Collaborative Research: Revisiting the Low-Frequency Variability of the Extratropical Circulation Using Non-Empirical Orthogonal Function (EOF) Modes and Linear Response Functions

点击翻译按钮获取中文摘要

One dominant pattern of the atmospheric circulation variability in the extratropical troposphere of both hemispheres is the oscillation between stronger and weaker westerly jet streams with a time scale longer than 10 days. Such low-frequency variability of extratropical westerly jet streams is called the annular mode. The annual mode influences the day-to-day weather and extreme events in the middle and high latitude regions and is therefore of great interest to understand. The annular mode in winter hemisphere also influences, and is influenced by, the stratospheric polar vortex. This project seeks a deeper understanding of the factors that control the annular mode. The outcome of this work will potentially transform the understanding of jet stream variability and weather in the middle and high latitudes. The outcome could also lead to advances in predictability past the current weather prediction barrier of about 10 days, and lead to improvements in capabilities of climate models. Furthermore, the new quantitative framework will aid the interpretation of the range of outcomes predicted by comprehensive climate models. These outcomes have the potential to advance the national and global efforts aimed at preparing for climate change and weather-related extremes, resulting in significant socio-economic benefits. This project will support the education and training of two PhD students and a postdoctoral researcher, thus preparing the next generation of atmospheric dynamists and climate scientists. Some of the tools developed during this work will be used by the PIs in their undergraduate and graduate-level teaching to help the students with visualizing and quantifying some aspects of the jet stream variability. Also, the project will engage K-12 students in climate and computer modeling-related research through several STEM outreach programs at Rice and Stanford.In this project, novel analysis methods will be developed, and will be employed along with computer models and observational data to gain a deeper understanding of this variability of the jet streams. Furthermore, a new framework will be developed to quantitively link this variability in the present day to variability in the future. This framework will integrate the response of the jet stream variability and polar vortex to various climate forcings, such as greenhouse gas increase or ozone depletion. The specific tasks of this project are 1) examining the coupling between the barotropic and baroclinic annular modes in observations and in climate models; 2) developing an eddy feedback model for propagating annular modes; 3) understanding stratospheric influence on the tropospheric annular mode in both hemispheres using numerical experiments; 4) studying low-frequency variability modes and fluctuation-dissipation relationship in climate model simulations to better evaluate the fidelity of the climate change projections in these simulations.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.