Reduced Weather Variability Indicated by Decreases in Atmospheric Energy Spectra

Recent studies have suggested that polar amplification may lead to a reduction in the number of storms in the Northern Hemisphere. Weather variability, including storms, as a function of spatial scale can be succinctly summarized through the use of horizontal energy spectra. In this paper, we first show that non-uniform spherical Fourier methods can be used to estimate horizontal energy spectra from weather station observations with an arbitrary network configuration. Using this new tool, we demonstrate that weather variability across the entire synoptic and mesoscales has decreased monotonically since the 1970s by as much as 50-60% in global reanalysis data and station observations. Future climate projections using a very-high resolution climate model suggest a continuation of these trends, resulting in an additional reduction of about 20% by 2090. Reanalysis data and projections for the Southern Hemisphere also suggest decreases in kinetic energy, but cannot be validated with ground-truth observations.