Portland State University. Department of Geography
Paul C. Loikith
Date of Award
Master of Science (M.S.) in Geography
1 online resource (vii, 47 pages)
Stratospheric circulation -- Seasonal variations -- Northern Hemisphere, Climatic changes
Regions that have experienced recent successive cold winters such as the Northeast of North America and Siberia have endured critical social and economic impacts from anomalous low temperatures in recent years, despite warming global temperatures. It is well known that the Tropospheric Polar Vortex (TPV), or jet stream, is a primary influence on many mid-latitude winter weather patterns. However, the strong circumpolar westerlies that maximize at around 60° latitude just above the tropopause, known as the Stratospheric Polar Vortex (SPV), can affect tropospheric circulation and thus winter weather in the Northern Hemisphere. Strong upward propagating waves can affect the geographic extent and strength of the SPV resulting in a weakened polar vortex state, which can in turn bring persistent weather events to the mid-latitudes. Here, an index of SPV spatiotemporal variability is presented using observation based analysis of zonal wind and geopotential height to show changes in SPV behavior at a seasonal scale from 1950-2018. Utilizing the CMIP5 suite of global climate models, historical and projected simulations of the SPV's climatological extent and strength are analyzed from 1915 to the end of this century, taking into account models with enhanced stratospheric representation. Simulated results are largely consistent with trends in the observational data, which suggest continued increases in average SPV size throughout this century. If future SPV disturbances increase in frequency, there could be negative impacts in ecosystem and agricultural health, infrastructure damage, and to human safety. A more advanced understanding of SPV trends and anomalous events could improve forecasts of cold air outbreaks (CAOs) and severe or persistent winter weather.
Rogers, John Earl, "Stratospheric Polar Vortex Variability in the Northern Hemisphere: the Effects of Climate Change on Polar Vortex Trends and Future Projections" (2019). Dissertations and Theses. Paper 4864.