Collaborative Research: Interhemispheric and Zonal Asymmetries of the ITCZ

卫星对地球的观测通常显示，在信风汇聚的热带海洋上空，有一条狭窄的深降水云带。这个带被称为热带辐合带（ITCZ），通常位于赤道以北，平均纬度约为北纬6度。ITCZ的许多方面，包括它的存在，它在全球大气环流中的作用，以及它对北半球的偏爱，都可以通过把ITCZ看作一个均匀的对流带来理解，它在所有经度上都具有相同的宽度、中心纬度和降雨强度。但是这种纵向平均的ITCZ视图忽略了ITCZ在热带周围纬度的实质性变化。特别值得一提的是，ITCZ位于赤道以南的印度洋，它有一个西南向东北的斜坡，横跨太平洋和大西洋。因此，ITCZ的纬度可以在北纬45度到北纬10度之间的任何地方，这取决于海洋盆地、该盆地内的经度和一年中的时间。本项目采用观测分析和精心设计的模式模拟相结合的方法，研究ITCZ纬度和其他特征的区域变化。例如，东太平洋中转区的北移被归因于北美和南美海岸线的地理位置，这一想法可以通过模拟来验证，在模拟中，美洲西海岸互为镜像。使用简化的海洋结构来测试海洋过程的重要性，简化的海洋结构允许某些机制，但禁止其他机制。海洋模型的配置包括一个简单的不动的“平板”海洋，一个改进的平板海洋，它捕获由地面风驱动的近地表热传输，以及一个“浅水”海洋模型，它允许由于来自深海的冷水上涌而使表面冷却。此外，该项目还开发了社区地球系统模型（CESM）的一个版本，其中应用通量修正来改进ITCZ的表示。鉴于ITCZ对热带降雨的重要性及其对地球气候和大气环流的巨大影响，这项工作具有实际意义。尽管ITCZ很重要，但在用于天气预报和气候变化预估的模式中并没有很好地模拟ITCZ，因此更好地了解ITCZ动力学对模式改进非常有用。这项工作对更广泛的研究企业也有价值，因为为该项目开发的模型配置将公开供全球研究社区采用。此外，该奖项还为两名研究生提供支持和培训，从而为科学劳动力的发展做出贡献。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Satellites views of the earth typically show a narrow band of deep precipitating clouds over the tropical oceans where the trade winds converge. This band, known as the inter-tropical convergence zone, or ITCZ, is generally found north of the equator with a mean latitude of about 6N. Many aspects of the ITCZ including its existence, its role in global atmospheric circulation, and its preference for the Northern Hemisphere can be understood by thinking of the ITCZ as a uniform strip of convection with the same width, central latitude, and rainfall intensity at all longitudes. But this longitudinally averaged view of the ITCZ overlooks substantial variations in ITCZ latitude around the tropics. In particular the ITCZ is found south of the equator in the Indian Ocean and it has a southwest to northeast slope across both the Pacific and Atlantic oceans. The latitude of the ITCZ can thus be anywhere from from 4S to 10N depending on the ocean basin, the longitude within that basin, and the time of year.This project uses combination of observational analysis and carefully designed model simulations to study regional variations in ITCZ latitude and other properties. For instance the northward displacement of the ITCZ in the eastern Pacific has been attributed to the geography of the North and South American coastlines, an idea which can be tested through simulations in which the west coasts of the Americas are mirror images of each other. The importance of oceanic processes is tested using simplified ocean configurations which allow some mechanisms but disable others. Ocean model configurations include a simple motionless "slab" ocean, a modified slab ocean which captures near-surface heat transport driven by surface winds, and a "shallow water" ocean model which allows surface cooling due to the upwelling of cold water from the deep ocean. In addition, the project develops a version of the Community Earth System Model (CESM) in which flux corrections are applied to improve the representation of the ITCZ.The work is of practical interest given the importance of the ITCZ for tropical rainfall as well as its outsized effects on the climate and atmospheric circulation of the earth. Despite its importance the ITCZ is not well simulated in models used for weather prediction and climate change projections, thus a better understanding of ITCZ dynamics could be quite useful for model improvement. The work also has value for the broader research enterprise, as model configurations developed for the project will be openly available for adoption by the worldwide research community. In addition, the award provides support and training for two graduate students, thereby contributing to scientific workforce development.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.