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By observing well‐known sea surface temperature (SST) indices and outputs from Climate Forecast System version 2 (CFSv2) hindcasts and predictions, in this study, we developed a hybrid statistical downscaling prediction model (HSDPM) based on a timescale decomposition approach, which effectively improved the forecasting ability of summer (June–August) precipitation over Hainan Island (HNSP) in China; this precipitation presented multiple obvious timescale variabilities. We found that the interannual variability of the HNSP is closely related to the observed North Atlantic tripole SST anomalies in the preceding winter and the summer sea level pressure over the South China Sea by CFSv2 predicted in March. On the other hand, the interdecadal variability in the HNSP is linked to the prewinter Pacific Interdecadal Oscillation (PDO) according to the observations, the CFSv2 predictions of the summer surface air temperature over the tropical central‐east Pacific. On this basis, both the interannual and interdecadal components of the HNSP are effectively predicted using the corresponding predictors via multiple regression; thus, the HSDPM is ultimately established by combining the above two components. Compared with the original CFSv2 model, the HSDPM model achieves a considerable improvement in performance in predicting the HNSP. Specifically, the temporal correlation coefficient, ratio of root‐mean‐square error and anomaly sign consistency rate between the observed and HSDPM‐predicted HNSPs are 0.70, 17.4% and 80.5%, respectively, which are significantly greater than the above three forecasting index values of 0.23, 38.3% and 48.8%, respectively, obtained from the original CFSv2 predictions. The application of the HSDPM may be beneficial for drought and flood prevention and mitigation in Hainan Island. [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]

Northeast China (NEC) is located between the subtropical monsoon and temperate-frigid monsoon regions and exhibits two successive rainy seasons with different natures: the northeast cold vortex rainy season in early summer (May–June) and the monsoon rainy season in late summer (July–August). Summer rainfall over NEC (NECR) has a fundamental influence on society, yet its successful seasonal prediction remains a long-term scientific challenge to current dynamical models. The poor NECR prediction skill is partly attributed to the large NECR variability at both the interannual and interdecadal time scales. Here, we focus on the oceanic drivers of the late summer NECR variability and associated physical processes at interannual time scale. Then, we establish an empirical prediction model to predict the interannual variability of summer NECR at 1-month lead time (in June). The analysis of observations spanning 40 years (1963–2002) reveals three physically and synergistically influencing predictors of the late summer NECR interannual variability. Above-normal NECR is preceded in the previous spring by (a) warm sea surface temperature (SST) anomalies in the tropical northern Indian Ocean, (b) a positive thermal contrast tendency in the tropical West–East Pacific SST, and (c) a positive tendency of the North Atlantic tripolar SST. These precursors enhance the anomalous low-level anticyclone over the western North Pacific and southerly anomalies over NEC in late summer, which are beneficial to enhancing NECR. An empirical prediction model built on these three predictors achieves a forecast temporal correlation coefficient (TCC) skill of 0.72 for 1961–2019, and a 17-year (2003–2019) independent forecast shows a significant TCC skill of 0.70. The skill is substantially higher than that of five state-of-the-art dynamical models and their ensemble mean for 1979–2019 (TCC = 0.24). These results suggest that the proposed empirical model is a meaningful approach for the prediction of NECR, although the dynamical prediction of NECR has considerable room for improvement. [ABSTRACT FROM AUTHOR]

The inter‐decadal variation of autumn rain of west China (ARWC) and its relationship with atmospheric circulation and sea surface temperature anomalies (SSTAs) was analysed. The intensity of ARWC shows significant inter‐decadal variability. The year 1990 is one of the abrupt change points of ARWC in both the southern and northern zone, and the year 2000 is another one in the northern zone. The inter‐annual correlation between the intensity of ARWC in the northern (southern) zone and the El Niño–Southern Oscillation continuously weakens (strengthens) from 1961. The relationship between the intensity of ARWC in the northern zone and atmospheric circulation of September–October mean significantly weakens after 2000, so does the relationship with the SSTAs in the equatorial central Pacific. On the contrary, the relationship between the intensity of ARWC in the southern zone and atmospheric circulation of September–October mean significantly strengthens after 1990, so does the relationship with the east–west contrast pattern of SSTAs in the equatorial central–western Pacific. The positive phase of the east–west contrast pattern of SSTAs in the equatorial central–western Pacific (i.e., when the tropical central [western] Pacific is colder [warmer] than normal) gradually strengthening and maintaining from the preceding spring to September–October is favourable for a stronger western Pacific subtropical high, which further facilitates northwards transportation of water vapour and provides better dynamic conditions for ARWC in the southern zone by strengthening the local Hadley circulation. [ABSTRACT FROM AUTHOR]

Accurate short-term climate predictions, specifically the prediction of dominant rain belts during flood seasons, represent a significant challenge, particularly in the absence of notable external forcing signal anomalies in the previous winter. To address this challenge, we propose a novel climate index based on an Auto-Encoder (AE) Neural Network that exhibits superior performance in indicating several significant precipitation events in the Yangtze and Huaihe River Basins under varying El Niño conditions. Notably, the novel climate index rectifies the discrepancy between the 2019/2020 Niño index and the 2020 summer precipitation. In order to understand the information source of AE, the causality between AE and other indices was further analyzed by Granger Causality. The results show that AE index mainly contains the information of subtropical high index and ocean index, which is consistent with previous studies. • AE obtained by Auto-encoder can make up for the "failure" of Nino index in abnormally heavy precipitation events. • In terms of magnitude and state, AE has better description of precipitation than Nino3.4. • The main indices of AE information are subtropical high-pressure index and sea surface temperature index. [ABSTRACT FROM AUTHOR]

In this study, we investigate the interdecadal variation characteristics of the dominant mode of summer precipitation over East Asia‐Northwest Pacific (EA‐NWP) before and after late 1990s, reveal the physical mechanism, and address its possible connection with the regional ocean warming background. Study results show that the empirical orthogonal function mode 1 (EOF1) of summer precipitation anomalies over EA‐NWP during the global ocean warming acceleration period (1979–1998) present a more significant dipole pattern between Yangtze River Basin (YRB) and tropical NWP compared with that during the global ocean warming slowdown period (1999–2012). And then we find that the anomalous dipoles of low‐level winds, geopotential height, convection, and associated wave activity fluxes over NWP significantly shift westward (eastward) and enhance (weaken) in 1979–1998 (1999–2012), which are regarded as the direct cause of the adjustment of dipole pattern between YRB and tropical NWP. Further analysis reveals that the negative sea surface temperature (SST) anomalies in the tropical NWP are prominent (not prominent), resulting in the stronger (weaker) Pacific–Japan Teleconnection over Japan and Tropics in NWP during the period 1979–1998 (1999–2012), and ultimately lead to the change of summer precipitation EOF1 in EA‐NWP. By regressing vertical velocity, outgoing longwave radiation, relative vorticity, wave activity fluxes, and precipitation onto the NWP SST in the two periods, the impacts of the SST in the NWP on the interdecadal variation of summer precipitation EOF1 in EA‐NWP are verified. Finally, the mechanism diagram of interdecadal variation of summer precipitation is given, which can be useful for short‐term precipitation prediction of East Asia. [ABSTRACT FROM AUTHOR]

The present study investigates relative contributions of interannual, intraseasonal, and synoptic variations of environmental factors to tropical cyclone (TC) genesis over the northern tropical Atlantic (NTA) during July–October. Analysis shows that convection, lower-level vorticity, and midlevel specific humidity contribute to TC genesis through intraseasonal and synoptic variations with a larger contribution of the latter. The relative contribution of three components of vertical wind shear depends largely on its magnitude. The contribution of sea surface temperature (SST) to TC genesis is mainly due to the interannual component when total SST is above 27.5°C. The barotropic energy for the development of synoptic-scale disturbances comes mainly from climatological mean flows and intraseasonal wind variations. The proportion of contribution between synoptic and intraseasonal variations of convection, relative vorticity, and specific humidity is larger over the eastern NTA than over the western NTA. The barotropic energy conversion has a larger part related to climatological mean flows and intraseasonal wind variations over the eastern and western NTA, respectively. There are notable differences between the NTA and the western North Pacific (WNP). One is that the relative contribution of synoptic variations of convection, relative vorticity, and specific humidity is larger over the NTA, whereas that of intraseasonal variations is larger over the WNP. The other is that the barotropic energy conversion related to climatological mean flows and intraseasonal wind variations is comparable over the NTA, whereas that related to climatological mean flows is larger over the WNP. [ABSTRACT FROM AUTHOR]