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Tropical and extra-tropical storms generate extreme waves, impacting both nearby and remote regions through swell propagation. Despite their devastating effects in tropical areas, the contribution of tropical cyclones (TCs) to global wave-induced coastal risk remains unknown. Here, we enable a quantitative assessment of TC's role in extreme waves approaching global coastlines, by designing twin oceanic wave simulations with and without realistic TC wind forcing. We find that TCs substantially contribute to extreme breaking heights in tropical regions (35-50% on average), reaching 100% in high-density TC areas like the North Pacific. TCs also impact remote TC-free regions, such as the equatorial Pacific experiencing in average 30% of its extreme wave events due to TCs. Interannual variability amplifies TC-induced wave hazards, notably during El Niño in the Central Pacific, and La Niña in the South China Sea, Caribbean Arc, and South Indian Ocean coastlines. This research offers critical insights for global risk management and preparedness. This paper shows that tropical cyclones contribute between 40% and 100% of the extreme wave events approaching coastlines in basins prone to tropical cyclone activity, while they can also impact remote areas via swell propagation across the ocean. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of advancing deforestation in the southwestern Amazon on local hydroclimate. For this purpose, a high-resolution mesoscale model, coupled with a land surface model and a hydrologic routing model, is integrated for five years in two experiments, one control without changes in land use and another changing land use annually. During the rainy season, simulated higher precipitation volumes are reduced with the expansion of pasture lands. In the dry periods, mainly in August, there is an increase in precipitation over some deforested areas, which can be associated with mesoscale circulations induced by the heterogeneous surface. In general, land-use changes reduce evapotranspiration and the net radiation at the surface and increase the sensible heat flux during the dry season. In the rainy period, there is an increase in evapotranspiration with the intensification of deforestation, which modifies the other components of energy balance. Results suggest that the impact of LUCC on the local climate is more affected by conditions that generate precipitation extremes (El Niño/La Niña events) than by the abrupt increase in the annual deforestation rate. Land-use changes reduce the streamflow in all sub-basins of Ji-Parana during the dry season. In the rainy season, LUCC increases the streamflow during periods with normal precipitation conditions and La Niña in almost all sub-basins, except in the sub-basin with more than 20% deforestation. [ABSTRACT FROM AUTHOR]

Nepal experienced record-breaking summer monsoon precipitation in 2020, becoming the wettest year of the last four decades (1980–2020). This paper explores the role of large-scale atmospheric circulation and sea surface temperature patterns in tipping an otherwise typical wet summer into an extreme one in 2020. The unusually high precipitation was fuelled by the Western North Pacific Anticyclone (WNPAC), concomitant with the strong presence of moist static energy and enhanced vertical velocity in and near Nepal. Sea surface temperature anomalies showed an intense Indian Ocean warming and features of a La Niña, succeeding a weak El Niño event that had sustained the WNPAC. The southwesterly winds on the northern flank of then WNPAC contributed excess moisture transport and convergence to Nepal, consequently resulting in elevated precipitation. This feature is consistent with previous wet summer years, but the presence of WNPAC in those years followed the El Niño event. Therefore, it appears that the Indo-western Pacific Ocean Capacitor (IPOC) effect exerts the above-normal precipitation for the summer of 2020 without involving the El Niño event, while anthropogenic warming may have further tipped the balance. [ABSTRACT FROM AUTHOR]

This paper discussed the use of stable isotope compositions of precipitation (δ2H and δ18O) to understand its characteristics and the parameters controlling meteorological conditions in Malaysia. The meteoric water line for Malaysia, or MMWL established in this study are δ2H = (7.43 ± 0.05)δ18O + (7.33 ± 0.11) (n = 595, r2 = 0.97) for individual values, and δ2H = (7.07 ± 0.20)δ18O + (4.90 ± 0.75) (n = 51, r2 = 0.96) for annual precipitation weighted means. No major variations in local meteoric water lines established between the stations, except for one (i.e., Cameron Highlands), which was found to be significantly different due to its high deuterium excess, or d value, attributed to moisture recycling (re–evapotranspiration) from the surrounding dense rainforest area. The precipitation moisture came from the two monsoon systems; the Northeast monsoon (NEM) and Southwest monsoon (SWM). They differ only slightly in their isotope signatures, where the NEM (winter monsoon) is 0.38‰ more negative than the SWM (summer monsoon), and the rainfall amount and temperature have a relatively weak influence on the stable isotopes in precipitation. Rainfall δ18O is poorly correlated with the monthly rainfall amount and temperature, with very low r2 values (–0.4‰/100 mm; 0.09 and 0.7‰/°C; 0.06, respectively). The seasonal variability of isotopic compositions of precipitation in this region is controlled by the insubstantial but conspicuous inverse correlation amount effect. The seasonal patterns of δ2H and δ18O are evident, with higher values observed during the NEM and lower values observed during SWM. However, the temporal variations of rainfall δ2H and δ18O during NEM and SWM are almost indistinguishable due to local climatic conditions, prevailing atmospheric circulations, and sources of precipitation. The apparent sign of El Niño and La Niña events (2015 and 2017, respectively) of the El Niño–Southern Oscillation (ENSO) cycle were successfully identified from this study, indicated by the heavier δ18O from the peaks in the annual precipitation amount versus δ18O annual precipitation weighted mean plot, while La Niña corresponds to the lighter values of the rainfall isotopes. [ABSTRACT FROM AUTHOR]

El Niño-Southern Oscillation (ENSO) asymmetry in predictability on springtime initial condition remains unclear. From the perspective of the spring predictability barrier (SPB), this paper investigates the ENSO asymmetry in SPB and explores the potential factors that may lead to this asymmetry. Both the observation and 29 Coupled Model Intercomparison Project Phase 6 (CMIP6) models show that the spring sea surface temperature (SST) persistence is significantly higher in El Niño years than that in La Niña years, and the SPB intensity is stronger in La Niña years than that in El Niño years. Through the recharge oscillator model, observation and CMIP6 models, we demonstrate that the nonlinear wind stress response to SST anomalies in spring is the main cause of the asymmetric SPB intensity. By the mixed-layer heat budget of the tropical Pacific in the spring, we further identify that a stronger response of zonal wind stress in El Niño events can cause a stronger zonal advection feedback, which finally leads to a weaker SPB and enhances the predictability of El Niño. In contrast, the cooling SST in the spring only leads to weak easterly anomalies, the zonal advection feedback is relatively weaker, thus SPB is stronger and the predictability of La Niña is lower. From the perspective of SPB, we suggest that El Niño is more predictable than La Niña. [ABSTRACT FROM AUTHOR]

Copyright of Advances in Atmospheric Sciences is the property of Springer Nature 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.)

This paper describes the use of a web application system, called 4-Dimensional Visual Delivery (4DVD), to visualize and deliver climate data. The focus of this paper is on the monthly data from the NOAA-CIRES-DOE Twentieth Century Reanalysis (20CR) project Version 2c. The 20CR is a global model at a spatial resolution about 2° latitude-longitude. The temporal coverage is from January 1851 to December 2014. The monthly data include numerous climate variables, such as temperature, pressure, precipitation rate, zonal wind, meridional wind, albedo, and longwave radiation flux. We show how to use the 4DVD system to conveniently visualize, deliver, and analyze the 20CR data of these parameters on a globe or on a 2D latitude-longitude map. We analyze the temporal and spatial patterns of zonal wind and precipitation over Niño 4 region (5° N-5° S, 160° E-150° W). The monthly NASA Global Precipitation Climatology Project (GPCP) data are used to compare the results from 20CR. GPCP data used in this 4DVD application are defined on 2.5° latitude-longitude grid boxes from January 1979 to January 2019. The 4DVD figures successfully show the reverse of zonal wind direction from the east-to-west wind to the west-to-east wind on the grid box (2° S, 176° W) in the Niño 4 region during an El Niño event. The spectral analysis shows the annual and semi-annual cycles in the zonal wind data on this grid box. The GPCP data are used to support the analysis results of 20CR zonal data. The precipitation data over the grid box (1.25° S, 176.25° W) in the Niño 4 region show clear El Niño signals (persistent extreme precipitation more than 6 mm/day) and clear La Niña signals (persistent "dry" with near-zero precipitation). The spectral analysis of the precipitation data time series over this grid box shows no annual cycle. [ABSTRACT FROM AUTHOR]

The Eastern African region is witnessing changes in climate conditions and rising sea levels due to the influences of global warming interacting with weather phenomena such as El Nino and La Nina. These trends, as well as more intense extreme weather events, highlight the urgent need for appropriate adaptation responses at both the national and local level. This is especially the case for the numerous small islands of the region that are particularly vulnerable to climate change. This paper reports on a study that examined coping and adaptation responses to climate and non-climate stressors among coastal communities on two Zanzibar islands (Pemba and Unguja) in Tanzania. The study focused on three of the primary livelihood activities on the islands, namely, seaweed growing, fishing, and crop and livestock farming. Using mainly survey data, we explored the responses of farmers, fishermen, and seaweed growers to multiple shocks and stressors. We further investigated responses that were discontinued for various reasons, as well as any barriers to adaptation encountered by these communities. We found that coastal communities in both Kiuyu Mbuyuni, Pemba and Matemwe, Unguja face a range of interrelated shocks and stressors linked to their livelihood activities, some of which they were able to respond to primarily through coping strategies. However, their attempts to adapt in the longer term as well as to venture outside their traditional activities were constrained by several barriers. Some of these barriers operate beyond the individual and community capability to overcome, while others—like social and cultural barriers—can be addressed at the local level but need a concerted effort and political will. We draw the findings together into a conceptual framework to help unpack the implications these hold for coastal communities on the two islands. We then suggest ways to build resilience in local livelihoods and overcome barriers to climate change adaptation in the future. [ABSTRACT FROM AUTHOR]

Previous studies have revealed that extratropical forcing can lead to changes in the intertropical convergence zone (ITCZ). Based on reanalysis data from 1979 to 2019, this paper discusses the influence of the South Pacific Ocean Dipole (SPOD, a dominant mode between the subtropics and extratropics in the South Pacific) and its coordination with ENSO in the ITCZ. Results show that SPOD has an effect on the position and intensity of the ITCZ, especially in the region around Niño4. From the latitudes of ITCZ axes and precipitation averaged over 160°E–160°W, positive (negative) SPOD events force a northward (southward) shift in the ITCZ in boreal winter (DJF), while the position moves in the opposite direction in boreal summer (JJA). In addition, ENSO can obviously enhance the influence of SPOD on the ITCZ. It is evident that there is a wider range of northward (southward) shift in the ITCZ under both positive SPOD and El Niño (negative SPOD and La Niña) conditions during DJF. Similar to DJF, both positive SPOD and El Niño (negative SPOD and La Niña) events still cause the ITCZ to move toward (away from) the equator during JJA, except that the magnitude of the movement in JJA is less than that in DJF. Precipitation averaged over 160°E–160°W is at a maximum under both positive SPOD and El Niño events, which have the greatest influence on ITCZ intensity, followed by both negative SPOD and La Niña in DJF, while in JJA, ITCZ intensity is most sensitive to negative SPOD events. [ABSTRACT FROM AUTHOR]

The effects of ENSO have been considered as the major variables in weather changes in the Middle East. This issue has been shown by regression indexes in a number of papers. Weather forecasts could be influenced by some variables that have uncertainty, so the deterministic approaches may lead to incorrect predictions. The proposed algorithm can be used when some variables have uncertainty. In this study, a fuzzy-based probabilistic approach has been chosen to show the effect of El Niño and La Niña on the monthly total precipitation in northern coasts of the Oman Gulf. [ABSTRACT FROM AUTHOR]

Copyright of Advances in Atmospheric Sciences is the property of Springer Nature 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.)

This paper investigates the causes for the interdecadal change in the relationships between early and late summer precipitation over South China (SC). It is found that the correlations of the precipitation over SC between June and August shift from weak positive in 1979–1995 to significantly negative in 1996–2019. Further analysis demonstrates that the distinct evolution of sea surface temperature (SST) pattern between the two periods accounts for the interdecadal variations of their relationships. Although the warming of the tropical western Indian Ocean (WIO) in June favors increasing precipitation over the SC via enhancing the Northwest Pacific Subtropical High (NWPSH) during the whole period, the associated SST anomalies in August are rather different between the two periods. Specifically, the WIO warming in June corresponds to slightly positive anomalies over the tropical central-eastern Pacific in August during the 1979–1995, which has weak impact on the NWPSH and results in a weak precipitation correlation between June and August. However, the WIO warming in June corresponds to La Niña's rapid development in August during the 1996–2019, which favors the enhancement of the NWPSH via increasing the regional Hadley circulation. Due to the climatologically northward movement of NWPSH from June to August, the enhanced NWPSH in August acts to decrease the precipitation over SC, causing a significantly negative correlation between precipitation in June and August. Overall, the distinct evolution of tropical SST pattern is the key factor inducing the change of the relationships between June and August precipitation in the two periods. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to determine the impact of rare disaster risks, captured by the El Niño-Southern Oscillation (ENSO) cycle, on the volatility of Treasury securities of the United States (US) involving 1- to 360-month maturities. We use a random coefficient panel-data-based heterogeneous autoregressive-realized variance (HAR-RV) model over the monthly period of 1961:06 to 2019:12, with the monthly RV derived from the sum of squared daily changes in yield within a month. Our results show a positive and statistically significant (at the 1% level) impact of the ENSO cycle on RV, with the results being robust to alternative metrics of the ENSO, consideration of lagged values, and decomposition of the ENSO cycle into El Niño and La Niña phases, with the former having a relatively stronger effect. Based on the panel estimation method using heterogeneous slope coefficients, we find that the impact on the entire term-structure is positive yet stronger at the two-ends and the middle-part of the term-structure. Our findings have important implications for investors in US Treasury securities. [ABSTRACT FROM AUTHOR]

Understanding past changes in the characteristics of climate extremes forms an essential part of viable countermeasures to cope with climate-induced risks in a rapidly warming world. Thus, this paper endeavored to explore possible non-monotonic trend components in heavy rainfall events over the Central Highlands (Vietnam) by employing Şen's innovative trend analysis method in conjunction with the well-defined extreme rainfall indices. The outcomes show less spatially coherent trends in the intensity, frequency, and duration of extreme rainfall events across the study area, and most analyzed indices exhibited non-monotonic trend forms. The overall trends in the intensity and frequency, represented by maximum 1-day, 5-day precipitation amount (Rx1day, Rx5day), very and extremely wet days (R95p and R99p), and the number of very and extremely heavy precipitation days (R20mm and R50mm), were characterized by significant increases at three or four sites. Concerning dry and wet extremes, observed increases in consecutive dry days (CDD) and decreases in consecutive wet days (CWD) were identified significantly simultaneously at three sites. There is high domination of significant increases in high-value subgroups of these indices. Several sites also exposed significantly increasing trend behaviors in these indices within all low-, medium-, and high-value subgroups, thereby implying the intensity and frequency have intensified over recent decades. This study also indicated potential linkages between annual peaks of several extreme rainfall indices, characterizing intensity, frequency, and wet duration, usually coincided with negative Indian Ocean Dipole and La Niña events, while dry extremes were usually found during El Niño events based on correlation analysis. [ABSTRACT FROM AUTHOR]

It is a commentary following a published paper in PNAS titled, 'Slowdown of the Walker circulation at solar cycle maximum', by Misios et al. (PNAS 116(15): 7186–7191, 2019). The article of Misios et al. (2019) claims that there is a slowdown of the Walker circulation during maximum periods of solar cycles. In support, they provided model results. They also gave directions of improved future predictive skill involving that knowledge of solar cycles. However, their work does not comply with various observational results. This contribution highlights those areas and pinpoints discrepancies. Knowing the limitations of models, if any model results match some very limited part of observations, it is not possible to make similar claims. It raises doubt on any improvement of future predictive skill. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to investigate the environmental nature of the French Guiana shrimp fishery dynamics through an empirical analysis. To do so, we specify a global harvest production function, in which the output depends on the number of days at sea and the stock level. In addition, we use some environmental variables representing the 'El Niño' and 'la Niña' phenomena, the sea surface temperature, and the flow of some Amazonian rivers as instruments. This method enables us to correct the well-known simultaneous bias between the harvest and the stock levels and to show that harvest is significantly dependent on the environmental factors analyzed, which may compromise the future of the French Guiana shrimp fishery in the context of climate change. [ABSTRACT FROM AUTHOR]

This paper studies the impacts of El Niño-Southern Oscillation (ENSO) on wintertime extreme precipitation in China from 1961 to 2017, and possibly different influences of two El Niño types are also examined. We find that ENSO poses profound influences on extreme precipitation in many portions of China. El Niño (La Niña) intensifies (weakens) the winter precipitation extremes in southeastern China (SEC) and slightly weakens (intensifies) those in central-north China, mainly by changing the frequency rather than the intensity of extreme precipitation. Further analysis suggests that the East Asian winter monsoon tends to be weaker during El Niño winters, suppressing the southward invasion of cold dry air. Via the weakened Walker circulation, El Niño also triggers anomalously descending motion and anticyclone over the western North Pacific (WNP), which exhibits southwesterly anomalies over SEC and is thus conducive to the transport of sufficient moisture into that area. The changes over WNP are also accompanied by ascending motions over East Asia via a local meridional circulation alike the Pacific–Japan pattern. Meanwhile, El Niño induces a southward-displaced East Asian jet stream, as characterized by intensified westerly over southern China, corresponding to anomalously ascending motion there. Together, these changes facilitate the updrafts of circulations and the condensation of water vapor, thus increasing the occurrence of extreme precipitation events in SEC. Moreover, we find that different Niño types exhibit distinct subregional influences. In particular, the canonical eastern Pacific El Niño significantly increases the frequency of extreme precipitation in South China, whereas the Modoki central Pacific El Niño mainly impacts that in East China. [ABSTRACT FROM AUTHOR]

Ocean chlorophyll (Chl)-induced heating can affect the climate system through the penetration of solar radiation in the upper ocean. Currently, the ocean biology-induced heating (OBH) feedback effects on the climate in the tropical Pacific are still not well understood, and the mechanisms regarding how SST is modulated remain elusive. In this paper, chlorophyll (Chl) data from satellites are combined with physical fields from Argo profiles to estimate OBH-related fields, including the penetration depth (Hp) and the ocean mixed-layer (ML) depth (Hm). In addition, some directly related heating terms with Hm and Hp are diagnosed, including the absorbed solar radiation component within the ML (denoted as Qabs), the rate of ML temperature changes that are directly induced by Qabs (denoted as Rsr = Qabs/(ρ0CpHm)), and the portion of solar radiation that penetrates through the bottom of the ML (denoted as Qpen). The structural relationships between these related fields are examined to illustrate how these heating terms are affected by Hp and Hm. The extent to which Rsr and Qpen are modulated by Hp is strikingly different during ENSO cycles. In the western-central equatorial Pacific, inter-annual variations in Hp tend to be out of phase with those in Hm. A decrease (increase) in Qabs from a positive (negative) Hp anomaly during El Niño (La Niña) tends to be offset by a negative (positive) Hm anomaly. Thus, Rsr is not closely related with Hp, even though Qabs is highly correlated with Hp, indicating that the direct thermal effect through Qabs is not a dominant factor that affects the SST. In contrast, the inter-annual variability of Qpen in the region is significantly enhanced by that of Hp, with their high positive correlation. The Hp-induced differential heating in the ML and subsurface layers from the Qpen and Qabs terms modifies the thermal contrast, stratification and vertical mixing, which represent a dominant indirect ocean dynamical effect on the SST. The revealed relationships between these related fields provide an observational basis for gaining structural insights into the OBH feedback effects and validating model simulations in the tropical Pacific. [ABSTRACT FROM AUTHOR]

The mechanism for asymmetric atmospheric responses to the central Pacific (CP) El Niño and La Niña over the western North Pacific (WNP) is studied in this paper. The negative anomalies of rainfall over the key region of WNP are explained by diagnosing the column-integrated equations of moisture and moist static energy (MSE). It is revealed that the nonlinear advection of moist enthalpy is critical to introduce negative rainfall anomalies over the region. The anomalous easterly (westerly) in La Niña (CP El Niño) causes negative advection of anomalous moist enthalpy, inducing negative heating anomaly and an anticyclone anomaly in the WNP, which weakens (strengthens) the cyclone (anticyclone) in La Niña (CP El Niño). The MSE budget analysis shows a larger nonlinear term in CP El Niño than in eastern Pacific (EP) El Niño, inconsistent with the amplitudes of sea surface temperature anomalies. The reason is that the nonlinear term transforms to positive above 700 hPa in EP El Niño, offsetting the negative advection below 700 hPa and thus making the nonlinear term smaller. The nonlinear term is negative at low levels in CP El Niño, resulting in a larger nonlinear term. The stronger precipitation anomalies in the WNP during EP El Niño can be attributed to the linear moist enthalpy advection. The mean easterly wind at mid levels causes a larger (smaller) positive moist enthalpy advection in CP (EP) El Niño, due to a larger (smaller) moist enthalpy gradient, resulting in a positive (negative) linear moist enthalpy advection, which weakens (strengthens) the negative precipitation anomalies in the key region. [ABSTRACT FROM AUTHOR]

In 2018, summer precipitation was above normal in North and Northwest China and below normal around the Yangtze River valley, due to an extremely strong East Asian summer monsoon (EASM). The atmospheric circulation anomalies in East Asia and key external forcing factors that influence the EASM in 2018 are explored in this paper. The results show that there existed an anomalous cyclonic circulation near the Philippines, while the western Pacific subtropical high was located more northward than its normal position. In the mid-high latitudes, a negative geo-potential height anomaly center was found near the Ural Mountains, suppressing the blocking activity. Under such a circulation pattern, precipitation near the Yangtze River valley decreased because local divergence and subsidence intensified, whereas precipitation in northern China increased due to large amounts of water vapor transport by anomalously strong southerly winds. Further analyses reveal that the strong EASM circulation in 2018 might result from the joint influences of several external forcing factors. The weak La Nina event that started from October 2017, the positive North Atlantic Tripolar mode (NAT) in spring 2018, and the reduced snow cover over the Tibetan Plateau in winter 2017/18 all collaboratively contributed to formation of the cyclonic circulation anomaly near the Philippines, leading to the extremely strong EASM. Especially, the positive NAT and the reduced Tibetan snow cover may have caused the negative geopotential height anomaly near the Ural Mountains, in favor of a strong EASM. The above external factors and their reinforcing impacts on the EASM are further verified by two groups of similar historical cases. [ABSTRACT FROM AUTHOR]

In this paper, mechanisms for the formation of quasi-stationary extratropical wave trains associated with four distinct winter patterns of seasonal mean tropical Pacific convection anomalies, including the western CP (W-CP) pattern, La Niña (LN) pattern, CP El Niño (CPEN) pattern and EP El Niño (EPEN) pattern, are investigated by utilizing observational and six Atmospheric Model Intercomparison Project Phase 5 (AMIP5) high-skilled models (ACCESS1.0, CanAM4, CCSM4, CMCC-CM, HadGEM2-A, MPI-ESM-LR) datasets. The observational results show that tropical Pacific forcing induces upper-level anomalous Rossby wave source that force vorticity over the central North Pacific through modulating the local Hadley circulation, then excite eastward propagation of quasi-stationary planetary waves penetrating into the North Atlantic, and finally establish the associated teleconnections in mid- and high-latitudes by local synoptic eddy–mean flow interaction. Different structures of wave trains may be explained by evident differences in intensity and scale of the extratropical vorticity forcing originating from distinct convection anomalies over the tropical Pacific. The MME results further confirm the possible physical processes obtained from observations, but there still exist some significant differences. These cover the North Pacific and North America and can possibly be attributed to the models' simulation ability of extratropical vorticity forcing and local storm track intensity. In addition, the stratosphere–troposphere interaction plays an important role for extratropical atmospheric circulation anomalies. The stratospheric polar vortex not only modulates the underlying wave train, especially for the North Atlantic/Europe sector, but is also affected by the upper-tropospheric disturbance in high-latitudes through the upward wave activity flux. [ABSTRACT FROM AUTHOR]

This paper investigates the impacts of the El Niño Southern Oscillation (ENSO) on various aspects of heat waves (HWs), including frequency, duration, and magnitude, over China during 1961-2014. Results show that El Niño (La Niña) significantly amplifies (weakens) the HW activities in most areas of China. Such influences are particularly strong in southern China. HW activities are enhanced (weakened) during the summers following mature El Niño (La Niña) episodes, with increased (reduced) occurrence of HW events and number of HW days, as well as prolonged (shortened) duration and elevated (decreased) amplitude of such events. These amplifying effects are substantially stronger for severe HWs (i.e., hottest and longest episodes) than for those events of average duration and intensity. Diagnosis by compositing reanalysis data over ENSO events indicates that the atmospheric circulation during the summers following El Niño is characterized by anomalous rising motion over the tropical central Pacific and Indian Oceans, and sinking motion over the western North Pacific (WNP). The anomalous subsidence over the WNP is accompanied by reduced precipitation and condensational heating, as well as anomalous anticyclonic flows in the lower troposphere. El Niño also induces a stronger South Asian high, which can strengthen the WNP anticyclone and subtropical high. These changes provide a favorable environment for the occurrence and sustenance of HWs in China. Analogous arguments apply to changes with the opposite polarity in association with La Niña events. [ABSTRACT FROM AUTHOR]

This paper presents a cultural geographic approach for understanding local social processes of territorial re-appropriation taking place in response to non-local forces and interests. This approach is applied to the small rural locality of La Niña, in Buenos Aires Province, Argentina. The small village of La Niña is currently in a locally-led process of recovering from a recent depopulation trend caused mainly by the irruption of transnational agribusiness. As economic opportunities have dwindled in the last decades, more recently local inhabitants and new settlers have set forth diverse strategies aimed at mitigating the effects of depopulation on the social structure. We focus our attention on the way the living experience of place is involved in all these strategies. We contend that despite economic and cultural homogenization caused by globalization, the experience of place is a permanent though ever-changing aspect of social life. Our research was based on archival and hemerographic surveys and ethnographic field techniques, encompassing participatory observation, semistructured and in-depth interviews with social and government leaders and local producers as well as field landscape appraisals. [ABSTRACT FROM AUTHOR]

In this paper, distinct patterns of boreal winter convection anomalies over the tropical Pacific and associated wave trains in the extratropics are addressed. The first leading mode (EOF1) of convection anomalies as measured by outgoing longwave radiation demonstrates an east-west oscillation of deep convection with centers over the equatorial central Pacific (CP) and over the tropical western North Pacific and the Maritime Continent. The second leading mode (EOF2) is also a dipole pattern with opposite centers straddling 170°W, possibly modifying EOF1 to some extent. Combining the first two leading modes, five major categories of tropical convection anomalies can be identified for the period 1979/80-2012/13. The comparison between these five categories and the corresponding SST anomaly patterns indicates a nonlinear relationship between convection and SST. The combination of EOF1 and EOF2 with in-phase PCs exhibits an east-west dipole pattern with opposite signs over west of the dateline and the Maritime Continent. The negative phase of the two PCs, named La Niña pattern, induces a negative Pacific/North American—positive North Atlantic Oscillation teleconnection in the extratropics. Approximately opposite responses can be detected in its positive phase, named CP El Niño pattern. The negative PC2 superposing positive PC1, named EP El Niño pattern, shows the strongest convection anomalies with enhanced (depressed) convection over the eastern (western) Pacific and leads to a Tropical/Northern Hemisphere-like teleconnection pattern and an anomalous anticyclone extending from the North Pacific to the North Atlantic. The positive PC2 with neutral PC1, named western CP pattern, shows weakly enhanced convection to the west of the dateline as a response to local SST warming around the dateline. This convection anomaly pattern, although weak, is important and excites a northeastward wave train from the tropics to Greenland, resulting in surface air temperature cooling covering the northeastern North America and warmer and wetter conditions over Western Europe. [ABSTRACT FROM AUTHOR]

Understanding the co-variability between the El Niño–Southern Oscillation (ENSO) and the background state in the tropical Pacific is critical for projecting future ENSO. The difficulty is rooted in a circular logic that the background state routinely defined by multi-decadal mean modulates, and is modulated by, ENSO. This circularity arises due to the asymmetry between El Niño and La Niña, resulting in a non-zero mean, referred to as the ENSO rectification effect. Here, we develop a method based on Box-Cox normalization to define the tropical Pacific background state and its associated anomalies, which removes the ENSO rectification effect and is referred to as the normalized mean state. The normalized mean state accurately quantifies ENSO-related anomalies, ENSO asymmetry, and the ENSO rectification effect. It is evident in both observations and model simulations that the normalized mean state has a clear asymmetric impact on the amplitude of ENSO. A warm background state weakens El Niño but strengthens La Niña through two key processes: the nonlinear response of precipitation to SST and oceanic zonal advection feedback. The normalized mean state successfully solves the circular reasoning fallacy resulting from ENSO asymmetry and offers a framework to study ENSO and tropical climate dynamics with far-reaching impacts on global climate. [ABSTRACT FROM AUTHOR]

This study examines the large-scale atmosphere-ocean environments that led to the winter tornado outbreak across the Ohio Valley on 10–11 December 2021, also known as the Quad-States Tornado Outbreaks. Here, we show that the Quad-States Tornado Outbreaks occurred under an exceptionally strong and prolonged negative Pacific-North American pattern (PNA), which developed around December 1 and persisted for a month. This unusual PNA produced a strong atmospheric ridge along the south and eastern US seaboard, which in turn helped warm the Gulf of Mexico and produced large-scale environments conducive for tornadogenesis across the Ohio Valley. Further analysis shows that a broad region across the Ohio Valley is particularly vulnerable to extensive winter tornado outbreaks during long-lived negative PNA, whereas a limited region in the central US is exposed to winter tornado activity during short-lived negative PNA. Finally, although the PNA is a mode of internal variability that occurs with or without El Niño—Southern Oscillation, the occurrence of prolonged negative PNA is more frequent during La Niña than during El Niño. [ABSTRACT FROM AUTHOR]

El Niño Southern Oscillation, a global climate phenomenon, occurs in the tropical Pacific with an anomalous warming phase (El Niño) and a cooling phase (La Niña) spanning for 2–5 years. A substantial decline of Niño3.4 region's spring bloom chlorophyll-a concentration (Chl-a) is an intrinsic characteristic of the central Pacific during the El Niño onset period, which has been considered as a predictor of the El Niño by earlier studies. This study investigated the concept, a marked decline of spring bloom Chl-a as the predictor of the El Niño, using satellite-measured Chl-a from MODIS Aqua for the period 2003–2023 in relation to the Oceanic Niño Index (ONI) and subsurface properties. It revealed that Chl-a exhibits a significant inverse relationship with ONI during past El Niño events. An intense, continuous decreasing phase of Chl-a during the spring season (February–April) of 2023 may indicate the onset of El Niño. The decline of the spring bloom Chl-a concentration has been explained as the response to the weakening of the upwelling strength in the study domain and associated nutrient depletion in the euphotic zone. [ABSTRACT FROM AUTHOR]

In 2023 Amazonia experienced both historical drought and warm conditions. On October 26th 2023 the water levels at the port of Manaus reached its lowest record since 1902 (12.70 m). In this region, October monthly maximum and minimum temperature anomalies also surpassed previous record values registered in 2015 (+ 3 °C above the normal considering the 1981–2020 average). Here we show that this historical dry and warm situation in Amazonia is associated with two main atmospheric mechanisms: (i) the November 2022–February 2023 southern anomaly of vertical integrated moisture flux (VIMF), related to VIMF divergence and extreme rainfall deficit over southwestern Amazonia, and (ii) the June–August 2023 downward motion over northern Amazonia related to extreme rainfall deficit and warm conditions over this region. Anomalies of both atmospheric mechanisms reached record values during this event. The first mechanism is significantly correlated to negative sea surface temperature (SST) anomalies in the equatorial Pacific (November–February La Niña events). The second mechanism is significantly correlated to positive SST anomalies in the equatorial Pacific, related to the impacts of June–September El Niño on the Walker Circulation. While previous extreme droughts were linked to El Niño (warmer North Tropical Atlantic SST) during the austral summer (winter and spring), the transition from La Niña 2022–23 to El Niño 2023 appears to be a key climatic driver in this record-breaking dry and warm situation, combined to a widespread anomalous warming over the worldwide ocean. [ABSTRACT FROM AUTHOR]

The present paper provides an analysis and a long-term forecasting scheme of the Oceanic Niño Index (ONI) using the continuous wavelet transform. First, it appears that oscillatory components with main periods of about 17, 31, 43, 61 and 140 months govern most of the variability of the signal, which is consistent with previous works. Then, this information enables us to derive a simple algorithm to model and forecast ONI. The model is based on the observation that the modes extracted from the signal are generally phased with positive or negative anomalies of ONI (El Niño and La Niña events). Such a feature is exploited to generate locally stationary curves that mimic this behavior and which can be easily extrapolated to form a basic forecast. The wavelet transform is then used again to smooth out the process and finalize the predictions. The skills of the technique described in this paper are assessed through retroactive forecasts of past El Niño and La Niña events and via classic indicators computed as functions of the lead time. The main asset of the proposed model resides in its long-lead prediction skills. Consequently, this approach should prove helpful as a complement to other models for estimating the long-term trends of ONI. [ABSTRACT FROM AUTHOR]

In July and August 2022, a notable "seesaw" extreme pattern emerged, characterized by the "Yangtze River Valley (YRV) drought" juxtaposed with the "Indus Basin (IB) flood", leading to enormous economic and human losses. We observed that the "seesaw" extreme pattern concurs with the second-strongest sea surface temperature (SST) gradient between the equatorial central and western Pacific caused by the triple-dip La Niña and western Pacific warming. The convergent statistical and numerical evidence suggested that the enhanced SST gradients tend to amplify the western Pacific convection and the descending Rossby responses to the La Niña cooling, promoting the "seesaw" extreme pattern through the westward expansion of the western Pacific subtropical high (WPSH). Further investigation demonstrated that the magnitude of the YRV surface temperature and IB rainfall exhibited a reversed change from July to August. The persistent cooling of the southern Indian Ocean induced by the triple-dip La Niña increases the cross-equatorial moisture transport, which played a significant role in the record-breaking IB rainfall during July. By contrast, the historic YRV surface temperature occurred in August with a decrease in IB rainfall. The Barents-Kara Sea warming extended the downstream impact of the North Atlantic Oscillation via local air-sea interaction that enhanced the WPSH and the YRV extreme surface temperature by emanating an equatorward teleconnection wave train. The overlay of the tropical thermal conditions and extra-tropical forcings largely aggravated the severity of the "YRV drought and IB flood". [ABSTRACT FROM AUTHOR]

This study examined the long-term (1980–2019) spatio-temporal trends, variability and teleconnections of Indian summer monsoon rainfall (ISMR) of all districts of Haryana, India and their impact on agricultural productivity. The gridded datasets of India Meteorological Department (IMD) were used to statistically analyse the rainfall distribution, trend, coefficient of variation and intensity of rainfall. The gridded datasets of European Centre for Medium‐Range Weather Forecasts (ECMWF) atmospheric reanalysis V5 (ERA5) were examined for lower and upper tropospheric wind circulation (850 hPa and 200hpa), vertically integrated moisture transport (VIMT) and surface moisture flux (SMF). The datasets of National Oceanic and Atmospheric Administration (NOAA) were correlated with ISMR and composite deviation of rainfall and rainfall intensity during El Niño and La Niña from neutral years was examined at district level. Our analysis revealed that districts lying in eastern agroclimatic zone (EAZ) of Haryana received more ISMR during each month of monsoon season as compared to the ones situated in western agroclimatic zone (WAZ). Trend-free pre-whitening Mann–Kendall (TFPW-MK) test revealed that Kurukshetra, Panipat, Ambala, Rohtak, Faridabad, Jhajjar, Sonipat, Fatehabad and Palwal have shown a decreasing trend while Mahendragarh and Panchkula have shown an increasing trend of rainfall. During the El Niño years, most of the locations in the state received deficient to large deficient category, whereas during the La Niña episodes, most of the locations received excess to large excess category of ISMR, which is indicative of the influence of El Niño–Southern Oscillation (ENSO) on the regional scale. The influence of ISMR on bajra productivity for the districts lying in WAZ and rice productivity for the districts lying in EAZ was undertaken. This study is beneficial for understanding the impacts of climate change and climate variability on ISMR dynamics in Haryana which may further guide the policy-makers and beneficiaries for optimising the use of hydrological resources. [ABSTRACT FROM AUTHOR]

The influence of strong Indian Ocean Dipole (IOD) events on the evolution of the following year's La Niña events is investigated using the National Marine Environmental Forecasting Center (NMEFC) operational seasonal forecasting system. The observation results show that when the strong IOD occurs, the tropical Pacific can be in different sea surface temperature states. As such prediction system can well reproduce the air-sea evolution of the 1998/1999 and 2020/2021 La Niña events, the ocean temperature initializations in December during above events were perturbed with the system to assess the role of the oceanic channel and atmospheric bridge across the maritime continent in the forecasting of the La Niña events 1 year later. In the case of the neutral state of the tropical Pacific at the peak of the 2019 positive IOD, pacemaker experiments have demonstrated that the Indian Ocean subsurface temperature initialization in December 2019 is critically important for the successful prediction of the 2020/2021 La Niña. Experiments of sea surface temperature initialization in December 2019, with only the Indo-Pacific atmospheric bridge at work, failed to predict the 2020/2021 La Niña 1 year in advance. The comparison underlined the dominant role of the oceanic channel dynamics in the evolution of the 2020/2021 La Niña. Forecasting experiments beginning from the 1997/98 El Niño with and without the IOD initializations suggest that the delayed feedback of the tropical Pacific coupled system is more important in the forecasting of the 1998/1999 La Niña, with the Indo-Pacific oceanic channel dynamics playing a secondary yet very important role. Our study has underscored the importance of the Indo-Pacific oceanic channel dynamics in ENSO prediction and suggested the effectiveness of IOD subsurface temperature initialization in La Niña predictions at the 1-year lead time. [ABSTRACT FROM AUTHOR]

Northerly low-level jets (LLJ) along the eastern Andes are important conduits of moisture transport and play central roles in modulating precipitation in South America. This study further investigates the variability of the LLJ during extended austral summers. A new method characterizes the spatial extent of the LLJ and finds four distinct types: Central, Northern, Andes and Peru. We show the existence of specific evolutions such that the LLJ may initiate in the central region, expands along the Andes and terminates in the northern region. Conversely, the LLJ may propagate from north-to-south. The spatiotemporal evolution of the LLJ is remotely forced by Rossby wave trains propagating from the Pacific Ocean towards South America, and the different phases of the wave trains favor the occurrences of Central, Northern or Andes types. Occurrences of Central and Northern types are more frequent in El Niño and La Niña years, respectively. The persistence of precipitation is shown to be directly related to the persistence of the LLJ. Lastly, the Madden-Julian Oscillation plays an important role in generating wave trains modulating the frequency of LLJ, especially the Central type. [ABSTRACT FROM AUTHOR]

Several aspects of regional climate including near-surface temperature and precipitation are predictable on interannual to decadal time scales. Despite indications that some climate states may provide higher predictability than others, previous studies analysing decadal predictions typically sample a variety of initial conditions. Here we assess multi-year predictability conditional on the phase of the El Niño–Southern Oscillation (ENSO) at the time of prediction initialisation. We find that predictions starting with El Niño or La Niña conditions exhibit higher skill in predicting near-surface air temperature and precipitation multiple years in advance, compared to predictions initialised from neutral ENSO conditions. This holds true in idealised prediction experiments with the Community Climate System Model Version 4 and to a lesser extent also real-world predictions using the Community Earth System Model and a multi-model ensemble of hindcasts contributed to the Coupled Model Intercomparison Project Phase 6 Decadal Climate Prediction Project. This enhanced predictability following ENSO events is related to phase transitions as part of the ENSO cycle, and related global teleconnections. Our results indicate that certain initial states provide increased predictability, revealing windows of opportunity for more skillful multi-year predictions. The study identifies windows of opportunity for multi-year climate predictions, depending on the state of ENSO. Predictions started during El Niño and La Niña exhibit higher skill than predictions started during neutral ENSO conditions. [ABSTRACT FROM AUTHOR]

The El Niño–Southern Oscillation (ENSO) has a quasi-biennial band with a period of two to three years. This quasi-biennial (QB) component of ENSO is one of the main factors influencing the spring persistence barrier of ENSO, but its root cause remains unclear. We presented a quasi-biennial cyclical process between the tropics and extratropics, which suggests that the North Pacific Victoria mode (VM) has a key role in the quasi-biennial variability of ENSO. The negative North Pacific Oscillation (NPO) during winter induces a positive VM-associated sea surface temperature pattern in the subsequent spring, which, in turn, forces an El Niño pattern in the subsequent winter through surface air–sea coupling in the subtropical/tropical Pacific. Meanwhile, associated with warming in the central-eastern equatorial Pacific, a positive SLP anomaly occurs near the Hawaiian region, and a negative SLP anomaly occurs in high latitudes near the Aleutian Islands, which eventually leads to the emergence of a positive NPO over the North Pacific during the El Niño mature winter. The positive NPO can then produce a negative VM in the spring of the next year, which further forces cooling in the equatorial Pacific, initiating a La Niña event in the following winter. Our findings suggest that the impact of the VM should be considered when we focus on the quasi-biennial-type ENSO. [ABSTRACT FROM AUTHOR]

In this study, based on the ECMWF 20-year (1997 ~ 2016) hindcasts, the subseasonal prediction of the weekly summer rainfall anomaly over the middle and lower reaches of the Yangtze River (YR) were studied. The skill at 2-week lead time exhibits prominent interannual variation, which is significantly correlated with the preceding winter ENSO. That is, rainfall anomaly can be better predicted in El Niño decaying summer than in La Niña decaying summer. Observation analyses show that in El Niño decaying summer the intraseasonal variation of YR summer rainfall is featured by strong low-frequency (> 30 days) intraseasonal oscillation (ISO) partly associated with the first boreal summer ISO mode (BSISO1) activity, in comparison with La Niña decaying summer. This is possibly because El Niño-induced mean state western North Pacific (WNP) anti-cyclone blocks the northward propagation of convection over the WNP, resulting in BSISO1 stagnation in phases 3–4. The phase stagnation could force stable atmospheric teleconnection, which is favorable to sufficient moisture transportation to the YR and persistent rainfall formation. Finally, prediction verification showed that more accurate prediction for the middle-low-level circulation contribute to the better prediction of rainfall anomaly in El Niño decaying summer than in La Niña decaying summer. [ABSTRACT FROM AUTHOR]

The role of the El Niño-Southern Oscillation (ENSO) in modulating the mean sea surface temperature (SST) in the tropical eastern Pacific is investigated. A strategy is developed to separate the observational record from 1958 to 2010 into two groups, ENSO and non-ENSO periods. A simple analytical framework is constructed to quantitatively delineate the contributions of oceanic dynamic heating (ODH) and surface heat fluxes to rectifying the mean SST. It is found that the differences in the mean SST between the two periods are evident, though minor, despite distinctive interannual SST variabilities. Both linear and nonlinear ODH, as well as surface heat fluxes, contribute to this slight mean SST difference. Idealized oceanic model experiments in the presence and absence of ENSO are conducted. The experiments confirm that ENSO moderately impacts the mean SST in the equatorial eastern Pacific. Although the amplitude of the linear ODH associated with ENSO is large, its impact on the long-term mean SST is small because the sign of its contribution changes between El Niño and La Niña phases. The nonlinear ODH, on the other hand, has the same sign during the warm and cold episodes. However, its accumulated effect on the mean SST is small due to its weak amplitude. [ABSTRACT FROM AUTHOR]

As the dominant form of mesoscale variability in the equatorial eastern Pacific, Tropical Instability Waves (TIWs) are known to interact with the El Niño and Southern Oscillation (ENSO) in complex ways. TIWs activity is modulated by the ENSO state and also provide significant feedback on ENSO via nonlinear dynamic heating (NDH), acting as a source of asymmetry between the El Niño and La Niña phases. In this work, we show that the interannual variability of TIWs-induced heat flux and NDH can be approximately expressed in terms of the mean meridional temperature gradient as TIWs tend to transport heat downgradient of the temperature anomalies along the Sea Surface Temperature (SST) front. The TIWs-induced NDH can be quantified as an asymmetric negative feedback on ENSO by a nonlinear thermal eddy diffusivity which depends on the background TIWs pattern and the ENSO-related linear and nonlinear processes. This proposed parameterization scheme can capture well the direct ENSO modulation on TIWs activity, the combination effect arising from the nonlinear interaction between ENSO and the cold tongue annual cycle, and associated ENSO nonlinearity. This parameterization scheme is effectively tested using four ocean reanalysis datasets with different horizontal resolutions that exhibit contrasted patterns of TIWs activity. This scheme may be useful for assessing the TIWs-induced feedback on ENSO in mechanistic ENSO models to better understand the dynamics of ENSO complexity. [ABSTRACT FROM AUTHOR]

The effects of El Niño-Southern Oscillation (ENSO) on winter precipitation in South China are considerably asymmetric. A positive correlation is significant between the sea surface temperature anomalies (SSTA) in the equatorial middle-eastern Pacific and the precipitation in South China during El Niño winters, whereas no significant relationship instead of a negative correlation between them during La Niña winters. The possible causes of abnormally positive precipitation in South China during La Niña winters remain a puzzle. The analysis indicates that positive precipitation anomalies in South China during La Niña winters are closely related to the strengthening of southerly winds over the South China Sea and convective activities over South China. Moreover, during La Niña winters, the low-level southerly wind anomalies over the South China Sea are modulated by an anomalous positive local zonal sea surface temperature gradient (SSTG) between the South China Sea and the tropical western Pacific, which strengthens in late autumn and maintains through the following winter. This positive local zonal SSTG is independent of La Niña and leads to the weakening of Walker circulation. The strengthened downward motion over the tropical western Pacific further promotes the weakening of local Hadley circulation. Weakened local Hadley circulation, with strengthened southerlies over the South China Sea in the lower troposphere, is conducive to the enhancement of water vapor transport from the South China Sea to South China. Besides, the weakened local Hadley circulation also shows strengthened upward motion over South China, which provides more advantageous dynamic conditions for precipitation. Therefore, the positive local zonal SSTG simultaneously promotes the two most important conditions affecting precipitation, resulting in positive precipitation anomalies over South China during La Niña winters. These results advance the understanding of prediction of winter precipitation in south China. [ABSTRACT FROM AUTHOR]

In 2022, South China suffered severe flooding due to unexpected persistent heavy rainfall in the pre-flood season. The in situ cumulative precipitation amount during May–June in South China broke the record established in 1981. The present study ascribed this record-breaking event to extreme warm sea surface temperature anomalies (SSTAs) in the Northeast Pacific (NP) and the Maritime Continent (MC) region. In May, the NP warming associated with La Niña and the negative phase of the Pacific Decadal Oscillation intensified extratropical diabatic heating and induced a cyclonic anomaly over Northeast Asia, which shifted the East Asian trough (EAT) southward. Subsequently, the westerly wind accelerated to the south of the anomalous EAT and strengthened the western North Pacific subtropical high, which led to increase in rainfall over South China. In June, the rainfall over South China remained above normal owing to anomalies of the meridional monsoon circulation manifested as a response to the development of a warm SSTA in the MC region. The anomalous warming in the deep tropics suppressed the Asian summer monsoon convection through anomalous atmospheric descent over South Asia, accompanied by enhanced atmospheric ascent and increased water vapor convergence over South China. Numerical sensitivity experiments validated the above processes and indicated that historic warm SSTAs in the NP and MC regions could increase the probability of extreme persistent above-normal pre-flood rainfall over South China. The results support improved predictability of pre-flood rainfall over South China on the interannual timescale outside the equatorial central–eastern Pacific. [ABSTRACT FROM AUTHOR]

Most tropical cyclones (TCs) generated over the eastern North Pacific (ENP) do not make landfall. Consequently, TCs in this basin have received less attention, especially those that occur away from the mainland. Furthermore, there have been few studies of the climatic effects of ENP TCs. This study explores the feedback relationship between ENP TCs and the intensity of the El Niño–Southern Oscillation (ENSO), including El Niño and La Niña events, from the perspective of accumulated cyclone energy (ACE). Observational and modeling results indicate that the ENP ACE 3 months earlier can still affect the intensity of El Niño and La Niña events, although the SST persistence is main contributor. Thereinto, the impact of ENP TCs on El Niño appears to be approximately equal to that on La Niña. Moreover, this impact is independent of the persistence of the sea surface temperature (SST) in the Niño 3.4 region and the Madden–Julian Oscillation. Generally, the greater the ENP ACE, the stronger the El Niño, and the smaller the ENP ACE, the stronger the La Niña; this is especially the case for those TCs that develop over the July‒September period. In addition, results show that the ENP TCs modulate ENSO intensity by changing anomalous zonal wind at the low-level atmospheric layer. And the joint impacts of the low-level zonal wind anomalies on the Walker circulation and the east–west thermocline gradient lead to the time characteristics that ENP TCs lead ENSO intensity by about 3 months. [ABSTRACT FROM AUTHOR]

Many researchers have recognized the long distance teleconnections between El Niño–Southern Oscillation (ENSO) events and some other processes in the global climate system happening in areas often very far from the equatorial zone of the Pacific Ocean. In this paper we investigate similar links between ENSO and extratropical processes taken in their whole set. For this goal we compute differences between the sea-level pressure and the near-surface air (sea surface) temperature global fields which correspond to either El Niño or La Niña events observed since the end of the XIX century and up to the beginning of the XXI century. As a result, we establish that an integrity exists of ENSO and the extratropical teleconnections such as North Atlantic Oscillation (NAO), Arctic Oscillation (AO), the Northern Hemisphere annular (NHA) mode as well as the Pacific–North American (PNA) pattern, and their analogs in the Southern Hemisphere in the interannual timescale. Named this integrity the Global Atmospheric Oscillation (GAO), we define two representative indices of GAO, and investigate the temporal dynamics of these indices. This investigation reveals that GAO's extratropical components may be real irrespective of ENSO while the latter accompanies GAO in all cases. Moreover, in view of a general eastward propagation of the GAO as a spatial structure, some its extratropical components show changes of their features prior the El Niño (La Niña) begins to form. Using these features as fingerprints of the forthcoming evolution of ENSO, we define another GAO index for the El Niño prediction with the lead-time of about 1 year. At last, we establish that some of the CMIP5-models reproduce GAO reasonably well. [ABSTRACT FROM AUTHOR]

The variability of the upper ocean heat content (OHC) of the South China Sea (SCS) has a significant regional climate impact on the surrounding East and Southeast Asian countries. In this paper, the spatial–temporal variations of the upper OHC in the SCS and their relations to El Niño-Southern Oscillation (ENSO) are analyzed using empirical orthogonal functions and correlation analysis. The mechanisms for the interannual OHC variability associated with ENSO and regime shift in 1998 are further examined using composite and correlation analysis methods. The results show that the OHC anomaly field is mainly composed of two leading modes, i.e., an in-phase oscillation mode and a zonal anti-phase oscillation mode. The in-phase oscillation mode exhibits strong interannual variability with periods of 2–5 years, which is well related to ENSO at a lead of 6 months, and experienced a regime shift in 1998. The anti-phase oscillation mode shows only a strong interannual variability with periods of 2–4 years well related to ENSO at a lag of 4 months. The composite analysis reveals that horizontal thermal advection mainly controlled by wind forcing plays a primary role in modulating the interannual OHC variability associated with ENSO, while net surface heat flux is the secondary source. And the OHC regime shift in 1998 primarily results from both the strong cold advection during the extremely strong El Niño in 1997 and the subsequent warm advection during the strong La Niña in 1998. [ABSTRACT FROM AUTHOR]

The tendency of El Niño/Southern Oscillation (ENSO) events to peak during boreal winter is known as ENSO phase-locking, whose accurate simulation is essential for ENSO prediction. However, the simulated peaks of ENSO events usually occur outside boreal winter in state-of-the-art climate models. Based on the Coupled Model Intercomparison Project Phase 6 (CMIP6) models, the model with a more reasonable diurnal amplitude (DA) in the sea surface temperature (SST) had a better simulation ability for ENSO phase-locking compared with other models. Further experiments based on the earth system model revealed that the DA is vital for ENSO phase-locking simulation primarily due to the spatial inhomogeneities in seasonal DA anomaly variations in ENSO years with positive/negative DA anomalies in the central equatorial Pacific and negative/positive in the western or eastern Pacific during El Niño/La Niña. Our findings indicate that DA simulation in climate models is crucial for resolving the long-standing failure associated with the ENSO phase-locking simulation accuracy. [ABSTRACT FROM AUTHOR]

The El Niño-Southern Oscillation (ENSO) is a consequential climate phenomenon affecting global extreme weather events often with largescale socioeconomic impacts. To what extent the impact affects the macroeconomy, how long the impact lasts, and how the impact may change in a warming climate are important questions for the field. Using a smooth nonlinear climate-economy model fitted with historical data, here we find a damaging impact from an El Niño which increases for a further three years after initial shock, amounting to multi-trillion US dollars in economic loss; we attribute a loss of US$2.1 T and US$3.9 T globally to the 1997-98 and 2015-16 extreme El Niño events, far greater than that based on tangible losses. We find impacts from La Niña are asymmetric and weaker, and estimate a gain of only US$0.06 T from the 1998-99 extreme La Niña event. Under climate change, economic loss grows exponentially with increased ENSO variability. Under a high-emission scenario, increased ENSO variability causes an additional median loss of US$33 T to the global economy at a 3% discount rate aggregated over the remainder of the 21st century. Thus, exacerbated economic damage from changing ENSO in a warming climate should be considered in assessments of mitigation strategies. Here the authors find economic damage from El Niño far greater than benefits from La Niña on the global economy, leading to an increased economic loss as ENSO variability intensifies under greenhouse warming. [ABSTRACT FROM AUTHOR]

Hot extremes impose severe effects on human health and the ecosystem, especially when high-temperature extremes sequentially occur in both daytime and nighttime within 1 day, known as Compound Hot Extremes (CHEs). Although a number of studies have focused on independent hot extremes, not enough work is devoted to compound ones, not to mention the coupling strength in covariations between the two variables (daytime and nighttime extreme temperature: Tmax and Tmin) over a given region. The instantaneous coupling strength can be derived by Dynamical System (DS) approach from covariations between Tmax and Tmin over a given region, and used to classify CHEs into coupled and decoupled types. Results show that more frequent coupled CHEs tend to be more intense with prolonged duration and extensive spatial extent compared with decoupled CHEs. Also, the mechanisms behind these two types of CHEs are largely different. Coupled CHEs are accompanied by a significant intensification and westward extension of the western North Pacific subtropical high (WNPSH), and the extremely high-temperature is mainly caused by receiving more solar radiation under the corresponding anticyclone. It is found that barotropic structure, weak jet stream and developing La Niña are conducive to the enhancement and persistence of WNPSH, in favor of the occurrence of long-lasting CHEs. Decoupled CHEs are associated with strong sea-land breeze (SLB), whose diurnal cycle could weaken the persistent large-scale circulation and suppress covariations between Tmax and Tmin. This kind of decoupled hot extremes are attributed to the combined effect of receiving more solar radiation during the day and trapping more long-wave radiation at night, where moisture and cloud cover play an important role. [ABSTRACT FROM AUTHOR]

The characteristics of tropical cyclones (TCs) in sub-seasonal forecasting with the Global Seasonal Forecast System 5 (GloSea5) of the Korea Meteorological Administration (KMA) were assessed for June–September (JJAS) from 1991 to 2010 over the western North Pacific (WNP). The performance of GloSea5 was examined for its ability to reproduce observed TC climatology as well as changes in TC genesis with the El Niño-Southern Oscillation (ENSO) and a 1998/1999 climate regime shift (e.g., frequency, genesis spatial distribution). GloSea5 showed skillful performance in predicting the frequency and genesis spatial distribution of TCs in climatology and both ENSO phases; this performance was best during periods of La Niña. Environmental fields related to TC genesis (e.g., sea surface temperature [SST], vertical wind shear [VWS], 850-hPa wind and relative vorticity) were also reasonably captured, despite some systematic biases in SST, low-level circulation, relative vorticity, and VWS. GloSea5 performed well in terms of characteristic of changes in TC genesis before and after the regime shift. However, there were biases in TC frequency before the regime shift and changes in TC-related environmental fields. Our results imply that GloSea5 with a high predictive skill for TC genesis over the WNP can be used as an operational model for sub-seasonal TC forecasting, although it requires continuous improvements to reduce systematic errors. [ABSTRACT FROM AUTHOR]

This study examines the modulation by ENSO of the diurnal cycle of precipitation in boreal winter for the period 1998–2016 over the maritime continent (MC), using the Tropical Rainfall Measuring Mission data and the weather research and forecasting (WRF) model. The diurnal cycles are composited for the ENSO warm (El Niño) and cold (La Niña) phases. It is found that there are statistically significant differences in the diurnal cycle amplitude between El Niño and La Niña, with a non-uniform spatial pattern over the MC. The amplitude of precipitation diurnal cycle is larger over the western MC but smaller over the eastern MC during El Niño, and vice versa for La Niña. A diagnosis of the moisture budget shows that the difference in the diurnal cycle amplitude is primarily attributed to the vertically integrated convergence of the interannual background moisture by diurnal winds. A further analysis indicates that the ENSO-related background moisture plays a key role in causing the difference in diurnal wind activity between El Niño and La Niña, which leads to the difference in the precipitation diurnal cycle. [ABSTRACT FROM AUTHOR]

The validity of the long-held understanding or assumption that El Niño-Southern Oscillation (ENSO) has a remote influence on the North Atlantic Oscillation (NAO) in the January–February–March (JFM) months has been questioned recently. We examine this claim further using atmospheric data filtered to separate the variability orthogonal and parallel to NAO. This decomposition of the atmospheric fields is based on the Principal Component/Empirical Orthogonal Function method whereby the leading mode of the sea-level pressure in the North Atlantic sector is recognised as the NAO, while the remaining variability is orthogonal (unrelated) to NAO. Composite analyses indicate that ENSO has statistically significant links with both the non-NAO and NAO variability at various atmospheric levels. Additional bootstrap tests carried out to quantify the uncertainty and statistical significance confirm these relationships. Consistent with previous studies, we find that an ENSO teleconnection in the NAO-related variability is characterised by lower-stratospheric eddy heat flux anomalies (related to the vertical propagation of planetary waves) which appear in November–December and strengthen through JFM. Under El Niño (La Niña), there is constructive (destructive) interference of anomalous eddy heat flux with the climatological pattern, enhancing (reducing) fluxes over the northern Pacific and Barents Sea areas. We further show that the teleconnection of extreme El Niño is essentially a non-NAO phenomenon. Some non-linearity of the teleconnections is suggested, with El Niño including more NAO-related variability than La Niña, but the statistical significance is degraded due to weaker signals and smaller sample sizes after the partitioning. Our findings have implications for the general understanding of the nature of ENSO teleconnections over the North Atlantic, as well as for refining methods to characterise and evaluate them in models. [ABSTRACT FROM AUTHOR]

In 2021, the Yangtze–Huaihe River Basin (YHRB) of China underwent normal precipitation during the classical Meiyu period in June–July but suffered extreme precipitation and severe floods in August. The present study revealed that the extreme heavy precipitation anomalies over the YHRB region were closely related to the combined effect of the strong western North Pacific anomalous anticyclone (WNPAC) and East Asian middle–high latitude circulation anomalies in August 2021. Moreover, the background of sea surface temperature (SST) anomalies was a strong eastern-Pacific La Niña event that rapidly decayed in spring and a second La Niña emerged in late summer, accompanied by a weak tropical Indian Ocean warming and a strong tropical Atlantic warming in summer. The rapidly decaying La Niña event and the weak tropical Indian Ocean warming alone seem to be insufficient to induce the strong WNPAC in August 2021. Observational evidence and numerical experiments suggest that the rapid tropical Atlantic warming from late spring to summer observably contributed to the enhancement and westward shift of the WNPAC, and the cold SST anomalies in the eastern tropical Pacific associated with the second La Niña event also provided favorable conditions for a strong WNPAC in August 2021. Overall, rapid tropical Atlantic warming and the development of the second La Niña contributed to the strong WNPAC in August 2021, while the maintenance mechanism of the East Asian middle–high latitude circulation anomalies that controlled cold air activity remains unclear. [ABSTRACT FROM AUTHOR]