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Global Models (global + models)
Selected AbstractsBridging the gap between field data and global models: current strategies in aeolian researchEARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2010Joanna Bullard Abstract Modern global models of earth-atmosphere-ocean processes are becoming increasingly sophisticated but still require validation against empirical data and observations. This commentary reports on international initiatives amongst aeolian researchers that seek to combine field-based data sets and geomorphological frameworks for improving the quality of data available to constrain and validate global models. These include a second iteration of the Dust Indicators and Records from Terrestrial Marine Palaeoenvironments (DIRTMAP2) database, the Digital Atlas of Sand Seas and Dunefields of the World and a new geomorphology-based land surface map produced by the QUEST (Quantifying Uncertainties in the Earth System) Working Group on Dust. Copyright © 2010 John Wiley & Sons, Ltd. [source] A Comparison of Cost of Equity Estimates of Local and Global CAPMsFINANCIAL REVIEW, Issue 4 2001Dev R. Mishra G12/G15/G32 Abstract Cost of equity estimates are compared for three pricing models: the traditional local CAPM, the single (market) factor global CAPM, and the two-factor global CAPM, with both market and currency index factors. For 2989 US stocks, the average difference in the cost of equity estimates is about 48 basis points between the local CAPM and the single-factor global CAPM, and is about 61 basis points between the two global models. For 70 developed-market ADRs, the corresponding average differences are 76 and 47 basis points, respectively. For 48 emerging-market ADRs, the corresponding average differences are 57 and 70 basis points. [source] Tropospheric O3 moderates responses of temperate hardwood forests to elevated CO2: a synthesis of molecular to ecosystem results from the Aspen FACE projectFUNCTIONAL ECOLOGY, Issue 3 2003D. F. Karnosky Summary 1The impacts of elevated atmospheric CO2 and/or O3 have been examined over 4 years using an open-air exposure system in an aggrading northern temperate forest containing two different functional groups (the indeterminate, pioneer, O3 -sensitive species Trembling Aspen, Populus tremuloides and Paper Birch, Betula papyrifera, and the determinate, late successional, O3 -tolerant species Sugar Maple, Acer saccharum). 2The responses to these interacting greenhouse gases have been remarkably consistent in pure Aspen stands and in mixed Aspen/Birch and Aspen/Maple stands, from leaf to ecosystem level, for O3 -tolerant as well as O3 -sensitive genotypes and across various trophic levels. These two gases act in opposing ways, and even at low concentrations (1·5 × ambient, with ambient averaging 34,36 nL L,1 during the summer daylight hours), O3 offsets or moderates the responses induced by elevated CO2. 3After 3 years of exposure to 560 µmol mol,1 CO2, the above-ground volume of Aspen stands was 40% above those grown at ambient CO2, and there was no indication of a diminishing growth trend. In contrast, O3 at 1·5 × ambient completely offset the growth enhancement by CO2, both for O3 -sensitive and O3 -tolerant clones. Implications of this finding for carbon sequestration, plantations to reduce excess CO2, and global models of forest productivity and climate change are presented. [source] Performance assessment of a GCM land surface scheme using a fine-scale calibrated hydrological model: an evaluation of MOSES for the Nile BasinHYDROLOGICAL PROCESSES, Issue 11 2009Mohamed Ezzat Elshamy Abstract Land surface schemes (LSSs) represent the interface between land surface and the atmosphere in general circulation models (GCMs). Errors in LSS-simulated heat and moisture fluxes can result from inadequate representation of hydrological features and the derivation of effective surface parameters for large heterogeneous GCM gridboxes from small-scale observations. Previous assessments of LSS performance have generally compared simulated heat and moisture fluxes to observations over a defined experimental domain for a limited period. A different approach has been evaluated in this study, which uses a fine-resolution calibrated hydrological model of the study basin to provide a quasi-observed runoff series for direct comparison with simulated runoff from a selected LSS at GCM scale. The approach is tested on two GCM gridboxes covering two contrasting regions within the Nile Basin. Performance is mixed; output from the LSS is generally compatible with that of the fine-resolution model for one gridbox while it cannot reproduce the runoff dynamics for the other. The results also demonstrate the high sensitivity of runoff and evapotranspiration to radiation and precipitation inputs and show the importance of subtle issues such as temporal disaggregation of climatic inputs. We conclude that the use of a fine-resolution calibrated model to evaluate a LSS has several advantages, can be generalized to other areas to improve the performance of global models and provides useful data that can be used to constrain LSS parameterizations. Copyright © 2009 John Wiley & Sons, Ltd. [source] Downscaling simulations of future global climate with application to hydrologic modellingINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 4 2005Eric P. Salathé Jr Abstract This study approaches the problem of downscaling global climate model simulations with an emphasis on validating and selecting global models. The downscaling method makes minimal, physically based corrections to the global simulation while preserving much of the statistics of interannual variability in the climate model. Differences among the downscaled results for simulations of present-day climate form a basis for model evaluation. The downscaled results are used to simulate streamflow in the Yakima River, a mountainous basin in Washington, USA, to illustrate how model differences affect streamflow simulations. The downscaling is applied to the output of three models (ECHAM4, HADCM3, and NCAR-PCM) for simulations of historic conditions (1900,2000) and two future emissions scenarios (A2 and B2 for 2000,2100) from the IPCC assessment. The ECHAM4 simulation closely reproduces the observed statistics of temperature and precipitation for the 42 year period 1949,90. Streamflow computed from this climate simulation likewise produces similar statistics to streamflow computed from the observed data. Downscaled climate-change scenarios from these models are examined in light of the differences in the present-day simulations. Streamflows simulated from the ECHAM4 results show the greatest sensitivity to climate change, with the peak in summertime flow occurring 2 months earlier by the end of the 21st century. Copyright © 2005 Royal Meteorological Society. [source] Marine Isotope Stage 7,6 transition age for beach sediments at Morston, north Norfolk, UK: implications for Pleistocene chronology, stratigraphy and tectonics,JOURNAL OF QUATERNARY SCIENCE, Issue 4 2009P. G. Hoare Abstract Optically stimulated luminescence age estimates for the Pleistocene beach at Morston, north Norfolk, UK, obtained by the single-aliquot regenerative-dose protocol, indicate a Marine Isotope Stage (MIS) 7,6 transition date. The view that the beach is of Ipswichian (MIS 5e) age, held virtually unanimously for the last 75 years, may now be discarded. The extant beach sequence lies up to ,5,m OD, yet global models suggest that MIS 7,6 sea levels were typically substantially below that of today. The explanation may lie with poorly understood regional tectonic movements. The MIS 7,6 date helps to constrain the ages of glacial deposits that bracket the beach sediments at Morston. The underlying Marly Drift till cannot be younger than MIS 8; this may also be true for the complex assemblage of glaciogenic landforms and sediments, including the Blakeney esker, in the adjacent lower Glaven valley. The well-established Late Devensian (MIS 2) age of the Hunstanton Till is not compromised by the date of the Morston beach. There is no indication of a proposed Briton's Lane glaciation during MIS 6 times. Copyright © 2009 John Wiley & Sons, Ltd. [source] Non-steady state effects in diurnal 18O discrimination by Picea sitchensis branches in the fieldPLANT CELL & ENVIRONMENT, Issue 5 2006U. SEIBT ABSTRACT We report diurnal variations in 18O discrimination (18,) during photosynthesis (18,A) and respiration (18,R) of Picea sitchensis branches measured in branch chambers in the field. These observations were compared with predicted 18, (18,pred) based on concurrent measurements of branch gas exchange to evaluate steady state and non-steady state (NSS) models of foliage water 18O enrichment for predicting the impact of this ecosystem on the ,18O of atmospheric CO2. The non-steady state approach substantially improved the agreement between 18,pred and observed 18, (18,obs) compared with the assumption of isotopic steady state (ISS) for the ,18O signature of foliage water. In addition, we found direct observational evidence for NSS effects: extremely high apparent 18, values at dusk, dawn and during nocturnal respiration. Our experiments also show the importance of bidirectional foliage gas exchange at night (isotopic equilibration in addition to the net flux). Taken together, neglecting these effects leads to an underestimation of daily net canopy isofluxes from this forest by up to 30%. We expect NSS effects to be most pronounced in species with high specific leaf water content such as conifers and when stomata are open at night or when there is high relative humidity, and we suggest modifications to ecosystem and global models of ,18O of CO2. [source] Recent developments in gravity-wave effects in climate models and the global distribution of gravity-wave momentum flux from observations and modelsTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 650 2010M. J. Alexander Abstract Recent observational and theoretical studies of the global properties of small-scale atmospheric gravity waves have highlighted the global effects of these waves on the circulation from the surface to the middle atmosphere. The effects of gravity waves on the large-scale circulation have long been treated via parametrizations in both climate and weather-forecasting applications. In these parametrizations, key parameters describe the global distributions of gravity-wave momentum flux, wavelengths and frequencies. Until recently, global observations could not define the required parameters because the waves are small in scale and intermittent in occurrence. Recent satellite and other global datasets with improved resolution, along with innovative analysis methods, are now providing constraints for the parametrizations that can improve the treatment of these waves in climate-prediction models. Research using very-high-resolution global models has also recently demonstrated the capability to resolve gravity waves and their circulation effects, and when tested against observations these models show some very realistic properties. Here we review recent studies on gravity-wave effects in stratosphere-resolving climate models, recent observations and analysis methods that reveal global patterns in gravity-wave momentum fluxes and results of very-high-resolution model studies, and we outline some future research requirements to improve the treatment of these waves in climate simulations. Copyright © 2010 Royal Meteorological Society and Crown in the right of Canada [source] Assessment of the impact of key terrestrial observing systems using DMI-HIRLAMTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 633 2008Bjarne Amstrup Abstract Following a EUCOS decision to make an assessment of the impact on NWP forecasts of different components of the current observing systems in various combinations, a number of OSEs (Observing System Experiments) have been made by a number of NWP centres, with some running global models and some limited-area models. The Danish Meteorological Institute (DMI) carried out OSEs with the limited-area model HIRLAM. The following runs were made by DMI (two periods, one month each): (1) A baseline system (BL); (2) BL + all aircraft wind and temperature data; (3) BL + non-GUAN radiosonde winds; (4) BL + non-GUAN radiosonde temperature and wind; (5) BL + wind profiler; (6) as (4) + aircraft wind and temperature; (7) as (4) + non-GUAN radiosonde humidity; (8) as BL + all in situ data (full combined system); and (9) BL + E-AMDAR only (no ACARS and no traditional AIREPs). The lateral boundaries for these OSEs were provided by runs made by ECMWF, which was one of the centres to make OSEs with a global model. The main conclusions are that the radiosonde data are the most important data, closely followed by the aircraft data, and that aircraft data and radiosonde data are complementary and not redundant data. Furthermore the results show that it is important to have both wind and temperature profile data; wind data alone produce much poorer impact. Copyright © 2008 Royal Meteorological Society [source] A global Eta model on quasi-uniform gridsTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 623 2007Hai Zhang Abstract The application of quasi-uniform grids in global models of the atmosphere is an attempt to increase the computational efficiency by a more cost-effective exploitation of the computing infrastructure. This paper describes the development of a global version of NCEP's regional, step-coordinate, Eta model on two quasi-uniform grids: cubic and octagonal. The governing equations are expressed in a general curvilinear form, so that the cubic and the octagonal versions of the model share the same code in spite of different mapping of the computational domain. The dynamical core of the derived global Eta model is successfully tested in the benchmark test of Held and Suarez. The model with the step-wise formulation of the terrain and full physics is integrated in a series of tests with real data, and the results are compared both with the analysis and the results of the regional Eta model. Copyright © 2007 Royal Meteorological Society [source] Differential rotation and meridional circulation in global models of solar convectionASTRONOMISCHE NACHRICHTEN, Issue 10 2007M.S. MieschArticle first published online: 27 DEC 200 Abstract In the outer envelope of the Sun and in other stars, differential rotation and meridional circulation are maintained via the redistribution of momentum and energy by convective motions. In order to properly capture such processes in a numerical model, the correct spherical geometry is essential. In this paper I review recent insights into the maintenance of mean flows in the solar interior obtained from high-resolution simulations of solar convection in rotating spherical shells. The Coriolis force induces a Reynolds stress which transports angular momentum equatorward and also yields latitudinal variations in the convective heat flux. Meridional circulations induced by baroclinicity and rotational shear further redistribute angular momentum and alter the mean stratification. This gives rise to a complex nonlinear interplay between turbulent convection, differential rotation, meridional circulation, and the mean specific entropy profile. I will describe how this drama plays out in our simulations as well as in solar and stellar convection zones. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||