Evaluation of the urban tile in MOSES using surface energy balance observations

The UK Met Office has introduced a new scheme for its urban tile in MOSES 2.2 (Met Office Surface Exchange Scheme version 2.2), which is currently implemented within the operational Met Office weather forecasting model. Here, the performance of the urban tile is evaluated in two urban areas: the historic core of downtown Mexico City and a light industrial site in Vancouver, Canada. The sites differ in terms of building structures and mean building heights. In both cases vegetation cover is less than 5%. The evaluation is based on surface energy balance flux measurements conducted at approximately the blend- ing height, which is the location where the surface scheme passes flux data into the atmo- spheric model. At both sites, MOSES 2.2 correctly simulates the net radiation, but there are discrepancies in the partitioning of turbulent and storage heat fluxes between predicted and observed values. Of the turbulent fluxes, latent heat fluxes were underpredicted by about one order of magnitude. Multiple model runs revealed MOSES 2.2 to be sensitive to changes in the canopy heat storage and in the ratio between the aerodynamic roughness length and that for heat transfer (temperature). Model performance was optimum with heat capacity values smaller than those generally considered for these sites. The results suggest that the current scheme is probably too simple, and that improvements may be obtained by increasing the complexity of the model

Resolving Orbital and Climate Keys of Earth and Extraterrestrial Environments with Dynamics 1.0: A General Circulation Model for Simulating the Climates of Rocky Planets

Resolving Orbital and Climate Keys of Earth and Extraterrestrial Environments with Dynamics (ROCKE-3D) is a 3-Dimensional General Circulation Model (GCM) developed at the NASA Goddard Institute for Space Studies for the modeling of atmospheres of Solar System and exoplanetary terrestrial planets. Its parent model, known as ModelE2 (Schmidt et al. 2014), is used to simulate modern and 21st Century Earth and near-term paleo-Earth climates. ROCKE-3D is an ongoing effort to expand the capabilities of ModelE2 to handle a broader range of atmospheric conditions including higher and lower atmospheric pressures, more diverse chemistries and compositions, larger and smaller planet radii and gravity, different rotation rates (slowly rotating to more rapidly rotating than modern Earth, including synchronous rotation), diverse ocean and land distributions and topographies, and potential basic biosphere functions. The first aim of ROCKE-3D is to model planetary atmospheres on terrestrial worlds within the Solar System such as paleo-Earth, modern and paleo-Mars, paleo-Venus, and Saturn's moon Titan. By validating the model for a broad range of temperatures, pressures, and atmospheric constituents we can then expand its capabilities further to those exoplanetary rocky worlds that have been discovered in the past and those to be discovered in the future. We discuss the current and near-future capabilities of ROCKE-3D as a community model for studying planetary and exoplanetary atmospheres.Comment: Revisions since previous draft. Now submitted to Astrophysical Journal Supplement Serie

Understanding climate: A strategy for climate modeling and predictability research, 1985-1995

The emphasis of the NASA strategy for climate modeling and predictability research is on the utilization of space technology to understand the processes which control the Earth's climate system and it's sensitivity to natural and man-induced changes and to assess the possibilities for climate prediction on time scales of from about two weeks to several decades. Because the climate is a complex multi-phenomena system, which interacts on a wide range of space and time scales, the diversity of scientific problems addressed requires a hierarchy of models along with the application of modern empirical and statistical techniques which exploit the extensive current and potential future global data sets afforded by space observations. Observing system simulation experiments, exploiting these models and data, will also provide the foundation for the future climate space observing system, e.g., Earth observing system (EOS), 1985; Tropical Rainfall Measuring Mission (TRMM) North, et al. NASA, 1984

Land-surface influences on weather and climate

Land-surface influences on weather and climate are reviewed. The interrelationship of vegetation, evapotranspiration, atmospheric circulation, and climate is discussed. Global precipitation, soil moisture, the seasonal water cycle, heat transfer, and atmospheric temperature are among the parameters considered in the context of a general biosphere model

Comparison and sensitivity studies of the land-surface schemes in the ECHAM General Circulation Model and the Europa-Model

This study presents the comparison of largely different land-surface schemes in the ECHAM GCM and the Europa-Modell (EM). The model runs were performed in an off-line mode using the Cabauw observational data as forcing at the lowest atmospheric model level. A detailed study on the sensitivities, over the entire physically possible range, of different key parameters gives insight into the differences in the two land- surface schemes. Emphasis is placed on the comparison of annual and diurnal cycles for the surface energy and water budget, as well as a detailed discussion of the differences in the parameterization equations. The study shows that sensitivity studies should not only focus on monthly means but also on diurnal cycles. Moreover, it is not sufficient to test a sensitivity for a certain value, but extend the investigation over the whole range because of its nonlinearity. In general, the sensitivity of both models is decreasing with increasing values of roughness length, leaf area index and Held capacity. ECHAM gener- ally shows higher sensitivity with respect to leaf area index and roughness length when compared to EM. This is mainly due to different parameterization of the transpiration. The sensitivity of the evaporation from the skin reservoir is higher in ECHAM for all varied surface parameters due to very efficient infiltration in EM. Total winter runoff is predominantly higher in ECHAM due to the implementation of 'fast drainage It has been shown that the different assessment of soil water largely influences the sensitivi- ties. In addition, ECI-IAM shows more distinct summer drying than EM. The boundary layer parameterization is typically the same in both models. However, differences in the von-Kérmcin-constant If can produce distinct differences in turbulent fluxes

Urban signals in high-resolution weather and climate simulations: role of urban land-surface characterisation

Two urban schemes within the Joint UK Land Environment Simulator (JULES) are evaluated offline against multi-year flux observations in the densely built-up city centre of London and in suburban Swindon (UK): (i) the 1-tile slab model, used in climate simulations, (ii) the 2-tile canopy model MORUSES (Met Office–Reading Urban Surface Exchange Scheme), used for numerical weather pre- diction over the UK. Offline, both models perform better at the suburban site, where differences between the urban schemes are less pronounced due to larger vegetation fractions. At both sites, the outgoing short- and longwave radiation is more accurately represented than the turbulent heat fluxes. The seasonal varia- tions of model skill are large in London, where the sensible heat flux in autumn and winter is strongly under-predicted if the large city-centre magnitudes of anthro- pogenic heat emissions are not represented. The delayed timing of the sensible heat flux in the 1-tile model in London results in large negative bias in the morning. The partitioning of the urban surface into canyon and roof in MORUSES improves this as the roof-tile is modelled with a very low thermal inertia, but phase and amplitude of the gridbox-averaged flux critically depend on accurate knowledge of the plan-area fractions of streets and buildings. Not representing non-urban land- cover (e.g. vegetation, inland water) in London results in severely under-predicted latent heat fluxes. Control runs demonstrate that the skill of both models can be greatly improved by providing accurate land-cover and morphology information and using representative anthropogenic heat emissions, which is essential if the model output is intended to inform integrated urban services

Suivi des flux d'énergie, d'eau et de carbone à la surface : apport de la télédétection et de la modélisation du rayonnement solaire absorbé par la végétation

It is known that a global 4% increase of land surface albedo (also called reflectivity) may result approximately in a decrease of 0.7°C in the Earth’s equilibrium temperature. Nowadays the surface properties (including albedo) are changing under climatic and human pressure. At the same time, there is a debate that divides the scientific community about the potential trends (increase or decrease) affecting the surface incoming solar radiation since mid-1980 (resulting of a decrease or increase of aerosol concentration in the atmosphere, respectively). The Earth is a complex system driven at the surface level by three cycles (energy, water, and carbon). These cycles are not insensitive to changes of surface reflectivity, incoming radiation, or aerosol properties. For example, some argue that the increase of diffuse radiation during the last decades would have led to an exceed of carbon uptake by the Earth’s vegetation of 9.3%. The main issue raised here is to assess the added value of the knowledge in absorbed solar radiation by the surface (combination of incoming solar radiation with surface albedo) and, especially, by the vegetation for the monitoring of energy, water and carbon fluxes.In this work, I have used satellite observations and modeled the radiative transfer theory in order to make dynamic mapping of solar radiation absorbed by the surface and through the vertical dimension of the vegetation. First, I quantified each uncertainty source affecting incoming solar radiation, surface albedo and the way radiation is split between horizontal and vertical heterogeneity. In a second step, I measured the added value of using this absorbed radiation mapping of the surface by satellite to estimate the energy and water fluxes at the surface. The resulting improved scores of weather forecast models in the short-range time scale suggested potential feedbacks at the climatic time scale over sensible areas such as the Sahel region. Another significant outcome is that the developments proposed to better characterize the vertical heterogeneity within the canopy led to an improvement of 15% of annual global terrestrial gross primary production (GPP). Moreover, this study has led to measure the impact of the lack of knowledge of spatial and temporal variability of aerosol properties (concentration and type). I have shown that the tracking of temporal changes of directional properties of reflectance allows me to retrieve to the amount of aerosols in the atmosphere as precisely as other widely used methods but with a higher frequency (5 times more) by using data from geostationary satellite. Finally, this study addresses some possibilities to better track temporal changes of properties of reflectivity of surface and aerosol of atmosphere, and to access to a better monitoring of biogeochemical cycles of the terrestrial biosphere.Au niveau global, il a été estimé qu’une augmentation de 4% de l’albédo (ou réflectivité) de la surface provoquerait une diminution de 0,7° de la température d’équilibre de la Terre. Or les propriétés des surfaces (dont l’albédo) changent sous la pression climatique et l’action de l’homme. Parallèlement à ce changement des propriétés de surface un débat divise la communauté scientifique sur une éventuelle diminution ou augmentation du rayonnement incident à la surface depuis le milieu des années 1980 (conséquence d’une augmentation ou diminution de la concentration d’aérosols dans l’atmosphère). La Terre est un système complexe piloté en sa surface par 3 cycles (énergie, eau et carbone). Ces cycles ne sont pas insensibles à ces changements de propriété de réflectivité de surface, de rayonnement solaire incident ou de concentration en aérosols. Certains avancent ainsi qu’une augmentation du rayonnement diffus durant les dernières décennies aurait déjà entraîné un excédent de captation de carbone par la végétation de 9.3%. La problématique ici soulevée est d’évaluer l’apport de la connaissance du flux solaire absorbé par la surface (combinaison du rayonnement solaire et de l’albédo de surface) et plus particulièrement par sa partie végétative pour le suivi des flux d’énergie, d’eau et de carbone. Dans ce travail, j’ai fait appel à l’observation satellitaire et à la modélisation du transfert radiatif pour cartographier la dynamique du rayonnement solaire absorbé par la surface et sur la verticale de la végétation. Dans un premier temps, chacune des sources d’incertitudes sur le rayonnement incident, sur l’albédo de surface mais aussi sur la répartition du rayonnement entre les hétérogénéités horizontales et verticales à la surface furent quantifiées. Puis tout en discutant l’effet de ces incertitudes, j’ai mesuré l’apport de l’utilisation de cette cartographie par satellite du rayonnement solaire absorbé pour estimer les flux d’énergie et d’eau en surface ; ce qui améliora les scores de prévision du temps à court terme et permis également de suggérer des rétroactions à l’échelle climatique sur des zones sensibles tel le Sahel. Aussi une correction de biais de 15% sur l’estimation de la production primaire brute de carbone à l’échelle planétaire démontra l’importance des développements réalisés afin de caractériser les hétérogénéités verticales dans le couvert. Finalement, ce travail m’a conduit à chiffrer l’impact de la méconnaissance des variabilités spatiales et temporelles des propriétés des aérosols (concentration et type). J’ai montré que le suivi au cours du temps des propriétés de directionalité de la réflectivité de surface (tel abordé dans la première partie de mon étude) pouvait aussi permettre de remonter à la quantité d’aérosol dans l’atmosphère. L’utilisation d’observations issues de satellite géostationnaire permet d’estimer la concentration en aérosol avec la même qualité mais avec une fréquence de détection plus élevée (x5 environ) que les méthodes classiques. Enfin, ce travail dresse des pistes pour améliorer la détection des changements des propriétés de réflectivité de surface et d’aérosols de l’atmosphère, et atteindre un suivi encore meilleur des cycles biogéochimiques de la biosphère terrestre