The Recent Decline and Recovery of Indian Summer Monsoon Rainfall: Relative Roles of External Forcing and Internal Variability
The Recent Decline and Recovery of Indian Summer Monsoon Rainfall: Relative Roles of External Forcing and Internal Variability
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DOI：
10.1175/jcli-d-19-0833.1
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发表时间：
2020-06-01
影响因子：
4.9
通讯作者：
Zou, Liwei
中科院分区：
文献类型：
--
作者：
Huang, Xin;Zhou, Tianjun;Zou, Liwei
印度夏季季风（ISM）降雨影响南亚的大量人口。观测结果显示，1950年至1999年ISM降雨量有所下降，1999年至2013年有所恢复。虽然这种下降被归因于全球变暖、气溶胶效应、森林砍伐和年代际太平洋涛动（IPO）的负向正相变，但复苏的原因在很大程度上仍不清楚。通过分析一个57个成员扰动参数集合的模式模拟，这项研究表明，外部强迫降雨趋势相对较弱，并在1950-99年和1999-2013年期间被大的内部变率所淹没。首次公开募股被确定为内部模式，有助于调节最近的下降和恢复的ISM降雨。IPO通过与异常步行者环流和纬向对流层温度梯度相关的水汽辐合异常以及由此产生的异常对流和纬向水汽平流引起ISM降水变化。从1950年到1999年的负到正的IPO阶段转变减少了在此期间0.01到-0.15毫米日（-1）十年（-1）的外部强迫降雨量微弱上升趋势，而1999 - 2013年的降雨趋势从0.42毫米日（-1）十年（-1）的强迫值增加到0.68毫米日（-1）十年（-1），与正到负的IPO相变相关。这样一个显着的调制的历史ISM降雨趋势的IPO证实了另一个100人的合奏模拟扰动初始条件。我们的研究结果强调，外部强迫和IPO的影响之间的相互作用需要考虑南亚的气候适应和减缓战略。
The Indian summer monsoon (ISM) rainfall affects a large population in South Asia. Observations show a decline in ISM rainfall from 1950 to 1999 and a recovery from 1999 to 2013. While the decline has been attributed to global warming, aerosol effects, deforestation, and a negative-to-positive phase transition of the interdecadal Pacific oscillation (IPO), the cause for the recovery remains largely unclear. Through analyses of a 57-member perturbed-parameter ensemble of model simulations, this study shows that the externally forced rainfall trend is relatively weak and is overwhelmed by large internal variability during both 1950-99 and 1999-2013. The IPO is identified as the internal mode that helps modulate the recent decline and recovery of the ISM rainfall. The IPO induces ISM rainfall changes through moisture convergence anomalies associated with an anomalous Walker circulation and meridional tropospheric temperature gradients and the resultant anomalous convection and zonal moisture advection. The negative-to-positive IPO phase transition from 1950 to 1999 reduces what would have been an externally forced weak upward rainfall trend of 0.01 to -0.15 mm day(-1) decade(-1) during that period, while the rainfall trend from 1999 to 2013 increases from the forced value of 0.42 to 0.68 mm day(-1) decade(-1) associated with a positive-to-negative IPO phase transition. Such a significant modulation of the historical ISM rainfall trends by the IPO is confirmed by another 100-member ensemble of simulations using perturbed initial conditions. Our findings highlight that the interplay between the effects of external forcing and the IPO needs be considered for climate adaptation and mitigation strategies in South Asia.