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The Holocene thermal maximum was characterized by strong summer solar heating that substantially increased the summertime temperature relative to preindustrial climate. However, the summer warming was compensated by weaker winter insolation, and the annual mean temperature of the Holocene thermal maximum remains ambiguous. Using multimodel mid-Holocene simulations, we show that the annual mean Northern Hemisphere temperature is strongly correlated with the degree of Arctic amplification and sea ice loss. Additional model experiments show that the summer Arctic sea ice loss persists into winter and increases the mid- and high-latitude temperatures. These results are evaluated against four proxy datasets to verify that the annual mean northern high-latitude temperature during the mid-Holocene was warmer than the preindustrial climate, because of the seasonally rectified temperature increase driven by the Arctic amplification. This study offers a resolution to the "Holocene temperature conundrum", a well-known discrepancy between paleo-proxies and climate model simulations of Holocene thermal maximum.

Mid-Holocene climate was characterized by strong summer solar heating that decreased Arctic sea ice cover. Motivated by recent studies identifying Arctic sea ice loss as a key driver of future climate change, we separate the influences of Arctic sea ice loss on mid-Holocene climate. By performing idealized climate model perturbation experiments, we show that Arctic sea ice loss causes zonally asymmetric surface temperature responses especially in winter: sea ice loss warms North America and the North Pacific, which would otherwise be much colder due to weaker winter insolation. In contrast, over East Asia, sea ice loss slightly decreases the temperature in early winter. These temperature responses are associated with the weakening of mid-high latitude westerlies and polar stratospheric warming. Sea ice loss also weakens the Atlantic meridional overturning circulation, although this weakening signal diminishes after 150-200 years of model integration. These results suggest that mid-Holocene climate changes should be interpreted in terms of both Arctic sea ice cover and insolation forcing.

North Atlantic midlatitude cyclones are among the most severe weather systems, causing enormous economic damages and threatening human lives. The cyclone is typically characterized by cyclonic convergent surface winds, strong updrafts, and precipitation. However, extreme surface winds are often observed within the cyclone where downdrafts develop. The present study investigates the dynamical and thermodynamical characteristics of the horizontal winds impinging on the cold frontal surface and the associated downdrafts. It is shown that the cyclonic winds into the cold frontal surface are mainly responsible for the downdrafts that transport the high‐altitude horizontal momentum to the surface and cause intense surface winds. About half of the North Atlantic midlatitude cyclones are accompanied by the downdrafts especially in the southern and western parts of the cyclone center. Plain Language Summary: In the midlatitudes, air temperature decreases toward the poles, and cyclone systems typically travel eastward along regions characterized by strong meridional temperature gradients. Over the cyclone‐influencing area, the cyclonic, counterclockwise rotating, wind induces southward cold advection on the western side of the cyclone center. Therefore, during the early phase of the North Atlantic midlatitude cyclone, the generation of the cold front, which has a steep gradient of temperature to the west of the cyclone center, and that is a common feature. Even after the formation of the cold front, the horizontal winds keep impinging on the frontal surface. Then the horizontal winds blocked by the frontal surface and downdrafts are induced. The downdrafts transport the upper‐level intense wind speed to the lower level strengthening the surface winds. Key Points: Surface winds within North Atlantic midlatitude cyclones are strengthened by strong downdrafts and downward momentum transportsDowndrafts can be generated by the horizontal winds impinging on the cold frontal surfaceCyclones tend to accompany the downdrafts more to the south and west of the cyclone center [ABSTRACT FROM AUTHOR]

The El Niño–Southern Oscillation (ENSO) has a significant impact on the surface climate of East Asia by modulating the atmospheric circulation over the Kuroshio Extension. Here, we show that the ENSO–East Asia teleconnections are strongest in early winter due to the combined effects of the Indian Ocean and Maritime Continent convections, but weakest in mid‐winter as these tropical convections weaken. During the early El Niño winter, convection is enhanced over the Indian Ocean and suppressed over the Maritime Continent. The associated Rossby wave trains constructively interfere over the Kuroshio Extension, resulting in anticyclonic circulation anomalies. The equatorial central Pacific convection has a minimal impact on the East Asia. This result suggests that the Indian Ocean and the Maritime Continent convections, rather than the equatorial central Pacific convection, are the precursors of the early winter ENSO–East Asia teleconnections, and need to be considered for subseasonal‐to‐seasonal prediction in East Asia. Plain Language Summary: The El Niño–Southern Oscillation (ENSO) significantly influences the winter surface climate in East Asia through atmospheric teleconnections. The ENSO teleconnections are particularly pronounced in early winter when an anomalous anticyclonic circulation developes over the Kuroshio Extension and transports warm and moist air to the East Asian continent, but weaken in mid‐winter. Here, we show that such subseasonal variability of the ENSO–East Asia teleconnections is primarily determined by tropical convection over the Indian Ocean and the Maritime Continent, with a minimal impact of convection over the equatorial central Pacific where ENSO develops. Key Points: The El Niño‐Southern Oscillation (ENSO) teleconnections show distinct subseasonal variability over East Asia, with the strongest teleconnections in early winterThe ENSO–East Asia teleconnections are modulated by anomalous tropical convection over the Indian Ocean and the Maritime Continent on subseasonal time scaleRossby wave trains induced by enhanced convection over the Indian Ocean and those by suppressed convection over the Maritime Continent constructively interfere over the East Asia during the early El Niño winter [ABSTRACT FROM AUTHOR]