Past and future evolution of the 3D Brewer-Dobson circulation

• Applicant: Dr. Axel Gabriel
• Subject Area: Atmospheric Science
• Term: from 2013 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 240559849

The Brewer-Dobson circulation (BDC) denotes the time-mean mass circulation of the middle atmosphere (10-100km). The BDC is driven by planetary waves, synoptic-scale waves and gravity waves, and transports ozone (O3), water vapour (H2O) and other trace gas constituents from the tropics to mid- and polar latitudes. The evolution of the zonal mean (2D) BDC in a changing climate and its interaction with the stratospheric ozone layer is an important issue of current research. However, the long-term changes of the 2D BDC and the wave driving strongly differ between the used models and the observations. Examinations based on a formulation of the three-dimensional (3D) BDC might lead to a more detailed picture and an improved understanding of the role of the BDC in a changing climate, but they are very sparse.The aim of the project is to investigate the past and future changes of the 3D BDC and the local wave driving based on the consortia simulations with the Earth-System Model MPI-ESM for the time period 1960-2005 and the climate projections up to the year 2100 (CMIP5). For validation and aspects which cannot be achieved by the CMIP5 simulations alone, the 3D BDC will also be analysed based on simulations with the high-altitude general circulation and chemistry model HAMMONIA (1957-2006), reanalysis (ERA-Interim 1979-2012, MERRA, 1979-2012) and recent satellite data (Aura/MLS 2004-2012). An algorithm will be developed to derive a new data set of daily-mean wind fields from the Aura/MLS data, which will provide a suitable tool for validating the 3D BDC particularly at altitudes where local wind measurements are very sparse (ca. 30-80km). The impact of the 3D BDC on the local long-term changes of O3, H2O, temperature and vorticity in the middle atmosphere, particularly on the ultra-long stationary waves, will be analysed based on linear solutions of the budget equations. The processes controlling the coupling the middle atmospheric 3D BDC, the tropospheric wave activity and wind-driven ocean currents will be examined based on additional model sensitivity simulations with the MPI-ESM including prescribed modulations of surface temperatures, tropospheric and stratospheric eddy fluxes, and middle atmospheric absorber distributions derived from observations. It is also planned to examine the impact of the 3D BDC on the local long-term changes of stratospheric O3 and middle atmospheric H2O based on the chemistry-climate model (CCM) simulations performed and provided by the SPARC (Stratospheric Processes and their Role in Climate) CCM-Validation project.

• DFG Programme: Research Grants