Change in the Mid-latitude Jet Stream Flow Due to Anthropogenic Climate Change, and Its Effect on Month-to-month Surface Temperature Variability

Change in the mid-latitude jet stream flow attributed to anthropogenic climate change has led to regional and seasonal shifts in blocking weather patterns – especially during northern hemisphere summer months. These changes are investigated in this study using the NCAR Reanalysis daily data to assess the shifting distribution of summer 500 mb geopotential height anomalies across North America over the last 70 years. This analysis shows a positive trend in the frequency of positive geopotential height anomalies (i.e., more ridging) in the Western US, especially during the late spring and summer months, compared to the Central and Eastern US. Next, an analysis of month-to-month variability in surface temperature anomalies will be presented that identifies regional changes in the variance of temperature extremes over the last 70 years across North America. We also quantify the trend in the monthly temperature anomalies throughout the entire data set. Finally, we will discuss how these trends impact hazardous weather risk in agricultural production including floods, drought, and wildfires, and we will discuss large scale atmospheric and oceanic drivers that play a role in these long term trends.