Understanding the Processes that Control the Interannual Variability of the Wintertime Polar Front and Subtropical Jet Streams

Abstract:

The movement and intensification of the subtropical and polar front jet streams have important implications for global and regional climate. Based on previous literature, the position and strength of the subtropical jet are usually related to tropical thermodynamic processes, whereas the position and strength of the polar front jet are more associated with mid-latitude eddies. These conclusions have largely resulted from studies using idealized models. In this study, we use ERA-Interim reanalysis data and CMIP6 global climate model output to examine the mechanisms responsible for controlling the variability of the polar front and subtropical jet at different longitudes in the Northern Hemisphere (NH) during the winter season. Consistent with idealized modeling studies, we find a close relationship between tropical outgoing longwave radiation (OLR) and the subtropical jet, and between mid-latitude surface temperature gradients and the polar front jet.

Preliminary results show that variations in tropical convection over the Pacific Ocean are linked to variations in the strength and position of the NH subtropical jet at almost all longitudes, with different phases of the El Niño-Southern Oscillation (ENSO) associated with the poleward shift and strengthening of the subtropical jet in different regions. CMIP6 models generally capture this relationship, but the models’ tropical convection is often displaced westward when compared to observations. The differences between models and observations may be attributed to a biased OLR climatology in the Eastern tropical Pacific Ocean in many models.