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Arctic warming is of growing interest because it could affect midlatitude climates. Even though numerous studies have paid attention to the relationship between Arctic warming and the midlatitude climate in winter, the influence of Arctic warming on the summer conditions has not been examined in depth. Here we identify a significant relationship between East Asia hot summers and Arctic warming over the Barents and Kara seas. To represent Arctic warming, we define a combined index by simply differencing the normalized surface air temperature and sea‐ice indices. We found that the combined index in July has significantly high correlations with the temperatures in China, Korea, and Japan. While the teleconnection mechanism is not completely revealed, it is evident that warming over the Barents and Kara seas is accompanied by the local development of an anomalous anticyclone and downstream wave trains, which yield a strong anticyclonic circulation over East Asia and the North Pacific. The anticyclonic circulation persists and intensifies until August, which leads to hot summer conditions in East Asia with warm advection and enhanced shortwave radiation. Our results suggest that Arctic climate conditions can be used as a useful precursor of East Asia temperature variations even in summer. [ABSTRACT FROM AUTHOR]

The impact of the quasi‐biennial oscillation (QBO) on the surface air temperature (SAT) in the Northern Hemisphere extratropics is investigated. It is found that the QBO, defined as 70‐hPa zonal wind in the deep tropics, is negatively correlated with the SAT over the western North Pacific in February and March. Cold temperature anomaly appears during the QBO westerly phase. Such relationship is likely mediated by the subtropical jet. During the QBO westerly phase, a horseshoe‐shaped zonal wind anomaly forms in the upper troposphere and lower stratosphere and is connected to the equatorward shift of the Asia‐Pacific jet. This equatorward jet shift is accompanied by a cyclonic circulation anomaly in the subtropical North Pacific and an anticyclonic circulation anomaly over northern Eurasia in the troposphere. The resultant temperature advection brings cold air to East Asia and the western North Pacific. This regional downward coupling in February and March, which is not sensitive to El Niño‐Southern Oscillation, has become statistically significant in recent decades. [ABSTRACT FROM AUTHOR]

Using the daily outgoing longwave radiation and 850‐hPa zonal wind over (10°S–30°N, 105°–150°E) during the extended boreal summer (May to October), the lifecycle of the western Pacific intraseasonal oscillation (WPISO) is divided into eight phases based on the first two principle components of multivariate empirical orthogonal function decomposition. Because of the pronounced northward propagation feature, the meridional location of the convection anomaly centre in each WPISO phase is quite different, leading to distinct surface air temperature (SAT) anomaly responses over the Northern Hemisphere, in which North America shows the most significant SAT anomalies, and the SAT anomalies vary significantly with WPISO phase. Under different WPISO phases, convection can induce different mid‐to‐high latitude Rossby wave trains emanating from East Asia to North America, resulting in different SAT anomaly patterns over North America. Four numerical experiments are conducted and demonstrate that the convection at different meridional locations in each WPISO phase could shape the pattern of the Rossby wave train and in turn lead to different SAT anomalies over North America. The results in this study are expected to provide predictability sources for the sub‐seasonal‐to‐seasonal (S2S) prediction of North American SAT anomalies. [ABSTRACT FROM AUTHOR]

Based on the Coordinated Regional Downscaling Experiment‐East Asia second phase (CORDEX‐EA‐II) with higher resolution, model results driven by ERA‐Interim reanalysis using WRF, RegCM4 and CCLM are evaluated against the observational datasets including CN05.1, CRU and GPCP during the period of 1989–2009. The results show that the RCMs have the capability to simulate the annual and seasonal mean surface air temperature and precipitation, however, some biases are produced. The biases are highly dependent on the geophysical locations and the RCMs applied, and CCLM agrees better with the observed precipitation over ocean. CCLM also outperforms the other two RCMs in simulating the interannual variations of temperature and precipitation in most sub‐regions, which can be attributed to its better presentation of the interannual variation of large scale circulation. Generally, all the three RCMs can well reproduce the seasonal cycles of the surface air temperature in most sub‐regions, however, only in the northern regions of China can the RCMs well reproduce the seasonal cycles of precipitation. [ABSTRACT FROM AUTHOR]

The robust negative correlation between the Siberian High (SH) intensity and winter surface air temperature (SAT) in Northeast China has been widely used for winter climate seasonal forecasting. However, this traditional viewpoint varies when considering the changes in SH spatial extension during boreal winter. Here, a newly defined SH index representing both SH intensity and spatial extension shows two distinct influences of a stronger SH on the SAT in Northeast China. The stronger SH with a decreasing eastern edge, which features a meridional see–saw dipole of abnormal circulations centred over the Arctic and Siberia, respectively, results in a warmer winter over Northeast China. In this situation, the decreasing SH is linked to the enhanced Arctic Polar vortex through a tropospheric–stratospheric interaction. However, a stronger SH with an expanding eastern edge is coupled with the East Asian trough (EAT) and results in a colder winter in Northeast China. The SH and EAT anomalies are embedded in a zonally oriented wave‐train originating from the North Atlantic in the troposphere. Because of the diversity of impacts, the SH intensity and zonal extension should be jointly considered for seasonal forecasting of winter SAT anomalies in Northeast China. [ABSTRACT FROM AUTHOR]