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

ATM-9316278尼加姆，马里兰夏季大学-学院公园标题：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试图通过对亚洲大陆(以及全球热带和温带外)夏季和季风爆发前(3-5月)季节观测到的对流层环流异常进行诊断模拟，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。将强调对低对流层和近地表环流异常的强迫作用的理解，因为这些异常对于季风降水异常和热带海洋环流异常的产生都是至关重要的。项目目标还包括A)北秋强迫(9月1日)的诊断性模拟/分析。-10月)(B)欧亚春季积雪异常对亚洲夏季风年际变化的潜在强迫作用。研究任务包括：1)从全球ECWMWF分析数据集估计三维非绝热加热场(和瞬变涡通量辐合)，该诊断项目基于业务分析而不是GCM对异常季风的模拟。2)用多层全球稳定原始方程模式对纬向变化的气候气流进行线性化的线性模拟--这是这种动力诊断分析的必要的第一步。(满足这一前提条件还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”改编应该允许比以前可能的更高的线性模型分辨率。3)确定了热带太平洋和印度洋3-5月和6-8月期间与厄尔尼诺相关的加热异常的特征结构，并计算了它们在亚洲上空的远程响应。还将评估仅太平洋盆地供暖异常的遥远影响。4)计算了近几年夏季“喜马拉雅-西藏地貌”强迫异常环流，并与遥强迫热响应的亚洲对流层低层异常环流的位相进行了比较。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的基础。一项初步研究的结果表明，这种动力诊断分析可能有助于提高我们对异常亚洲夏季风和厄尔尼诺/拉尼娜事件之间相互作用(和潜在反馈)的了解，这两种全球范围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.