Interdecadal Variations of the March Atmospheric Heat Source over the Southeast Asian Low-Latitude Highlands

Abstract

Based on the fifth-generation reanalysis dataset from the European Centre for Medium-Range Weather Forecasts for 1979–2019, we investigated the effects of the circumglobal teleconnection (CGT) on the interdecadal variation of the March atmospheric heat source (AHS) over the Southeast Asian low-latitude highlands (SEALLH). The dominant mode of the March AHS over the SEALLH features a monopole structure with an 8–11-year period. Decadal variations in the AHS make an important contribution to the 11-year low-pass filtered component of the AHS index, whichexplains 54.3% of the total variance. The CGT shows a clear interdecadal variation, which explains 59.3% of the total variance. The March AHS over the SEALLH is significantly related to the CGT on interdecadal timescales. When the CGT is optimally excited by a significant cyclonic vorticity source near northern Africa (i.e., in its positive phase), the SEALLH is dominated by anomalous southerly winds and ascending motions on the east of the anomalous cyclone. The enhanced advection and upward transfer result in a high-enthalpy air mass that converges into and condenses over the SEALLH, leading to a larger-than-average March AHS over this region. The key physical processes revealed by this diagnostic analysis are supported by numerical experiments.

摘 要

本文利用1979–2019年欧洲中期天气预报中心提供的ERA5资料,研究了初春环球遥相关(CGT)对东南亚低纬高原(SEALLH)大气热源年代际变化的影响。研究发现初春SEALLH 大气热源显著的8–11年变化主要呈现全场一致型的分布。11年低通滤波的初春大气热源指数年代际分量的方差贡献率高达54.3%。11年低通滤波的初春CGT的方差贡献率为59.3%,也呈现显著的年代际变化。在年代际时间尺度上,初春SEALLH 大气热源与CGT存在显著的相关关系。当北非出现异常气旋式罗斯贝波源时,在北非至东亚上空激发出异常“反气旋、气旋、反气旋、气旋、反气旋”的CGT波列。异常的偏南风使得高湿焓气团输送到SEALLH并发生异常辐合上升,进而导致初春SEALLH 大气热源偏强。数值模拟结果验证了观测事实所揭示的关键物理过程。