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This study investigates interannual variations of surface air temperature (SAT) over mid-and high latitudes of Eurasia during boreal spring and their association with snow, atmospheric circulation, and sea surface temperature (SST) changes. The leading mode of spring SAT variations is featured by same-sign anomalies over most regions. The second mode features a tripole anomaly pattern with anomalies over the central part opposite to those over the eastern and western parts of Eurasia. A diagnosis of surface heat flux anomalies suggests that snow change contributes partly to SAT anomalies in several regions mainly by modulating surface shortwave radiation but cannot explain SAT changes in other regions. Atmospheric circulation anomalies play an important role in spring SAT variability via wind-induced heat advection and cloud-induced surface radiation changes. Positive SAT anomalies are associated with anomalous westerly winds from the North Atlantic Ocean or with anomalous anticyclone and southerly winds. Negative SAT anomalies occur in regions of anomalous cyclone and northerly winds. Atmospheric circulation anomalies associated with the first mode have a close relationship to spring Arctic Oscillation (AO), indicating the impact of the AO on continental-scale spring SAT variations over the mid-and high latitudes of Eurasia. The atmospheric circulation anomalies associated with the second mode feature a wave pattern over the North Atlantic and Eurasia. Such a wave pattern is related to a tripole SST anomaly pattern in the North Atlantic Ocean, signifying the contribution of the North Atlantic Ocean state to the formation of a tripole SAT anomaly pattern over the mid-and high latitudes of Eurasia.

Previous studies suggest that the zonally averaged Hadley circulation (ZAHC) has experienced a robust poleward expansion, and its trend in intensity displays inconsistency among different data sets. This study examines changes in regional HC intensity and poleward edge using six reanalyses, outgoing longwave radiation, and precipitation data sets. HCs in six regions, including Africa (AFHC), the Indian Ocean (IOHC), the western Pacific (WPHC), the eastern Pacific (EPHC), South America (SAHC), and the Atlantic (ATHC), are investigated. Intensity trends in the Northern Hemisphere (NH) WPHC and ATHC and the Southern Hemisphere (SH) EPHC and ATHC are in agreement with each other in the six reanalyses. Furthermore, regional HCs in these domains appear to be intensifying, although not all of the reanalyses show statistically significant trends. For the poleward edge, its trend in the NH AFHC, IOHC, EPHC, SAHC, and ATHC is significantly larger than zero, and the northern HC poleward edge exhibits uniform poleward migrations in these five regions. In the SH, only the trend in the SAHC poleward edge is significantly different from zero. Furthermore, the trend in the SH SAHC poleward edge is significantly larger than those in the SH AFHC, IOHC, and ATHC. The results indicate that the poleward migration of the southern ZAHC poleward edge during recent decades that has been identified by previous studies may be attributed mainly to the poleward migration of the southern SAHC poleward edge. Further analyses suggest that changes in regional HC poleward edges could have a significant impact on regional precipitation anomalies.

The relationship between interannual variations of boreal winter North Atlantic Oscillation (NAO) and northern tropical Atlantic (NTA) sea surface temperature (SST) experienced obvious interdecadal changes during 1870–2012. Similar interdecadal changes are observed in the amplitude of NTA SST anomalies. The mean NTA SST change may be a plausible reason for several changes in the NAO–NTA SST connection. Under a higher mean NTA SST, NTA SST anomalies induce larger wind anomalies over the North Atlantic that produce a tripole SST anomaly pattern and amplify NTA SST anomalies. Comparison of the evolution of anomalies between 1970–86 and 1996–2012 unravels changing roles of El Niño–Southern Oscillation (ENSO) and extratropical atmospheric disturbances in the formation of NTA SST anomalies. During 1970–86, ENSO events play a key role in initiating NTA SST anomalies in the preceding spring through atmospheric circulation changes. With the decay of ENSO, SST anomalies in the midlatitude North Atlantic weaken in the following summer, whereas NTA SST anomalies are maintained up to winter. This leads to a weak NAO–NTA SST connection in winter. During 1996–2012, the preceding spring atmospheric circulation disturbances over the midlatitude North Atlantic play a dominant role in the genesis of a North Atlantic horseshoe (NAH)-like SST anomaly pattern in the following summer and fall. This NAH-like SST anomaly pattern contributes to the development of the NAO in late fall and early winter. The atmospheric circulation anomaly, in turn, is conducive to the maintenance of NTA SST anomalies to winter via changing surface latent heat flux and shortwave radiation. This leads to a close NAO–NTA SST connection in winter.

Haze pollution is a serious air quality issue in China. Previous studies over the North China Plain (NCP) mainly focused on analysing the haze during boreal winter. However, the variation in haze during spring and the related factors remain unclear. This study investigates inter-annual variation of the spring haze, which is represented by the humidity-corrected dry extinction coefficient (DEC) over the NCP. During high DEC years, pronounced positive DEC anomalies appear over the NCP and its surrounding regions. Correspondingly, a notable anticyclonic anomaly is observed over Northeast Asia, inducing significant southeasterly wind anomalies over the NCP. The anomalous southeasterly winds reduce wind speed and increase relative humidity, which provides favourable meteorological conditions for accumulation and growth of aerosol pollutants. Further analysis shows that the North Atlantic Oscillation (NAO) contributes to the formation of anticyclonic anomalies over Northeast Asia via downstream propagating atmospheric wave trains. Additionally, positive sea surface temperature (SST) anomalies over the subtropical northeastern Atlantic Ocean may also impact the DEC variation. The linear barotropic model experiment further confirms the important role of subtropical northeastern Atlantic SST anomalies in contributing to the anomalous anticyclone over Northeast Asia and southerly wind anomalies over the NCP region, which are triggered via eastwards propagating atmospheric wave trains. This study gives support to the idea that the NAO and the North Atlantic SST may be potential predictors for the frequently observed springtime NCP haze variation.

The influence of boreal winter‐spring eastern Tibetan Plateau snow anomalies on the East Asian summer rainfall variability has been the focus of previous studies. The present study documents the impacts of boreal summer western and southern Tibetan Plateau snow cover anomalies on summer rainfall over East Asia. Analysis shows that more snow cover in the western and southern Tibetan Plateau induces anomalous cooling in the overlying atmospheric column. The induced atmospheric circulation changes are different corresponding to more snow cover in the western and southern Tibetan Plateau. The atmospheric circulation changes accompanying the western Plateau snow cover anomalies are more obvious over the midlatitude Asia, whereas those corresponding to the southern Plateau snow cover anomalies are more prominent over the tropics. As such, the western and southern Tibetan Plateau snow cover anomalies influence the East Asian summer circulation and precipitation through different pathways. Nevertheless, the East Asian summer circulation and precipitation anomalies induced by the western and southern Plateau snow cover anomalies tend to display similar distribution so that they are more pronounced when the western and southern Plateau snow cover anomalies work in coherence. Analysis indicates that the summer snow cover anomalies over the Tibetan Plateau may be related to late spring snow anomalies due to the persistence. The late spring snow anomalies are related to an obvious wave train originating from the western North Atlantic that may be partly associated with sea surface temperature anomalies in the North Atlantic Ocean.

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