Exploration of Atmospheric Oscillations with a Hierarchy of Models: A focus on scale and geographic location

Abstract:

Recent research has revealed unexpected dynamical variability in the extratropical atmosphere. Work by Thompson & Woodworth (2013) and Thompson & Barnes (2014) has demonstrated the existence of a baroclinic annular mode (BAM), a 20-30 day oscillation of the zonally averaged eddy-kinetic energy (EKE). This study explores EKE oscillations in the Southern Hemisphere in the context of two distinct questions: (1) At what zonal scale does the BAM signal appear? (2) Do different regions of the Southern Hemisphere contribute more to the BAM than others?

In order to answer these two questions, the study uses data from two different models: the GFDL gray-radiation aquaplanet model and the GFDL-CM3 GCM. Analysis of the aquaplanet power spectra isolates the question of scale while the GFDL-CM3 analysis is used to investigate both the question of scale and geographic distribution. Results indicate EKE oscillations with peaks within the frequencies of analysis (20-30 days) to ranges as small as 35 degrees zonal width in the aquaplanet, and 120 degrees zonal width in the fully-coupled GCM. The geographic distribution of EKE in the GCM suggests the Indian Ocean and Western Pacific Ocean regions contribute more to the BAM signal. Preliminary results suggest possibile variations in frequency/period at different geographic locations that warrant further investigation. Ultimately, the scale and geographic location of EKE oscillations/the BAM may have important implications for precipitation at regional scales.