Initial Transient Response of the Polar Stratospheric Vortex to Idealized Equatorial Pacific Sea Surface Temperature Anomalies in WACCM

We investigate the response of the Northern Hemisphere stratospheric polar vortex to equatorial central (CPW) and eastern Pacific warming (EPW) through perpetual-winter experiments conducted with the National Center for Atmospheric Research (NCAR) Whole Atmosphere Community Climate Model (WACCM). Previous studies have shown that canonical El Niño (eastern Pacific warming) events can weaken the stratospheric polar vortex, depending on the phase of the Quasi-Biennial Oscillation (QBO). However, it is less clear whether CPW results in a weakening or strengthening of the vortex. Perturbation experiments with the idealized sea surface temperature (SST) fields designed to roughly mimic CPW and EPW are run to explore the initial transient response of the vortex to CPW and EPW. Preliminary results indicate that the initial transient response to CPW and EPW is sensitive to the initial strength of the vortex, especially in the CPW case. A strong westerly initial condition of the vortex favors a weakening response for both CPW and EPW, but strengthening of the vortex occurs with CPW and weak westerly and easterly initial conditions. Differences in the response of the extratropical tropospheric planetary waves to CPW and EPW play a critical role in determining the simulated response of the vortex. Results from experiments with an idealized SST seasonal cycle will also be discussed.