to be slightly stronger during El Niño than La Niña. The regional and seasonal differences in PM2.5 concentrations between El Niño and La Niña can be partially explained by the differences in the anomalous atmospheric circulation patterns, particularly the low-level wind and surface precipitation patterns. • The influence of El Niño and La Niña on PM2.5 concentrations across China is explored. • The influence of El Niño-La Niña on PM2.5 in China differ by region and season. • The relationship between PM2.5 and Niño indices is opposite in north and south China. • PM2.5 seasonal and intra-seasonal oscillations are stronger with El Niño than La Niña. • The ENSO-PM2.5 connection is consistent with anomalous circulation and precipitation. [ABSTRACT FROM AUTHOR]

Using hourly observations of fine particulate matter (PM2.5) from a nationwide air-quality monitoring network of nearly 1500 stations, augmented with gridded atmospheric reanalysis data, we examined the differential influences of the eastern Pacific El Niño and central Pacific El Niño also known as El Niño Modoki on surface PM2.5 concentrations in different regions of China during different seasons. We show that the influence can be opposite during warm season, with PM2.5 anomalies overwhelmingly positive (negative) across China under El Niño (El Niño Modoki), although in both cases the largest anomalies appear in North China and the adjacent areas and smallest in the Qinghai-Tibet Plateau. The cold-season PM2.5 concentration is less sensitive to the El Niño type, with a general pattern of positive anomalies in the North, Northeast, Inner Mongolia, northern parts of the Central and East and along the southern and southeastern coasts and negative anomalies in most other regions. Nevertheless, negative cold-season anomalies are stronger and more widespread during El Niño Modoki compared to El Niño, and they could be opposite in some areas of the Northwest and Qinghai-Tibet Plateau where positive (negative) anomalies may prevail during El Niño (Niño Modoki). Much of these differences can be attributed to the differences in the anomalous atmospheric conditions associated with El Niño and El Niño Modoki, particularly the low-level anomalous wind direction that controls regional PM2.5 transport and precipitation leading to PM2.5 removal. These findings could assist in developing a nuanced approach to seasonal PM2.5 forecasting for different regions in China. [Display omitted] • The sensitivity of PM2.5 concentration distribution in China to ENSO type is particularly notable in the warm season. • China's warm-season PM2.5 shows opposite response to El Niño (increase) and El Niño Modoki (decrease) in most regions. • Cold-season PM2.5 response to ENSO type varies in western/southern China, but remains consistent elsewhere. • PM2.5's response to El Niño types is largely due to differences in anomalous atmospheric circulations. [ABSTRACT FROM AUTHOR]