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Model Resolution (model + resolution)

Distribution by Scientific Domains

Earth and Environmental Science	76%
Engineering	15%

Kinds of Model Resolution

horizontal model resolution

Selected Abstracts

Iterative resolution estimation in least-squares Kirchhoff migration

GEOPHYSICAL PROSPECTING, Issue 6 2002
Sergey Fomel
ABSTRACT We apply iterative resolution estimation to least-squares Kirchhoff migration. Reviewing the theory of iterative optimization uncovers the common origin of different optimization methods. This allows us to reformulate the pseudo-inverse, model resolution and data resolution operators in terms of effective iterative estimates. When applied to Kirchhoff migration, plots of the diagonal of the model resolution matrix reveal low illumination areas on seismic images and provide information about image uncertainties. Synthetic and real data examples illustrate the proposed technique and confirm the theoretical expectations. [source]

A new global biome reconstruction and data-model comparison for the Middle Pliocene

GLOBAL ECOLOGY, Issue 3 2008
U. Salzmann
ABSTRACT Aim, To produce a robust, comprehensive global biome reconstruction for the Middle Pliocene (c. 3.6,2.6 Ma), which is based on an internally consistent palaeobotanical data set and a state-of-the-art coupled climate,vegetation model. The reconstruction gives a more rigorous picture of climate and environmental change during the Middle Pliocene and provides a new boundary condition for future general circulation model (GCM) studies. Location, Global. Methods, Compilation of Middle Pliocene vegetation data from 202 marine and terrestrial sites into the comprehensive GIS data base TEVIS (Tertiary Environmental Information System). Translation into an internally consistent classification scheme using 28 biomes. Comparison and synthesis of vegetation reconstruction from palaeodata with the outputs of the mechanistically based BIOME4 model forced by climatology derived from the HadAM3 GCM. Results, The model results compare favourably with available palaeodata and highlight the importance of employing vegetation,climate feedbacks and the anomaly method in biome models. Both the vegetation reconstruction from palaeobotanical data and the BIOME4 prediction indicate a general warmer and moister climate for the Middle Pliocene. Evergreen taiga as well as temperate forest and grassland shifted northward, resulting in much reduced tundra vegetation. Warm-temperate forests (with subtropical taxa) spread in mid and eastern Europe and tropical savannas and woodland expanded in Africa and Australia at the expense of deserts. Discrepancies which occurred between data reconstruction and model simulation can be related to: (1) poor spatial model resolution and data coverage; (2) uncertainties in delimiting biomes using climate parameters; or (3) uncertainties in model physics and/or geological boundary conditions. Main conclusions, The new global biome reconstruction combines vegetation reconstruction from palaeobotanical proxies with model simulations. It is an important contribution to the further understanding of climate and vegetation changes during the Middle Pliocene warm interval and will enhance our knowledge about how vegetation may change in the future. [source]

On the effects of triangulated terrain resolution on distributed hydrologic model response

HYDROLOGICAL PROCESSES, Issue 11 2005
Enrique R. Vivoni
Abstract Distributed hydrologic models based on triangulated irregular networks (TIN) provide a means for computational efficiency in small to large-scale watershed modelling through an adaptive, multiple resolution representation of complex basin topography. Despite previous research with TIN-based hydrology models, the effect of triangulated terrain resolution on basin hydrologic response has received surprisingly little attention. Evaluating the impact of adaptive gridding on hydrologic response is important for determining the level of detail required in a terrain model. In this study, we address the spatial sensitivity of the TIN-based Real-time Integrated Basin Simulator (tRIBS) in order to assess the variability in the basin-averaged and distributed hydrologic response (water balance, runoff mechanisms, surface saturation, groundwater dynamics) with respect to changes in topographic resolution. Prior to hydrologic simulations, we describe the generation of TIN models that effectively capture topographic and hydrographic variability from grid digital elevation models. In addition, we discuss the sampling methods and performance metrics utilized in the spatial aggregation of triangulated terrain models. For a 64 km2 catchment in northeastern Oklahoma, we conduct a multiple resolution validation experiment by utilizing the tRIBS model over a wide range of spatial aggregation levels. Hydrologic performance is assessed as a function of the terrain resolution, with the variability in basin response attributed to variations in the coupled surface,subsurface dynamics. In particular, resolving the near-stream, variable source area is found to be a key determinant of model behaviour as it controls the dynamic saturation pattern and its effect on rainfall partitioning. A relationship between the hydrologic sensitivity to resolution and the spatial aggregation of terrain attributes is presented as an effective means for selecting the model resolution. Finally, the study highlights the important effects of terrain resolution on distributed hydrologic model response and provides insight into the multiple resolution calibration and validation of TIN-based hydrology models. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Preliminary climatology and improved modelling of south Indian Ocean and Southern Ocean mid-latitude cyclones

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 10 2004
Bruce W. Buckley
Abstract The intense mid-latitude cyclones that traverse the southern waters of the Indian Ocean, between South Africa and southwestern Western Australia, are among the strongest depressions found anywhere in the world, outside tropical waters. Near-surface winds that exceed storm force (i.e. 24 m/s or 48 knots), and central pressures of 960 hPa and lower, are relatively common for these systems. They pose a constant threat to both open ocean and coastal shipping, and regularly generate severe weather over the populated southwestern corner of Australia. Large ocean waves and swell produce extensive coastal inundation and erosion. There were two main aims in this study. The first aim was to develop a preliminary climatology of these intense mid-latitude cyclones, for the region 20,60 °S, 30,130 °E. The climatology, which is the first that we are aware of for this notoriously data-sparse region, is based largely upon satellite observations, particularly scatterometer data, and is supplemented by ship, buoy and all available land observations. The climatology revealed that, historically, the frequency and intensity of the mid-latitude cyclones in this domain have been significantly underestimated. This underestimation has resulted in analyses that have serious flaws, and the resultant operational forecasts provided to the duty forecasters in the regional forecast centre located in Perth, Western Australia, are of highly variable quality. A number of other climatological features of these storms are discussed in this article. The second aim was to identify the factors that can contribute to a significant improvement in model forecasts of these storms. So far, there have been very few studies of explosively developing cyclones over this part of the world. Results are presented here from a series of high-resolution numerical simulations of an intense cool season Southern Ocean cyclone that developed in 2003, using the HIRES numerical weather prediction model developed by L.M. Leslie. Here, we examine the sensitivity of the cyclone predictions to both model resolution and the initial analyses. The predicted variables of most interest are the central pressure, maximum sustained near-surface wind speeds, extent of storm-force winds, and the horizontal and vertical structure of the storm. Increased detail in the initial state is provided mainly by the assimilation into the archived global operational analyses of high-resolution satellite-derived data, including QuikSCAT scatterometer winds and sea-surface temperatures. The combination of increased horizontal and vertical model resolution, and improved initial model states, was found to produce numerical forecasts with significantly more accurate wind speeds than those obtained from the coarser resolution operational models, which also did not have the benefits of all the additional data. Finally, areas of future research are outlined, including coupling the HIRES atmospheric model with ocean and wave models, to improve forecasts of the sea state, including wind wave heights, swell and storm surges. Copyright © 2004 Royal Meteorological Society [source]

Sensitivity of the southern African circulation to dipole sea-surface temperature patterns in the south Indian Ocean

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 4 2002
C. J. C. Reason
Abstract Previous observational work suggests that when sea-surface temperature (SST) is warm (cool) in the southwest Indian Ocean and cool (warm) in the southeast Indian Ocean, increased (decreased) summer rains may occur over large areas of southeastern Africa. In this study, an atmospheric general circulation model is used to investigate the sensitivity of the regional circulation and rainfall over southern Africa to these dipole SST anomalies in the subtropical south Indian Ocean. When the model is forced with positive SST anomalies in the west and negative SST anomalies in the east, increased rainfall occurs over southeastern Africa as a result of the enhanced convergence of moister than average air over the region. Enhanced evaporation occurs over the warm pole in the southwest Indian Ocean and this moist air is advected towards southeastern Africa as a result of the low-pressure anomaly generated over this pole, which strengthens the onshore flow. Increased and more intense extra-tropical cyclones occur to the southeast of South Africa, favourable for tropical,temperate trough formation. When the SST poles are reversed in sign, decreased precipitation occurs over southeastern Africa as a result of increased low-level divergence of low-level flow and this flow being drier than average. Weaker and fewer extra-tropical cyclones occur southeast of South Africa in this case. The model results are sensitive to the proximity of the southwest Indian Ocean pole to southeastern Africa. There is also sensitivity in the model low-level wind changes and precipitation anomaly over low-latitude southern Africa (but not over South Africa to any significant extent) to the presence or absence of the SST pole over the southeast Indian Ocean. Although the model resolution does not capture the details of the local SST and topographic gradients as well as one would like, the changes in model circulation and precipitation in the experiments with different SST anomalies are consistent with previous observational and theoretical work, hence increasing confidence in the robustness of the results. Copyright © 2002 Royal Meteorological Society [source]

Modeling Postfire Response and Recovery using the Hydrologic Engineering Center Hydrologic Modeling System (HEC-HMS),

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 3 2009
Kristina Cydzik
Abstract:, This paper investigates application of the Army Corps of Engineers' Hydrologic Engineering Center Hydrologic Modeling System (HEC-HMS) to a burned watershed in San Bernardino County, California. We evaluate the HEC-HMS' ability to simulate discharge in prefire and postfire conditions in a semi arid watershed and the necessary parameterizations for modeling hydrologic response during the immediate, and subsequent recovery, period after a wildfire. The model is applied to City Creek watershed, which was 90% burned during the Old Fire of October 2003. An optimal spatial resolution for the HEC-HMS model was chosen based on an initial sensitivity analysis of subbasin configurations and related model performance. Five prefire storms were calibrated for the selected model resolution, defining a set of parameters that reasonably simulate prefire conditions. Six postfire storms, two from each of the following rainy (winter) seasons were then selected to simulate postfire response and evaluate relative changes in parameter values and model behavior. There were clear trends in the postfire parameters [initial abstractions (Ia), curve number (CN), and lag time] that reveal significant (and expected) changes in watershed behavior. CN returns to prefire (baseline) values by the end of Year 2, while Ia approaches baseline by the end of the third rainy season. However, lag time remains significantly lower than prefire values throughout the three-year study period. Our results indicate that recovery of soil conditions and related runoff response is not entirely evidenced by the end of the study period (three rainy seasons postfire). Understanding the evolution of the land surface and related hydrologic properties during the highly dynamic postfire period, and accounting for these changes in model parameterizations, will allow for more accurate and reliable discharge simulations in both the immediate, and subsequent, rainy seasons following fire. [source]

Impact of horizontal model resolution and orography on the simulation of a western disturbance and its associated precipitation

METEOROLOGICAL APPLICATIONS, Issue 2 2004
A. P. Dimri
A nonhydrostatic version of Pennsylvania State University/National Center for Atmospheric Research (PSU/NCAR) Mesoscale Model (MM5) is used to study the effects of the horizontal model resolution and orography while simulating an active western disturbance (WD) that affected northwest India from 21 to 25 January 1999. Two numerical experiments are conducted with six combinations of two factors: horizontal model resolution and topography. National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysed data are used for the initial and boundary conditions. Simulation results indicate that the distribution and the rate of simulated precipitation due to a WD over northwest India is highly sensitive to the horizontal model resolution and topography. The model with finer resolution (30 km) is better able to estimate effects of mesoscale forcing on precipitation over the selected domain. The amount of precipitation simulated over the coarse domain is much less than the observed precipitation owing to the model's unrealistic representation of orographic effects and mesoscale forcing. Simulated terrain, vertical velocity, wind and streamline at different horizontal model resolutions are presented. The detailed structure and distribution of wind speed are simulated in the finer domain. Simulated vertical velocity and precipitation are less in the second experiment when a flat topography is used across the domain, which indicates that topography plays a significant role in modulating the WD. Sensitivity of the horizontal model resolution for precipitation is assessed and it is found that the finer domain of the model simulation gives better results. Copyright © 2004 Royal Meteorological Society. [source]

The optimal density of atmospheric sounder observations in the Met Office NWP system

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 629 2007
M. L. Dando
Abstract Large numbers of satellite observations are discarded from the numerical weather prediction (NWP) process because high-density observations may have a negative impact on the analysis. In current assimilation schemes, the observation error covariance matrix R is usually represented as a diagonal matrix, which assumes there are no correlations in the observation errors and that each observation is an independent piece of information. This is not the case when there are strong error correlations and this can lead to a degraded analysis. The experiments conducted in this study were designed to identify the optimal density and to determine if there were circumstances when exceeding this density might be beneficial to forecast skill. The global optimal separation distance of Advanced TIROS Operational Vertical Sounder (ATOVS) observations was identified by comparing global forecast errors produced using different densities of ATOVS. The global average of the absolute forecast error produced by each different density was found for a 3-week period from December 2004 to January 2005. The results showed that, when using the Met Office NWP system with a horizontal model resolution of ,60 km, the lowest global forecast errors were produced when using separation distances of 115,154 km. However, localized regions of the atmosphere containing large gradients such as frontal regions may benefit from thinning distances as small as 40 km and therefore the global optimal separation distance is not necessarily applicable in these circumstances. Copyright © 2007 Royal Meteorological Society [source]

The interaction between model resolution, observation resolution and observation density in data assimilation: A one-dimensional study

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 582 2002
Z.-Q. Liu
Abstract In this paper, the optimal configurations of model resolution, observation resolution and observation density are investigated in a simple one-dimensional framework. In this context, the representativeness error is formalized and estimated before being used in the analysis-error formulation. Some optimal and suboptimal assimilation-schemes, differing from different approximations of observation-error covariance and observation operator, are compared. The optimal observation-extent is determined as a function of model resolution. Increasing the observation density is usually beneficial, except for suboptimal schemes similar to the ones used in operational practice. The impact of thinning the observations with correlated error is also studied from a suboptimal viewpoint. Copyright © 2002 Royal Meteorological Society [source]