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Marine heatwaves (MHWs) are extreme climatic events that can have a significant impact on marine ecosystems and their services across the world. We examine the spatiotemporal variation of summer MHWs in the north Indian Ocean (NIO) and find that the whole NIO Basin exhibits a pronounced spatial variability as well as a significant increasing trend in MHW frequency. We show that the NIO has two leading MHW modes linked to two distinct sea surface temperature (SST) patterns during summer. The first MHW mode is associated with basinwide warming, which is preconditioned by a decaying El Niño-Southern Oscillation (ENSO) and sustained throughout the summer by anomalous northeasterlies extending from the anticyclonic circulation of the western North Pacific subtropical high (WNPSH). The combined effect of thermocline warming due to downwelling oceanic planetary waves, decreased wind-induced evaporative cooling, and enhanced insolation cause basinwide summer MHWs. The second MHW mode exhibits a zonal dipole pattern, which has unfavorable cooling conditions in the previous seasons. The second MHW mode is associated with a phase change of ENSO and is greatly influenced by the formation of an interhemispheric pressure difference (IHPD) due to strengthening of the Australian high (AH) and weakening of the WNPSH. The IHPD induces cross-equatorial southerly winds across the eastern Indian Ocean. These winds favor the transformation of basinwide cooling conditions into zonal SST patterns via wind-evaporation-SST and thermocline-SST feedback, causing MHWs with a zonal dipole pattern. These MHW modes have a significant influence on the distribution and intensity of summer precipitation in the NIO. [ABSTRACT FROM AUTHOR]

The impact of El Nino –Southern Oscillation (ENSO) on the winter stratospheric polar vortex intensity (PVI) is re-examined, using JRA-55 datasets and the CESM2 model. Our results show that the negative correlation between ENSO and PVI has weakened in recent decades and is no longer statistically significant after the mid-1990s. This weakening ENSO–PVI relationship after the mid-1990s is associated with wave-1 fluxes entering the stratosphere; that is, the ENSO-induced increasing wave-1 fluxes are weaker after the mid-1990s than before the mid-1990s. Except for the Pacific–North America (PNA)-like wave train, the stratospheric wave flux changes are related to ENSO-induced geopotential height changes over East Asia. The ENSO-induced tropical zonal circulation anomalies are enhanced from the central Pacific to East Asia, leading to more substantial wave flux anomalies propagating westward from the central Pacific to East Asia and a more significant high center over Northeast Asia after the mid-1990s than before the mid-1990s. This ENSO-induced high center after the mid-1990s is out of phase with the climatological center of wave 1, leading to a relatively weaker increase in wave 1. Model results show that changes in the ENSO–PVI relationship and ENSO–Asia circulation are associated with changes in ENSO-related SST combined with global mean SST. [ABSTRACT FROM AUTHOR]

The summer moisture circulation anomaly over East Asia and the western North Pacific (WNP) couples well with the El Niño-Southern Oscillation (ENSO) in a quasi-4-yr period. The moisture circulation is dominated by two well-separated modes. The first mode exhibits an anticyclonic (cyclonic) moisture circulation over tropical-subtropical East Asia-WNP with an easterly (westerly) transport over the tropical WNPIndian Ocean; the second mode displays an alternating pattern with an anticyclonic (cyclonic) moisture circulation over the subtropical WNP layered between two cyclonic (anticyclonic) circulations. Both modes couple well with the ENSO signal during its quasi-4-yr cycle. Within the cycle, in the summer of a developing warm episode, the positive phase of the second mode plays a key role, while in the transitional summer between a decaying warm episode and a developing cool episode, the positive phase of the first mode tends to take effect. In the summer of a developing cool episode, the negative phase of the second mode plays an important role, while the negative phase of the first mode tends to take effect in the transitional summer between a decaying cool episode and a developing warm episode. The anticyclone (cyclone) over the Philippine Sea region serves as a bridge in the quasi-four-year coupling. Its establishment and eastward extension modify moisture circulation over East Asia-WNP. Conversely, the easterly (westerly) wind to the south of the anticyclone (cyclone) is beneficial for the formation and eastward propagation of the Kelvin wave and, hence, to the development of the quasi-4-yr periodic ENSO episode. [ABSTRACT FROM AUTHOR]

This study examines the interannual variability of three groups of tropical cyclones (TCs)-super typhoons (STYs), typhoons (TYs), and tropical storms and tropical depressions (TSTDs)-and their relationship with the El Niño-Southern Oscillation (ENSO). Both wavelet analysis and correlation studies of upper-ocean heat content reveal significant differences for the three types of TCs. In particular, an increase (decrease) in the frequency of STYs is usually associated with the mature phase of El Niño (La Niña) events, while the converse is true for TSTDs. In contrast, the frequency of TYs increases (decreases) during the transition period from La Nina to El Niño (El Niño to La Nina) events. The results suggest that the timing with which ENSO impacts STYs, TYs, and TSTDs varies and that their corresponding changes in frequency closely follow the evolution of the ENSO cycle. Empirical orthogonal function analysis is also conducted to investigate the impact of different environmental factors influenced by ENSO on TCs. The vertical wind shear and moist static energy associated with ENSO are identified as the dominant factors that control the frequency of STYs. In comparison, the frequency of TYs is found to be closely related to the relative vorticity and vertical wind shear associated with both the transition phase of ENSO and with other types of climate variability. [ABSTRACT FROM AUTHOR]

The article presents a study on the impacts of the Indian Ocean basin-scale sea surface temperature anomaly (SSTA) on the onset of the summer monsoon on South China Sea. It is observed that basin-wide warming in tropical Indian Ocean occurs after an El Niño event. Changes in the sea-surface temperature sustain the El Niño-Southern Oscillation (ENSO) effects towards the summer monsoon in Asia and modifies the strength of the Philippine Sea anti-cyclone, which causes delay to the South China Sea monsoon onset. The methods and the conclusion of the study are discussed.

The Taiwan Strait is the only direct passage between the South China Sea (SCS) and the East China Sea. Variations in the intensity of Kuroshio Branch and surface currents in the SCS result in seasonal and inter-annual variability in the hydrography of the SE Taiwan Strait, where the northwardly pointing funnel-like Penghu Channel is located. These currents vary with the intensity and direction of monsoons. The teleconnection between air-sea interaction of the east Pacific and west Pacific reportedly has time differences. The data in this study reveal that the salinity of the seawater in the Penghu Channel is highest during El Niño events with a seven-month lag to the monthly Niño 3.4 index, and lowest during La Niña periods, also with a lag of seven months to the monthly Niño 3.4 index. The chemical parameters also vary with these events. The concentrations of apparent oxygen utilization, nutrients, and hydrogen ions vary with the mixing ratio of SCS water and Kuroshio Branch water. The maximum concentrations of nutrients are significantly higher during the summer, seven months after a La Niña event (La Niña-7), than in other seasons. However, biological activities also affected these chemical parameters. In spring, active photosynthesis consumes more nutrients and hydrogen ion concentrations in La Niña-7 periods than in normal-7 periods. [ABSTRACT FROM AUTHOR]

The article explores the spatiotemporal features of the Indian Ocean Dipole (IOD) on the sea surface and the subsurface ocean. It was found that the previous positive IOD is associated with the normal South China Sea summer monsoon. Also, a stronger 100-hPa South Asian High is induced by a positive IOD in the summer after an IOD year. Summer rainfall in China is said to exhibit various patterns corresponding to different phases of the IOD, as influenced by the 850-hPa Asian monsoon circulations, as well as the position of the 500-hPa subtropical high ridge.