Interdecadal Changes in the Dominant Modes of Spring Snow Cover over the Tibetan Plateau around the Early 1990s

The current work investigated the interdecadal changes in the leading empirical orthogonal function (EOF) pattern of the interannual variation in spring [March-May (MAM)] snow-cover extent (SCE) over the Tibetan Plateau (TP) (SSC_TP). The leading EOF pattern of the SSC_TP is transformed from an east to west dipole pattern during the pe-riod 1970-89 (P1) to a monopole structure during the period 1991-2020 (P2). Observational analysis shows that during P1, the negative Antarctic Oscillation (AAO) (-AAO) is associated with low-level cross-equator southeasterly anomalies across the Bay of Bengal and transports more water vapor to the eastern TP. Moreover, at a high level, anomalous north-erly winds accompanied by an anomalous sinking motion dominate the western TP, favoring an east-wet-west-dry dipole pattern of SSC_TP. Further analysis shows that the-AAO induces anomalous divergence over the Antarctic, which con-tributes to the formation of a Rossby wave source (RWS). This RWS is related to a northeastward-propagating atmo-spheric wave train that crosses the equator and contributes to the SSC_TP variation during P1. In contrast, in P2, the Arctic Oscillation (AO) is associated with a barotropic atmospheric wave train originating from southern Greenland, mov-ing across the North Atlantic Ocean and North Africa and reaching the TP. This wave train results in significant positive vorticity and ascending airflow above the TP and favors a monopole pattern of the SSC_TP. Further analysis shows that the AO can induce divergence anomalies over southeastern Greenland and RWS anomalies there. This RWS induces an atmospheric wave train that propagates eastward and reaches the TP during P2. The above mechanisms have been sup-

Automated summary

The study investigates the interdecadal changes in the leading empirical orthogonal function (EOF) pattern of interannual variation in spring snow-cover extent (SCE) over the Tibetan Plateau (TP) (SSC_TP). It finds that during the period 1970-89, the leading EOF pattern transforms from an east-west dipole to a monopole structure, and the negative Antarctic Oscillation (AAO) plays a role in this transformation. In contrast, during the period 1991-2020, the Arctic Oscillation (AO) is associated with the monopole pattern. The mechanisms behind these changes are further analyzed.