Comparison between archived and off-line diagnosed convective mass fluxes in the chemistry transport model TM3

The 40-year reanalysis data set ERA-40 from the European Centre for Medium-Range Weather Forecasts includes, unlike ERA-15, archived convective mass fluxes. These convective fluxes are useful for off-line chemistry transport modeling. The impact of using these archived convective mass fluxes (based on a convective parameterization described in Gregory et al. [2000] ) instead of off-line diagnosed mass fluxes (based on a convective parameterization described in Tiedtke [1989] ) was investigated with the chemistry transport model TM3. At first sight the two types of mass fluxes look similar. However, some differences can be noted: the archived updrafts extend higher than the off-line diagnosed ones; they are also less intense below 500 hPa over sea. The archived downdrafts are much weaker than the off-line diagnosed downdrafts. With archived convective mass fluxes, we found slightly higher ²²²Rn concentrations in the boundary layer, lower ²²²Rn values in the free troposphere and significantly higher ²²²Rn values in the upper troposphere and lower stratosphere. The effect on tropospheric chemistry of using archived mass fluxes instead of diagnosed ones is an increase of NO x and O3 in the free troposphere, but a decrease in the upper troposphere. The differences amount to up to 20% for O3 in the zonal and seasonal mean. Our results thus underline the sensitivity of tropospheric ozone chemistry to the description of convective transport. Comparison with ²²²Rn observations shows that the archived convective mass fluxes give better agreement in the tropical upper troposphere. More comparisons to free tropospheric observations of ²²²Rn or another tracer of convective transport will be needed to unambiguously identify either of the convective data sets as optimal for use in chemistry transport models

Stable atmospheric boundary layers and diurnal Cycles-Challenges for Weather and Climate Models

The representation of the atmospheric boundary layer is an important part of weather and climate models and impacts many applications such as air quality and wind energy. Over the years, the performance in modeling 2 m temperature and 10 m wind speed has improved but errors are still significant. This is in particular the case under clear skies and low wind-speed conditions at night as well as during winter in stably stratified conditions over land and ice. In this paper, we review these issues and provide an overview of the current understanding and model performance. Results from weather forecast and climate models are used to illustrate the state of the art, as well as findings and recommendations from three inter-comparison studies held within the “Global Energy and Water Exchanges (GEWEX)” Atmospheric Boundary Layer Study (GABLS). Within GABLS, the focus has been on the examination of the representation of the stable boundary layer and the diurnal cycle over land in clear sky conditions. For this purpose, single-column versions of weather and climate models have been compared with observations, research models and Large Eddy Simulations. The intercomparison cases are based on observations taken in the Arctic, Kansas and at Cabauw in the Netherlands. From these studies, we find that even for the non-cloudy boundary layer important parameterization challenges remain

Natural land carbon dioxide exchanges in the ECMWF integrated forecasting system: Implementation and offline validation

The European Centre for Medium-Range Weather Forecasts land surface model has been extended to include a carbon dioxide module. This relates photosynthesis to radiation, atmospheric carbon dioxide (CO2) concentration, soil moisture, and temperature. Furthermore, it has the option of deriving a canopy resistance from photosynthesis and providing it as a stomatal control to the transpiration formulation. Ecosystem respiration is based on empirical relations dependent on temperature, soil moisture, snow depth, and land use. The CO2 model is designed for the numerical weather prediction (NWP) environment where it benefits from good quality meteorological input (i.e., radiation, temperature, and soil moisture). This paper describes the CO2 model formulation and the way it is optimized making use of off-line simulations for a full year of tower observations at 34 sites. The model is then evaluated against the same observations for a different year. A correlation coefficient of 0.65 is obtained between model simulations and observations based on 10 day averaged CO2 fluxes. For sensible and latent heat fluxes there is a correlation coefficient of 0.80. To study the impact on atmospheric CO2, coupled integrations are performed for the 2003 to 2008 period. The global atmospheric growth is well reproduced. The simulated interannual variability is shown to reproduce the observationally based estimates with a correlation coefficient of 0.70. The main conclusions are (i) the simple carbon dioxide model is highly suitable for the numerical weather prediction environment where environmental factors are controlled by data assimilation, (ii) the use of a carbon dioxide model for stomatal control has a positive impact on evapotranspiration, and (iii) even using a climatological leaf area index, the interannual variability of the global atmospheric CO2 budget is well reproduced due to the interannual variability in the meteorological forcing (i.e., radiation, precipitation, temperature, humidity, and soil moisture) despite the simplified or missing processes. This highlights the importance of meteorological forcing but also cautions the use of such a simple model for process attribution