Collaborative Research: Processes Determining the Climatology of Atmospheric Unstable Layers

This research seeks to answer a number of questions that have arisen from recent observations of unstable layers at various altitudes in the atmosphere; that is, these layers are characterized with air temperature decreasing with height. Unstable layers have been identified by examining a fast meteorological sensor attached to meteorological balloons launched from stations operated by the United States (US) Weather Service. The fast meteorological sensor can take air temperature at every second, which is at every 5 meters as a balloon rises. Unstable layers are commonly associated with turbulence. Within each turbulent layer, air motions cascade from large eddies to small ones due to kinetic energy dissipation. Atmospheric turbulence is dangerous for aircraft operations and has impacts on remote sensing atmospheric phenomena. The researchers for the project will investigate what causes these unstable layers. Understanding of the origin of these unstable layers could improve safety of aircraft operations. Recently global observations using this type of fast meteorological balloon sensors become available. The investigators also plan to organize an international workshop to stimulate international research for using this dataset.

The research team will answer two principal questions: 1) Why are there more unstable layers in the lower stratosphere at midnight Greenwich Mean Time (GMT) in the western contiguous US than at noon GMT, with the opposite being true in the eastern US? 2) Is the observed phenomenon of a great number of thick unstable layers and a relative paucity of thinner layers at near 12 km altitude at Koror (7.3 N, 134.5 E), which is also called 'notch', present at other near equatorial stations? In what way might this 'notch' be related to the minimum in atmospheric stability that has been noted earlier by other authors in the same general atmospheric region? The research plan to address question 1 is to try to identify differences in the times and locations of atmospheric gravity buoyancy waves that lead to the lower stratospheric unstable layers. This is planned to be done using a ray-tracing methodology. The research plan to address question 2 is to compare the geographical and temporal variation of the 'notch' feature to that of the stability minimum. The investigators also plan to identify the 'notch' feature with in-cloud and cloud-outflow turbulence.

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.