In the first half of winter 2020/21, China has experienced an extremely cold period across both northern and southern regions, with record-breaking low temperatures set in many stations of China. Meanwhile, a moderate La Niña event which exceeded both oceanic and atmospheric thresholds began in August 2020 and in a few months developed into its mature phase, just prior to the 2020/21 winter. In this report, the mid−high-latitude large-scale atmospheric circulation anomalies in the Northern Hemisphere, which were forced by the negative phase of Arctic Oscillation, a strengthened Siberian High, an intensified Ural High and a deepened East Asian Trough, are considered to be the direct reason for the frequent cold surges in winter 2020/21. At the same time, the synergistic effect of the warm Arctic and the cold tropical Pacific (La Niña) provided an indispensable background, at a hemispheric scale, to intensify the atmospheric circulation anomalies in middleto-high latitudes. In the end, a most recent La Niña prediction is provided and the oncoming evolution of climate is discussed for the remaining part of the 2020/21 winter for the purpose of future decision-making and early warning.

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The prediction skill and source of the predictability of the East Asian summer monsoon (EASM) system are examined in this work based on four state‐of‐the‐art seasonal climate forecast models including BCC_CSM1.1, ECMWF_SYS4, NCEP_CFS2 and TCC_CPS2. The prediction of the climatology and interannual EASM pattern and the impact on the prediction are further investigated. It is noted that the four models have some skill in predicting summer rainfall in the East Asia, however, the skill is low on average and also largely regional dependence. The interannual variation of EASM measured by monsoon circulation index is well reproduced, implying that the broad‐scale feature/pattern of EASM has higher predictability than the detailed spatial variation of EASM rainfall. The possible sources of predictability of the interannual variability of EASM are associated with the El Niño‐Southern Oscillation (ENSO) and the north Indian Ocean (NIO) sea surface temperature (SST) anomalies. The correlation pattern of rainfall with the NIO SST is characterized by a tripole pattern from south to north of East Asia, which is different from the correlation distribution of the southern‐northern dipole with ENSO, suggesting that NIO SST may exert influence on the EASM independently. The major biases in climatology of EASM in the models are the northward shift of the western Pacific subtropical high (WPSH) and weak monsoonal southerly over the coast of East Asia, which leads to the prediction bias of the Meiyu/Baiu/Changma (MBC) rainfall belt. The prediction of the interannual EASM pattern presents two deficiencies: too weak rainfall variability and northward shift of the dipole rainfall pattern (opposite variation between MBC and the northwestern Pacific), that may be caused by the biases of WPSH in the models.

A record-breaking heat wave hit the Yangtze River valley during the boreal summer of 2022, and caused severe social and economic losses. One prominent feature of this long-lived heat event was its persistence and abnormal intensification in August. This study investigated the physical mechanisms be responsible for the intensification of this heat event in late summer under the background of a La Niña event. The prolonged heat event was directly related to the intensification and westward extension of the western North Pacific subtropical high, which can be attributed to the synergistic effects of an anomalous western North Pacific anticyclone and the eastward extension of the South Asian high in the upper troposphere. The anomalous anticyclone in the western North Pacific, which was induced by negative sea surface temperature anomalies in the central tropical Pacific, strengthened in August. The positive sea surface temperature anomaly in the western Pacific warm pool and enhanced in-situ convection led to anomalous high pressure over the Yangtze River valley via the local meridional circulation. Atmospheric convergence and descending motion over the Yangtze River valley was amplified in August as a result of the zonal shift in the South Asian high from the Iranian Plateau to the Tibetan Plateau. The Silk Road pattern index of August 2022 was the lowest since the 1990s. The abnormal negative phase of the Silk Road pattern contributed to both the zonal shift in the South Asian high and the westward extension of the western North Pacific subtropical high, which led to the abnormal intensification of the heat event over the Yangtze River valley in August 2022.

Dynamic recycling model (DRM) and reanalysis data were used to study the interaction between the land surface and atmosphere during the warm season from 1979 to 2010 across the arid and semi-arid regions of China. The nonlinear trends common to the key land-atmosphere interaction variables were extracted. For the whole study region, the precipitation recycling ratio showed an increasing trend, especially in the period before the 1990s. Simultaneously, increasing trends were also found in variables regionally related to precipitation, such as soil moisture, evaporation, precipitation efficiency, low-level cloud and precipitable water. However, the moisture transport due to westerly moisture flux showed a remarkable weakening throughout the whole study region. Based on significantly positive correlation between the precipitation efficiency and precipitation recycling ratio under relatively low moisture advection, it was concluded that the precipitation recycling process should not been ignored, for both direct and indirect precipitation processes, in the study region. The spatial patterns of nonlinear trends in land-atmosphere interaction variables indicated reverse tendencies in two sub-regions divided by the meridional boundary at approximately 110 ∘ E. For the western sub-region, although decreasing westerly moisture flow was found, the strengthening southerly moisture flux mainly resulted in an increase of precipitable water. Positive relationships among precipitable water, low cloud, precipitation, soil moisture, evaporation and the precipitation recycling ratio were also found. The soil becoming wetter and the precipitation recycling process becoming enhanced suggested the existence of positive land-atmosphere interaction in the western sub-region. However, the opposite tendencies were found in the eastern sub-region, where a weakening of advected moisture convergence was caused by decreases in both westerly and southerly moisture transport. Furthermore, less evaporation and warming temperatures suggested the climate in the eastern sub-region shifted towards relatively warmer and drier conditions throughout the course of the study period.

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Based on the observational datasets of rime and glaze from 743 stations in China and the atmospheric circulation data from the NCEP-NCAR reanalysis during 1954-2009, large-scale atmospheric and oceanic conditions for extensive and persistent rime and glaze events were examined with a composite analysis. Results show that rime events mostly occur in northern China while glaze events are mainly observed in southern China. The icing events are accompanied by low temperature and high humidity but not necessarily by abovenormal precipitation. The Asian low, blocking highs, strong moisture transport, and an inversion layer related to major abnormal circulation systems contribute to the occurrence and persistence of icing events in China. The Ural blocking high plays a major role in the glaze events, and the Okhotsk blocking high is closely related to the rime events. For glaze events, extratropical circulation anomalies and the southward outbreak of cold air play a dominant role. In contrast, the strong northward transport of warm and moist airflows plays a leading role and the blocking high and the southward outbreak of extratropical cold air take a supporting role for rime events. There is nearly an equal chance for occurrences of rime events under La Niña and El Niño backgrounds. However, glaze events more likely occur under the background of La Niña. Additionally, the sea surface temperatures from the tropical Indian Ocean to the tropical northwestern Pacific Ocean also contribute to the occurrence and maintenance of icing events in China.