The El Niño-Southern Oscillation (ENSO) and the variability in the Pacific subtropical highs (PSHs) have major impacts on social and ecological systems. Here we present an Atlantic capacitor effect mechanism to suggest that the Atlantic is a key pacemaker of the biennial variability in the Pacific including that in ENSO and the PSHs during recent decades. The ‘charging’ (that is, ENSO imprinting the North Tropical Atlantic (NTA) sea surface temperature (SST) via an atmospheric bridge mechanism) and ‘discharging’ (that is, the NTA SST triggering the following ENSO via a subtropical teleconnection mechanism) processes alternate, generating the biennial rhythmic changes in the Pacific. Since the early 1990s, a warmer Atlantic due to the positive phase of Atlantic multidecadal oscillation and global warming trend has provided more favourable background state for the Atlantic capacitor effect, giving rise to enhanced biennial variability in the Pacific that may increase the occurrence frequency of severe natural hazard events.

This study finds a relationship between the distribution of the seven-year mean relative vorticity of surface winds (RVSW) derived from 25-kilometer-resolution measurements of ocean winds from the Quick Scatterometer (QuikSCAT) satellite and the genesis locations of tropical cyclones (TCs) in the South China Sea (SCS). The results show the effects of the background mean RVSW on TC formation in the SCS. During the summer monsoon, TCs are formed in the northern SCS, where monsoon trough and coastal mountains contribute to positive mean RVSW, while during the winter monsoon TCs form in the southern SCS with positive mean RVSW. No TCs formed in the southern part of the SCS during the summer monsoon nor in the northern part during the winter monsoon during the period from 1945 to 2005, both of which coincide with negative mean RVSW induced by the coastal mountains. The mean RVSW prior to TC formation in regions around the TC genesis locations are calculated using the QuikSCAT measurements averaged over...

The Indo-Pacific warm pool (IPWP), which affects the global climate system through supporting tropical convection, has been reported to expand significantly under greenhouse warming. Although early research revealed that the sea surface temperature (SST) threshold for deep convection (σ_conv) increases with global warming, many latest relevant works were still conducted based on the traditional IPWP definition (e.g., static SST = 28 °C threshold, and is referred to as the oceanic warm pool, OWP₂₈). Here, we claim that the OWP₂₈expansion differs from the deep convection favoring pool (DCFP) area change and may not reflect the direct impacts of Indo-Pacific warming on the climate system. Results show that, because of the long-term increase in σ_conv, the DCFP expands at a rate 2.6 times slower than the OWP₂₈from 1979 to 2020. The difference reaches 12–27 times from 2015–2100 under different emission scenarios, based on CMIP6 model simulations. While the OWP₂₈expands to the eastern Pacific, the DCFP will remain within the Indian Ocean and western Pacific Ocean regardless of emission levels. This study emphasizes the necessity of considering the response of the relationship between deep convection and SST to climate change when studying the long-term variability of the IPWP.

The El Niño Modoki is separated into two types, El Niño Modoki I and El Niño Modoki II, which are characterized by substantially different mechanism. According to comparisons between the evolution of air-sea coupled processes and heat budget analyses, this study discovered the distinct dynamical mechanism of the onset of El Niño Modoki II compared to that of El Niño Modoki I. For El Niño Modoki I, westerly wind anomalies in the western Pacific appear earlier than warm sea surface temperature (SST) anomalies in the central tropical Pacific; in addition, zonal advection is responsible for changes in mixed-layer temperature in the Niño-4 region during the developing phase in spring and summer. However, warm SST anomalies accompany easterly anomalies in the central tropical Pacific, and there are no westerly anomalies in the western tropical Pacific during the developing phase in spring and summer for El Niño Modoki II. For El Niño Modoki II, Ekman feedback is the major contributor to changes in mixed-layer temperature. According to reanalysis data, the 2.5-layer model results and coupled model simulations, anomalous westerly wind stress in the subtropical North Pacific and easterly wind stress in the central–eastern tropical Pacific can lead to equatorward and westward oceanic current anomalies, thus enhancing meridional and zonal convergences at upper layer. Because anomalous convergence at upper layer can inhibit upwelling motion in the central tropical Pacific, SST anomalies in the central tropical Pacific tend to be warm, even without anomalous westerlies in the western Pacific.

This article presents a comprehensive analysis of interannual and interdecadal variations of summer precipitation and precipitation‐related extreme events in East China associated with variations of the East Asian summer monsoon (EASM) from 1979 to 2012. A high‐quality daily precipitation data set covering 2076 observational stations in China is analysed. Based on the precipitation pattern analysis using empirical orthogonal functions and the regime shift detection method, three sub‐periods of 1979–1992 (period I), 1993–1999 (period II) and 2000–2012 (period III) are identified to be representative of the precipitation variability. Similar significant variability of the extreme precipitation indices is found across four sub‐regions in eastern China. The spatial patterns of summer mean precipitation, the number of days with daily rainfall exceeding 95th percentile precipitation (R95p) and the maximum number of consecutive wet days (CWD) anomalies are consistent, but opposite to that of maximum consecutive dry days (CDD) anomalies to some extent during the three sub‐periods. However, the spatial patterns of hydroclimatic intensity (HY‐INT) are notably different from that of the other three extreme indices, but highly correlated to the dry events. The changes of precipitation anomaly patterns are accompanied by the change of the EASM regime and the abrupt shift of the position of the west Pacific subtropical high around 1992/1993 and 1999/2000, respectively, which influence the moisture transport and contributes to the precipitation anomalies. In addition, the EASM intensity is linked to sea surface temperature anomaly over the tropical Indian and Pacific Ocean through its effects on convective activity over the west Pacific that induces the cyclonic or anticyclonic anomaly over the South China and northwest Pacific.

The seasonal cycle of marine boundary layer (MBL) clouds over the eastern Pacific Ocean is studied with the International Pacific Research Center (IPRC) Regional Atmospheric Model (iRAM). The results show that the model is capable of simulating not only the overall seasonal cycle but also the spatial distribution, cloud regime transition, and vertical structure of MBL clouds over the eastern Pacific. Although the modeled MBL cloud layer is generally too high in altitude over the open ocean when compared with available satellite observations, the model simulated well the westward deepening and decoupling of the MBL, the rise in cloud base and cloud top of the low cloud decks off the Peru and California coasts, and the cloud regime transition from stratocumulus near the coast to trade cumulus farther to the west in both the southeast and northeast Pacific. In particular, the model reproduced major features of the seasonal variations in stratocumulus decks off the Peru and California coasts, including cloud amount, surface latent heat flux, subcloud-layer mixing, and the degree of MBL decoupling. In both observations and the model simulation, in the season with small low-level cloudiness, surface latent heat flux is large and the cloud base is high. This coincides with weak subcloud-layer mixing and strong entrainment at cloud top, characterized by a high degree of MBL decoupling, while the opposite is true for the season with large low-level cloudiness. This seasonal cycle in low-cloud properties resembles the downstream stratocumulus-to-cumulus transition of marine low clouds and can be explained by the “deepening–decoupling” mechanism proposed in previous studies. It is found that the seasonal variations of low-level clouds off the Peru coast are mainly caused by a large seasonal variability in sea surface temperature, whereas those off the California coast are largely attributed to the seasonal cycle in lower-tropospheric temperature.