Future changes in the influence of the quasi-biennial oscillation on the northern polar vortex simulated with an MRI chemistry climate model

The effect of climate change on the dynamics of the Holton-Tan (HT) relationship (i.e., the influence of the quasi-biennial oscillation (QBO) on extratropical circulation) is examined for a set of three-member simulations and a sensitivity simulation with constant greenhouse gases (GHGs) at 1960 levels, focusing on the Northern Hemisphere extended winter. The simulations are conducted by the MRI chemistry climate model (MRI-CCM), which internally generates the QBO; the set is driven by the REF-B2 scenario from 1960 through 2100, and constant GHG simulation by the same halogen scenario and fixed greenhouse gases. Future climate change results in a colder stratosphere with a temperature decrease of 6 K and with a westerly increase of similar to 4 m s(-1). Although the HT relationship is present in early winter in the recent climate interval from 1960 through 1999 in the ERA-40 reanalysis data and the simulation, the HT relationship in the future climate interval from 2060 through 2099 is predicted to be stronger in late winter. The analysis of the constant GHG simulation indicates that the HT relationship holds for the future in which forcings are almost constants and possible contributions to the HT effect are due to long-term natural variability. Further, we suggest that the climate change, or the increase in the atmospheric CO2, is responsible for the regime shift between the current climate interval and the future climate interval in the REF-B2 scenario. Further research is required to determine how a multidecadal oscillation could modulate the HT effect.