Dynamical Diagnoses of the Observed 'Asian Summer-Monsoon Rainfall - El Nino' Relationship

摘要：马里兰苏曼特大学尼甘校区ATM-9316278号观测到的“亚洲夏季季风降水-厄尔尼诺”关系的动力学诊断该项目旨在通过对观测到的亚洲大陆（以及全球热带和温带地区）在北部夏季和东部夏季的对流层环流异常的月度/季节性诊断模拟，为亚洲夏季季风降水的年际波动与厄尔尼诺/拉尼娜事件之间的经验联系建立动力学基础“季风来临”前（三月至五月）季节。对对流层下层和近地表环流异常的强迫的理解将被强调，因为它们对于季风降雨异常和热带海洋环流异常的产生都是至关重要的。该项目的目标还包括诊断建模/分析：A)太平洋北部秋季（9 - 10月）环流异常的强迫作用，以揭示亚洲夏季季风异常降雨对随后的厄尔尼诺/拉尼娜发展的潜在反馈；B)欧亚春季积雪异常对亚洲夏季季风年际变率的潜在温带强迫作用。研究任务包括：1)基于全球ecwmwf分析数据集估算三维非绝热加热场（和瞬态涡通量辐合），而不是基于异常季风的GCM模拟。用线性化的多层全局稳定原始方程模型对纬向变化的气候流进行线性模拟，这是这种动力诊断分析的必要的第一步。（满足这一先决条件也将有助于确定最一致的绝热估算。）对LU分解方法的“直接访问”适应应该允许比以前更高的线性模型分辨率。3) 3 - 5月和6 - 8月期间热带太平洋和印度洋地区厄尔尼诺相关加热异常的特征结构识别及其对亚洲地区的远程响应计算。还将评估太平洋盆地加热异常的远程影响。4)最近所有夏季“喜马拉雅-西藏地形”强迫异常环流的计算，以及其在亚洲对流层下层相对于远程强迫异常热响应的阶段的检验。提出的研究的这一方面可能有助于解释季风-厄尔尼诺联系中令人困惑的阈值依赖性的基础。一项初步研究的结果表明，这种动态诊断分析可以提供潜在的见解，以提高我们对异常亚洲夏季季风和厄尔尼诺/拉尼娜事件之间相互作用（和潜在反馈）的理解——这两种全球尺度的气候异常的理解、模拟和最终预测将是TOGA/GOALS任务成功的核心。

Abstract ATM-9316278 Nigam, Sumant University of Maryland - College Park Title: Dynamical Diagnoses of the Observed 'Asian Summer-Monsoon Rainfall - El Nino' Relationship The project seeks to establish the dynamical basis for an empirical linkage between interannual fluctuations in the Asian summer- monsoon rainfall and the El Nino/La Nina episodes through diagnostic modeling of the observed monthly/ seasonal tropospheric circulation anomalies over the Asian continent (and global tropics and extratropics) during both the northern summer and the pre-'monsoon-onset' (March-May) seasons. An understanding of the forcing of the lower-tropospheric and near-surface circulation anomalies will be emphasized as these are critical both to the generation of monsoon-rainfall anomalies and tropical oceanic- circulation anomalies. The project objectives also include diagnostic modeling/analysis of A) the forcing of the northern-autumn (Sept. - Oct.) circulation anomalies over the Pacific in order to reveal potential feedback of the anomalous Asian summer-monsoon rainfall on the subsequent El Nino/La Nina development, and B) of the potential extratropical forcing of interannual-variability of the Asian summer-monsoons by Eurasian springtime snow-cover anomalies. The research-tasks include: 1) Estimation of the 3-dimensional diabatic heating field (and transient eddy-flux convergence) from the global ECWMWF-analyses data sets for this diagnostic project is based on operational- analyses rather than GCM simulation of anomalous monsoons. 2) Linear simulations with a multi-layer global steady primitive-equation model linearized about a zonally-varying climatological flow -- a necessary first-step in such dynamical- diagnostic analysis. (Meeting this prerequisite will also allow identification of the most consistent diabatic-heating estimate.) A 'direct-access' adaptation of an LU decomposition method should permit higher linear-model resolution than previously possible. 3) Identification of the characteristic structure of the El Nino-related heating anomalies over the tropical Pacific and Indian oceans during March - May and June - August periods, and a computation of their remote response over Asia. The remote impact of just the Pacific-basin heating anomalies will also be assessed. 4) Calculation of the 'Himalayan-Tibetan orography' - forced anomalous circulation during all recent summers, and an examination of its phase in the Asian lower troposphere vis-a-vis that of the remotely-forced anomalous thermal response. This aspect of the proposed research may help explain the basis for the perplexing threshold-dependence in the Monsoon-El Nino linkage. Results of a pilot study are indicative of the potential insight that such dynamical-diagnostic analysis can provide in improving our understanding of the interactions (and potential feedback) between anomalous Asian summer-monsoons and El Nino/La Nina episodes--the two global-scale climate anomalies whose understanding, simulations and ultimately prediction will be central to the success of the TOGA/GOALS missions.