Intensified Impact of Spring Tibetan Plateau Snow Cover on Summer Compound Heat Waves in Western Europe after 1998

This study revealed a significant interdecadal change in the impact of spring western Tibetan Plateau (TP) snow cover (TPSC) on subsequent summer compound heat waves (CHWs) in western Europe (WE) after 1998. This interdecadal change is attributed to a change in a western Europe high-western TP low (WEH-TPL) atmospheric circulation pattern. This pattern arises due to both the inherent variability of TPSC and the phase transition of the Atlantic multidecadal oscillation (AMO) after 1998. The increased magnitude and persistence of western TPSC from spring to summer after 1998 enhanced the snow-atmosphere coupling effect, intensifying ascent and decent motion over the TP and WE, respectively, and strengthening the WEH-TPL pattern. In addition, the post -1998 positive AMO phase favors continuous and stable downstream Rossby wave propagation, enhancing the WEH-TPL pattern and the TPSC-CHWs relationship. Further analyses reveal that the interdecadal changes in the TPSC and the AMO around 1998 contribute to the presence of "double jets" over the North Atlantic-central Eurasian sectors. The TPSC-related anomalous atmospheric circulation and AMO phase shift contribute to the southern and northern branches of the intensified westerly jet, respectively. These conditions create a favorable environment for the formation and persistence of summer CHWs in WE. Numerical modeling experiments with a linear baroclinic model confirm these findings. Our findings suggest that in the context of a changing climate, TPSC plays a pivotal role in the genesis of summer CHWs in WE and may serve as a valuable predictor for CHWs.