Regional modelling of tracer transport by tropical convection – Part 2: Sensitivity to model resolutions

Arteta, Joaquim; Marécal, Virginie; Rivière, Emmanuel

doi:10.5194/acp-9-7101-2009

Cited by 12 publications

(9 citation statements)

References 31 publications

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“…In order to simulate halogen chemistry in volcanic plumes, we have added 16 halogen species and 54 reactions to the chemical scheme including photolysis and gas-phase and heterogeneous reactions. The gas-phase constant rates and photolysis cross sections are from the Jet Propulsion Laboratory (Sander et al, 2006) and the International Union of Pure and Applied Chemistry (Atkinson et al, 2007). The heterogeneous reactions include the hydrolysis of BrONO 2 and the reaction of HOBr + X − (aq) + H + (aq) , where X = Br or Cl on sulfate aerosol.…”

Section: Model Chemistrymentioning

confidence: 99%

Modeling the reactive halogen plume from Ambrym and its impact on the troposphere with the CCATT-BRAMS mesoscale model

Jourdain¹,

Roberts²,

Pirre³

et al. 2016

Atmos. Chem. Phys.

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Abstract. Ambrym Volcano (Vanuatu, southwest Pacific) is one of the largest sources of continuous volcanic emissions worldwide. As well as releasing SO2 that is oxidized to sulfate, volcanic plumes in the troposphere are shown to undergo reactive halogen chemistry whose atmospheric impacts have been little explored to date. Here, we investigate with the regional-scale model CCATT-BRAMS (Coupled Chemistry Aerosol-Tracer Transport model, Brazilian developments on the Regional Atmospheric Modeling System, version 4.3) the chemical processing in the Ambrym plume and the impact of this volcano on the atmospheric chemistry on both local and regional scales. We focus on an episode of extreme passive degassing that occurred in early 2005 and for which airborne DOAS (differential optical absorption spectroscopy) measurements of SO2 and BrO columns in the near-downwind plume between 15 and 40 km from the vents have been reported. The model was developed to include reactive halogen chemistry and a volcanic emission source specific to this extreme degassing event. In order to test our understanding of the volcanic plume chemistry, we performed very high-resolution (500 m  ×  500 m) simulations using the model nesting grid capability and compared each DOAS measurement to its temporally and spatially interpolated model counterpart “point-by-point”. Simulated SO2 columns show very good quantitative agreement with the DOAS observations, suggesting that the plume direction as well as its dilution in the near-downwind plume are well captured. The model also reproduces the salient features of volcanic chemistry as reported in previous work, such as HOx and ozone depletion in the core of the plume. When a high-temperature chemistry initialization is included, the model is able to capture the observed BrO ∕ SO2 trend with distance from the vent. The main discrepancy between observations and model is the bias between the magnitudes of observed and simulated BrO columns that ranges from 60 % (relative to the observations) for the transect at 15 km to 14 % for the one at 40 km from the vents. We identify total in-plume depletion of ozone as a limiting factor for the partitioning of reactive bromine into BrO in the near-source (concentrated) plume under these conditions of extreme emissions and low background ozone concentrations (15 ppbv). Impacts of Ambrym in the southwest Pacific region were also analyzed. As the plume disperses regionally, reactive halogen chemistry continues on sulfate aerosols produced by SO2 oxidation and promotes BrCl formation. Ozone depletion is weaker than on the local scale but still between 10 and 40 % in an extensive region a few thousands of kilometers from Ambrym. The model also predicts the transport of bromine to the upper troposphere and stratosphere associated with convection events. In the upper troposphere, HBr is re-formed from Br and HO2. Comparison of SO2 regional-scale model fields with OMI (Ozone Monitoring Instrument) satellite SO2 fields confirms that the Ambrym SO2 emissions estimate based on the DOAS observations used here is realistic. The model confirms the potential of volcanic emissions to influence the oxidizing power of the atmosphere: methane lifetime (calculated with respect to OH and Cl) is increased overall in the model due to the volcanic emissions. When considering reactive halogen chemistry, which depletes HOx and ozone, the lengthening of methane lifetime with respect to OH is increased by a factor of 2.6 compared to a simulation including only volcanic SO2 emissions. Cl radicals produced in the plume counteract 41 % of the methane lifetime lengthening due to OH depletion. Including the reactive halogen chemistry in our simulation also increases the lifetime of SO2 in the plume with respect to oxidation by OH by 36 % compared to a simulation including only volcanic SO2 emissions. This study confirms the strong influence of Ambrym emissions during the extreme degassing event of early 2005 on the composition of the atmosphere on both local and regional scales. It also stresses the importance of considering reactive halogen chemistry when assessing the impact of volcanic emissions on climate.

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Section: Model Chemistrymentioning

confidence: 99%

Modeling the reactive halogen plume from Ambrym and its impact on the troposphere with the CCATT-BRAMS mesoscale model

Jourdain¹,

Roberts²,

Pirre³

et al. 2016

Atmos. Chem. Phys.

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“…265-165 hPa) altitude matched the measurements best. Arteta et al (2009a) used an online regional model, CATT-BRAMS, to investigate the sensitivity of tropical tracer transport to the convective parameterisation, and Arteta et al (2009b) evaluated the effect of resolution on the simulated tracer distributions, showing that the higher resolution versions of their model produce more convective transport which reaches higher altitudes. Various studies (Wild and Prather, 2006;Rind et al, 2007;Deng et al, 2004) have shown that increases in horizontal and vertical resolution improve the skill of the model in predicting tracer transport by convection.…”

Section: Introductionmentioning

confidence: 99%

Tropical deep convection and its impact on composition in global and mesoscale models – Part 2: Tracer transport

Hoyle¹,

Marécal²,

Russo³

et al. 2010

Preprint

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The tropical transport processes of 14 different models or model versions were compared, within the framework of the SCOUT-O3 (Stratospheric-Climate Links with Emphasis on the Upper Troposphere and Lower Stratosphere) project. The tested models range from the regional to the global scale, and include numerical weather prediction (NWP), chemistry transport, and climate chemistry models. Idealised tracers were used in order to prevent the model's chemistry schemes from influencing the results substantially, so that the effects of modelled transport could be isolated. We find large differences in the vertical transport of very short lived tracers (with a lifetime of 6 hours) within the tropical troposphere. Peak convective outflow altitudes range from around 300 hPa to almost 100 hPa among the different models, and the upper tropospheric tracer mixing ratios differ by up to an order of magnitude. The timing of convective events is found to differ between the models, even among those which source their forcing data from the same NWP model (ECMWF). The differences are less pronounced for longer lived tracers, however they could have implications for the modelling of the halogen burden of the lowermost stratosphere through species such as bromoform, or for the transport of short lived hydrocarbons into the lowermost stratosphere. The modelled tracer profiles are found to be strongly influenced by the convective transport parameterisations, and boundary layer mixing parameterisations of the models. The location of rapid transport into the upper troposphere is similar among the models, and is mostly concentrated over the western Pacific, the Maritime Continent and the Indian Ocean. In contrast, none of the models indicates significant enhancement in upward transport over western Africa. The mean mixing ratios of an idealised CO like tracer in the upper tropical troposphere are found to be sensitive to the surface CO mixing ratios in the regions with the most active convection, revealing the importance of correctly modelling both the location of convective transport and the geographical pollutant emission patterns

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“…265-165 hPa) matched the measurements best. Arteta et al (2009a) used an online regional model, CATT-BRAMS, to investigate the sensitivity of tropical tracer transport to the convective parameterisation, and Arteta et al (2009b) evaluated the effect of resolution on the simulated tracer distributions, showing that the higher resolution versions of their model exhibited more efficient convective transport, reaching higher altitudes. Various studies (Deng et al, 2004;Wild and Prather, 2006;Rind et al, 2007) have shown that increased horizontal and vertical resolution improves the skill of the model in predicting tracer transport by convection.…”

Section: Introductionmentioning

confidence: 99%

Representation of tropical deep convection in atmospheric models – Part 2: Tracer transport

et al. 2011

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Abstract. The tropical transport processes of 14 different models or model versions were compared, within the framework of the SCOUT-O3 (Stratospheric-Climate Links with Emphasis on the Upper Troposphere and Lower Stratosphere) project. The tested models range from the regional to the global scale, and include numerical weather prediction (NWP), chemical transport, and chemistry-climate models. Idealised tracers were used in order to prevent the model's chemistry schemes from influencing the results substantially, so that the effects of modelled transport could be isolated. We find large differences in the vertical transport of very short-lived tracers (with a lifetime of 6 h) within the tropical troposphere. Peak convective outflow altitudes rangeCorrespondence to: C. R. Hoyle (christopher.hoyle@env.ethz.ch) from around 300 hPa to almost 100 hPa among the different models, and the upper tropospheric tracer mixing ratios differ by up to an order of magnitude. The timing of convective events is found to be different between the models, even among those which source their forcing data from the same NWP model (ECMWF). The differences are less pronounced for longer lived tracers, however they could have implications for modelling the halogen burden of the lowermost stratosphere through transport of species such as bromoform, or short-lived hydrocarbons into the lowermost stratosphere. The modelled tracer profiles are strongly influenced by the convective transport parameterisations, and different boundary layer mixing parameterisations also have a large impact on the modelled tracer profiles. Preferential locations for rapid transport from the surface into the upper troposphere are similar in all models, and are mostly concentrated over the western Pacific, the Maritime Continent and the Indian Published by Copernicus Publications on behalf of the European Geosciences Union. Ocean. In contrast, models do not indicate that upward transport is highest over western Africa.

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Regional modelling of tracer transport by tropical convection – Part 2: Sensitivity to model resolutions

Cited by 12 publications

References 31 publications

Modeling the reactive halogen plume from Ambrym and its impact on the troposphere with the CCATT-BRAMS mesoscale model

Modeling the reactive halogen plume from Ambrym and its impact on the troposphere with the CCATT-BRAMS mesoscale model

Tropical deep convection and its impact on composition in global and mesoscale models – Part 2: Tracer transport

Representation of tropical deep convection in atmospheric models – Part 2: Tracer transport

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