Cumulus Momentum Fluxes in the Tropics and Subtropics

热带和亚热带的积云动量通量

• 批准号: 9877021
• 负责人: Christopher Bretherton
• 金额: $ 19.95万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-04-15 至 2003-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9877021&HistoricalAwards=false
• 关键词: Cumulus; Momentum; Fluxes; Tropics; Subtropics

Vertical fluxes of momentum due to cumulus convection are a significant but poorly understood contributor to atmospheric circulations, particularly in the tropics and subtropics. Reliable observations of cumulus momentum flux are scarce. It is very difficult to judge the accuracy of the widely varying parameterizations of cumulus momentum fluxes currently used in different global weather and climate models. Tropical convection also exhibits many types of mesoscale organization. An important issue for parameterization is whether the cumulus momentum fluxes can be predicted adequately without knowing the mesoscale organization of the convection. This project will bolster observational knowledge of cumulus momentum fluxes using three extensive and complementary new data sets. Specifically, momentum fluxes will be computed (1) as budget residuals in global reanalyses for the TOGA-COARE region, other convective regimes, and as zonal averages, (ii) from an extensive set of dual-Doppler airborne radar analyses of tropical mesoscale convective systems from TOGA-COARE, and (iii) from output from cloud ensemble model simulations of tropical convection. The TOGA-COARE experiment is particularly promising to study because the persistent deep convection coupled to the large temporal variations in vertical wind shear can be expected to produce large and easily detectable changes in the cumulus momentum fluxes.The goals of the project are to quantify the significance of cumulus momentum fluxes on large scale transient and mean circulations in the tropics, particularly the intraseasonal oscillation, and (ii) to determine the relative importance of the circulations in the convective versus stratiform region of mesoscale convective systems in producing the momentum fluxes, in a variety of wind shear regimes, and (iii) to compare the results to several different parameterizations that have been proposed. These analyses should help to improve the performance of weather and climate models in the tropics.

积云对流引起的动量垂直通量是大气环流的一个重要的贡献者，但人们对它的认识却很少，特别是在热带和亚热带地区。 可靠的积云动量通量观测是稀缺的。 目前在不同的全球天气气候模式中使用的积云动量通量参数化变化很大，很难判断其准确性。 热带对流也表现出许多类型的中尺度组织。 参数化的一个重要问题是，在不知道对流的中尺度组织的情况下，积云动量通量是否能够被充分地预测。该项目将利用三个广泛和互补的新数据集加强积云动量通量的观测知识。 具体而言，动量通量将计算（1）作为TOGA-COARE地区全球再分析中的预算残差，其他对流制度，并作为纬向平均值，（ii）从TOGA-COARE的热带中尺度对流系统的一组广泛的双多普勒机载雷达分析，以及（iii）从热带对流的云集合模型模拟的输出。 TOGA-COARE试验是一个特别有前途的研究项目，因为持续的深对流与垂直风切变的大的时间变化相耦合，可以预期会产生大的和容易检测的积云动量通量的变化。该项目的目标是量化积云动量通量对热带大尺度瞬变和平均环流，特别是季节内振荡的重要性，和（ii）以确定相对重要性的环流在对流与层状区域的中尺度对流系统中产生的动量通量，在各种风切变制度，和（iii）比较的结果，几个不同的参数化已提出。 这些分析应该有助于提高热带地区天气和气候模型的性能。