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Mesoscale Model (mesoscale + model)
Selected AbstractsImpact of horizontal model resolution and orography on the simulation of a western disturbance and its associated precipitationMETEOROLOGICAL APPLICATIONS, Issue 2 2004A. 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] Simulations of low-level convergence lines over north-eastern AustraliaTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 616 2006Gerald L. Thomsen Abstract We describe high-resolution numerical model simulations of low-level convergence lines over north-eastern Australia using the Pennsylvania State University/National Center for Atmospheric Research Mesoscale Model (MM5). The simulations are for selected events that were documented during the Gulf Lines Experiment, held in September,October 2002. The calculations provide further insights into the dynamics of the convergence lines and the mechanisms involved in their formation. In particular they show two clearly distinct convergence lines, one that corresponds to the morning glory and one which corresponds to the North Australian Cloud Line; the former originates from the east-coast sea breeze over Cape York Peninsula south of about 14°S, while the latter originates from the east-coast sea breeze north of this latitude. They support also a recently proposed conceptual model for the generation of southerly morning glories and show for the first time the separation of a bore-like disturbance following the collision of a nocturnal cold front to the south of the inland trough with a sea-breeze front to the north of the trough. Moreover, they show the progressive transition of the east-coast sea-breeze front and the inland cold front from gravity-current-like flows to bore-like disturbances overnight to form north-easterly and southerly morning glories, respectively. Copyright © 2006 Royal Meteorological Society. [source] Climate warming, dispersal inhibition and extinction riskGLOBAL CHANGE BIOLOGY, Issue 3 2008MANUEL MASSOT Abstract Global warming impels species to track their shifting habitats or adapt to new conditions. Both processes are critically influenced by individual dispersal. In many animals, dispersal behaviour is plastic, but how organisms with plastic dispersal respond to climate change is basically unknown. Here, we report the analysis of interannual dispersal change from 16 years of monitoring a wild population of the common lizard, and a 12-year manipulation of lizards' diet intended to disentangle the direct effect of temperature rise on dispersal from its effects on resource availability. We show that juvenile dispersal has declined dramatically over the last 16 years, paralleling the rise of spring temperatures during embryogenesis. A mesoscale model of metapopulation dynamics predicts that in general dispersal inhibition will elevate the extinction risk of metapopulations exposed to contrasting effects of climate warming. [source] Assessing the spatial and temporal variation in the skill of precipitation forecasts from an NWP modelMETEOROLOGICAL APPLICATIONS, Issue 1 2008Nigel Roberts Abstract It is becoming increasingly important to be able to verify the spatial accuracy of precipitation forecasts, especially with the advent of high-resolution numerical weather prediction (NWP) models. In this article, the fractions skill score (FSS) approach has been used to perform a scale-selective evaluation of precipitation forecasts during 2003 from the Met Office mesoscale model (12 km grid length). The investigation shows how skill varies with spatial scale, the scales over which the data assimilation (DA) adds most skill, and how the loss of that skill is dependent on both the spatial scale and the rainfall coverage being examined. Although these results come from a specific model, they demonstrate how this verification approach can provide a quantitative assessment of the spatial behaviour of new finer-resolution models and DA techniques. Copyright © 2008 Royal Meteorological Society [source] Mesoscale simulations of atmospheric flow and tracer transport in Phoenix, ArizonaMETEOROLOGICAL APPLICATIONS, Issue 3 2006Ge Wang Abstract Large urban centres located within confining rugged or complex terrain can frequently experience episodes of high concentrations of lower atmospheric pollution. Metropolitan Phoenix, Arizona (United States), is a good example, as the general population is occasionally subjected to high levels of lower atmospheric ozone, carbon monoxide and suspended particulate matter. As a result of dramatic but continuous increase in population, the accompanying environmental stresses and the local atmospheric circulation that dominates the background flow, an accurate simulation of the mesoscale pollutant transport across Phoenix and similar urban areas is becoming increasingly important. This is particularly the case in an airshed, such as that of Phoenix, where the local atmospheric circulation is complicated by the complex terrain of the area. Within the study presented here, a three-dimensional time-dependent mesoscale meteorological model (HOTMAC) is employed for simulation of lower-atmospheric flow in Phoenix, for both winter and summer case-study periods in 1998. The specific purpose of the work is to test the model's ability to replicate the atmospheric flow based on the actual observations of the lower-atmospheric wind profile and known physical principles. While a reasonable general agreement is found between the model-produced flow and the observed one, the simulation of near-surface wind direction produces a much less accurate representation of actual conditions, as does the simulation of wind speed over 1,000 metres above the surface. Using the wind and turbulence output from the mesoscale model, likely particle plume trajectories are simulated for the case-study periods using a puff dispersion model (RAPTAD). Overall, the results provide encouragement for the efforts towards accurately simulating the mesoscale transport of lower-atmospheric pollutants in environments of complex terrain. Copyright © 2006 John Wiley & Sons, Ltd. [source] Wind speed-up in the Dover Straits with the Met Office New Dynamics ModelMETEOROLOGICAL APPLICATIONS, Issue 3 2003Rachel Anne Capon It is part of British sailing and forecasting folklore that the wind speed increases in the Dover Straits when there is an established wind-flow ,westerly/south-westerly or easterly/north-easterly ,along the English Channel. However the underlying mechanism of the phenomenon is unclear. We have used the Met Office ,New Dynamics' mesoscale model to perform a case study on an occasion when this phenomenon was observed in the Channel but not forecast well by the operational model, UM 4.5. Results are presented showing the sensitivity of forecasts to horizontal resolution (down to 2 km) and to vertical resolution. We probe the physical mechanism of the Channel jet by altering the surrounding orography and the land or sea surface roughness. Both the orography and the surface roughness are shown to influence the jet formation. Copyright © 2003 Royal Meteorological Society [source] Interaction of katabatic winds and mesocyclones near the eastern coast of GreenlandMETEOROLOGICAL APPLICATIONS, Issue 4 2002Thomas Klein Satellite images occasionally show the existence of mesocyclones (MCs) close to the eastern coast of Greenland, especially in the region of Angmagssalik/Tasiilaq. The forcing mechanisms of such MCs are investigated by means of numerical simulations with a three-dimensional mesoscale model. The special characteristics of the East Greenland topography are shown to be a key factor for the development of the MCs. The channeling of the flow in large valleys along the East Greenland coast leads to a convergence, implying a vertical stretching of the flow through the valleys and the generation of cyclonic vorticity. This convergence can be strong during intense katabatic storms, so-called Piteraqs, which are a much-feared phenomenon in that area of Greenland. During these situations the synoptic environment enforces the katabatic flow. The results of the simulations suggest a close relationship between the occurrence of Piteraqs and the generation of mesoscale vortices close to the East Greenland coast. An improved understanding of these processes will help forecasters to advise aircraft and ship operations near the coast of East Greenland. Copyright © 2002 Royal Meteorological Society. [source] The effects of aerosols on intense convective precipitation in the northeastern United States,THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 643 2009Alexandros A. Ntelekos Abstract A fully coupled meteorology-chemistry-aerosol mesoscale model (WRF-Chem) is used to assess the effects of aerosols on intense convective precipitation over the northeastern United States. Numerical experiments are performed for three intense convective storm days and for two scenarios representing ,typical' and ,low' aerosol conditions. The results of the simulations suggest that increasing concentrations of aerosols can lead to either enhancement or suppression of precipitation. Quantification of the aerosol effect is sensitive to the metric used due to a shift of rainfall accumulation distribution when realistic aerosol concentrations are included in the simulations. Maximum rainfall accumulation amounts and areas with rainfall accumulations exceeding specified thresholds provide robust metrics of the aerosol effect on convective precipitation. Storms developing over areas with medium to low aerosol concentrations showed a suppression effect on rainfall independent of the meteorological environment. Storms developing in areas of relatively high particulate concentrations showed enhancement of rainfall when there were simultaneous high values of convective available potential energy, relative humidity and wind shear. In these cases, elevated aerosol concentrations resulted in stronger updraughts and downdraughts and more coherent organization of convection. For the extreme case, maximum rainfall accumulation differences exceeded 40 mm. The modelling results suggest that areas of the northeastern US urban corridor that are close to or downwind of intense sources of aerosols, could be more favourable for rainfall enhancement due to aerosols for the aerosol concentrations typical of this area. Copyright © 2009 Royal Meteorological Society [source] Sources of water vapour contributing to the Elbe flood in August 2002,A tagging study in a mesoscale modelTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 638 2009H. Sodemann Abstract In this study we investigate the contribution of various moisture sources to the Elbe flood that occurred in Central Europe during August 2002. An 8-day simulation with the mesoscale numerical weather prediction model CHRM, including newly implemented water vapour tracers, has been performed. According to the simulation, rather than drawing moisture from one single dominant source region, water vapour from widely separated moisture sources contributed to the extreme precipitation in the most affected area, notably at distinct, subsequent periods of time, and each in significant amounts. These moisture sources include the Atlantic and Mediterranean ocean areas inside the model domain, evapotranspiration from land areas, and long-range advection from subtropical areas outside the model domain. The results highlight the importance of the concurrent upper-level circulation and the mesoscale flow structures associated with the cyclone for producing extreme precipitation in parts of Germany, Austria, and the Czech Republic during that period. Furthermore, the numerical and technical problems of implementing water vapour tracers into a limited-area model are discussed, including conservative tracer advection, initialization, boundary treatment, and the handling of precipitation parametrizations. An evaluation of the consistency of the method in terms of water vapour, cloud water, and precipitation is provided, with generally satisfying results. The model with its detailed water vapour tracer implementation can now be used for further case-studies and climatological simulations, and serve as a reference for evaluating the performance of other moisture tracking methods, such as those based on backward trajectories. Copyright © 2009 Royal Meteorological Society [source] Data assimilation of high-density observations.THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 605 2005I: Impact on initial conditions for the MAP/SOP IOP2b Abstract An attempt is made to evaluate the impact of the data assimilation of high-frequency data on the initial conditions. The data assimilation of all the data available on the Mesoscale Alpine Program archive for a test case is performed using the objective analysis and the Variational Data Assimilation (Var) techniques. The objective analysis is performed using two different schemes: Cressman and multiquadric; 3D-Var is used for the variational analysis. The European Centre for Medium-Range Weather Forecasts analyses are used as first guess, and they are blended together with the observations to generate an improved set of mesoscale initial and boundary conditions for the Intensive Observing Period 2b (17,21 September 1999). A few experiments are performed using the initialization procedure of MM5, the mesoscale model from Penn State University/National Center for Atmospheric Research. The comparison between improved initial conditions and observations shows: (i) the assimilation of the surface and upper-air data has a large positive impact on the initial conditions depending on the technique used for the objective analysis; (ii) a large decrease of the error for the meridional component of the wind V at the initial time is found, if assimilation of three-hourly data is performed by objective analysis; (iii) a comparable improvement of the initial conditions with respect to the objective analysis is found if 3D-Var is used, but a large error is obtained for the V component of the wind. Copyright © 2005 Royal Meteorological Society [source] Data assimilation of high-density observations.THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 605 2005II: Impact on the forecast of the precipitation for the MAP/SOP IOP2b Abstract The impact of the data assimilation of high-density (space and time) data on the precipitation forecast is evaluated by improving the initial conditions of a mesoscale model. The high-frequency data allow for improving the three-hourly initial and boundary conditions as well. The data assimilation is performed using initial objective analysis (Cressman and multiquadric schemes) and 3D-Var. The MM5 (version 3) mesoscale model from Penn State University/National Center for Atmospheric Research is used to evaluate the impact of the improved initial and boundary conditions on the model simulations. The comparison of model results with observations shows: (i) the forecast of the precipitation at high resolution produces better results than those without data assimilation only if three-hourly data are assimilated by multiquadric; (ii) the mean error of the model rainfall largely decreases only if 3D-Var is used, but no comparable improvement in the spatial distribution of the precipitation is found; (iii) the improvement for the rainfall is not as good as it is for the initial conditions for all experiments. Moreover, the observations ingested by objective analysis modify both the amount and the timing of the precipitation on the Po valley. On the other hand, 3D-Var modifies only the amount of the precipitation, but both techniques barely recover large-model failure. Copyright © 2005 Royal Meteorological Society [source] Coriolis effects in mesoscale flows with sharp changes in surface conditionsTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 603 2004J. C. R. Hunt Abstract A general linearized ,shallow-layer' perturbation model, where the approximately neutral lower layer of thickness h0 is situated below a stable upper layer (i.e. an inversion with temperature change ,T), is developed for steady, mesoscale atmospheric flows over low-lying topography whose height is less than h0. With the Coriolis parameter f, sharp changes in surface conditions (surface roughness, terrain elevation, heat flux) are modelled as a distributed body force through the lower layer. The Froude number of this layer is small. Typical cases of mesoscale discontinuities are examined. The results are compared with those of a continuously stratified model and observations, and with numerical mesoscale model results for a meteorological case-study over the Dover Straits region of the English Channel. The main results are: (i) If the wind direction is parallel to the edge-line separating the change in surface roughness, there are marked increases and decreases in these coastal winds whose maxima can occur over the sea within a distance of order h0(,1 km) of a coast. The strength of these wind ,jets', which do not occur in the absence of Coriolis force, decrease away from the edge-line gradually over transverse length-scales of the order of the Rossby deformation radius . Changes to surface roughness lead to an increase in the wind speed perturbation in the downwind direction until limited by non-linear effects. When the wind is at an angle to a roughness change or coast, the maxima occur at the coastline. (ii) Where there are sharp changes in the orientation of contours of constant roughness length (e.g. at capes or bays on the coastline or wakes of high-drag areas), ,detached' jets are formed in the downwind direction. (iii) Changes in surface elevation at a coast produce effects different from those of roughness; a positive wind jet forms parallel to the coast in the direction of the wind when the coast is on the right (looking downwind) and a negative jet when the coast is on the left. These jets do not increase in strength along the flow and do not persist downwind. (iv) Coriolis effects also determine how the inversion height varies near coastlines and surface roughness changes; for example, increasing/decreasing inland over a distance LR when stable airflow approaches from the sea and the coast is on the right/left of an observer looking downwind (opposite in the southern hemisphere). This mechanism is consistent with observed increasing/decreasing cloudiness inland from a coast. (v) Other effects occur where the surface elevation changes gradually over a distance of order LR (e.g. a wide, shallow valley); frictional effects are comparable with buoyancy and Coriolis forces, and flows perpendicular to the elevation change are deflected to the left (in the northern hemisphere), as observed in the Rhine valley. (vi) The shallow-layer model simulates the major features of the low-level flow field computed using the numerical mesoscale model with a horizontal resolution of 2 km, i.e. of order h0. Broad features were captured using a coarser resolution of 12 km. (vii) The analysis provides a method of estimating errors associated with finite grid size in numerical mesoscale models. Copyright © 2004 Royal Meteorological Society [source] A cloud-resolving regional simulation of tropical cyclone formationATMOSPHERIC SCIENCE LETTERS, Issue 1 2002Jordan G. Powers Abstract The development of Tropical Cyclone Diana (1984) is simulated with a mesoscale model using 1.2 km grid spacing over a regional-scale (>1000 km) domain in the first known experiment of this kind. With only a synoptic-scale disturbance in the initial conditions, the model first develops a mesoscale convective system along a remnant frontal zone, which yields a mesoscale vortex. After a period of quiescence, banded convection organizes about the vortex from isolated, grid-resolved cells, with the system becoming warm-core and intensifying into Tropical Storm Diana. Copyright © 2002 Royal Meteorological Society. [source] | ||||||||||