The meteorological environment of the tropospheric ozone maximum over the tropical South Atlantic Ocean

Abstract

Atmospheric flow patterns are examined over the South Atlantic Ocean where a maximum of tropospheric ozone has been observed just west of southern Africa. We investigate the flow climatology during October and perform a case study for 6 days during October 1989. Analyses from the European Center for Medium‐Range Weather Forecasting are employed, and a high‐resolution global spectral model is used to prepare forecasts during the period. Horizontal and vertical motions are examined and used to prepare three‐dimensional backward trajectories from the region of greatest ozone. An initially zonally symmetric distribution of ozone is treated as a passive tracer and advected by three‐dimensional flows forecast by the global model. Results from the passive tracer simulation indicate that three‐dimensional advection alone can produce a maximum of tropospheric ozone in the observed location. In addition, the trajectories suggest that by‐products of biomass burning could be transported to the area of maximum ozone. Low‐level flow from commonly observed regions of burning in Africa streams westward to the area of interest. Over Brazil, if the burning by‐products are carried into the upper troposphere by convective process, they then could be transported eastward to the ozone feature in approximately 5 days. There is considerable subsidence over the tropical southern Atlantic, such that stratospheric influences also are a factor in producing the ozone maximum. Both planetary‐scale and transient synoptic‐scale circulation features play major roles in the various transport processes that influence the region. In summary, the observed tropospheric ozone maximum appears to be caused by a complex set of horizontal and vertical advections, transport from regions of biomass burning, and stratospheric influences.

Tracing biomass burning plumes from the Southern Hemisphere during the AMMA 2006 wet season experiment

“…2). The coincidence of biomass burning and cloud convection was proposed as a key mechanism for the export of biomass burning emissions far away from the source regions (Krishnamurti et al, 1993;Chatfield et al, 1996;Pickering et al, 1996;Folkins et al, 1997;Jenkins et al, 1997;Trentmann et al, 2006;Sauvage et al, 2007a;Sauvage et al, 2007b) with potential intrusions into the upper troposphere and stratosphere (Fromm and Servranckx, 2003;Jost et al, 2004). Other mechanisms have been proposed for the vertical transport of biomass burning emissions: convergence between the baroclinic low-level circulations associated with the AEJ-S and the equatorward branch of the Hadley cell (Sauvage et al, 2007c) and the vertical turbulent mixing favored by the intertropical interoceanic front (Chatfield et al, 1996;Bachmeier and Fuelberg, 1996;Delmas et al, 1999).…”

Tropospheric ozone at tropical and middle latitudes derived from TOMS/MLS residual: Comparison with a global model

“…The seasonal contrast is greatest in the Atlantic with maximum values during austral spring over the southern tropical Atlantic. The high values of TCO in this region during austral spring have been attributed to biomass burning, lightning, and dynamics as part of TRACE-A [Krishnamurti et al, 1993[Krishnamurti et al, , 1996Jacob et al, 1996;Pickering et al, 1996;Thompson et al, 1996]. Outside the tropics, the zonal contrast decreases but seasonal contrast intensifies over all longitudes.…”

Influence of stratosphere‐troposphere exchange on tropospheric ozone over the tropical Indian Ocean during the winter monsoon

“…The stratosphere is a third source region through stratosphere-troposphere exchange (STE) by, for example, tropopause folds [Shapiro, 1980]. Apart from the studies from Pacific Exploratory Mission-West (PEM-West) and Measurements of Ozone by Airbus In-Service Aircraft (MOZAIC) [Newell et al, 1996[Newell et al, , 1999Browell et al, 1996;Wu et al, 1997] and PEM-Tropics [Fenn et al, 1999], other studies also indicated stratospheric influences in the tropical troposphere [Krishnamurti et al, 1993;Kley et al, 1996;Suhre et al, 1997;Cammas et al, 1998;Taupin et al, 1999]. Shear-induced differential advection can cause tracer surfaces to stretch which leads to quasi-horizontal laminae-like tracer structures [see Appenzeller and Holton, 1997, Figure 1; Ambaum, 1997].…”