1. Introduction

1. 20 June measured CO2 Simultaneous use of greenhouse gas concentration measurements and meteorological measurements in a mesoscale model to improve regional scale budget estimates R.Kretschmer, C. Gerbig, R.Ahmadov, D.K.Pillai, S.Körner Max-Planck-Institute for Biogeochemistry, Jena, Germany 1. Introduction 2. Method In forward mode the Weather Research & Forecasting (WRF) atmospheric model with coupled Vegetation Photosynthesis and Respiration (VPRM) biospheric model ([Mahadevan et al., 2008; Ahmadov et al., 2007]) will be used to characterize MH uncertainties by validating model output against MHs derived from meteorological measurements such as radiosoundings, satellite and ceilometer backscatter profiles. Analysis of MHs near measurement stations for CO2 and CH4 will be used to assess the impact on model-data mismatch for tracers. In inverse mode the Stochastic Time Inverted Lagrangian Transport model (STILT, [Lin et al., 2003]) with coupled VPRM model will be run to propagate derived MH uncertainties into regional budget estimates. In addition, WRF-VPRM model output will be nudged to match observed MH and used as input for the STILT model. The impact of these modifications on tracer flux estimates will be examined. Quantifying greenhouse gas budgets on regional scales from atmospheric mixing ratios measurements requires high resolution transport model combined with an inverse modeling or data assimilation approach. However, uncertainties in mixing layer heights (MH) in the transport model (Fig. 1) yields errors in mixing ratio estimates, which for CO2 during summertime amounts to several ppm, much larger than measurement uncertainties [Gerbig et al., 2008]. This presentation gives an outlook of work in progress that focuses on the usage of additional meteorological information together with measurements of CO2 and CH4 to quantify uncertainties of MH within the model (Fig. 2), and eventually utilize this information to improve flux estimates on regional scales. Figure 3: The domain that will be used for the study covers large parts of western and eastern Europe. Horizontal resolution of the model for the domain will be 200x480 grid cells at 10 km. Measurements of CO2 and CH4 tracers will be obtained from different stations throughout the area indicated by white circles which are also part of CarboEurope measurement network. Colors in the figure indicate different terrain heights. Figure 4: Radio sounding measurements near tracer observing sites can be used to derive MH, e.g. using the bulk Richardson number method [Vogelezang and Holtslag, 1996]. Relevant measurement locations are indicated by dots in Fig. 2. Figure 2: Temporally averaged daytime residuals (May-June 2005) between ECMWF based and radio sounding based MHs in [Gerbig et al., 2008]. Dots represent measurement locations. Figure 1: Colors indicate mixing heights as represented in the WRF model at 5am UTC (left) and at 5pm (right) on 2003-07-02. CO2 simulations for the domain shown were used asses subgrid variability of coarser models in context of an ESA A-Scope feasibility study. 3. Approach b)‏ a)‏ • forward modelling using WRF-VPRM (Fig. 6) for CO2 and CH4 • validation of WRF mixing heights against observations • reshuffling of tracers between PBL and FT to match observed mixing heights • Hypothesis: modifications lead to better agreement between simulated and measured tracers • nudging of variables in WRF to match observed mixing heights • inverse modelling with STILT to derive improved estimates of regional scale CO2 and CH4 fluxes and their uncertainties • comparison with independent flux estimates [CERES Experiment, provided by Pierre Durand, Lab. d’Aérologie] c)‏ Figure 5: Rremote sensing systems like ceilometers (part b) and satellites, e.g. NASA's IceSAT (part c) can be utilized to derive mixing heights from backscatter profiles (part a). [Eresmaa et al., 2006] compare different methods to infer mixing heights from these backscatter profiles. However under certain circumstances if the measurement instrument has no clear sight through the atmosphere, it's not possible to rely on these systems. In such cases other methods like radio sounding can be used (Fig. 4). The Deutsche Wetterdienst maintains a ceilometer network of ca. 100 sites in Europe which may be used for this study. Figure 6: Different parts of the modelling framework which will also be used in the current study. The VPRM model is a simple diagnostic model to account for CO2 emission and uptake of the biosphere. The WRF model driven by ECMWF analysis for initial and boundary conditions is run in forward mode to simulate CO2 distribution but also provides meteorological fields for the STILT model which is used in inverse mode to calculate tracer footprints. [Fig. used with permission of D.K.Pillai] [icesat.gsfc.nasa.gov] References Gerbig, C., S.Körner, and J.C.Lin, Vertical mixing in atmospheric tracer transport models: error characterization and propagation, Journal of Atmospheric Chemistry and Physics, 8, 591-602, 2008 Lin, J.C., C. Gerbig, S.C. Wofsy, A.E. Andrews, B.C. Daube, K.J. Davis, and C.A. Grainger, A near-field tool for simulating the upstream influence of atmospheric observations: The Stochastic Time-Inverted Lagrangian Transport (STILT) model, Journal of Geophysical Research-Atmospheres, 108 (D16), 2003 Mahadevan, P., S. Wofsy, D. M. Matross, X. Xiao, A. Dunn, J. C. Lin, C. Gerbig, J. W. Munger, V. Y. Chow, and E. Gottlieb, A Satellite-Based Biosphere Parameterization for Net Ecosystem CO2 Exchange: Vegetation Photosynthesis and Respiration Model (VPRM), Global Biogeochem. Cycles, doi:10.1029/2006GB002735, in press, 2008 Vogelezang, D.H.P., and Holtslag, A.A.M., Evaluation and model impacts of alternative boundary-layer height formulations, Bound.-Lay. Meteorol., 81, 245-269, 1996 Ahmadov, R., Gerbig, C., Kretschmer, R., Koerner, S., Neininger, B., Dolman, A., Sarrat, C., Mesoscale covariance of transport and CO2 fluxes: evidence from observations and simulations using the WRF-VPRM coupled atmosphere-biosphere model, Journal of Geophysical Research, 112, D22107,2007 Eresmaa, N., Karppingen, A., Joffre, S.M., Räsänen, J., and Talvitie, H., Mixing height determination by ceilometer, Atmos. Chem. Phys., 6, 1485-1493, 2006