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

观测到的“亚洲夏季-季风降雨-厄尔尼诺”关系的动力学诊断

• 批准号: 9316278
• 负责人: Sumant Nigam
• 金额: $ 29.3万
• 依托单位: University of Maryland, College Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1994
• 资助国家: 美国
• 起止时间: 1994-03-01 至 1999-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9316278&HistoricalAwards=false
• 关键词: Dynamical; Diagnoses; Observed; Asian; Summer

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.

摘要 ATM-9316278 Nigam，马里兰州苏曼特大学帕克分校 标题：观测到的“亚洲夏季-季风降雨 - 厄尔尼诺”关系的动态诊断 该项目旨在为亚洲夏季年际波动之间的经验联系建立动态基础- 通过对亚洲大陆观测到的每月/季节性对流层环流异常进行诊断模型，得出季风降雨和厄尔尼诺/拉尼娜事件（以及全球热带和温带地区）北部夏季和“季风爆发前”（三月至五月）季节。 将强调对低对流层和近地表环流异常的强迫的理解，因为这些对于季风降雨异常和热带海洋环流异常的产生都至关重要。 该项目的目标还包括对 A) 太平洋北部秋季（9 月至 10 月）环流异常的强迫进行诊断建模/分析，以揭示亚洲夏季季风降雨异常对随后厄尔尼诺现象的潜在反馈/拉尼娜现象的发展，以及B)欧亚春季积雪异常对亚洲夏季风年际变化的潜在温带强迫。 研究任务包括： 1) 根据该诊断项目的全球 ECWMWF 分析数据集估算 3 维非绝热加热场（和瞬态涡流收敛）基于操作分析，而不是异常季风的 GCM 模拟。 2）使用多层全局稳定原方程模型对带状变化的气候流进行线性模拟——这是动态诊断分析中必要的第一步。 （满足这个先决条件也将允许识别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厄尔尼诺相关加热异常的特征结构识别及其在亚洲的远程响应计算。 还将评估太平洋盆地供暖异常的远程影响。 4) 计算“喜马拉雅-西藏地形”——最近所有夏季的强迫异常环流，并检查其在亚洲对流层低层相对于远程强迫异常热响应的相位。 拟议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。 一项试点研究的结果表明，这种动态诊断分析可以提供潜在的见解，帮助我们更好地理解亚洲夏季季风异常与厄尔尼诺/拉尼娜事件（这两个全球性的事件）之间的相互作用（和潜在反馈）。规模气候异常的理解、模拟和最终预测对于 TOGA/GOALS 任务的成功至关重要。