In January 2008, central and southern China experienced persistent low temperatures, freezing rain, and snow. The large-scale conditions associated with the occurrence and development of these snowstorms are examined in order to identify the key synoptic controls leading to this event. Three main factors are identified: 1) the persistent blocking high over Siberia, which remained quasi-stationary around 65°E for 3 weeks, led to advection of dry and cold Siberian air down to central and southern China; 2) a strong persistent southwesterly flow associated with the western Pacific subtropical high led to enhanced moisture advection from the Bay of Bengal into central and southern China; and 3) the deep inversion layer in the lower troposphere associated with the extended snow cover over most of central and southern China. The combination of these three factors is likely responsible for the unusual severity of the event, and hence a long return period.

Interdecadal variations in the early (May–June) summer monsoon rainfall over South China (SCMR) are found to be related to the ENSO (El Niño/Southern Oscillation) and the PDO (Pacific Decadal Oscillation). An interdecadal variation in SCMR can be identified, with more dry (wet) monsoon years during the periods of high (low) PDO index. Such variations are also related to ENSO in association with PDO. When ENSO and PDO are in phase, i.e. high PDO phase/El Niño events, or low PDO phase/La Niña events, the SCMR tends to be below or above normal respectively more often. But when the ENSO and PDO are out‐of‐phase, the SCMR has no wet or dry preference. Such relationships appear to be related to the intensity of the subtropical high determined by the superposition of the effects of ENSO and PDO.

In this study, we investigate the different impacts of El Niño and El Niño Modoki on China rainfall in their decaying phases. During spring, in the decaying year of El Niño events, there are positive rainfall anomalies south of the Yangtze River, whereas no obvious rainfall signals are found in the same season for the decaying El Niño Modoki. In the subsequent summer season, the wet signal south of the Yangtze River associated with El Niño continues, while suppressed rainfall now appears in the northern Yangtze–Huaihe River region. In contrast, the rainfall is above normal in the region from the Huaihe River to the Yellow River, and below normal in southern China during the summer of the decaying El Niño Modoki events. The distinct China rainfall anomaly is mainly attributed to the difference between the evolution and location of the anomalous western North Pacific (WNP) anti‐cyclone associated with El Niño and El Niño Modoki events. For the case of El Niño, the WNP anti‐cyclone brings plentiful moisture to southern China; meanwhile it shifts the ridge of sub‐tropical high westward in both spring and summer. These tend to induce positive rainfall anomalies in the southern Chinese region. In contrast, due to fast decaying of El Niño Modoki, the anomalous WNP anti‐cyclone becomes weak so that there are no significant rainfall anomalies in China. In summer, however, the WNP anti‐cyclone re‐invigorates possibly associated with a subsequent developing La Niña and extends more northwestward towards the inland region, compared to its El Niño counterpart. The anomalous moisture transport and sub‐tropical high activity associated with this WNP anti‐cyclone result in different summer rainfall anomalies in China. Copyright © 2010 Royal Meteorological Society

This paper investigates the relationship between the onset date of the South China Sea summer monsoon (SCSSM) and the El Niño/Southern Oscillation (ENSO). The monsoon onset date (MOD) is defined on the basis of the switch of the 850‐hPa zonal winds over the South China Sea (SCS) from easterly to westerly for two consecutive pentads. The ENSO signal is represented by the ocean heat content (OHC), which is proportional to the depth of the 20 °C isotherm.It is found that, in years associated with a warm (cold) ENSO event or the year after, the monsoon tends to have a late (an early) onset and the intensity of the SCSSM also tends to be weaker (stronger). During a 2‐year period prior to the onset, anomalies of OHC have an obvious eastward propagation. The 850‐hPa flow east of the Philippines, specifically the strength of the subtropical high, is also found to be critical in determining the MOD. The link between these two results appears to be the propagation of cold (warm) subsurface water into the western North Pacific (WNP), which strengthens (weakens) the subtropical high, and hence a late (an early) SCSSM onset. Copyright © 2006 Royal Meteorological Society.