Publications (12)0 Total impact
-
Dataset: gmd-3-445-2010-supplement
-
Article: A comparison of different inverse carbon flux estimation approaches for application on a regional domain
[show abstract] [hide abstract]
ABSTRACT: We have implemented six different inverse carbon flux estimation methods in a regional carbon dioxide (CO2) flux modeling system for The Netherlands. The system consists of the Regional Atmospheric Mesoscale Modeling System (RAMS) coupled to a simple carbon flux scheme which is run in a coupled fashion on relatively high resolution (10 km). Using an Ensemble Kalman filter approach we try to estimate spatiotemporal carbon exchange patterns from atmospheric CO2 mole fractions over The Netherlands for a two week period in spring 2008. The focus of this work is the different strategies that can be employed to turn first-guess fluxes into optimal ones, which is known as a fundamental design choice that can affect the outcome of an inversion significantly. Different state-of-the-art approaches with respect to the estimation of net ecosystem exchange (NEE) are compared quantitatively: (1) where NEE is scaled by one linear multiplication factor per land-use type, (2) where the same is done for photosynthesis (GPP) and respiration (R) separately with varying assumptions for the correlation structure, (3) where we solve for those same multiplication factors but now for each grid box, and (4) where we optimize physical parameters of the underlying biosphere model for each land-use type. The pattern to be retrieved in this pseudo-data experiment is different in nearly all aspects from the first-guess fluxes, including the structure of the underlying flux model, reflecting the difference between the modeled fluxes and the fluxes in the real world. This makes our study a stringent test of the performance of these methods, which are currently widely used in carbon cycle inverse studies. Our results show that all methods struggle to retrieve the spatiotemporal NEE distribution, and none of them succeeds in finding accurate domain averaged NEE with correct spatial and temporal behavior. The main cause is the difference between the structures of the first-guess and true CO2 flux models used. Most methods display overconfidence in their estimate as a result. A commonly used daytime-only sampling scheme in the transport model leads to compensating biases in separate GPP and R scaling factors that are readily visible in the nighttime mixing ratio predictions of these systems. Overall, we recommend that the estimate of NEE scaling factors should not be used in this regional setup, while estimating bias factors for GPP and R for every grid box works relatively well. The biosphere parameter inversion is best at simultaneously producing space and time patterns of fluxes and CO2 mixing ratios, but non-linearity may significantly reduce the information content in the inversion if true parameter values are far from the prior estimate. Our results suggest that a carefully designed biosphere model parameter inversion or a pixel inversion of the respiration and GPP multiplication factors are the best tools to optimize spatiotemporal patterns of NEE.Atmospheric Chemistry and Physics Discussions. 01/2011; -
Article: The global chemistry transport model TM5: description and evaluation of the tropospheric chemistry version 3.0
[show abstract] [hide abstract]
ABSTRACT: We present a comprehensive description and benchmark evaluation of the tropospheric chemistry version of the global chemistry transport model TM5 (Tracer Model 5, version TM5-chem-v3.0). A full description is given concerning the photochemical mechanism, the interaction with aerosol, the treatment of the stratosphere, the wet and dry deposition parameterizations, and the applied emissions. We evaluate the model against a suite of ground-based, satellite, and aircraft measurements of components critical for understanding global photochemistry for the year 2006. The model exhibits a realistic oxidative capacity at a global scale. The methane lifetime is ~8.9 years with an associated lifetime of methyl chloroform of 5.86 years, which is similar to that derived using an optimized hydroxyl radical field. The seasonal cycle in observed carbon monoxide (CO) is well simulated at different regions across the globe. In the Northern Hemisphere CO concentrations are underestimated by about 20 ppbv in spring and 10 ppbv in summer, which is related to missing chemistry and underestimated emissions from higher hydrocarbons, as well as to uncertainties in the seasonal variation of CO emissions. The model also captures the spatial and seasonal variation in formaldehyde tropospheric columns as observed by SCIAMACHY. Positive model biases over the Amazon and eastern United States point to uncertainties in the isoprene emissions as well as its chemical breakdown. Simulated tropospheric nitrogen dioxide columns correspond well to observations from the Ozone Monitoring Instrument in terms of its seasonal and spatial variability (with a global spatial correlation coefficient of 0.89), but TM5 fields are lower by 25–40%. This is consistent with earlier studies pointing to a high bias of 0–30% in the OMI retrievals, but uncertainties in the emission inventories have probably also contributed to the discrepancy. TM5 tropospheric nitrogen dioxide profiles are in good agreement (within ~0.1 ppbv) with in situ aircraft observations from the INTEX-B campaign over (the Gulf of) Mexico. The model reproduces the spatial and seasonal variation in background surface ozone concentrations and tropospheric ozone profiles from the World Ozone and Ultraviolet Radiation Data Centre to within 10 ppbv, but at several tropical stations the model tends to underestimate ozone in the free troposphere. The presented model results benchmark the TM5 tropospheric chemistry version, which is currently in use in several international cooperation activities, and upon which future model improvements will take place.Geoscientific Model Development Discussions. 01/2010; -
Article: The global chemistry transport model TM5: description and evaluation of the tropospheric chemistry version 3.0
[show abstract] [hide abstract]
ABSTRACT: We present a comprehensive description and benchmark evaluation of the tropospheric chemistry version of the global chemistry transport model TM5 (Tracer Model 5, version TM5-chem-v3.0). A full description is given concerning the photochemical mechanism, the interaction with aerosol, the treatment of the stratosphere, the wet and dry deposition parameterizations, and the applied emissions. We evaluate the model against a suite of ground-based, satellite, and aircraft measurements of components critical for understanding global photochemistry for the year 2006. The model exhibits a realistic oxidative capacity at a global scale. The methane lifetime is ~8.9 years with an associated lifetime of methyl chloroform of 5.86 years, which is similar to that derived using an optimized hydroxyl radical field. The seasonal cycle in observed carbon monoxide (CO) is well simulated at different regions across the globe. In the Northern Hemisphere CO concentrations are underestimated by about 20 ppbv in spring and 10 ppbv in summer, which is related to missing chemistry and underestimated emissions from higher hydrocarbons, as well as to uncertainties in the seasonal variation of CO emissions. The model also captures the spatial and seasonal variation in formaldehyde tropospheric columns as observed by SCIAMACHY. Positive model biases over the Amazon and eastern United States point to uncertainties in the isoprene emissions as well as its chemical breakdown. Simulated tropospheric nitrogen dioxide columns correspond well to observations from the Ozone Monitoring Instrument in terms of its seasonal and spatial variability (with a global spatial correlation coefficient of 0.89), but TM5 fields are lower by 25–40%. This is consistent with earlier studies pointing to a high bias of 0–30% in the OMI retrievals, but uncertainties in the emission inventories have probably also contributed to the discrepancy. TM5 tropospheric nitrogen dioxide profiles are in good agreement (within ~0.1 ppbv) with in situ aircraft observations from the INTEX-B campaign over (the Gulf of) Mexico. The model reproduces the spatial and seasonal variation in background surface ozone concentrations and tropospheric ozone profiles from the World Ozone and Ultraviolet Radiation Data Centre to within 10 ppbv, but at several tropical stations the model tends to underestimate ozone in the free troposphere. The presented model results benchmark the TM5 tropospheric chemistry version, which is currently in use in several international cooperation activities, and upon which future model improvements will take place.Geoscientific Model Development. 01/2010; -
Article: Regional scale modelling of meteorology and CO<sub>2</sub> for the Cabauw tall tower, The Netherlands
[show abstract] [hide abstract]
ABSTRACT: We simulated meteorology and atmospheric CO<sub>2</sub> transport over the Netherlands with the mesoscale model RAMS-Leaf3 coupled to the biospheric CO<sub>2</sub> flux model 5PM. The results were compared with meteorological and CO<sub>2</sub> observations, with particular attention to the tall tower of Cabauw. An analysis of the coupled exchange of energy, moisture and CO<sub>2</sub> showed that the surface fluxes in the domain strongly influenced the atmospheric properties. The majority of the variability in the afternoon CO<sub>2</sub> mixing ratio in the middle of the domain was determined by biospheric and fossil fuel CO<sub>2</sub> fluxes in the limited area domain (640×640 km). Variation of the surface CO<sub>2</sub> fluxes, reflecting the uncertainty of the parameters in the CO<sub>2</sub> flux model 5PM, resulted in a range of simulated atmospheric CO<sub>2</sub> mixing ratios of about 12 ppm in the well-mixed boundary layer. Additionally, we identified an uncertainty in the surface energy fluxes. The spread caused by this uncertainty in the simulated atmospheric vertical mixing caused a CO<sub>2</sub> transport error of 1.7 ppm. This is an important source of uncertainty and should be accounted for to avoid biased estimates of the CO<sub>2</sub> mixing ratio, but does not overwhelm the signal in the CO<sub>2</sub> mixing ratio due to the spread in CO<sub>2</sub> surface fluxes.Biogeosciences Discussions. 01/2009; -
Article: Modelling representation errors of atmospheric CO<sub>2</sub> concentrations at a regional scale
[show abstract] [hide abstract]
ABSTRACT: Inverse modelling of carbon sources and sinks requires an accurate estimate of the quality of the observations to obtain a realistic estimate of the inferred fluxes and their uncertainties. Representation errors, defined here as the mismatch between point observations and grid cell averages, may add substantial uncertainty to the interpretation of atmospheric CO<sub>2</sub> concentration data. We used a high resolution (2 km) mesoscale model (RAMS) to simulate the variations in the CO<sub>2</sub> concentration to estimate the representation errors for grid sizes of 10–100 km. Meteorology is the main driver of representation errors in our study causing spatial and temporal variations in the error estimate. Within the nocturnal boundary layer the representation errors are relatively large and mainly determined by unresolved topography at lower model resolutions. During the day, surface CO<sub>2</sub> flux variability and mesoscale circulations were found to be the main sources of representation errors. Careful up-scaling of point observations can reduce the importance of the representation error substantially. The remaining representation error is in the order of 0.5–1.5 ppm at 20–100 km resolution.Atmospheric Chemistry and Physics Discussions. 01/2008; -
Article: Modelling representation errors of atmospheric CO<sub>2</sub> mixing ratios at a regional scale
[show abstract] [hide abstract]
ABSTRACT: Inverse modelling of carbon sources and sinks requires an accurate quality estimate of the modelling framework to obtain a realistic estimate of the inferred fluxes and their uncertainties. So-called "representation errors" result from our inability to correctly represent point observations with simulated average values of model grid cells. They may add substantial uncertainty to the interpretation of atmospheric CO<sub>2</sub> mixing ratio data. We simulated detailed variations in the CO<sub>2</sub> mixing ratios with a high resolution (2 km) mesoscale model (RAMS) to estimate the representation errors introduced at larger model grid sizes of 10–100 km. We found that meteorology is the main driver of representation errors in our study causing spatial and temporal variations in the error estimate. Within the nocturnal boundary layer, the representation errors are relatively large and mainly caused by unresolved topography at lower model resolutions. During the day, convective structures, mesoscale circulations, and surface CO<sub>2</sub> flux variability were found to be the main sources of representation errors. Interpreting observations near a mesoscale circulation as representative for air with the correct footprint relative to the front can reduce the representation error substantially. The remaining representation error is 0.5–1.5 ppm at 20–100 km resolution.Atmospheric Chemistry and Physics. 01/2008; -
Article: The two-way nested global chemistry-transport zoom model TM5: algorithm and applications
[show abstract] [hide abstract]
ABSTRACT: This paper describes the global chemistry Transport Model, version 5 (TM5) which allows two-way nested zooming. The model is used for global studies which require high resolution regionally but can work on a coarser resolution globally. The zoom algorithm introduces refinement in both space and time in some predefined regions. Boundary conditions of the zoom region are provided by a coarser parent grid and the results of the zoom area are communicated back to the parent. A case study using <sup>222</sup>Rn measurements that were taken during the MINOS campaign reveals the advantages of local zooming. As a next step, it is investigated to what extent simulated concentrations over Europe are influenced by using an additional zoom domain over North America. An artificial ozone-like tracer is introduced with a lifetime of twenty days and simplified non-linear chemistry. The concentration differences at Mace Head (Ireland) are generally smaller than 10%, much smaller than the effects of the resolution enhancement over Europe. Thus, coarsening of resolution at some distance of a sampling station seems allowed. However, it is also noted that the budgets of the tracers change considerably due to resolution dependencies of, for instance, vertical transport. Due to the two-way nested algorithm, TM5 offers a consistent tool to study the effects of grid refinement on global atmospheric chemistry issues like intercontinental transport of air pollution.Atmospheric Chemistry and Physics. 01/2005; -
Article: On the role of hydroxyl radicals in the self-cleansing capacity of the troposphere
[show abstract] [hide abstract]
ABSTRACT: Thousands of megatons natural and anthropogenic gases are released and subsequently removed from the troposphere each year. Photochemical reactions, initiated by hydroxyl (OH) radicals, oxidise most gases to products which are more easily removed by precipitation and dry deposition at the earth's surface. Since human-induced pollution emissions strongly affect OH formation and loss, large global changes in OH concentrations are possible. Global models and observations of trace gas distributions from global networks have been used to study geographical and temporal changes in tropospheric OH. Here we present a synopsis of recent studies, indicating that global mean OH has changed remarkably little in the past century, even though regional changes have probably been substantial. Globally, depletion of OH by reactive carbon gases has been compensated by increased OH formation by nitrogen oxides, an act of 'inadvertent geo-engineering'. However, OH analyses for the past 1-2 decades, partly based on methyl chloroform measurements, are inconclusive. Some work, assuming that methyl chloroform emissions have largely ceased, suggests a very strong downward global OH trend in the 1990s, inconsistent with modelling studies. The discrepancy could be much reduced by assuming continued small emissions of methyl chloroform. We recommend the continuation of high precision monitoring of this compound and improved analyses based on detailed meteorological-chemical models.Atmospheric Chemistry and Physics. 01/2004; -
Article: Hydroxyl radicals maintain the self-cleansing capacity of the troposphere
[show abstract] [hide abstract]
ABSTRACT: Billions of tons natural and anthropogenic gases are released and subsequently removed from the troposphere each year. Photochemical reactions, initiated by hydroxyl (OH) radicals, oxidise most gases to products which are more easily removed by precipitation and dry deposition at the Earth's surface. Since human-induced pollution emissions strongly affect OH formation and loss, large global changes in OH concentrations are possible. The available evidence as reviewed here, however, indicates that global mean OH has changed relatively little in the past century. Depletion of OH by reactive carbon gases has been compensated by increased OH formation by nitrogen oxides, an act of "inadvertent geo-engineering". Analyses of global mean OH for the past 2.5 decades, however, partly based on methyl chloroform measurements, are ambiguous. Especially the OH trend in the 1990s based on these analyses is at odds with present understanding. Since the discrepancy is dominated by the uncertainty in methyl chloroform emission estimates, improvements of source inventories and model analyses, combined with continued high precision methyl chloroform measurements, will help resolve this problem.Atmospheric Chemistry and Physics Discussions. 01/2004; -
Article: Chemistry-transport modeling of the satellite observed distribution of tropical troposheric ozone
[show abstract] [hide abstract]
ABSTRACT: We have compared the 14-year record of satellite derived tropical tropospheric ozone columns (TTOC) from the NIMBUS--7 Total Ozone Mapping Spectrometer (TOMS) to TTOC calculated by achemistry-transport model (CTM). An objective measure of error, based on the zonal distribution of TTOC in the tropics, is applied to perform this comparison systematically. In addition, the sensitivity of the model to several key processes in the tropics is quantified to select directions for future improvements. The comparisons indicate a widespread, systematic (20%) discrepancy over the tropical Atlantic Ocean, which maximizes during austral Spring. Although independent evidence from ozonesondes shows that some of the disagreement is due to satellite overestimate of TTOC, the Atlantic mismatch is largely due to a misrepresentation of seasonally recurring processes in the model. Only minor differences between the model and observations over the Pacific occur, mostly due to interannual variability not captured by the model. Although chemical processes determine the TTOC extent, dynamical processes dominate the TTOC distribution, as the use of actual meteorology pertaining to the year of observations always leads to a better agreement with TTOC observations than using a random year or a climatology. The modeled TTOC is remarkably insensitive to many model parameters due to efficient feedbacks in the ozone budget. Nevertheless, the simulations would profit from an improved biomass burning calendar, as well as from an increase in NO<sub>x </sub>abundances in free tropospheric biomass burning plumes. The model showed the largest response to lightning NO<sub>x </sub> emissions, but systematic improvements could not be found. The use of multi-year satellite derived tropospheric data to systematically test and improve a CTM is a promising new addition to existing methods of model validation, and is a first step to integrating tropospheric satellite observations into global ozone modeling studies. Conversely, the CTM may suggest improvements to evolving satellite retrievals for tropospheric ozone.Atmospheric Chemistry and Physics. 01/2002; -
Article: Chemistry-transport modeling of the satellite observed distribution of tropical tropospheric ozone
[show abstract] [hide abstract]
ABSTRACT: We have compared the 14-year record of satellite derived tropical tropospheric ozone columns (TTOC) from the NIMBUS-7 Total Ozone Mapping Spectrometer (TOMS) to TTOC calculated by a chemistry-transport model (CTM). An objective measure of error, based on the zonal distribution of TTOC in the tropics, is applied to perform this comparison systematically. In addition, the sensitivity of the model to several key processes in the tropics is quantified to select directions for future improvements. The comparison indicates a widespread, systematic (~20%) underestimate of TTOC over the tropical Atlantic Ocean, which maximizes during austral spring. This 'Atlantic mismatch' is largely due to a misrepresentation of seasonally recurring processes in the model, while minor differences between model and observations over the tropical Pacific Ocean are mostly due to uncaptured interannual variability. Although chemical processes determine the TTOC extent, dynamical processes dominate the TTOC distribution, as the use of actual meteorology pertaining to the year of observations always leads to a better agreement with TTOC observations than using a random year or a climatology. The modeled TTOC is remarkably insensitive to many model parameters due to efficient feedbacks in the ozone budget. Nevertheless, the simulations would profit from an improved biomass burning calendar, as well as from an increase in NOx abundances in free tropospheric biomass burning plumes. The use of multi-year satellite derived tropospheric data to systematically test and improve a CTM is a promising new addition to existing methods of model validation, and is a first step to integrate tropospheric satellite observations into global ozone modeling studies.Atmospheric Chemistry and Physics Discussions. 01/2001;
Top co-authors
Institutions
-
2008
-
Wageningen University
Wageningen, Provincie Gelderland, Netherlands
-
