This study applies the maximum temperatures at more than 2000 Chinese stations to investigate the dominant modes of China summer heat waves (HWs). The first empirical orthogonal function (EOF) mode of the HW days reflects an increased frequency of HWs in northern China (NC), while the second and third modes represent two distinct interannual modes, with key regions over the Yangtze River valley (YRV) and southern China (SC), respectively. The NC HWs are possibly associated with the Atlantic–Eurasian teleconnection, showing zonally propagating wave trains over the North Atlantic and Eurasian continent. The YRV HWs are proposed to be linked to the North Atlantic Oscillation, which may trigger a southeastward-propagating wave train over northern Russia and East Asia that results in a high pressure anomaly over the YRV. The SC HWs are obviously dominated by the Indian Ocean and northwest Pacific warm SSTs owing to the transition from the preceding El Niño to La Niña, which excites above-normal highs over SC. The anomalously high pressures over NC, the YRV, and SC are usually accompanied by descending air motions, clear skies, decreased precipitation, and increased solar radiation, which jointly cause a drier and hotter soil condition that favors the emergence of HWs. The GFDL HiRAM experiments are able to reproduce the historical evolution of NC and SC HWs, but fail to capture the YRV HWs. The correlation coefficient between model PC1 (PC2) and observed PC1 (PC3) for the period of 1979–2008 is 0.65 (0.38), which significantly exceeds the 95% (90%) confidence level, indicating that this model has a more faithful representation for the SST-forced HWs.

Arctic climate changes include not only changes in trends and mean states but also strong interannual variations in various fields. Although it is known that tropical-extratropical teleconnection is sensitive to changes in flavours of El Niño, whether Arctic climate variability is linked to El Niño, in particular on interannual timescale, remains unclear. Here we demonstrate for the first time a long-range linkage between central Pacific (CP) El Niño and summer Arctic climate. Observations show that the CP warming related to CP El Niño events deepens the tropospheric Arctic polar vortex and strengthens the circumpolar westerly wind, thereby contributing to inhibiting summer Arctic warming and sea-ice melting. Atmospheric model experiments can generally capture the observed responses of Arctic circulation and robust surface cooling to CP El Niño forcing. We suggest that identification of the equator-Arctic teleconnection, via the ‘atmospheric bridge', can potentially contribute to improving the skill of predicting Arctic climate.

This study investigates the leading pattern of Eurasian summer heat waves (HWs) using observed and simulated data sets and reveals an intensified mode of variability that bridges the HWs in eastern Europe (EE) and northern China (NC). The concurrent variability of the HWs in EE and NC is primarily driven by an atmospheric circum-global teleconnection that induces anomalous anticyclones over the two regions. The observed upward trends in EE and NC HW days could be related to the warm sea surface temperatures around Greenland Island, which may weaken the Atlantic westerly jet stream and lead to amplified wave trains at the exit of the jet, resulting in strengthened anticyclones over EE and NC that favor the occurrences of HWs. The Geophysical Fluid Dynamics Laboratory high-resolution atmospheric model fails to simulate the EE and NC HWs, due probably to the model's poor representation of the South Asian summer rainfall.Plain Language Summary Heat waves (HWs) in eastern Europe (EE) and northern China (NC) are found to be bridged via an atmospheric teleconnection, which induces abnormal highs over EE and NC. As a result, the soil conditions in EE and NC become drier and hotter due to the decreased precipitation and increased solar radiation, which favors the occurrences of HWs. The North Atlantic warming may lead to the increases in EE and NC HWs by altering the Atlantic westerly jet stream and associated wave trains. The Geophysical Fluid Dynamics Laboratory high-resolution atmospheric model fails to simulate the EE and NC HWs, due probably to model's poor representation of the South Asian summer rainfall. Recently, Wu et al. (2012) and Zhou and Wu (2016) have surveyed the leading pattern of Eurasian summer HWs, which was characterized by an increasing variability centered over Europe and northern China (NC), indicating an intimate linkage of HWs in these two regions. Meanwhile, Lau and Kim (2012) have proposed

Performance in simulating atmospheric rivers (ARs) over western North America based on AR frequency and landfall latitude is evaluated for 10 models from phase 5 of the Coupled Model Intercomparison Project among which the CanESM2 model performs well. ARs are classified into southern, northern, and middle types using self-organizing maps in the ERA-Interim reanalysis and CanESM2. The southern type is associated with the development and eastward movement of anomalous lower pressure over the subtropical eastern Pacific, while the northern type is linked with the eastward movement of anomalous cyclonic circulation stimulated by warm sea surface temperatures over the subtropical western Pacific. The middle type is connected with the negative phase of North Pacific Oscillation–west Pacific teleconnection pattern. CanESM2 is further used to investigate projected AR changes at the end of the twenty-first century under the representative concentration pathway 8.5 scenario. AR definitions usually reference fixed integrated water vapor or integrated water vapor transport thresholds. AR changes under such definitions reflect both thermodynamic and dynamic influences. We therefore also use a modified AR definition that isolates change from dynamic influences only. The total AR frequency doubles compared to the historical period, with the middle AR type contributing the largest increases along the coasts of Vancouver Island and California. Atmospheric circulation (dynamic) changes decrease northern AR type frequency while increasing middle AR type frequency, indicating that future changes of circulation patterns modify the direct effect of warming on AR frequency, which would increase ARs (relative to fixed thresholds) almost everywhere along the North American coastline.