Mesoscale modelling of the CO2 interactions between the surface and the atmosphere applied to the April 2007 CERES field experiment

This paper describes a numerical interpretation of the April 2007, CarboEurope Regional Experiment Strategy (CERES) campaign, devoted to the study of the CO2 cycle at the regional scale. Four consecutive clear sky days with intensive observations of CO2 concentration, fluxes at the surface and in the boundary layer have been simulated with the Meso-NH mesoscale model, coupled to ISBA-A-gs land surface model. The main result of this paper is to show how aircraft observations of CO2 concentration have been used to identify surface model errors and to calibrate the CO2 driving component of the surface model. In fact, the comparisons between modelled and observed CO2 concentrations within the Atmospheric Boundary Layer (ABL) allow to calibrate and correct not only the parameterization of respired CO2 fluxes by the ecosystem but also the Leaf Area Index (LAI) of the dominating land cover. After this calibration, the paper describes systematic comparisons of the model outputs with numerous data collected during the CERES campaign, in April 2007. For instance, the originality of this paper is the spatial integration of the comparisons. In fact, the aircraft observations of CO2 concentration and fluxes and energy fluxes are used for the model validation from the local to the regional scale. As a conclusion, the CO2 budgeting approach from the mesoscale model shows that the winter croplands are assimilating more CO2 than the pine forest, at this stage of the year and this case study

Dis-aggregation of airborne flux measurements using footprint analysis

Aircraft measurements of turbulent fluxes are generally being made with the objective to obtain an estimate of regional exchanges between land surface and atmosphere, to investigate the spatial variability of these fluxes, but also to learn something about the fluxes from some or all of the land cover types that make up the landscape. In this study we develop a method addressing this last objective, an approach to disentangle blended fluxes from a landscape into the component fluxes emanating from the various land cover classes making up that landscape. The method relies on using a footprint model to determine which part of the landscape the airborne flux observation refers to, using a high resolution land cover map to determine the fractional covers of the various land cover classes within that footprint, and finally using multiple linear regression on many such flux/fractional cover data records to estimate the component fluxes. The method is developed in the context of three case studies of increasing complexity and the analysis covers three scalar fluxes: sensible and latent heat fluxes and carbon dioxide flux, as well as the momentum flux. A basic assumption under the dis-aggregation method is that the composite flux, i.e. the landscape flux, is a linear average of the component fluxes, i.e. the fluxes from the various land elements. We test and justify this assumption by comparing linear averages of component fluxes in simple ‘binary landscapes’, weighted by their relative area, with directly aircraft observed fluxes. In all case studies dis-aggregation of mixed values for fluxes from heterogeneous areas into component land cover class specific fluxes is feasible using robust least squares regression, both in simple binary ‘landscapes’ and in more complex cases. Both the differences between land cover classes and the differences between synoptic conditions can be resolved, for those land cover classes that make up sufficiently large fractions of the landscape. The regression F-statistic and the closely associated p-values are good indicators for this latter prerequisite and for other sources of uncertainty in the dis-aggregated flux estimates that render it meaningful or not. An analysis of the effect of various sources of errors in input data, footprint estimates and of skewed land cover class distributions is presented. A validation of flux estimates obtained through the dis-aggregation method against independent ground data proved satisfactorily. Recommendations for the use of the method are given as are suggestions for further developmen

Calibration and Quality Assurance of Flux Observations from a Small Research Aircraft

Small environmental research aircraft (ERA) are becoming more common for detailed studies of air–surface interactions. The Sky Arrow 650 ERA, used by multiple groups, is designed to minimize the complexity of high-precision airborne turbulent wind measurement. Its relative wind probe, of a nine-port design, is furthermore used with several other airplanes. This paper gives an overview of 1) calibration of the model that converts the probe’s raw measurements to meteorological quantities; 2) quality control and assurance (QC–QA) in postprocessing of these quantities to compute fluxes; and 3) sensitivity of fluxes to errors in calibration parameters. The model, an adapted version of standard models of potential flow and aerodynamic upwash, is calibrated using an integrated method to derive a globally optimum set of parameters from in-flight maneuvers. Methods of QC–QA from the tower flux community are adopted for use with airborne flux data to provide more objective selection criteria for large datasets. Last, measurements taken from a standard operational flight are used to show fluxes to be most sensitive to calibration parameters that directly affect the vertical wind component. In another test with the same data, varying all calibration parameters simultaneously by ±10% of their optimum values, the model computes a response in the fluxes smaller than 10%, though a larger response may occur if only a subset of parameters is perturbed. A MATLAB toolbox has been developed that facilitates the procedures presented her

Regional carbon dioxide and energy fluxes from airborne observations using flight-path segmentation based on landscape characteristics

This paper presents an analysis of regional fluxes obtained with a small aircraft over heterogeneous terrain in the south-west of France, during the large scale field experiment CERES’07. We use a method combining variable flight-path segmentation with basic airborne footprint analysis. The segmentation is based on topography, land use and soil type, using a.o. satellite imagery and digital maps.This paper presents an analysis of regional fluxes obtained with a small aircraft over heterogeneous terrain in the south-west of France, during the large scale field experiment CERES'07. We use a method combining variable flight-path segmentation with basic airborne footprint analysis. The segmentation is based on topography, land use and soil type, using a.o. satellite imagery and digital maps. The segments are delineated using an average footprint length, based on all flights, and segment lengths, which are variable in space but not in time. The method results in segment averaged carbon and energy fluxes, which are shown to be representative of regional fluxes. Our analysis is focussed on carbon dioxide, heat and evaporative fluxes around solar noon. We will show that spatial and seasonal variations in the fluxes can be linked to the underlying landscape. In addition, a comparison between the airborne data and ground flux data is made to support our results. However, due to the incompleteness of ground data for some predominant vegetation types (even in such a data dense context), upscaling of ground data to regional fluxes was not possible. Without the comparison, we are still able to demonstrate that aircraft can provide direct and meaningful estimates of regional fluxes of energy and carbon dioxide

The VELD experiment: An evaluation of the ammonia emissions and concentrations in an agricultural area

From July 2002until September 2003, a detailed ammonia emission inventory was carried out in concurrence with detailed measurements of the ammonia concentrations in air in a 3 × 3 km area in the East of the Netherlands. The main goal of the project was to validate the emission inventory by comparing modelled ammonia concentrations based on these emissions to the measured concentrations. It was found that the emissions from animal housings are the dominant source of ammonia over the year. Only incidentally, emissions of manure spreading were larger. The spatial and temporal variations in the concentrations over the year are well represented by the OPS model based on these emissions. For the entire period, the model shows an underestimation of the concentrations of about 15% (explained variance of the regression line of 76%). In the winter period, which is characterized by a dominance of the emissions from animal housings, the underestimation is only 5%. This most likely indicates that the emissions from animal housings, which in the area is mainly from pigs, are estimated correctly, as well as the modeling of the concentrations, for this period. In both the Spring and August 2003 period, a gap between calculated and measured ammonia concentrations was found. Under spring conditions, this gap is most likely the result of an underestimation of the emission during manure spreading. A part of the underestimation may be attributed to a reduction in the dry deposition process in the successive weeks after spreading which is caused by a saturation of the grassland with ammonium. Taking into account the uncertainty in this dry deposition process, it was estimated that the underestimate of the emissions by manure spreading could amount from 15% to 60%. The gap in August 2003, which was a very warm and dry month, is most probably caused by re-emission of ammonia at a large scale in and around the VELD area. The re-emission of ammonia from grass and crop land in August 2003 has a typical density of 14 g/ha/day during daytime. On a national scale this would mean for the Netherlands a re-emission of about 1 Gg during these three weeks of August

The VELD experiment: An evaluation of the ammonia emissions and concentrations in an agricultural area

From July 2002until September 2003, a detailed ammonia emission inventory was carried out in concurrence with detailed measurements of the ammonia concentrations in air in a 3 × 3 km area in the East of the Netherlands. The main goal of the project was to validate the emission inventory by comparing modelled ammonia concentrations based on these emissions to the measured concentrations. It was found that the emissions from animal housings are the dominant source of ammonia over the year. Only incidentally, emissions of manure spreading were larger. The spatial and temporal variations in the concentrations over the year are well represented by the OPS model based on these emissions. For the entire period, the model shows an underestimation of the concentrations of about 15% (explained variance of the regression line of 76%). In the winter period, which is characterized by a dominance of the emissions from animal housings, the underestimation is only 5%. This most likely indicates that the emissions from animal housings, which in the area is mainly from pigs, are estimated correctly, as well as the modeling of the concentrations, for this period. In both the Spring and August 2003 period, a gap between calculated and measured ammonia concentrations was found. Under spring conditions, this gap is most likely the result of an underestimation of the emission during manure spreading. A part of the underestimation may be attributed to a reduction in the dry deposition process in the successive weeks after spreading which is caused by a saturation of the grassland with ammonium. Taking into account the uncertainty in this dry deposition process, it was estimated that the underestimate of the emissions by manure spreading could amount from 15% to 60%. The gap in August 2003, which was a very warm and dry month, is most probably caused by re-emission of ammonia at a large scale in and around the VELD area. The re-emission of ammonia from grass and crop land in August 2003 has a typical density of 14 g/ha/day during daytime. On a national scale this would mean for the Netherlands a re-emission of about 1 Gg during these three weeks of August

De broeikasgasbalans van het landschap. Dual contstraint methode voor verificatie.

Nederland is verplicht om in het kader van het Kyoto protocol elk jaar broeikasgasemissie aan de UNFCCC te rapporteren. De huidige rapportage is niet zozeer gebaseerd op directe metingen maar op inventarisaties. Emissiebronnen en -putten worden vastgesteld en vermenigvuldigd met emissiefactoren die bepaald zijn voor Nederland. Dit artikel schetst een raamwerk voor verificatie van de nationale rapportages en geeft elementen aan die voor verbetering op termijn kunnen zorgen

De broeikasgasbalans van het landschap : Dual constraint methode voor verificatie

Nederland is verplicht om in het kader van het Kyoto protocol elk jaar broeikasgasemissie aan de UNFCCC te rapporteren. De huidige rapportage is niet zozeer gebaseerd op directe metingen maar op inventarisaties. Emissiebronnen en -putten worden vastgesteld en vermenigvuldigd met emissiefactoren die bepaald zijn voor Nederland. Dit artikel schetst een raamwerk voor verificatie van de nationale rapportages en geeft elementen aan die voor verbetering op termijn kunnen zorgen