Out-of-Phase Relationship between Boreal Spring and Summer Decadal Rainfall Changes in Southern China*

Abstract

A multivariate empirical orthogonal function (MV-EOF) analysis for 1979-2010 shows that low-level circulation and rainfall over East Asia experienced a significant decadal shift around the mid-1990s. During boreal spring (March-May), the first principal component (PC) of the MV-EOF exhibits a marked decadal change around the mid-1990s, while during boreal summer (June-August) the second PC shows a pronounced decadal shift around the same time. It is further noted that the decadal rainfall change over southern China experienced an out-of-phase relationship between boreal spring and summer; that is, from the pre-1994 to the post-1994 period, the rainfall tends to decrease in boreal spring but increase in boreal summer.A mechanism is put forward to explain the out-of-phase decadal rainfall change over southern China between boreal spring and summer. In boreal spring, the composite differences of SST between the latter and former decadal periods indicate a La Niña-like pattern with warming in the western Pacific and cooling in the eastern Pacific. This pattern leads the enhanced convection over the Maritime Continent, which may further induce anomalous subsidence and thus negative rainfall anomalies over southern China through the local Hadley circulation. In boreal summer, dominant decadal SST warming appears in the entire tropical Indian Ocean while the negative SST anomalies in eastern Pacific are much weaker. The warm SST anomaly over the Indian Ocean leads to suppressed convection over the Maritime Continent, which, through the local Hadley cell, favors the strengthening the East Asian monsoon trough and leads to a positive rainfall anomaly over southern China.

Water vapor transport for spring persistent rains over southeastern China based on five reanalysis datasets

“…Although this is beyond the scope of this study, we note that several mechanisms have been suggested. The dynamics of spring rainfall reduction in recent decades over southeastern China is associated with anomalous atmospheric circulation induced by the La Niña-like pattern with warming in the tropical Indian Ocean and western Pacific region (Qiu et al 2009;Zhu et al 2014). In addition, the reduction of late spring precipitation concurs with the upper-level cooling, which is associated with an anomalous meridional cell over southeastern China and is found to strongly link to the North Atlantic Oscillation (Xin et al 2006(Xin et al , 2008.…”

“…These circulation anomalies favor strengthened southwestern warm and moist flow and enhanced convergence of water vapor fluxes over southeastern China, leading to a significant increase in precipitation . In recent decades, southeastern China has experienced a significant decrease in precipitation in the boreal spring and has frequently suffered from persistent drought, and the droughts are consistent with anomalous overturning circulation and local anomalous descent motion (Xin et al 2006;Sun and Yang 2012;Feng et al 2014;Zhu et al 2014;Li et al 2016), but the long-term behavior of SPR precipitation in different reanalysis datasets remains unestablished.…”

Relative contributions of the Tibetan Plateau thermal forcing and the Indian Ocean Sea surface temperature basin mode to the interannual variability of the East Asian summer monsoon

“…Moreover, warm Indian Ocean SST can excite a warm Kelvin wave in the lower atmosphere over the tropical ocean, which inhibits convection over the northwestern Pacific, thus strengthening the northwestern Pacific high Xie et al 2009). Another possible mechanism for the IOBM's influence on the EASM is via warm Indian Ocean SST strengthening the local Hadley circulation between the Maritime Continent and the northwestern Pacific, resulting in more intense descending motion over the northwestern Pacific Zhu et al 2014). We choose the IOBM in the present study as the main ocean mode because it is adjacent to the EASM region and has the closest simultaneous correlation with the EASM compared to the Indian Ocean dipole mode (IOD) and ENSO, as well as ENSO Modoki (Fig.…”

Empirical Subseasonal Prediction of Summer Rainfall Anomalies over the Middle and Lower Reaches of the Yangtze River Basin Based on Atmospheric Intraseasonal Oscillation

“…Six pentad previous predictors and six pentad succeeding predictands are concatenated in the ESVD to conduct the 5-30-day (5, 10, 15, 20, 25 and 30 days, respectively) lead-time forecasts simultaneously. For example, at the forecast time of early pentad 31, the predictors at pentads 25-30 are concatenated to forecast the predictand at pentads [31][32][33][34][35]. In the present study, the forecast time starts at early pentad 31 and ends at early pentad 55.…”

“…This SSTA pattern could cause strong easterlies blowing from the central Pacific to the tropical Indian Ocean, and leads to a pronounced negative rainfall anomalies over the western and central Pacific (east of the Philippines) via anomalous zonal circulation [35,36]. The rainfall condensation cooling excites a Rossby wave response to the northwest in terms of anticyclonic anomalies.…”