Modeling Dynamics and Impacts of a new class of Kelvin-Helmholtz Instabilities that Drive Enhanced Turbulence and Mixing in the MLT

Global Atmospheric Technologies And Sciences, Inc., Newport News VA

Investigators

Abstract

State-of-the-art general circulation models (GCMs) used for weather and climate prediction underestimate the amount of turbulent mixing in the middle atmosphere by up to a factor of 2, and as a result, mischaracterize the transport and global distributions of CO2 and other primary atmospheric constituents. GCMs attribute mixing to a single dynamical source that neglects newly discovered, small-scale turbulent processes thought to be widespread, and perhaps even ubiquitous, in the middle atmosphere and beyond. This project will identify these unique “tube and knot” (T&K) instability dynamics and their implications for mixing through observationally guided, high-resolution modeling studies. Sophisticated turbulence and chemical analysis capabilities will be employed to address scientific goals among a diverse range of atmospheric research communities. The resulting knowledge of T&K-driven momentum transport and deposition will aid the development of improved mixing parameterizations in GCMs and yield higher accuracy weather and climate forecasting to address a critical societal need. It will also support the education of a University of Colorado Boulder graduate student and a Utah State University undergraduate student while facilitating outreach events that promote climate science education to under-represented pre-college students in the surrounding communities. This project will identify and quantify Kelvin Helmholtz instability (KHI) T&K dynamics and implications for mixing in the MLT via high-resolution modeling, utilizing the unique capabilities of in-house models CGCAM and SAM to characterize instability dynamics extending to turbulence scales and mixing in deep domains with realistic environments. The results will improve mixing parameterization schemes in weather and climate models by addressing GCM underestimation of the eddy diffusion coefficient Kzz. The goals of this research are to identify and quantify the large-scale (mean and tidal) and GW environments that enable KHI T&K dynamics, and account for their spatial scales and intensities; to quantify the diversity of KHI T&K dynamics, and their implications for energy dissipation, mixing, and influences in the MLT via high-resolution modeling; and to employ our KHI T&K modeling to assess their enhancements of energy dissipation rates, mixing, and implied Kzz relative to those expected for GW breaking. The analysis and modeling approach addressing these research goals will employ KHI T&K observations by USU Advanced Mesospheric Temperature Mapper (AMTM) OH airglow imaging and GATS SAAMER radar and lidar profiling of winds, temperatures, and Na densities in Tierra del Fuego, Chile, and Poker Flat, Alaska, to guide representative modeling environments (e.g., GW and tidal shears, multi-scale superpositions). Informed by these observations, a wide range of KHI T&K simulations will be performed to capture the diversity of responses for varying environmental conditions and evaluate KHI T&K mixing, enabling definition of the parameters dictating a KHI Kzz for representative shear layer scales and Richardson and Reynolds numbers. This research will directly result in a better understanding of unresolved mixing dynamics in the MLT and how they impact constituent particles and energy transport to higher levels of the atmosphere. 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.