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          Institute: MPI für Meteorologie     Collection: Atmosphere in the Earth System     Display Documents



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ID: 20270.0, MPI für Meteorologie / Atmosphere in the Earth System
Methyl iodide: Atmospheric budget and use as a tracer of marine convection in global models
Authors:Bell, N.; Hsu, L.; Jacob, D. J.; Schultz, Martin; Blake, D. R.; Butler, J. H.; King, D. B.; Lobert, J. M.; Maier-Reimer, Ernst
Language:English
Date of Publication (YYYY-MM-DD):2002-09
Title of Journal:Journal of Geophysical Research-Atmospheres
Journal Abbrev.:J. Geophys. Res.-Atmos.
Volume:107
Issue / Number:D17
Sequence Number of Article:4340
Review Status:Peer-review
Audience:Not Specified
Abstract / Description:We simulate the oceanic and atmospheric distribution of methyl iodide (CH3I) with a global 3-D model driven by assimilated meteorological observations from the Goddard Earth Observing System of the NASA Data Assimilation Office and coupled to an oceanic mixed layer model. A global compilation of atmospheric and oceanic observations is used to constrain and evaluate the simulation. Seawater CH3I( aq) in the model is produced photochemically from dissolved organic carbon, and is removed by reaction with Cl- and emission to the atmosphere. The net oceanic emission to the atmosphere is 214 Gg yr(-1). Small terrestrial emissions from rice paddies, wetlands, and biomass burning are also included in the model. The model captures 40% of the variance in the observed seawater CH3I( aq) concentrations. Simulated concentrations at midlatitudes in summer are too high, perhaps because of a missing biological sink of CH3I( aq). We define a marine convection index (MCI) as the ratio of upper tropospheric (8-12 km) to lower tropospheric (0-2.5 km) CH3I concentrations averaged over coherent oceanic regions. The MCI in the observations ranges from 0.11 over strongly subsiding regions (southeastern subtropical Pacific) to 0.40 over strongly upwelling regions (western equatorial Pacific). The model reproduces the observed MCI with no significant global bias (offset of only +11%) but accounts for only 15% of its spatial and seasonal variance. The MCI can be used to test marine convection in global models, complementing the use of radon-222 as a test of continental convection.
Free Keywords:methyl iodide; marine convection; atmospheric tracer; global budget of methyl iodide
External Publication Status:published
Document Type:Article
Affiliations:MPI für Meteorologie/Biogeochemical System/Atmospheric Chemistry
MPI für Meteorologie/Biogeochemical System/Ocean Biogeochemistry
External Affiliations:NASA, Goddard Inst Space Studies, 2880 Broadway, New York, NY; 10025 USA; Harvard Univ, Div Engn & Appl Sci, Cambridge, MA 02138 USA; Univ Calif Irvine, Dept Chem, Irvine, CA 92697 USA; NOAA, Climate Monitoring & Diagnost Lab, Boulder, CO 80303 USA; Adv Pollut Instrumentat, San Diego, CA 92121 USA
Identifiers:ISI:000180427200020
ISSN:0747-7309
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