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

摘要ATM-9316278 Nigam，Sumant University of马里兰州- College Park标题： 观测到的亚洲夏季风的动力学诊断 降雨与厄尔尼诺的关系 该项目试图通过对北方夏季和2005年夏季观测到的亚洲大陆（以及全球热带和热带外）对流层环流异常进行诊断建模，为亚洲夏季季风降水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（3月至5月）的季节。 将强调对对流层下部和近地面环流异常的强迫的理解，因为这些对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）北秋季（9月）的强迫。- （10月） 太平洋环流异常，揭示亚洲夏季风降水异常对随后厄尔尼诺/拉尼娜发展的潜在反馈; B）欧亚春季积雪异常对亚洲夏季风年际变率的潜在非热带强迫。 研究任务包括： 1)从全球ECWMWF分析资料中估计三维非绝热加热场（和瞬态涡动通量辐合）是基于业务分析，而不是基于异常季风的GCM模拟。 2)用一个多层全球定常连续方程模式进行线性模拟，该模式对纬向变化的气候流进行线性化-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允许确定最一致的非绝热加热估计。 LU分解方法的“直接访问”适应应该允许比以前可能的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上空与厄尔尼诺有关的加热异常的特征结构的识别及其在亚洲上空的远程响应的计算。 还将评估太平洋盆地加热异常的远程影响。 4)在最近所有夏季期间“喜马拉雅-西藏地形”强迫的异常环流的计算，和它在亚洲对流层低层中的相位维斯远程强迫的异常热响应的比较的检验。 这方面的拟议研究可能有助于解释令人困惑的阈值依赖季风厄尔尼诺联系的基础。 一项试点研究的结果表明，这种动力诊断分析可以提供潜在的洞察力，帮助我们更好地了解亚洲夏季季风异常和厄尔尼诺/拉尼娜现象之间的相互作用（和潜在的反馈），这两种全球规模的气候异常现象的理解、模拟和最终预测将是TOGA/GOALS飞行任务成功的关键。

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.