Tropical-Extratropical Interactions in a Hierarchy of Model Complexity

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项目编号	1650209
	Tropical-Extratropical Interactions in a Hierarchy of Model Complexity
	Amy Clement
主持机构	University of Miami Rosenstiel School of Marine&Atmospheric Sci
项目开始年	2017
	2017-05-15
项目结束日期	2020-04-30
资助机构	US-NSF
项目类别	Continuing grant
项目经费	183935(USD)
国家	美国
语种	英语
英文摘要	Most weather systems in middle and high latitudes (the "extratropics") originate in the extratropics and are driven by extratropical processes, in particular temperature contrasts along fronts and the Coriolis force that compels winds to circulate around highs and lows. But extratropical weather systems can interact strongly with tropical weather and climate through a variety of pathways. One consequential example is atmospheric rivers (ARs), in which southerly winds in midlatitude systems produce narrow filaments of moisture extending from the tropics to the midlatitudes, where they produce heavy rain and flooding in regions such as coastal California. Another example is the Madden-Julian Oscillation (MJO), a large pattern of tropical precipitation and atmospheric circulation that forms in the Indian Ocean and propagates slowly eastward into the central tropical Pacific. The MJO has a variety of effects on midlatitude weather, including an increase in ARs along the US west coast and meanders of the jet stream that cause heat waves and cold air outbreaks. A key question for the MJO and for tropical-extratropical interactions on longer timescales is the role of air-sea coupling, as the importance of changes in sea surface temperature (SST) and subsurface ocean heat storage due to wind-driven evaporation is currently an open question. This project attempts to isolate the fundamental dynamics which drive the MJO, ARs, and slower variations known as meridional modes in which variability in the midlatitudes causes SST anomalies which propagate into the tropics over a year or two. The PIs develop and use a hierarchy of numerical model configurations at varying levels of complexity, in which the most complex configuration is used to realistically simulate the phenomena of interest. Progressively simpler model versions are used to reduce the complexity of the simulation so that the PIs can factor out non-essential details, allowing them to analyze the underlying dynamics in their simplest and most comprehensible form. For example, preliminary work shows that ARs can be produced in an "aquaplanet" model, in which the continents are replaced by ocean surface and SSTs are approximated as a simple function of latitude (warm near the equator and gradually cooling towards the poles). The simulation produces credible ARs despite the lack of continents, seasonality, and realistic SSTs, suggesting that the fundamental dynamics of ARs are best examined in simple models which lack these complexities. Models in the hierarchy are versions of the Community Atmosphere Model version 5 (CAM5), to which the PIs will add an aquaplanet version with "superparameterized" convection that is more appropriate for simulating the MJO, and two new representations of the ocean mixed layer. One version adds a simplified cooling rate calculation and relaxation to a specified temperature profile, a configuration which is sufficient to reproduce cold wakes behind tropical cyclones. The other is essentially the full physics mixed layer model from the Parallel Ocean Program, implemented in stand-alone columns at each ocean surface gridpoint. Comparisons between simulations with simpler and more complex mixed layers are used to understand the dependence of the MJO and meridional mode on the physics determining heat and moisture exchange between the ocean and overlying atmosphere. The work has scientific broader impacts through the development of the model hierarchy. The model versions developed in this project will be made available to the research community as part of the Community Earth System Model (CESM), which is hosted by the National Center for Atmospheric Research. They are part of an ongoing effort to developer simpler models using the CESM code base (which includes CAM5), and will be supported with documentation and reference simulations. More broadly, tropical-extratropical interactions are of societal as well as scientific interest due to their influence on US weather extremes.
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文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/71064
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Amy Clement.Tropical-Extratropical Interactions in a Hierarchy of Model Complexity.2017.