A study on the formation and trend of the Brewer-Dobson circulation

The Brewer-Dobson circulation (BDC) is approximately expressed by the residual circulation (RC) and considered to be driven by the body force induced by the breaking and/or dissipation of atmospheric waves. The contribution of different types of waves to the RC in the Center for Climate System Research/National Institute for Environmental Studies (CCSR/NIES) Chemistry Climate Model (CCM) is diagnosed using the downward control principle (DC). Gravity wave drag (GWD) including orographic gravity wave drag (OGWD) has a great influence on the RC in the low and middle latitudes of the lower stratosphere. In particular, the summer hemispheric low-latitude part of winter circulation is mainly formed by the GWD. These results are consistent with the estimates of the GWD contribution using reanalysis data by subtracting the resolved wave contribution from the RC with DC principle. In addition, it is seen that the net upward mass flux on the 70 hPa surface is strengthened during the 21st century because of the upward shift of the OGWD, which is consistent with previous studies. These conclusions indicate that gravity waves play an important role in maintaining the BDC.