Collaborative Research: Investigating Thermal Structure, Dynamics, and Dehydration in the Tropical Tropopause Layer with Fiber Optic Temperature Profiling from Strateole-2 Balloons

GSTDTAP

项目编号	1642277
	Collaborative Research: Investigating Thermal Structure, Dynamics, and Dehydration in the Tropical Tropopause Layer with Fiber Optic Temperature Profiling from Strateole-2 Balloons
	Lars Kalnajs
主持机构	University of Colorado at Boulder
项目开始年	2017
	2017-02-01
项目结束日期	2022-01-31
资助机构	US-NSF
项目类别	Continuing grant
项目经费	247809(USD)
国家	美国
语种	英语
英文摘要	The tropical tropopause layer (TTL) is transition zone between the troposphere (the domain of clouds, precipitation, and weather systems) and the stratosphere (the cold and dry region above it which contains the ozone layer). The TTL extends from about 14 to 18.5km over the tropics and is above the tops of all but the tallest convective clouds. It often contains thin cirrus clouds which, though difficult to see, play an outsized role in trapping outgoing radiation and thus warming the troposphere. It is sometimes called the "gateway to the stratosphere" because most of the water vapor in the stratosphere, and many other stratospheric constituents, enter the stratosphere by moving upward through the TTL. The stratosphere is extremely dry compared to the troposphere, but stratospheric water vapor is of interest because it has an important greenhouse effect and can lead to the formation of polar stratospheric clouds which play a role in ozone hole formation. Work under this project seeks to improve understanding of the TTL by developing and deploying a temperature profiler as part of a long-duration ballooning campaign. The profiler, with the acronym FLOATS (Fiber-optic Laser Operated Atmospheric Temperature Sensor), measures temperature along a fiber optic cable 2km long which is suspended below a balloon gondola. FLOATS works by injecting laser light into a fiber optic cable and sensing Raman backscattered light. It can measure temperature with 0.3K precision and a vertical resolution of 3m, generating a profile every two to five minutes. A proof-of-concept prototype was developed under an EAGER award, AGS-1419932. FLOATS is deployed as part of the Strateole-2 field campaign organized by the Centre National d'Etudes Spatiales (CNES), the French Space Agency, and the Laboratoire de Meteorologie Dynamic (LMD) of the University of Paris-Saclay. Strateole-2 is a five-year campaign, with a small validation deployment in 2018 and full science deployments in 2020-2021 and 2022-2023. Balloons are launched from the Seychelles (about 5S in the Indian Ocean), with the expectation that each balloon will circle the earth for up to 90 days and observe the TTL between 20S and 15N. This award supports US participation in the validation campaign and the first full science deployment, along with post-campaign analysis. It is one of three awards made to US PIs for participation in Strateole-2, the full set being AGS-1643022, AGS-1642277/1642246, and AGS-1642650/1653644. The FLOATS measurements are used to address three scientific objectives, all of which use temperature variations along the fiber optic cable to examine the behavior of gravity waves (wave motions in the air in which buoyancy provides the restoring force). The first is the depression of the cold point tropopause (CPT) temperature by vertically propagating gravity waves, which is a key factor in determining how much water vapor enters the stratosphere through the TTL. If condensation or sublimation occurs when relative humidity reaches 100%, then the amount of water vapor entering the stratosphere should not exceed the amount corresponding to 100% relative humidity at the CPT temperature. Earlier work by one of the PIs and others suggests that wave-induced CPT temperature depression could be significant, and an increase in wave activity could be responsible for a substantial portion of the decrease in CPT temperature and stratospheric water vapor believed to have occurred in the first decade of the 21st century. The second science objective is to understand the role of gravity waves in producing cirrus clouds in the TTL. The problem is complementary to stratospheric dehydration produced by temperature depression, as water vapor prevented from entering the stratosphere by colder temperatures instead freezes out to form cirrus ice particles. The third objective is to measure the vertical momentum flux associated with the waves. These waves are critical for the stratospheric quasi-biennial oscillation (QBO), which can influence the skill of long-range weather forecasts. Momentum flux would be estimated by combining FLOATS measurements (which give wave amplitude, vertical wavelength, and phase speed) with additional measurement taken on the balloon gondola including wave-induced directional displacement inferred from GPS positioning. The work has scientific broader impacts due to the value of the observations for addressing a variety of questions regarding TTL processes and the stratospheric QBO. In particular, wave momentum flux data is of value for developing gravity wave parameterizations for use in improving numerical models used for weather forecasting. FLOATS observations will be made available to the research community from servers at the Laboratory for Atmospheric and Space Physics at the University of Colorado Boulder, so that they can be freely examined by the research community. In addition, the project constitutes a demonstration of a novel technology for meteorological observations which could have a wide array of scientific applications. Beyond these considerations, the project supports a postdoctoral research associate, thereby developing the future scientific workforce in this research area.
来源学科分类	Geosciences - Atmospheric and Geospace Sciences
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/70756
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Lars Kalnajs.Collaborative Research: Investigating Thermal Structure, Dynamics, and Dehydration in the Tropical Tropopause Layer with Fiber Optic Temperature Profiling from Strateole-2 Balloons.2017.