Abstract
Abstract. This study examines the seasonality of precipitation amount and δ18O over the monsoon region of China (MRC). We found that the precipitation amount associated with the East Asian summer monsoon (EASM) in the spring persistent rain (SPR) region is equivalent to that of the nonsummer monsoon (NSM). The latter contributes ∼50 % to amount-weighted annual δ18O values, in contrast with other areas in the MRC, where the δ18O of annual precipitation is dominated by EASM precipitation. Interannual relationships between the El Niño–Southern Oscillation (ENSO) index, simulated δ18O data from IsoGSM, and seasonal precipitation amount in the SPR region were also examined. We found that on interannual timescales, the seasonality of precipitation amount (EASM ∕ NSM ratio) was modulated by ENSO and primarily influences the variability of amount-weighted annual precipitation δ18O values in the SPR region, although integrated regional convection and moisture source and transport distance may also play subordinate roles. During El Niño (La Niña) phases, less (more) EASM and more (less) NSM precipitation leading to lower (higher) EASM ∕ NSM precipitation amount ratios results in higher (lower) amount-weighted annual precipitation δ18O values and, consequently, in higher (lower) speleothem δ18O values. Characterizing spatial differences in seasonal precipitation is, therefore, key to correctly interpreting speleothem δ18O records from the MRC.
Highlights
Summertime rainfall over the MRC is largely associated with the East Asian summer monsoon (EASM) (Fig. 1a) (Ding, 1992)
(Fig. 3), we find that (1) in northern and southwestern regions of the MRC δ18Ow values are mainly controlled by the amount and δ18O of EASM precipitation, because the precipitation amount of the EASM with rather low δ18Op values accounts for 70 % of the annual precipitation and the nonsummer monsoon (NSM) precipitation is only a small contribution to the δ18Ow. (2) In southeastern China, especially in the spring persistent rain (SPR)
We find that the precipitation seasonality modulated by El Niño–Southern Oscillation (ENSO) mainly controls the δ18Ow values in the SPR region, with lower EASM / NSM ratios associated with El Niño (La Niña) phases resulting in higher δ18Ow values
Summary
Summertime rainfall over the MRC is largely associated with the East Asian summer monsoon (EASM) (Fig. 1a) (Ding, 1992). The SPR occurs mostly south of the middle and lower reaches of the Yangtze river (∼ 24 to 30◦ N, 110 to 120◦ E) (Fig. 1b) and is a unique synoptic and climatic phenomenon in East Asia (Tian and Yasunari, 1998; Wan and Wu, 2007, 2009). The SPR is another rainy period before the Meiyu rain period in early summer, and it covers the region from southeastern China to the south of Japan. It has long been debated whether the SPR marks the onset of EASM. Other studies suggest that the SPR is unrelated to EASM rainfall, and they consider it as an extension of winter atmospheric circulation (Tian and Yasunari, 1998; Wan and Wu, 2009). Wang and Lin (2002) proposed that the SPR over southeastern China is not a part of the EASM, because the large-scale circulation and rainbearing systems differ from those associated with summer monsoon rainfall. Tian and Yasunari (1998) suggested that
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