Interdecadal shift in the impact of winter land–sea thermal contrasts on following spring transcontinental dust transport pathways in North Africa

Abstract. North Africa, the largest and most active dust source region globally, plays a critical role in the Earth's environment by dispersing dust over remote areas, especially in terms of circum-global transport that has occurred many times since the start of the 21st century. As a key indicator of the thermodynamic structure and dynamical circulation of the troposphere, the land–sea thermal contrast (LSC) can influence the variability in dust and subsequent large-scale propagation, but the extent of such influence is still unknown. This study reveals that in around the late 1990s, the influence of pre-winter LSC on the spring dust transport pathway was reversed in North Africa, which is attributed to the bridging effect of the North Atlantic Oscillation (NAO). Before 2000, the warm land–cold ocean (+WLCO) pattern in pre-winter was typically associated with the NAO+ mode, and the anomalous northeasterly and zonal circulation in the following spring facilitated the westward transport of dust from the lower troposphere in western North Africa towards the Atlantic. Since 2000, the reversed zonal temperature pattern (−WLCO) has led to the NAO− mode and enhanced mid-latitude westerlies in winter, which has persisted into the next spring. Under conditions of unusually dry soil and strong dry convection, dust has been mixed into the middle to upper troposphere and subsequently transported eastward globally, affecting regions including West Asia, northern China, the Pacific, and southeastern North America after 2000. This study underscores the critical role of sea–land–atmosphere interaction in circum-global dust propagation and offers new perspectives for investigating dust change mechanisms in the context of climate change.