Intraseasonal oscillation intensity over the western North Pacific: Projected changes under global warming

Abstract

The 30–60-day intraseasonal oscillation (ISO) and 10–20-day ISO are two dominant oscillation modes over the western North Pacific during boreal summer. With daily data derived from eight CMIP5 models, changes of the ISO intensities are projected under the 1.5 and 2.0 °C global warming levels under the Representative Concentration Pathway (RCP) 4.5 and RCP8.5 scenarios. Most of the models agree that the ISO intensities increase along a belt region from the south Indochina Peninsula (ICP) to the east to the Philippines. The variation pattern shows little difference between different warming levels or scenarios. Results indicate that the spatial distribution of ISO anomalies is related with the variation of background fields. Enriched lower-level humidity and moist static energy favor the intensity increases of ISOs, which are projected to be larger over the whole western North Pacific, with the most conspicuous changes located over the east to the Philippines for humidity but over the south of the ICP for moist static energy. In contrast, the ISOs over the west to Indonesia and northeast to the Philippines decrease, which is consistent with the local descending motions.摘要本文利用8个CMIP5模式的日资料, 预估了RCP4.5和RCP8.5情景下全球增温达1.5 °C和2.0 °C时西北太平洋夏季30~60天和10~20天季节内振荡 (ISO) 强度的变化情况. 大多数模式都认为, 无论增温水平或情景如何, 预估结果均显示从中南半岛南部到菲律宾以东的带状区域内ISO强度增加, 并且关键气象要素背景的变化会对ISO强度异常的空间分布造成影响. 具体表现为, ISO强度增大的区域往往伴随着低层湿度和湿静力能的增加. 其中菲律宾东部的湿度变化最为明显, ICP南部的湿静力能变化最为明显, 上述区域的ISO强度均增强. 相反, 印度尼西亚西部和菲律宾东北部有局地下沉运动增强, 当地的ISO强度减小.