The Arctic plays a fundamental role in the climate system and has shown significant climate change in recent decades, including the Arctic warming and decline of Arctic sea-ice extent and thickness. In contrast to the Arctic warming and reduction of Arctic sea ice, Europe, East Asia and North America have experienced anomalously cold conditions, with record snowfall during recent years. In this paper, we review current understanding of the sea-ice impacts on the Eurasian climate. Paleo, observational and modelling studies are covered to summarize several major themes, including: the variability of Arctic sea ice and its controls; the likely causes and apparent impacts of the Arctic sea-ice decline during the satellite era, as well as past and projected future impacts and trends; the links and feedback mechanisms between the Arctic sea ice and the Arctic Oscillation/North Atlantic Oscillation, the recent Eurasian cooling, winter atmospheric circulation, summer precipitation in East Asia, spring snowfall over Eurasia, East Asian winter monsoon, and midlatitude extreme weather; and the remote climate response (e.g., atmospheric circulation, air temperature) to changes in Arctic sea ice. We conclude with a brief summary and suggestions for future research.

The Inner Tibetan Plateau (ITP; or called Qiangtang Plateau) appears to have experienced an overall wetting in summer (June, July and August) since the mid-1990s, which has caused the rapid expansion of thousands of lakes. In this study, changes in atmospheric circulations associated with the wetting process are analyzed for the years 1979 ∼ 2018. These analyses show that the wetting is associated with simultaneously weakened westerlies over the Tibetan Plateau (TP). The latter is further significantly correlated with the Atlantic Multidecadal Oscillation (AMO) on interdecadal time scales. The AMO has been in a positive phase (warm anomaly of the North Atlantic sea surface) since the mid-1990s, which has led to both a northward shift and weakening of the subtropical westerly jet stream at 200 hPa near the TP through a wave train of cyclonic and anticyclonic anomalies over Eurasia. These anomalies are characterized by an anomalous anticyclone to the east of the ITP and an anomalous cyclone to the west of the ITP. The former weakens the westerly winds, trapping water vapor over the ITP, while the latter facilitates water vapor intruding from the Arabian Sea into the ITP. Accordingly, summer precipitation over the ITP has increased since the mid-1990s.

Satellite data, characterized by extensive regional coverage and relatively high spatial resolution, have a distinct advantage for examining elevation-dependent warming (EDW) across rugged topography in mountain regions where there are sparse in situ observations. Based on recent (2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015) comprehensive satellite-based data sets (2 m air temperature, land surface temperature, snow cover, and daytime and nighttime cloud), this study finds that annual mean 2 m air temperature warming rates show rapid decrease above 4,500 m despite increasing from 2,000 to 4,500 m. This indicates a reversal in EDW at the highest elevations on the Tibetan Plateau, which is somehow different from the EDW derived from short-term land surface temperature presented in earlier research. The decrease of warming rate above 4,500 m coincides with the elevation at which most of the current solid water resources reside. Thus, their decline may be less rapid than previously thought. Trends in nighttime cloud and snow cover are both correlated with patterns of EDW on the Tibetan Plateau, but the leading factor varies on an annual and seasonal basis. These results provide important evidence for understanding EDW and its controlling mechanisms in an extreme high-elevation context. Key Points:• The warming rate of satellite-based 2 m air temperatures rapidly decreases above 4,500 m despite an increase from 2,000 to 4,500 m over the Tibetan Plateau • The decrease of warming rate above 4,500 m is conducive to less rapid decline of 83% of the current plateau solid water resources • Changes in nighttime cloud cover and snow cover have a strong control on EDW patterns on the plateau

The possible influence of Atlantic sea surface temperature (SST) on winter haze days in China at interannual and decadal time scales is investigated using the observed haze-day data from 329 meteorological stations, National Centers for Environmental Prediction-National Centers for Atmospheric Research (NCEP-NCAR) reanalysis, and a SST dataset for 1978-2012. Wintertime haze days in China show robust interannual variations and significant increases over time. The SST anomalies over the North Atlantic from summer to the following winter exhibit a significant in-phase relationship with winter haze days on both decadal and interannual time scales, whereas the anomalous negative-positive SSTs from north to south over the South Atlantic from autumn to the following winter show a significant positive relationship with winter haze days on the interannual time scale. The anomalous warm SST over the North Atlantic, i.e., the positive phase of the Atlantic multidecadal oscillation (AMO), corresponds to the positive phase of the Arctic oscillation (AO). This result implies that a stable mean flow and strong westerly anomalies exist over north China. The anomalous dipole pattern in the South Atlantic results in the abnormal southerly airflow in the troposphere over eastern China. Neither the westerly anomalies over north China nor the southerly anomalies over eastern China, which are associated with the North Atlantic and South Atlantic SST anomalies, respectively, are conducive to occurrences of cold air. Consequently, the weakened cold airflow from north of eastern China suppresses the dispersion of pollutants over China and results in above-normal haze days.

Frequent extreme precipitation events have resulted in severe disasters to agriculture, the economy, and human health in recent decades. Widespread concerns about extreme precipitation have been aroused among the public, the government, and the research community. Researchers have conducted numerous studies on the mechanisms responsible for extreme precipitation events (Agel et al., 2018;Collow et al., 2016). Favorable local dynamic conditions (ascending motion) and instability are critical for the occurrence of extreme precipitation. Abundant moisture supply is another indispensable condition for extreme precipitation.In recent years, many studies have focused on moisture transport and sources for precipitation, including precipitation extremes. Two main approaches are widely used in studies on moisture transport. One is in the Eulerian view by calculating water vapor transport or by identifying and tracking the variation in atmospheric rivers (Sun & Wang, 2013;Tan et al., 2021). A deficiency of the Eulerian view is that it can neither track moisture from the sources to the precipitation area nor track moisture from the target region back to its sources. The other is in the Lagrangian view by tracking the moisture of particles (or air parcels) forward or backward using Lagrangian trajectory models (Sodemann et al., 2008;Sodemann & Zubler, 2010). The Lagrangian model can provide moisture variation processes from evaporation to precipitation along the transport trajectories. Several Lagrangian trajectory models are available, such as the Lagrangian particle dispersion model FLEXPART (

A significant correlation between the boreal spring Antarctic Oscillation (AAO) and the Yangtze River valley summer rainfall (YRVSR) has been found in previous studies, although the mechanisms that might lead to such far-reaching teleconnection remain unresolved. In this study, one of possible mechanisms responsible for the co-variability of the boreal spring AAO and the YRVSR is proposed. It follows that the convection activity over the region of the Maritime Continent serves as a bridge linking the boreal spring AAO and the YRVSR. This physical process can be described schematically as follows: during the boreal spring, a positive-phase (negative-phase) AAO is concurrent with a strong (weak) convection activity over the region of the Maritime Continent via anomalous meridional circulations along the central South Pacific and two meridional teleconnection wave train patterns, with one over the southern Indian Ocean at the lower level and the other along the central South Pacific at the upper level. Thereafter, the anomalous convection propagates northward along the seasonal cycle, and then changes the western Pacific subtropical high in the following seasons, consequently impacting on the summer rainfall in the Yangtze River valley.

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