An extreme positive Indian Ocean Dipole (IOD) event occurred in 2019 boreal autumn, which has induced severe climate impacts around the Indian Ocean basin. In this study, the cause for 2019 IOD event ...and the related mechanism are explored. We find that the remarkable strengthening of Australian high and weakening of sea level pressure over South China Sea/Philippine Sea have been evidently visible since May 2019. Such a record‐breaking interhemispheric pressure gradient (IHPG) induced northward cross‐equatorial flow over the western Maritime Continent, which triggered strong wind‐evaporation‐SST and thermocline feedbacks in 2019. In addition to 2019 case, historical IOD events are highly correlated with IHPG from boreal late spring to summer. We show that skillful IHPG prediction can be made in March by European Centre for Medium‐Range Weather Forecasts seasonal forecast system, which makes it quite possible for the early warning of extreme IOD events by two to three seasons ahead.
Plain Language Summary
During 2019 fall, an extreme Indian Ocean Dipole (IOD) event occurred. In this paper, the possible cause and mechanism of this event are investigated. We find that Australian high was strengthened, and Philippine Sea Anticyclone was weakened since May 2019. This interhemispheric sea level pressure gradient (IHPG) anomaly generates the northward cross equator over the Maritime Continent, which is crucial for the IOD growth. Not only for 2019 IOD, IHPG is a good indicator for almost all the IOD events in history. Since IHPG is predictable in March, the early warning of IOD events and resultant climate disasters could be possible.
Key Points
An extreme positive Indian Ocean Dipole (IOD) event occurred in 2019
The interhemispheric sea level pressure gradient (IHPG) across the Maritime Continent is suggested to be the cause of this IOD event
The skillful prediction of IHPG could give rise to the successful IOD prediction by two to three seasons ahead
This study investigates modulation of El Niño–Southern Oscillation (ENSO) on the Madden–Julian oscillation (MJO) propagation during boreal winter. Results show that the spatiotemporal evolution of ...MJO manifests as a fast equatorially symmetric propagation from the Indian Ocean to the equatorial western Pacific (EWP) during El Niño, whereas the MJO during La Niña is very slow and tends to frequently “detour” via the southern Maritime Continent (MC). The westward group velocity of the MJO is also more significant during El Niño. Based on the dynamics-oriented diagnostics, it is found that, during El Niño, the much stronger leading suppressed convection over the EWP excites a significant front Walker cell, which further triggers a larger Kelvin wave easterly wind anomaly and premoistening and heating effects to the east. However, the equatorial Rossby wave to the west tends to decouple with the MJO convection. Both effects can result in fast MJO propagation. The opposite holds during La Niña. A column-integrated moisture budget analysis reveals that the sea surface temperature anomaly driving both the eastward and equatorward gradients of the low-frequency moisture anomaly during El Niño, as opposed to the westward and poleward gradients during La Niña, induces moist advection over the equatorial eastern MC–EWP region due to the intraseasonal wind anomaly and therefore enhances the zonal asymmetry of the moisture tendency, supporting fast propagation. The role of nonlinear advection by synoptic-scale Kelvin waves is also nonnegligible in distinguishing fast and slow MJO modes. This study emphasizes the crucial roles of dynamical wave feedback and moisture–convection feedback in modulating the MJO propagation by ENSO.
Rainfall in southern China reaches its annual peak in early summer (May–June) with strong interannual variability. Using a combination of observational analysis and numerical modeling, the present ...study investigates the leading modes of this variability and its dynamic drivers. A zonal dipole pattern termed the southern China Dipole (SCD) is found to be the dominant feature in early summer during 1979–2014, and is closely related to a low-level anomalous anticyclone over the Philippine Sea (PSAC) and a Eurasian wave-train pattern over the mid–high latitudes. Linear regressions based on observations and numerical experiments using the CAM5 model suggest that the associated atmospheric circulation anomalies in early summer are linked to decaying El Niño-Southern Oscillation-like sea surface temperature (SST) anomalies in the tropical Pacific, basin-scale SST anomalies in the tropical Indian Ocean, and meridional tripole-like SST anomalies in the North Atlantic in the previous winter to early summer. The tropical Pacific and Indian Ocean SST anomalies primarily exert an impact on the SCD through changing the polarity of the PSAC, while the North Atlantic tripole-like SST anomalies mainly exert a downstream impact on the SCD by inducing a Eurasian wave-train pattern. The North Atlantic tripole-like SST anomalies also make a relatively weak contribution to the variations of the PSAC and SCD through a subtropical teleconnection. Modeling results indicate that the three-basin combined forcing has a greater impact on the SCD and associated circulation anomalies than the individual influence from any single oceanic basin.
The El Niño–Southern Oscillation (ENSO) is mainly manifested as the quasi‐biennial (QB) and low‐frequency (LF) coupled modes centered at different longitudes. Based on the recharge oscillator ...framework, we propose a new method to diagnose the linear periodicity dynamics of spatiotemporally diverse ENSOs, for example, the two coupled modes, to which the traditional Wyrtki index method is ineligible. This method is applied to reanalysis data sets and models and validated by comparisons with the Wyrtki index, which shows that the periodicity of the LF mode is dominated by the thermocline feedback (TH) and effectively reproduced by models, whereas the periodicity of the QB mode is equally driven by the TH and zonal advective feedback (ZA) and poorly simulated in most models due to the insufficient ZA simulations. The new method provides an effective tool for a deeper understanding of the multi‐timescale nature of diverse ENSOs and improving their representations in future models.
Plain Language Summary
The El Niño–Southern Oscillation (ENSO) has two relatively separated main period bands, viz., the 3–7‐year low‐frequency (LF) and 2–3‐year quasi‐biennial (QB), which have been found to be accompanied by the eastern‐Pacific and central‐Pacific spatial types of ENSO sea surface temperature anomalies. What controls such periodicity is a fundamental question in ENSO dynamics. In this study, we propose a new method to diagnose the ENSO linear periodicity dynamics and the role of key feedbacks in determining ENSO periods due to the limitation of the traditional volume‐averaged scheme concerning ENSO pattern diversity. Our method, validated by comparison with the Wyrtki period index originating from the ENSO recharge oscillator framework, clearly shows that the thermocline feedback dominates in shaping the periodicity of the LF mode, whereas its role is equal to the zonal advective feedback in the QB mode. Most of the Coupled Model Intercomparison Project 6 models can effectively reproduce the linear periodicity of the LF mode following the canonical ENSO dynamics but struggle with capturing that of the QB mode. This new method and its related results could increase our understanding of the dynamics of the spatiotemporal diversity of ENSO.
Key Points
A new method is proposed and validated to diagnose the linear periodicity dynamics of The El Niño–Southern Oscillation (ENSO) for its both quasi‐biennial (QB) and low‐frequency (LF) spatiotemporal modes
The thermocline feedback dominates periodicity of the LF mode, but its role is equal to the zonal advective feedback in the QB mode
Most Coupled Model Intercomparison Project 6 models can effectively reproduce linear periodicity of the LF mode like canonical ENSO dynamics, but struggle with the QB mode
We study the active dynamics of self-propelled asymmetrical colloidal particles (Janus particles) fueled by an AC electric field. Both the speed and direction of the self-propulsion, and the strength ...of the attractive interaction between particles can be controlled by tuning the frequency of the applied electric field and the ion concentration of the solution. The strong attractive force at high ion concentration gives rise to chain formation of the Janus particles, which can be explained by the quadrupolar charge distribution on the particles. Chain formation is observed irrespective of the direction of the self-propulsion of the particles. When both the position and the orientation of the heads of the chains are fixed, they exhibit beating behavior reminiscent of eukaryotic flagella. The beating frequency of the chains of Janus particles depends on the applied voltage and thus on the self-propulsive force. The scaling relation between the beating frequency and the self-propulsive force deviates from theoretical predictions made previously on active filaments. However, this discrepancy is resolved by assuming that the attractive interaction between the particles is mediated by the quadrupolar distribution of the induced charges, which gives indirect but convincing evidence on the mechanisms of the Janus particles. This signifies that the dependence between the propulsion mechanism and the interaction mechanism, which had been dismissed previously, can modify the dispersion relations of beating behaviors. In addition, hydrodynamic interaction within the chain, and its effect on propulsion speed, are discussed. These provide new insights into active filaments, such as optimal flagellar design for biological functions.
We study self-propulsion of a half-metal coated colloidal particle under laser irradiation. The motion is caused by self-thermophoresis: i.e., absorption of a laser at the metal-coated side of the ...particle creates local temperature gradient which in turn drives the particle by thermophoresis. To clarify the mechanism, temperature distribution and a thermal slip flow field around a microscale Janus particle are measured for the first time. With measured temperature drop across the particle, the speed of self-propulsion is corroborated with the prediction based on accessible parameters. As an application for driving a micromachine, a microrotor is demonstrated.
•The highest algal lipid content of 63.65% was obtained at 10 μg L−1 Tl+treatment.•Microalgae can remove 100% of Tl+at a concentration range of 0–25 μg L−1.•NO played an essential role in regulating ...lipid accumulation in microalgae.•NO was involved in antioxidant defense system to regulate the ROS level.•Extra NO donor SNP improved lipid synthesis and GSH content in microalgae.
Thallium (Tl+) is a trace metal with extreme toxicity and is highly soluble in water, posing a great risk to ecological and human safety. This work aimed to investigate the role played by Tl+ in regulating lipid accumulation in microalgae and the removal efficiency of Tl+. The effect of Tl+ on the cell growth, lipid production and Tl+ removal efficiency of Parachlorella kessleri R-3 was studied. Low concentrations of Tl+ had no significant effect on the biomass of microalgae. When the Tl+ concentration exceeded 5 μg L−1, the biomass of microalgae showed significant decrease. The highest lipid content of 63.65% and lipid productivity of 334.55 mg L−1 d−1 were obtained in microalgae treated with 10 and 5 μg L−1 Tl+, respectively. Microalgae can efficiently remove Tl+ and the Tl+ removal efficiency can reach 100% at Tl+ concentrations of 0–25 μg L−1. The maximum nitric oxide (NO) level of 470.48 fluorescence intensity (1 × 106 cells)−1 and glutathione (GSH) content of 343.51 nmol g−1 (fresh alga) were obtained under 5 μg L−1 Tl+ stress conditions. Furthermore, the exogenous donor sodium nitroprusside (SNP) supplemented with NO was induced in microalgae to obtain a high lipid content (59.99%), lipid productivity (397.99 mg L−1 d−1) and GSH content (430.22 nmol g−1 (fresh alga)). The corresponding analysis results indicated that NO could participate in the signal transduction pathway through modulation of reactive oxygen species (ROS) signaling to activate the antioxidant system by increasing the GSH content to eliminate oxidative damage induced by Tl+ stress. In addition, NO regulation of ROS signaling may enhance transcription factors associated with lipid synthesis, which stimulates the expression of genes related to lipid synthesis, leading to increased lipid biosynthesis in microalgae. Moreover, it was found that the change in Tl+ had little effect on the fatty acid components and biodiesel properties. This study showed that Tl+ stress can promote lipid accumulation in microalgae for biodiesel production and simultaneously effectively remove Tl+, which provided evidence that NO was involved in signal transduction and antioxidant defense, and improved the understanding of the interrelation between NO and ROS to regulate lipid accumulation in microalgae.
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Abstract The Yangtze River basin (YRB) and its southern region in China (20°–34°N, 104°–123°E, YRBSC) are highly susceptible to climate change and experience extreme hydrological events. To ...understand the spatial and temporal distribution of summer runoff in these regions, a statistical diagnosis method was applied using monthly mean runoff grid data, global Sea Surface Temperature (SST) data and meteorological reanalysis data from 1980 to 2022. The analysis revealed that variations in the isotropic phase within the YRBSC and the north–south inverse phase with the Yangtze River as the boundary are the main modes of summer runoff. Furthermore, a strong correlation was observed between winter SST anomalies (SSTAs) and late summer runoff in the YRBSC, as determined through singular value decomposition (SVD). In the first type of positive SSTA years, the eastward advance of the South Asian high pressure (SAH) and westward shift of the subtropical high pressure (SH) result in sufficient water vapour, strong upward movement and increased summer runoff. The second type of positive SSTA years exhibits a westward retreat of the SAH, upward movement north of 28°N, and downward movement between 20°N and 28°N. These conditions, combined with water vapour intermixing and dispersion, lead to a northward increase and southward decrease of summer runoff in the YRBSC, with the boundary at 28°N. Additionally, the study analysed the extreme drought situation observed in the YRB during the summer of 2022. The findings of this research provide valuable insights for ecological environmental protection, water resource planning and management in the region.
The development of flexible zinc‐air batteries (FZABs) has attracted broad attention in the field of wearable electronic devices. Gel electrolyte is one of the most important components in FZABs, ...which is urgent to be optimized to match with Zn anode and adapt to severe climates. In this work, a polarized gel electrolyte of polyacrylamide‐sodium citric (PAM‐SC) is designed for FZABs, in which the SC molecules contain large amount of polarized −COO− functional groups. The polarized −COO− groups can form an electrical field between gel electrolyte and Zn anode to suppress Zn dendrite growth. Besides, the −COO− groups in PAM‐SC can fix H2O molecules, which prevents water from freezing and evaporating. The polarized PAM‐SC hydrogel delivers a high ionic conductivity of 324.68 mS cm−1 and water retention of 96.85 % after being exposed for 96 h. FZABs with the PAM‐SC gel electrolyte exhibit long cycling life of 700 cycles at −40 °C, showing the application prospect under extreme conditions.
A polarized gel electrolyte of polyacrylamide‐sodium citric (PAM‐SC) is synthesized for flexible zinc‐air batteries. The polarized −COO− functional groups in gel electrolyte not only form an electrical field to suppress Zn dendrite growth, but also prevent water from freezing and evaporating. The FZABs with the PAM‐SC gel electrolyte exhibit long cycling life of 700 cycles at −40 °C, showing the application prospect under extreme conditions.
α-Synuclein (α-Syn), a pathological hallmark of Parkinson's disease (PD), has been recognized to induce the production of interleukin-1β in a process that depends, at least in vitro, on nod-like ...receptor protein 3 (NLRP3) inflammasome in monocytes. However, the role of NLRP3 inflammasome activation in the onset of PD has not yet been fully established.
In this study, we showed that NLRP3 inflammasomes were activated in the serum of PD patients and the midbrain of PD model mice. We further clarified that α-syn activated the NLRP3 inflammasome through microglial endocytosis and subsequent lysosomal cathepsin B release. Deficiency of caspase-1, an important component of NLRP3 inflammasome, significantly inhibited α-syn-induced microglia activation and interleukin-1β production, which in turn alleviated the reduction of mesencephalic dopaminergic neurons treated by microglia medium. Specifically, we demonstrated for the first time that Nlrp3 is a target gene of microRNA-7 (miR-7). Transfection of miR-7 inhibited microglial NLRP3 inflammasome activation whereas anti-miR-7 aggravated inflammasome activation in vitro. Notably, stereotactical injection of miR-7 mimics into mouse striatum attenuated dopaminergic neuron degeneration accompanied by the amelioration of microglial activation in MPTP-induced PD model mice.
Our study provides a direct link between miR-7 and NLRP3 inflammasome-mediated neuroinflammation in the pathogenesis of PD. These findings will give us an insight into the potential of miR-7 and NLRP3 inflammasome in terms of opening up novel therapeutic avenues for PD.
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