On the structural changes in the Brewer-Dobson circulation after 2000

H. Bönisch, A. Engel, Th. Birner, P. Hoor, D. W. Tarasick, E. A. Ray
2010 Atmospheric Chemistry and Physics Discussions  
In this paper we present evidence that the observed increase in tropical upwelling after the year 2000 may be attributed to a change in the Brewer-Dobson circulation pattern. For this purpose, we use the concept of transit times derived from residual circulation trajectories and different in-situ measurements of ozone and nitrous dioxide. 5 Observations from the Canadian midlatitude ozone profile record, probability density functions of in-situ N 2 O observations and a shift of the N 2 O-O 3
more » ... of the N 2 O-O 3 correlation slopes, taken together, indicate that the increased upwelling in the tropics after the year 2000 appears to have triggered an intensification of tracer transport from the tropics into the extratropics in the lower stratosphere below about 500 K. This finding is corroborated 10 by the fact that transit times along the shallow branch of the residual circulation into the LMS have decreased for the same time period (1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003). On a longer time scale , the transit time of the shallow residual circulation branch show a steady decrease of about −1 month/decade over the last 30 years, while the transit times of the deep branch remain unchanged. This highlights the fact that a change in 15 the upwelling across the tropical tropopause is not a direct indicator for changes of the whole Brewer-Dobson circulation. tion is the main driver of trace gas distributions and thus also moderates the radiative 28400 Abstract ACPD Abstract 15
doi:10.5194/acpd-10-28399-2010 fatcat:qjsbawwllbhp7oyvz7aejj5sje