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Trend turning of North China summer extreme precipitations around early 2000s and its possible reason
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DOI：10.1007/s00382-023-06860-1.png)
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Abstract
En 中文
This study focuses on regional extreme precipitation (REP) in North China. We found a trend turning in summer (July to August) REP frequencies and intensities from a decrease trend in 1961-2002 to an increase trend in 2003-2020, accompanied by a southward shift of the extreme rain belt, and an enhanced connection with the Ural blocking (UB) and the Western Pacific Subtropical High Pressure (WPSH) in 2003-2020. Rains in North China are accompanied by a west-east low-high dipole at upper troposphere. During the REP, the high of the low-high dipole at Northeast China (the NEH) is strongly amplified from a pre-existing stationary ridge over northeast Asia under the influence of eastward propagating Rossby wave energies along the subpolar/subtropical wave guide over Eurasia. For the REP years, an enhanced stationary ridge over the Ural Mountains in the period 2003-2020 replaces the stationary Ural trough in the period 1961-2002, favouring the development of the UB and leading to a change of the Rossby wave propagation path from along the subtropical waveguide in 1961-2002 to along the polar wave guide in 2003-2020. Therefore, a connection between the NEH and the UB forms, which may lead to a higher probability of extreme precipitation in North China since blocking is a major source of strong circulation anomalies. The mean summer WPSH expands more westward-northward in 2003-2020 than in 1961-2002, which provides a background conditions for a further westward-northward expanding of the daily WPSH under the influence of the NEH leading to a strong moisture transport from north Pacific. As a result, the intensity and probability of extreme precipitation over southern North China increase.
Keywords:
North China extreme precipitation
Ural blocking
Western Pacific subtropical high
Trend turning
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