HR: 0800h
AN: A51D-0727    [Abstracts]
TI: Using Beryllium-7 to Assess Cross-Tropopause Transport in Global Models
AU: * Liu, H
EM: hyl@nianet.org
AF: National Institute of Aerospace, 100 Exploration Way, Hampton, VA 23666, United States
AU: Considine, D
EM: david.b.considine@nasa.gov
AF: NASA Langley Research Center, Mail Stop 401B, Hampton, VA 23681, United States
AB: The stratosphere-troposphere exchange (STE) flux of ozone plays an important role in the tropospheric ozone budget. Representing this flux in global models is critical to quantitatively understanding the tropospheric ozone budget. Beryllium-7 (⁷Be), produced cosmogenically in the stratosphere and upper troposphere, has long been used to determine the stratospheric origin of tropospheric air. Here we use the Global Modeling Initiative (GMI) modeling framework to assess the utility of ⁷Be for evaluating STE in global models. The GMI chemistry and transport model (CTM) was used to simulate atmospheric ⁷Be distributions using four different meteorological data sets, featuring significantly different STE characteristics. The data sets were generated by the Goddard Space Flight Center Global Modeling and Assimilation Office (GMAO) GEOS-STRAT assimilation, the Goddard Institute for Space Studies GISS II' general circulation model (GISS II' GCM), the GMAO finite-volume GCM (fvGCM), and the GMAO GEOS-4 data assimilation system (GEOS-4 DAS). The simulations were compared with observed ⁷Be concentrations at the surface and in the upper troposphere / lower stratosphere (UT/LS), as well as surface deposition fluxes. The UT/LS observations are climatologies constructed from ~25 years of aircraft and balloon data from the US Environmental Measurements Laboratory RANDAB database. All simulations capture the observations at 12-16km, but underestimate concentrations at higher altitudes, especially at Northern Hemisphere middle/high latitudes with GEOS-STRAT. Comparison of the surface fraction of air of stratospheric origin estimated from the ⁷Be simulations with observationally-derived estimates indicates excessive cross-tropopause transport at middle latitudes in simulations using GEOS-STRAT and at high latitudes using GISS II' meteorological data. These simulations also overestimate ⁷Be deposition flux at middle latitudes (GEOS-STRAT) and at high latitudes (GISS II'). We conclude that ⁷Be concentrations and deposition fluxes may be used routinely to assess cross- tropopause transport in global models. The relationship between the STE fluxes of ⁷Be and ozone will also be discussed.
UR: http://research.nianet.org/~hyl
DE: 0368 Troposphere: constituent transport and chemistry
DE: 3315 Data assimilation
DE: 3319 General circulation (1223)
DE: 3337 Global climate models (1626, 4928)
DE: 3362 Stratosphere/troposphere interactions
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting