Global Atmospheric Modeling Hierarchy Development

GSTDTAP

项目编号	1733818
	Global Atmospheric Modeling Hierarchy Development
	Isaac Held
主持机构	Princeton University
项目开始年	2017
	2017-07-01
项目结束日期	2020-06-30
资助机构	US-NSF
项目类别	Standard Grant
项目经费	368228(USD)
国家	美国
语种	英语
英文摘要	This project seeks to advance understanding in theoretical climate dynamics through the development and use of idealized models of varying levels of complexity. The models are designed to be only as complex as necessary to capture the phenomena of interest, which are assumed to be manifestations of fundamental climate system processes. One such model is the Held-Suarez model (HS, named for its creators), which does not include clouds or moist processes and uses thermal relaxation to generate the temperature contrast between the equator and the poles. Despite its simplicity the model reproduces many features of the atmospheric circulation including jet streams, reasonable approximations of middle-latitude weather systems, and the tropical overturning circulations known as Hadley cells. One use of the HS model is to test the hypothesis that key aspects of the atmospheric circulation, including the vigor of kinetic energy generation and the amount of heat transported from warmer to colder latitudes, can be understood in terms of Maximum Entropy Production (MEP). MEP can be used to derive an upper bound on kinetic energy generation in the HS model, but the upper bound is too large to be useful unless constraints are imposed which make it dependent on planetary rotation rate and other fundamental parameters. Research conducted here attempts to identify the appropriate constraints in the HS model and assess their relevance for more sophisticated models and the observed atmosphere. Other problems to be addressed include the role of lower tropospheric wave momentum fluxes in stormtrack dynamics, wave instabilities that transport westerly momentum from the middle latitudes into the tropics, and generation mechanisms for external Rossby waves. Additional problems are addressed with the HS model by incorporating a simplified representation of the hydrological cycle in which water vapor is treated as a passive tracer without radiative effects. Surface evaporation proceeds according to a standard bulk formula and water vapor condenses when it saturates at higher and colder altitudes. But the condensation does not result in clouds or latent heating and water cycling has no effect on atmospheric circulation. Despite these omissions the model produces water vapor streamers, frontal precipitation patterns, and atmospheric rivers which resemble their real-world counterparts. The model is used here to study kinematic constraints on the mean strength of the hydrological cycle and its response over continents to warmer conditions. For the latter application continents are specified using a simplified "bucket" representation of soil moisture. Further research is conducted with a model at a somewhat higher level of complexity, which uses simplified atmospheric radiative transfer (the grey-body approximation) rather than thermal relaxation to produce the pole-to-equator temperature contrast. The model allows the hydrological cycle to affect circulation through condensational heating, but water vapor has no effect on radiative transfer and clouds are not represented. This version of the model is used to study the behavior of the intertropical convergence zone (ITCZ), the narrow band of clouds and precipitation usually found near the equator. One strategy is to modify the model so that it represents only a limited zonal sector of the atmosphere, so that disturbances of the ITCZ caused by phenomena larger than the width of the sector are eliminated. The work has scientific broader impacts through the sharing of model codes and documentation with the research community through a web portal. Versions of the models have already gained broad acceptance as research tools, but they have been disseminated largely through personal connections with the PIs' research group. Beyond their value for isolating and examining specific climate system processes, the models have proven useful for testing numerical methods used in comprehensive climate models. In addition, the models can play an important role in communicating climate science to the public and researchers in other scientific fields. Simple models are valuable for this purpose as they can be used to demonstrate that the simplifications required for effective communication correctly represent, albeit in approximate form, the workings of the climate system. The project also provides support and training for a graduate student, thereby providing for workforce development in this research area.
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/71251
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Isaac Held.Global Atmospheric Modeling Hierarchy Development.2017.