Abstract
Abstract. Bromoform (CHBr3) is a short-lived species with an important but poorly quantified ocean source. It can be transported to the Tropical Tropopause Layer (TTL), in part by rapid, deep convective lifting, from where it can influence the global stratospheric ozone budget. In a modelling study, we investigate the importance of the regional distribution of the emissions and of model resolution for the transport of bromoform to the TTL. We use two idealized CHBr3 emission fields (one coastal, one uniformly distributed across the oceans) implemented in high- and coarse-resolution (HR and CR) versions of the same global model and focus on February as the period of peak convection in the West Pacific. Using outgoing long-wave radiation and precipitation as metrics, the HR version of the model is found to represent convection better. In the more realistic HR model version, the coastal emission scenario leads to 15–20 % more CHBr3 in the global TTL, and up to three times more CHBr3 in the TTL over the Maritime Continent, than when uniform emissions of the same tropical magnitude are employed. Using the uniform emission scenario in both model versions, the distribution of CHBr3 at 15.7 km (approximately the level of zero net radiative heating) is qualitatively consistent with the differing geographic distributions of convection. However, averaged over the whole tropics, the amount of CHBr3 in the TTL in the two model versions is similar. Using the coastal scenario, in which emissions are particularly high in the Maritime Continent because of its long coastlines, the mixing ratio of CHBr3 in the TTL is enhanced over the Maritime Continent in both model versions. The enhancement is larger, and the peak in CHBr3 mixing ratio occurs at a higher altitude, in the HR model version. Our regional-scale results indicate that using aircraft measurements and coarse global models to infer CHBr3 emissions will be very difficult, particularly if (as is possible) emissions are distributed heterogeneously and in regions of strong convective activity. In contrast, the global-scale agreement between our CR and HR calculations suggests model resolution is less vital for studies focused on the transport of bromine into the global stratosphere.
Highlights
Very short-lived halogenated substances (VSLS) are thought to make a significant but uncertain contribution to bromine in the stratosphere (5 ± 3 ppt [i.e. ∼ 10–40 %] Br, Carpenter et al, 2014)
Mean maps of Tropical Rainfall Measuring Mission (TRMM) observations of precipitation and from the Atmospheric Infrared Sounder (AIRS) observations of out-going long-wave radiation (OLR) are shown in Fig. 2 for February 2005 chosen as a representative February for which an HR run was available
The most obvious differences compared to the observations are with the CR integration and are (a) the misplaced location of the convection in the CR run in the West Pacific with the maximum being incorrectly restricted to a narrow band associated with the Inter-Tropical Convergence Zone (ITCZ); and (b) the overly strong continental convection in the CR model over S
Summary
Very short-lived halogenated substances (VSLS) are thought to make a significant but uncertain contribution to bromine in the stratosphere (5 ± 3 ppt [i.e. ∼ 10–40 %] Br, Carpenter et al, 2014). Very short-lived halogenated substances (VSLS) are thought to make a significant but uncertain contribution to bromine in the stratosphere ∼ 10–40 %] Br, Carpenter et al, 2014) Much of this uncertainty is linked to the contribution of bromoform (CHBr3), which has both the shortest lifetime and the largest emissions of the commonly observed brominated VSLS. The short lifetime of CHBr3 (∼ 15 days in the tropical boundary layer; Carpenter et al, 2014) means that measurements in a particular location can only be used to constrain emissions over relatively small areas of the globe (e.g., Ashfold et al, 2014), and inventories are uncertain (Quack and Wallace, 2003). Russo et al.: On the emissions and transport of bromoform tion and relative strength of the dominant macro- and microalgal sources (Ordóñez et al, 2012; Stemmler et al, 2015)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
