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  • 1
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    Analysis of diurnal and seasonal cycles and trends in climatic records with arbitrary observation times : DIURNAL AND SEASONAL CYCLES AND TRENDS
    American Geophysical Union (AGU) ; 2004
    In:  Geophysical Research Letters Vol. 31, No. 6 ( 2004-03), p. n/a-n/a
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 31, No. 6 ( 2004-03), p. n/a-n/a
    Materialart: Online-Ressource
    ISSN: 0094-8276
    URL: Article
    DOI: 10.1029/2003GL019196
    Sprache: Englisch
    Verlag: American Geophysical Union (AGU)
    Publikationsdatum: 2004
    ZDB Id: 2021599-X
    ZDB Id: 7403-2
    SSG: 16,13
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  • 2
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    Arctic Oscillation response to the 1991 Mount Pinatubo eruption: Effects of volcanic aerosols and ozone depletion
    American Geophysical Union (AGU) ; 2002
    In:  Journal of Geophysical Research: Atmospheres Vol. 107, No. D24 ( 2002-12-27)
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 107, No. D24 ( 2002-12-27)
    Kurzfassung: Observations show that strong equatorial volcanic eruptions have been followed by a pronounced positive phase of the Arctic Oscillation (AO) for one or two Northern Hemisphere winters. It has been previously assumed that this effect is forced by strengthening of the equator‐to‐pole temperature gradient in the lower stratosphere, caused by aerosol radiative heating in the tropics. To understand atmospheric processes that cause the AO response, we studied the impact of the 1991 Mount Pinatubo eruption, which produced the largest global volcanic aerosol cloud in the twentieth century. A series of control and perturbation experiments were conducted with the GFDL SKYHI general circulation model to examine the evolution of the circulation in the 2 years following the Pinatubo eruption. In one set of perturbation experiments, the full radiative effects of the observed Pinatubo aerosol cloud were included, while in another only the effects of the aerosols in reducing the solar flux in the troposphere were included, and the aerosol heating effects in the stratosphere were suppressed. A third set of perturbation experiments imposed the stratospheric ozone losses observed in the post‐Pinatubo period. We conducted ensembles of four to eight realizations for each case. Forced by aerosols, SKYHI produces a statistically significant positive phase of the AO in winter, as observed. Ozone depletion causes a positive phase of the AO in late winter and early spring by cooling the lower stratosphere in high latitudes, strengthening the polar night jet, and delaying the final warming. A positive phase of the AO was also produced in the experiment with only the tropospheric effect of aerosols, showing that aerosol heating in the lower tropical stratosphere is not necessary to force positive AO response, as was previously assumed. Aerosol‐induced tropospheric cooling in the subtropics decreases the meridional temperature gradient in the winter troposphere between 30°N and 60°N. The corresponding reduction of mean zonal energy and amplitudes of planetary waves in the troposphere decreases wave activity flux into the lower stratosphere. The resulting strengthening of the polar vortex forces a positive phase of the AO. We suggest that this mechanism can also contribute to the observed long‐term AO trend being caused by greenhouse gas increases because they also weaken the tropospheric meridional temperature gradient due to polar amplification of warming.
    Materialart: Online-Ressource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2002JD002090
    Sprache: Englisch
    Verlag: American Geophysical Union (AGU)
    Publikationsdatum: 2002
    ZDB Id: 2033040-6
    ZDB Id: 3094104-0
    ZDB Id: 2130824-X
    ZDB Id: 2016813-5
    ZDB Id: 2016810-X
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    ZDB Id: 2969341-X
    ZDB Id: 161665-1
    ZDB Id: 3094268-8
    ZDB Id: 710256-2
    ZDB Id: 2016804-4
    ZDB Id: 3094181-7
    ZDB Id: 3094219-6
    ZDB Id: 3094167-2
    ZDB Id: 2220777-6
    ZDB Id: 3094197-0
    SSG: 16,13
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  • 3
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    Land surface model spin‐up behavior in the North American Land Data Assimilation System (NLDAS)
    American Geophysical Union (AGU) ; 2003
    In:  Journal of Geophysical Research: Atmospheres Vol. 108, No. D22 ( 2003-11-27)
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 108, No. D22 ( 2003-11-27)
    Kurzfassung: The process of a model adjusting to its forcing (model spin‐up) can severely bias land surface simulations, and result in questionable land surface model (LSM) output during the spin‐up process. To gain a better understanding of how spin‐up processes affect complex spatial and temporal land surface modeling situations in general, and the Retrospective North American Land Data Assimilation System (NLDAS) simulations in particular, a two‐phase study was conducted. The first phase examined results from Control, Wet, and Dry 11 year‐long Mosaic simulations, while the second phase attempted to explain spin‐up behavior in NLDAS Retrospective simulations from the Mosaic, Noah, VIC and Sacramento LSMs based in part on the results from phase 1. Total column and root zone soil moisture spin up slowly, while evaporation and deep soil temperature spin up more quickly. Mosaic soil moisture initialization with NCEP/DOE Global Reanalysis 2 (NCEP/DOE R‐2) data (Control run) leads to a faster spin‐up time than saturated (Wet run) or dry (Dry run) initialization, with the Control run reaching equilibrium 1 to 2 years sooner than the Wet run and 3 to 4 years more quickly than the Dry run. Overall, practical drift of land surface stores and output ceased in the Control run within approximately 1 year, and fine‐scale equilibrium was reached within 5.5 years. Spin‐up times exhibited large spatial variability, and although no single causal factor could be determined, they were correlated most strongly with precipitation and temperature forcing. In general, NLDAS models reach a state of rough equilibrium within the first 1 to 2 years of the 3‐year Retrospective simulation. The Sacramento LSM has the shortest spin‐up phase, followed by the Mosaic, VIC, and Noah LSMs. Initial NCEP/DOE R‐2 conditions were too dry in general for the VIC and Noah LSMs, and too moist for the Mosaic and Sacramento LSMs. These results indicate that in most cases, the 1‐year spin‐up time used in the Retrospective NLDAS simulations eliminated spin‐up problems from the subsequent period that was used for analysis.
    Materialart: Online-Ressource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2002JD003316
    Sprache: Englisch
    Verlag: American Geophysical Union (AGU)
    Publikationsdatum: 2003
    ZDB Id: 2033040-6
    ZDB Id: 3094104-0
    ZDB Id: 2130824-X
    ZDB Id: 2016813-5
    ZDB Id: 2016810-X
    ZDB Id: 2403298-0
    ZDB Id: 2016800-7
    ZDB Id: 161666-3
    ZDB Id: 161667-5
    ZDB Id: 2969341-X
    ZDB Id: 161665-1
    ZDB Id: 3094268-8
    ZDB Id: 710256-2
    ZDB Id: 2016804-4
    ZDB Id: 3094181-7
    ZDB Id: 3094219-6
    ZDB Id: 3094167-2
    ZDB Id: 2220777-6
    ZDB Id: 3094197-0
    SSG: 16,13
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  • 4
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    Stratospheric Forcing Needed for Dynamical Seasonal Prediction
    American Meteorological Society ; 2001
    In:  Bulletin of the American Meteorological Society Vol. 82, No. 10 ( 2001-10), p. 2189-2192
    Details
    In: Bulletin of the American Meteorological Society, American Meteorological Society, Vol. 82, No. 10 ( 2001-10), p. 2189-2192
    Materialart: Online-Ressource
    ISSN: 0003-0007 , 1520-0477
    URL: Article
    DOI: 10.1175/1520-0477(2001)082〈2189:SFNFDS〉2.3.CO;2
    Sprache: Englisch
    Verlag: American Meteorological Society
    Publikationsdatum: 2001
    ZDB Id: 2029396-3
    ZDB Id: 419957-1
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  • 5
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    Simulations of a Boreal Grassland Hydrology at Valdai, Russia: PILPS Phase 2(d)
    American Meteorological Society ; 2000
    In:  Monthly Weather Review Vol. 128, No. 2 ( 2000-2), p. 301-321
    Details
    In: Monthly Weather Review, American Meteorological Society, Vol. 128, No. 2 ( 2000-2), p. 301-321
    Materialart: Online-Ressource
    ISSN: 1520-0493
    URL: Article
    DOI: 10.1175/1520-0493(2000)128〈0301:SOABGH〉2.0.CO;2
    Sprache: Unbekannt
    Verlag: American Meteorological Society
    Publikationsdatum: 2000
    ZDB Id: 2033056-X
    ZDB Id: 202616-8
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  • 6
    Online-Ressource
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    A comparison of single column model simulations of summertime midlatitude continental convection
    American Geophysical Union (AGU) ; 2000
    In:  Journal of Geophysical Research: Atmospheres Vol. 105, No. D2 ( 2000-01-27), p. 2091-2124
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 105, No. D2 ( 2000-01-27), p. 2091-2124
    Kurzfassung: Eleven different single‐column models (SCMs) and one cloud ensemble model (CEM) are driven by boundary conditions observed at the Atmospheric Radiation Measurement (ARM) program southern Great Plains site for a 17 day period during the summer of 1995. Comparison of the model simulations reveals common signatures identifiable as products of errors in the boundary conditions. Intermodel differences in the simulated temperature, humidity, cloud, precipitation, and radiative fluxes reflect differences in model resolution or physical parameterizations, although sensitive dependence on initial conditions can also contribute to intermodel differences. All models perform well at times but poorly at others. Although none of the SCM simulations stands out as superior to the others, the simulation by the CEM is in several respects in better agreement with the observations than the simulations by the SCMs. Nudging of the simulated temperature and humidity toward observations generally improves the simulated cloud and radiation fields as well as the simulated temperature and humidity but degrades the precipitation simulation for models with large temperature and humidity biases without nudging. Although some of the intermodel differences have not been explained, others have been identified as model problems that can be or have been corrected as a result of the comparison.
    Materialart: Online-Ressource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/1999JD900971
    Sprache: Englisch
    Verlag: American Geophysical Union (AGU)
    Publikationsdatum: 2000
    ZDB Id: 2033040-6
    ZDB Id: 3094104-0
    ZDB Id: 2130824-X
    ZDB Id: 2016813-5
    ZDB Id: 2016810-X
    ZDB Id: 2403298-0
    ZDB Id: 2016800-7
    ZDB Id: 161666-3
    ZDB Id: 161667-5
    ZDB Id: 2969341-X
    ZDB Id: 161665-1
    ZDB Id: 3094268-8
    ZDB Id: 710256-2
    ZDB Id: 2016804-4
    ZDB Id: 3094181-7
    ZDB Id: 3094219-6
    ZDB Id: 3094167-2
    ZDB Id: 2220777-6
    ZDB Id: 3094197-0
    SSG: 16,13
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  • 7
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    Soil moisture simulations in revised AMIP models
    American Geophysical Union (AGU) ; 2000
    In:  Journal of Geophysical Research: Atmospheres Vol. 105, No. D21 ( 2000-11-16), p. 26635-26644
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 105, No. D21 ( 2000-11-16), p. 26635-26644
    Kurzfassung: Soil moisture is important both in its influence on climate and for assessing impacts of future climate change. It is therefore necessary to simulate it correctly in global climate models. We have used the revisit simulations contributed by six of the Atmospheric Model Intercomparison Project 1 participating modeling groups to examine the impacts of model revisions, particularly the land surface representations, on soil moisture simulations, by comparing the simulations to actual soil moisture observations. The revised models do not show any systematic improvement in their ability to simulate observed seasonal variations of soil moisture over the regions studied. Many of the revised models continue to have a strong tendency toward dry soil conditions during Northern Hemisphere summer months, both globally and regionally. There are no indications of conceptually more realistic land surface representations producing better soil moisture simulations in the revised climate models. As the revised models continue to produce incorrect simulations of the seasonal cycle of regional precipitation, it is not possible to isolate the effect of land surface schemes on the simulations. The European Centre for Medium Range Weather Forecasts and National Centers for Environmental Prediction/National Center for Atmospheric Research reanalyses, however, which are driven by observed precipitation, do capture some of the observed interannual variability of soil moisture over Illinois.
    Materialart: Online-Ressource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2000JD900443
    Sprache: Englisch
    Verlag: American Geophysical Union (AGU)
    Publikationsdatum: 2000
    ZDB Id: 2033040-6
    ZDB Id: 3094104-0
    ZDB Id: 2130824-X
    ZDB Id: 2016813-5
    ZDB Id: 2016810-X
    ZDB Id: 2403298-0
    ZDB Id: 2016800-7
    ZDB Id: 161666-3
    ZDB Id: 161667-5
    ZDB Id: 2969341-X
    ZDB Id: 161665-1
    ZDB Id: 3094268-8
    ZDB Id: 710256-2
    ZDB Id: 2016804-4
    ZDB Id: 3094181-7
    ZDB Id: 3094219-6
    ZDB Id: 3094167-2
    ZDB Id: 2220777-6
    ZDB Id: 3094197-0
    SSG: 16,13
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  • 8
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    Real‐time and retrospective forcing in the North American Land Data Assimilation System (NLDAS) project
    American Geophysical Union (AGU) ; 2003
    In:  Journal of Geophysical Research: Atmospheres Vol. 108, No. D22 ( 2003-11-27)
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 108, No. D22 ( 2003-11-27)
    Kurzfassung: The accuracy of forcing data greatly impacts the ability of land surface models (LSMs) to produce realistic simulations of land surface processes. With this in mind, the multi‐institutional North American Land Data Assimilation System (NLDAS) project has produced retrospective (1996–2002) and real‐time (1999–present) data sets to support its LSM modeling activities. Featuring 0.125° spatial resolution, hourly temporal resolution, nine primary forcing fields, and six secondary validation/model development fields, each data set is based on a backbone of Eta Data Assimilation System/Eta data and is supplemented with observation‐based precipitation and radiation data. Hourly observation‐based precipitation data are derived from a combination of daily National Center for Environmental Prediction Climate Prediction Center (CPC) gauge‐based precipitation analyses and hourly National Weather Service Doppler radar‐based (WSR‐88D) precipitation analyses, wherein the hourly radar‐based analyses are used to temporally disaggregate the daily CPC analyses. NLDAS observation‐based shortwave values are derived from Geostationary Operational Environmental Satellite radiation data processed at the University of Maryland and at the National Environmental Satellite Data and Information Service. Extensive quality control and validation efforts have been conducted on the NLDAS forcing data sets, and favorable comparisons have taken place with Oklahoma Mesonet, Atmospheric Radiation Measurement Program/cloud and radiation test bed, and Surface Radiation observation data. The real‐time forcing data set is constantly evolving to make use of the latest advances in forcing‐related data sets, and all of the real‐time and retrospective data are available online at http://ldas.gsfc.nasa.gov for visualization and downloading in both full and subset forms.
    Materialart: Online-Ressource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2002JD003118
    Sprache: Englisch
    Verlag: American Geophysical Union (AGU)
    Publikationsdatum: 2003
    ZDB Id: 2033040-6
    ZDB Id: 3094104-0
    ZDB Id: 2130824-X
    ZDB Id: 2016813-5
    ZDB Id: 2016810-X
    ZDB Id: 2403298-0
    ZDB Id: 2016800-7
    ZDB Id: 161666-3
    ZDB Id: 161667-5
    ZDB Id: 2969341-X
    ZDB Id: 161665-1
    ZDB Id: 3094268-8
    ZDB Id: 710256-2
    ZDB Id: 2016804-4
    ZDB Id: 3094181-7
    ZDB Id: 3094219-6
    ZDB Id: 3094167-2
    ZDB Id: 2220777-6
    ZDB Id: 3094197-0
    SSG: 16,13
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  • 9
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    Evaluation of the North American Land Data Assimilation System over the southern Great Plains during the warm season
    American Geophysical Union (AGU) ; 2003
    In:  Journal of Geophysical Research: Atmospheres Vol. 108, No. D22 ( 2003-11-27)
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 108, No. D22 ( 2003-11-27)
    Kurzfassung: North American Land Data Assimilation System (NLDAS) land surface models have been run for a retrospective period forced by atmospheric observations from the Eta analysis and actual precipitation and downward solar radiation to calculate land hydrology. We evaluated these simulations using in situ observations over the southern Great Plains for the periods of May–September of 1998 and 1999 by comparing the model outputs with surface latent, sensible, and ground heat fluxes at 24 Atmospheric Radiation Measurement/Cloud and Radiation Testbed stations and with soil temperature and soil moisture observations at 72 Oklahoma Mesonet stations. The standard NLDAS models do a fairly good job but with differences in the surface energy partition and in soil moisture between models and observations and among models during the summer, while they agree quite well on the soil temperature simulations. To investigate why, we performed a series of experiments accounting for differences between model‐specified soil types and vegetation and those observed at the stations, and differences in model treatment of different soil types, vegetation properties, canopy resistance, soil column depth, rooting depth, root density, snow‐free albedo, infiltration, aerodynamic resistance, and soil thermal diffusivity. The diagnosis and model enhancements demonstrate how the models can be improved so that they can be used in actual data assimilation mode.
    Materialart: Online-Ressource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2002JD003245
    Sprache: Englisch
    Verlag: American Geophysical Union (AGU)
    Publikationsdatum: 2003
    ZDB Id: 2033040-6
    ZDB Id: 3094104-0
    ZDB Id: 2130824-X
    ZDB Id: 2016813-5
    ZDB Id: 2016810-X
    ZDB Id: 2403298-0
    ZDB Id: 2016800-7
    ZDB Id: 161666-3
    ZDB Id: 161667-5
    ZDB Id: 2969341-X
    ZDB Id: 161665-1
    ZDB Id: 3094268-8
    ZDB Id: 710256-2
    ZDB Id: 2016804-4
    ZDB Id: 3094181-7
    ZDB Id: 3094219-6
    ZDB Id: 3094167-2
    ZDB Id: 2220777-6
    ZDB Id: 3094197-0
    SSG: 16,13
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  • 10
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    Snow process modeling in the North American Land Data Assimilation System (NLDAS): 1. Evaluation of model‐simulated snow cover extent
    American Geophysical Union (AGU) ; 2003
    In:  Journal of Geophysical Research: Atmospheres Vol. 108, No. D22 ( 2003-11-27)
    Details
    In: Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), Vol. 108, No. D22 ( 2003-11-27)
    Kurzfassung: This study evaluates the cold season process modeling in the North American Land Data Assimilation System (NLDAS) and consists of two parts: (1) assessment of land surface model simulations of snow cover extent and (2) evaluation of snow water equivalent. In this first part, simulations of snow cover extent from the four land surface models (Noah, MOSAIC, Sacramento land surface model (SAC), and variable infiltration capacity land surface model (VIC)) in the NLDAS were compared with observational data from the Interactive Multisensor Snow and Ice Mapping System for a 3 year retrospective period over the conterminous United States. In general, all models simulate reasonably well the regional‐scale spatial and seasonal dynamics of snow cover. Systematic biases are seen in the model simulations, with consistent underestimation of snow cover extent by MOSAIC (−19.8% average bias) and Noah (−22.5%), and overestimation by VIC (22.3%), with SAC being essentially unbiased on average. However, the level of bias at the regional scale varies with geographic location and elevation variability. Larger discrepancies are seen over higher elevation regions of the northwest of the United States that may be due, in part, to errors in the meteorological forcings and also at the snow line boundary, where most temporal and spatial variability in snow cover extent is likely to occur. The spread between model simulations is fairly low and generally envelopes the observed data at the mean regional scale, indicating that the models are quite capable of simulating the general behavior of snow processes at these scales. Intermodel differences can be explained to some extent by differences in the model representations of subgrid variability and parameterizations of snow cover extent.
    Materialart: Online-Ressource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2002JD003274
    Sprache: Englisch
    Verlag: American Geophysical Union (AGU)
    Publikationsdatum: 2003
    ZDB Id: 2033040-6
    ZDB Id: 3094104-0
    ZDB Id: 2130824-X
    ZDB Id: 2016813-5
    ZDB Id: 2016810-X
    ZDB Id: 2403298-0
    ZDB Id: 2016800-7
    ZDB Id: 161666-3
    ZDB Id: 161667-5
    ZDB Id: 2969341-X
    ZDB Id: 161665-1
    ZDB Id: 3094268-8
    ZDB Id: 710256-2
    ZDB Id: 2016804-4
    ZDB Id: 3094181-7
    ZDB Id: 3094219-6
    ZDB Id: 3094167-2
    ZDB Id: 2220777-6
    ZDB Id: 3094197-0
    SSG: 16,13
    Standort Signatur Einschränkungen Verfügbarkeit
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