The importance of transport model uncertainties for the estimation of CO2 sources and sinks using satellite measurements

This study presents a synthetic model intercomparison to investigate the importance of transport model errors for estimating the sources and sinks of CO2 using satellite measurements. The experiments were designed for testing the potential performance of the proposed CO2 lidar A-SCOPE, but also apply to other space borne missions that monitor total column CO2. The participating transport models IFS, LMDZ, TM3, and TM5 were run in forward and inverse mode using common a priori CO2 fluxes and initial concentrations. Forward simulations of column averaged CO2 (xCO2) mixing ratios vary between the models by s=0.5 ppm over the continents and s=0.27 ppm over the oceans. Despite the fact that the models agree on average on the sub-ppm level, these modest differences nevertheless lead to significant discrepancies in the inverted fluxes of 0.1 PgC/yr per 106 km2 over land and 0.03 PgC/yr per 106 km2 over the ocean. These transport model induced flux uncertainties exceed the target requirement that was formulated for the A-SCOPE mission of 0.02 PgC/yr per 106 km2, and could also limit the overall performance of other CO2 missions such as GOSAT. A variable, but overall encouraging agreement is found in comparison with FTS measurements at Park Falls, Darwin, Spitsbergen, and Bremen, although systematic differences are found exceeding the 0.5 ppm level. Because of this, our estimate of the impact of transport model uncerainty is likely to be conservative. It is concluded that to make use of the remote sensing technique for quantifying the sources and sinks of CO2 not only requires highly accurate satellite instruments, but also puts stringent requirements on the performance of atmospheric transport models. Improving the accuracy of these models should receive high priority, which calls for a closer collaboration between experts in atmospheric dynamics and tracer transpor

Evaluation of various observing systems for the global monitoring of CO2 surface fluxes

In the context of rising greenhouse gas concentrations, and the potential feedbacks between climate and the carbon cycle, there is an urgent need to monitor the exchanges of carbon between the atmosphere and both the ocean and the land surfaces. In the so-called top-down approach, the surface fluxes of CO2 are inverted from the observed spatial and temporal concentration gradients. The concentrations of CO2 are measured in-situ at a number of surface stations unevenly distributed over the Earth while several satellite missions may be used to provide a dense and better-distributed set of observations to complement this network. In this paper, we compare the ability of different CO2 concentration observing systems to constrain surface fluxes. The various systems are based on realistic scenarios of sampling and precision for satellite and in-situ measurements. It is shown that satellite measurements based on the differential absorption technique (such as those of SCIAMACHY, GOSAT or OCO) provide more information than the thermal infrared observations (such as those of AIRS or IASI). The OCO observations will provide significantly better information than those of GOSAT. A CO2 monitoring mission based on an active (lidar) technique could potentially provide an even better constraint. This constraint can also be realized with the very dense surface network that could be built with the same funding as that of the active satellite mission. Despite the large uncertainty reductions on the surface fluxes that may be expected from these various observing systems, these reductions are still insufficient to reach the highly demanding requirements for the monitoring of anthropogenic emissions of CO2 or the oceanic fluxes at a spatial scale smaller than that of oceanic basins. The scientific objective of these observing system should therefore focus on the fluxes linked to vegetation and land ecosystem dynamics

Modelling the optical properties of fresh biomass burning aerosol produced in a smoke chamber: results from the EFEU campaign

A better characterisation of the optical properties of biomass burning aerosol as a function of the burning conditions is required in order to quantify their effects on climate and atmospheric chemistry. Controlled laboratory combustion experiments with different fuel types were carried out at the combustion facility of the Max Planck Institute for Chemistry (Mainz, Germany) as part of the "Impact of Vegetation Fires on the Composition and Circulation of the Atmosphere" (EFEU) project. The combustion conditions were monitored with concomitant CO<sub>2</sub> and CO measurements. The mass scattering efficiencies of 8.9±0.2 m<sup>2</sup> g<sup>−1</sup> and 9.3±0.3 m<sup>2</sup> g<sup>−1</sup> obtained for aerosol particles from the combustion of savanna grass and an African hardwood (musasa), respectively, are larger than typically reported mainly due to differences in particle size distribution. The photoacoustically measured mass absorption efficiencies of 0.51±0.02 m<sup>2</sup> g<sup>−1</sup> and 0.50±0.02 m<sup>2</sup> g<sup>−1</sup> were at the lower end of the literature values. Using the measured size distributions as well as the mass scattering and absorption efficiencies, Mie calculations provided effective refractive indices of 1.60−0.010<i>i</i> (savanna grass) and 1.56−0.010<i>i</i> (musasa) (λ=0.55 μm). The apparent discrepancy between the low imaginary part of the refractive index and the high apparent elemental carbon (EC<sub>a</sub>) fractions (8 to 15%) obtained from the thermographic analysis of impactor samples can be explained by a positive bias in the elemental carbon data due to the presence of high molecular weight organic substances. Potential artefacts in optical properties due to instrument bias, non-natural burning conditions and unrealistic dilution history of the laboratory smoke cannot be ruled out and are also discussed in this study

First results of the earth observation water cycle multi-mission observation strategy (WACMOS) + Corrigendum

Observing and monitoring the different components of the global water cycle and their dynamics are essential steps to understand the climate of the Earth, forecast the weather, predict natural disasters like floods and droughts, and improve water resources management. Earth observation technology is a unique tool to provide a global understanding of many of the essential variables governing the water cycle and monitor their evolution from global to basin scales. In the coming years, an increasing number of Earth observation missions will provide an unprecedented capacity to quantify several of these variables on a routine basis. However, this growing observational capacity is also increasing the need for dedicated research efforts aimed at exploring the potential offered by the synergies among different and complementary EO data records. In this context, the European Space Agency (ESA) launched the Water Cycle Multi-mission Observation Strategy (WACMOS) in 2009 aiming at enhancing, developing and validating a novel set of multi-mission based methods and algorithms to retrieve a number of key variables relevant to the water cycle. In particular the project addressed four major scientific challenges associated to a number of key variables governing the water cycle: evapotranspiration, soil moisture, cloud properties related to surface solar irradiance and precipitation, and water vapour. This paper provides an overview of the scientific results and findings with the ultimate goal of demonstrating the potential of strategies based on utilizing multi-mission observations in maximizing the synergistic use of the different types of information provided by the currently available observation systems and establish the basis for further work

Improving direct normal irradiance retrieval in cloud-free, but high aerosol load conditions by using aerosol optical depth

Measurements of the global surface solar irradiation and its direct and diffuse components performed at three Egyptian sites (Aswan, Cairo, and Port Said) are used to test the ability of two published decomposition models to estimate the hourly direct normal irradiance from the measured global horizontal one in cloud-free conditions. The tested models failed to reproduce the temporal variability of the measurements, which we show to be partly induced by the large variability of the atmospheric content in aerosols. We propose a revised formulation of the decomposition models that takes into account the aerosol optical depth (AOD) at 1000 nm derived from onsite measurements. It leads to a significant reduction of the bias and root mean square deviation of the original models and this at the three Egyptian sites. However, because the AOD is rarely measured at the meteorological stations, we also quantify the performance of the revised models when the AOD is either derived from the MODIS observations or obtained by the products from Copernicus Atmospheric Monitoring Service (CAMS). Probably because of their finer temporal resolution that makes them more apt to reproduce the rapid variations of the AOD, the best results are obtained with the CAMS products. Therefore, we recommend using a combination of the revised decomposition models and these CAMS products to estimate the hourly direct normal irradiance in areas such as Egypt where aerosols are ubiquitous. Note that the improved decomposition models are generally applicable in all-sky conditions, although their benefit has been demonstrated to be significant, and probably limited to, cloud-free conditions

A database of multi-year (2004–2010) quality-assured surface solar hourly irradiation measurements for the Egyptian territory

A database containing the global and diffuse components of the surface solar hourly irradiation measured from 1 January 2004 to 31 December 2010 at eight stations of the Egyptian Meteorological Authority is presented. For three of these sites (Cairo, Aswan and El-Farafra), the direct component is also available. In addition, a series of meteorological variables including surface pressure, relative humidity, temperature, wind speed and direction is provided at the same hourly resolution at all stations. The details of the experimental sites and instruments used for the acquisition are given. Special attention is paid to the quality of the data and the procedure applied to flag suspicious or erroneous measurements is described in detail. Between 88 and 99  % of the daytime measurements are validated by this quality control. Except at Barrani where the number is lower (13 500), between 20 000 and 29 000 measurements of global and diffuse hourly irradiation are available at all sites for the 7-year period. Similarly, from 9000 to 13 000 measurements of direct hourly irradiation values are provided for the three sites where this component is measured. With its high temporal resolution this consistent irradiation and meteorological database constitutes a reliable source to estimate the potential of solar energy in Egypt. It is also adapted to the study of high-frequency atmospheric processes such as the impact of aerosols on atmospheric radiative transfer. It is planned to update regularly the current 2004&ndash;2010 database, which has been placed on the PANGAEA repository (doi:<a href="http://dx.doi.org/10.1594/PANGAEA.848804" target="_blank">10.1594/PANGAEA.848804</a>) and contains the individual meteorological and irradiation data files of the eight stations