Responses of midlatitude blocks and wave amplitude to changes in the meridional temperature gradient in an idealized dry GCM

Abstract

The response of atmospheric blocks and the wave amplitude of midlatitude jets to changes in the midlatitude to pole, near-surface temperature difference (ΔT), is studied using an idealized dry general circulation model (GCM) with Held-Suarez forcing. Decreasing ΔT results in slower zonal winds, a mean state with reduced meridional gradient of the 500 hPa geopotential height (Z500), a smaller variance of Z500 anomalies, and a robust decrease in blocks and meridional amplitude of waves. Neglecting the decrease of variance associated with reduced ΔT would lead to the incorrect expectation that mean states with smaller Z500 gradients produce more blocks and higher wave amplitudes. Our results suggest further investigation of the hypothesis that reduced ΔT due to Arctic Amplification would increase blocking events and wave amplitude, hence leading to more midlatitude extreme weather events. © 2014. American Geophysical Union. All Rights Reserved.