Asian zonal-dipole climate extremes in 2022 and 2025: role of upper-tropospheric zonal flow

Abstract During summer 2025, subtropical Asia experienced concurrent flooding over western South Asia and hot–dry extremes over the Yangtze River Basin, forming a pronounced zonal dipole across the western and eastern flanks of the Tibetan Plateau (TP) near 30° N. While this pattern closely resembles the record-breaking extremes of 2022, the associated lower-tropospheric circulation anomalies differ remarkably. From a historical perspective, we identify anomalous upper-tropospheric zonal flow over the TP as a key triggering mechanism. Given the climatological warm center over the TP in summer, upper-tropospheric easterly (westerly) anomalies induce anomalous ascent (descent) over the western flank and descent (ascent) over the eastern flank of the TP, thereby generating a zonal dipole in surface climate. Upper-tropospheric easterly anomalies reached record strength in 2022 and were the second strongest in 2025 since 1979, providing a unified dynamical explanation for these Asian zonal-dipole climate extremes. Variability of the zonal flow over the TP is primarily a regional manifestation of subtropical zonal-mean zonal flow, modulated by meridional sea surface temperature (SST) contrasts between the tropical and North Pacific. Exceptionally weak Pacific meridional SST contrasts, as observed in 2022 and 2025, reduce the meridional tropospheric temperature gradient and weaken subtropical upper-tropospheric westerlies through thermal wind balance. These results identify subtropical upper-tropospheric zonal flow as a key bridge linking Pacific SST variability to Asian zonal-dipole climate variability across the TP.