Abstract
Abstract. We evaluate the sensitivity of Bry entering the stratosphere with a simplified model that allows calculations over a wide parameter range for parameters that are currently poorly quantified. The model examines the transport process uncertainties in the source concentrations and lifetimes, in the convective parameterization and in the inorganic bromine washout process due to dehydration. Source concentrations at the surface and lifetimes were found to have a slight effect on the resultant Bry (1 ppt), however this was highly dependent upon, with increasing significance, the BL component of convectively delivered air. Efficiency of convective delivery of boundary layer (BL) air to the tropical tropopause layer (TTL) along with washout at the CPT were found to substantially affect Bry at 400 K – altering the delivered Bry by 3.3 ppt and 2.9 ppt, respectively. We find that the results critically depend on free tropospheric bromine source gas concentrations due to dilution of convective updrafts, and the processes that control free tropospheric bromine source gas concentrations require further attention.
Highlights
Bromine was first proposed to play a key role in ozone destruction by Wofsy et al (1975), and subsequently has been shown to be very efficient at both mid- and polar latitudes in the lower stratosphere (Dvortsov et al, 1999; Lee et al, 2002)
Note that CH3Br is usually treated as a long lived species i.e. possible degradation in the tropical tropopause layer (TTL) is not usually accounted for, there is some loss of CH3Br to inorganic bromine after only 15 days, the time required for ∼80% of ascending trajectories to reach the cold point from 365 K and ∼0.5 ppt CH3Br to decay to product gases (PGs)
We have been able to explore the sensitivity of Bry arriving at 400 K due to emission sources, convection and washout
Summary
Bromine was first proposed to play a key role in ozone destruction by Wofsy et al (1975), and subsequently has been shown to be very efficient at both mid- and polar latitudes in the lower stratosphere (Dvortsov et al, 1999; Lee et al, 2002). OH concentrations in the TTL are uncertain but likely lower than in the free troposphere, and VSLS lifetimes may be longer. The modelling of deep convective events is challenging: capturing the timing, location and the proportion of BL air detraining into the TTL remains uncertain. We use a lagrangian model with trajectories based on data from the European Centre for Medium-range Weather Forecasts (ECMWF) ERA-Interim data (Simmons et al, 2007) as representation of the global circulation in combination with a simplified representation of the processes affecting VSLS concentrations during transport from troposphere to stratosphere. 3 we discuss the sensitivities of the resultant stratospheric Bry budget to the conceptualized chemical, microphysical and convective processes that control the stratospheric bromine budget
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