Brewer–Dobson Circulation: Recent-Past and Near-Future Trends Simulated by Chemistry-Climate Models

Dingzhu Hu,Meichen Liu,Qi Xu,Wenjun Sang,Yuanpu Li,Xudong Wang,Feiyang Wang,Yipeng Guo

doi:10.1155/2017/2913895

Abstract

Based on data from 16 chemistry-climate models (CCMs) and separate experimental results using a state-of-the-art CCM, the trends in the Brewer–Dobson circulation (BDC) during the second half of the 20th century (1960–2000) and the first half of the 21st century (2001–2050) are examined. From the ensemble mean of the CCMs, the BDC exhibits strengthening trends in both the 20th and 21st centuries; however, the acceleration rates of tropical upwelling and southern downwelling during 2001–2050 are smaller than those during 1960–2000, while the acceleration rate of the northern downward branch of the BDC during 2001–2050 is slightly larger than that during 1960–2000. The differences in the extratropical downwelling trends between the two periods are closely related to changes in planetary-wave propagation into the stratosphere caused by the combined effects of increases in the concentrations of greenhouse gases (GHGs) and changes in stratospheric ozone. Model simulations demonstrate that the response of southern downwelling to stratospheric ozone depletion is larger than that to the increase in GHGs, but that the latter plays a more important role in the strengthening of northern downwelling. This result suggests that, under the expected future climate, northern downwelling will play a more important role in balancing tropical upwelling.

Highlights

The Brewer–Dobson circulation (BDC) consists of an upward transport branch across the tropical tropopause in the tropics and downward and poleward transport branches in the extratropics in the two hemispheres [1]
Ozone-depleting substances that follow the BDC are transported into the polar stratosphere where they influence the concentration of ozone [8,9,10,11,12]
As the meridional distribution of trace gases in the stratosphere is closely related to the BDC [2, 10, 13], changes in the BDC are important to the formation and recovery of the stratospheric ozone hole

Summary

Introduction

The Brewer–Dobson circulation (BDC) consists of an upward transport branch across the tropical tropopause in the tropics and downward and poleward transport branches in the extratropics in the two hemispheres [1]. Xie et al [2] showed that an increase in stratospheric ozone results in a decrease in the tropical mass flux across the tropopause and, recently, Hu et al [10] found that the potential ozone recovery under the expected future climate will result in a weaker BDC during boreal winter. The remainder of this paper is organized as follows: Section 2 describes the CCM data, method, and the design of the numerical experiments; Section 3 analyzes the BDC trends in the recent-past (1960–2000) and in the near-future (2001–2050); Section 4 examines the planetary-wave flux trends of the two periods; Section 5 discusses the effects of GHGs and stratospheric ozone changes on the BDC; and Section 6 summarizes the study and our conclusions. Differences between the runs of GHG2000 and REF, as well as those between OZONE2000 and REF, are used to investigate the impacts of GHGs increases and stratospheric ozone depletion on the BDC

BDC Trends in the CCMs

Planetary-Wave Flux Trends

Effects of GHGs and the Stratospheric Ozone on the BDC

Findings

Conclusions and Discussion