共查询到20条相似文献，搜索用时 265 毫秒
1.
U. Corsmeier N. Kalthoff B. Vogel M.-U. Hammer F. Fiedler Ch. Kottmeier A. Volz-Thomas S. Konrad K. Glaser B. Neininger M. Lehning W. Jaeschke M. Memmesheimer B. Rappenglück G. Jakobi 《Journal of Atmospheric Chemistry》2002,42(1):289-321
During the BERLIOZ field phase on 20 July 1998 a 40 km wide ozone-plume 30 to 70 km north of Berlin in the lee of the city was detected. The ozone mixing ratio inside the plume was app. 15 ppb higher than outside, mainly caused by high ozone precursor emissions in Berlin, resulting in a net chemical ozone production of 6.5 ppb h–1, which overcompensates ozone advection of –3.6 ppb h–1 andturbulent diffusion of –1.1 ppb h–1. That means, although moreozone leaves the control volume far in the lee of Berlin than enters it at the leeside cityborder and although turbulent diffusion causes a loss of ozone in the leeside control volume the chemical production inside the volume leads to a net ozone increase. Using a semi-Lagrangian mass budget method to estimate the net ozone production, 5.0 ppb h–1 are calculated for theplume. This means a fraction of about 20% of ozone in the plume is producedby local emissions, therefore called `home made' by the Berlin emissions. For the same area KAMM/DRAIS simulations using an observation based initialisation, results in a net production rate between 4.0 and 6.5 ppbh–1, while the threefold nested EURAD model gives 6.0 ppbh–1. The process analysis indicates in many cases goodagreement (10% or better) between measurements and simulations not only in the ozone concentrations but also with respect to the physical and chemical processes governing the total change. Remaining differences are caused by different resolution in time and space of the models and measurements as well as by errors in the emission calculation.The upwind-downwind differences in PAN concentrations are partly similar to those of ozone, because in the BERLIOZ case they are governed mainly by photochemical production. While in the stable boundary layer at night and windward of Berlin 0.1 to 0.3 ppb are detected, in the centre of the plume at noon concentrations between 0.75 ppb and 1.0 ppb are measured. The O3/PAN ratio is about 80 to 120 and thus due to the relatively lowPAN concentrations significantly higher than found in previous studies. The low PAN formation on 20 July, was mainly restricted by the moderate nonmethane hydrocarbon levels, whereas high PAN concentrations of 3.0 ppb on 21 July, are caused by local production in the boundary layer and by large scale advection aloft. 相似文献
2.
Results from two air quality models (LOTOS, EURAD) have been used toanalyse the contribution of the different terms in the continuity equationto the budget of ozone, NOx and PAN. Both models cover largeparts of Europe and describe the processes relevant for troposphericchemistry and dynamics. One of the models is designed to simulate episodesin the order of 1–2 weeks (EURAD), the other is focussing on theseasonal scale (LOTOS). Based on EURAD simulations it is found that theatmospheric boundary layer (ABL) in Central Europe during a summer-smogepisode in 1990 acts as a source of ozone, which is partly exported from theproduction region in Central Europe. About 40% of the ozone producedchemically in the ABL is lost from Central Europe due to net transport(large-scale and turbulent), 40% are deposited within the domain. Vertical mass exchange of ozone is dominated by the prevailing subsidenceand averaged vertical mass fluxes are directed downward. Averaged massfluxes of PAN, which has no stratospheric source, are upward in the upperpart of the ABL. The results from LOTOS are discussed for the same episodeand for a two month period (July/August 1990). The budget calculation showlarger chemical production for the LOTOS model compared to EURAD. Therelative importance of deposition and net transport, however, is in the sameorder. Differences between the two-month calculation and the one weekepisode are only important for Western Europe where the chemical production is enhanced by 30% during the summer-smog episode. The dependence ofthe results on initial and boundary values is discussed for ozone on thebasis of a simple sensitivity study with EURAD where ozone in the FT is setto 10 ppb initially. This leads to a reversal in the direction of averagedozone mass fluxes in the upper part of the ABL. 相似文献
3.
Summary A diagnostic model (DIAMOD) for the atmosphere over Europe is use at the University of Vienna. Central parameters in each diagnostic column (horizontal resolution 100 km, time resolution 12 hours) are the vertical moisture plus heat flux (the total convective heat fluxh) and the vertical rain flux (r); both are functions of pressure. In this study DIAMOD is applied to validate the output of a forecast model for the simulation of acid deposition (EURAD) which is in use at the University of Cologne. The basic equations of both DIAMOD and EURAD models are summarized with emphasis on the sub-gridscale hydrologic components.First, the nontrivial problem of validating model output versus observations is discussed. Two different validation techniques based upon the budget equations are indentified. The fully prognostic technique compares the forecast of EURAD for the total verification period with the corresponding DIAMOD output. The semiprognostic validation technique involves only one-time-step tendencies. Neither yields an exact correspondence between EURAD and DIAMOD; however, the semiprognostic technique comes somewhat closer to the ideal of an objective validation. The quantities investigated are: The fields, the time tendencies and the fluxesh andr.Second, EURAD is validated versus DIAMOD with both techniques for the EUMAC Joint Wet Case (the Chernobyl episode) in April 1986; the output fields include selected profiles ofh(p) over France (a moist night situation) and over Greece (a dry day situation). The comparison demonstrates for both that the EURAD forecasts are acceptable for ther-fluxes but are relatively poor for theh-fluxes. Reasons for the differences are discussed.With 11 Figures 相似文献
4.
A comparison of two separate MM5 land-use datasets (i.e., ‘US Geological Survey (USGS)’ and ‘Pollutants in the Atmosphere and their Transport over Hong Kong (PATH)’, each with different parameter values and different spatial distributions) was performed to understand the importance of land-surface processes and land-atmosphere interactions in the evolution of mesoscale weather phenomena during a high pollution episode in Hong Kong from 28 December 1999 through 1 January 2000. Also, a series of high resolution mesoscale numerical experiments was performed to investigate the possible roles of various surface characteristics or land-use parameters in this high pollution episode. Specifically, the relative importance of six land-use parameters including the roughness length, thermal inertia, soil moisture availability, albedo, surface heat capacity and surface emissivity are studied. Results from this study suggest that the soil moisture availability is the most important controlling parameter on the flow pattern and on surface fluxes. Sensitivity tests also show that the general flow pattern is insensitive to the other five land-use parameters 相似文献
5.
Summary The vertically averaged balance equation of atmospheric trace constituents that customarily serves as a basis for one- and two-layer (box) models of the atmospheric boundary layer and the whole troposphere is derived and discussed. It is shown that this kind of balance equation is accompanied by several prominent short-comings so that the capability of such models to predict real situations of photochemical smog formation and depletion is strongly limited. Three of these short-comings are theoretically elucidated, namely (1) the vertically averaged source and sink terms owing to chemical reactions, (2) the parameterisation of the dry deposition and exhalation fluxes at the earths surface that serve as lower boundary conditions, and (3) the parameterisation of the upper boundary conditions. Even though the consumption of computing time is much smaller than those of sophisticated Eulerian air pollution models like ADOM, DRAIS, EURAD, RADM, and TADAP, we have to conclude from our theoretical results that one- and two-layer (box) models should not be considered as a true alternative to such air pollution models.We also suggest that the influence of these short-comings on the predicted results has to be estimated and evaluated in a reliable manner before vertically averaged balance equations of atmospheric trace constituents are introduced into general circulation models to investigate the influence of air pollution on climate change on the basis of long-term simulations. 相似文献
6.
Simulations of a mesoscale convective system (MCS), which propagated across Northern India on 2nd May 2018 - leading to many fatalities when the gust front knocked down homes and tore apart building roofs - have been performed using the National Centre for Medium Range Weather Forecasting (NCMRWF) Unified Model – Regional (4 km horizontal grid spacing), to evaluate the model’s convective treatments. Though the model captures many of the qualitative and quantitative features, it slightly lags behind the observed MCS organisation and movement, produces lesser precipitation, and lacks the spatial separation between two adjacent organised convective systems in the satellite observations – leading to a faintly offset MCS track. Sensitivity simulations are then performed, for this non-equilibrium MCS case, with different partitioning between parametrized and explicit convection to assess the reliance of the convective treatments on the large-scale environment, as well as to test the notion of a breakdown of convective parametrization at the mesoscale model resolution. Fully parametrized (FP) convection produces even lesser rainfall and are dominated by orographic precipitations along the foot hills of Himalayas with no any trace of the MCS. Fully explicit (FE) convection realistically simulates most of the prominent convective cells and enhance precipitation along the MCS track that agree better with the observations, though the ‘two lobes’ of intense precipitation are not resolved; instead it produces a squall line of precipitation. The FE configuration generates the most vigorous convective updraft, along with a vertical shear that is tilted westward. The simulation with partially parametrized and partially explicit convection resembles the fashion in the FP and FE scenarios, with a transition over the duration of the run from parametrized to explicit precipitation. The results are in line with the notion from previous studies; that the majority of successful explicit simulations of mesoscale organisation are those associated with strong large-scale forcing for convection, wherein resolved vertical motions are sufficient to minimise delays in onset. 相似文献
7.
G. Adrian 《Meteorology and Atmospheric Physics》1995,55(3-4):223-234
Summary Starting with a linear theory of the flow around and over mountains a similarity hypothesis of the wind field over complex terrain is formulated and tested by simulations with the numerical mesoscale model KAMM (Karlsruhe Atmospheric Mesoscale Model) and applied to observations of the orographically induced phenomenon Moehlin-Jet, which were performed and analysed by Dütsch (1985). Because this hypothesis combines parameters describing the state of the large scale flow with form parameters of the orography it can be used to regionalize large scale climatological informations to smaller scale. It allows to generalize observations of typical mesoscale phenomena like channeling in broad valleys or orographically induced jet-like currents.With 9 Figures 相似文献
8.
I. J. Ackermann H. Hass M. Memmesheimer C. Ziegenbein A. Ebel 《Meteorology and Atmospheric Physics》1995,57(1-4):101-114
Summary Because of the obvious importance of aerosols for atmospheric modelling, an aerosol module has been developed as part of the European Acid Deposition Model (EURAD). The chemical and physical processes have been restricted to the sulfate-nitrate-ammonia system to study the influence of aerosols on acid deposition. Special consideration is given to the reversible formation process ofNH
4
NO
3 aerosols and the influence of the dissociation constant on the aerosol and gas phase concentrations. This component appears to be important in particular for regions where large ammonia emissions are found as in Europe.Concentration and deposition fields as predicted by EURAD are analysed for a simulation with and without the new aerosol module. Due to their smaller dry deposition velocities in the aerosol phase, the amount of nitrogen species in air is larger and the spatial distribution is considerably different if aerosols are taken into account. On the other hand wet deposition of nitrogen is enhanced due to the presence of easily soluble ammonium nitrate aerosols.A comparison with observations from the EMEP network has been conducted to evaluate the performance of the aerosol module. Modelling with the aerosol phase leads to a much better agreement between modelled and measured concentration fields.With 12 Figures 相似文献
9.
C. Cacciamani D. Cesari F. Grazzini T. Paccagnella M. Pantone 《Meteorology and Atmospheric Physics》2000,72(2-4):147-159
Summary In this paper we describe the results of several numerical experiments performed with the limited area model LAMBO, based
on a 1989 version of the NCEP (National Center for Environmental Prediction) ETA model, operational at ARPA-SMR since 1993.
The experiments have been designed to assess the impact of different horizontal resolutions and initial conditions on the
quality and detail of the forecast, especially as regards the precipitation field in the case of severe flood events. For
initial conditions we developed a mesoscale data assimilation scheme, based on the nudging technique. The scheme makes use
of upper air and surface meteorological observations to modify ECMWF (European Centre for Medium Range Weather Forecast) operational
analyses, used as first-guess fields, in order to better describe smaller scales features, mainly in the lower troposphere.
Three flood cases in the Alpine and Mediterranean regions have been simulated with LAMBO, using a horizontal grid spacing
of 15 and 5 km and starting either from ECMWF initialised analysis or from the result of our mesoscale analysis procedure.
The results show that increasing the resolution generally improves the forecast, bringing the precipitation peaks in the flooded
areas close to the observed values without producing many spurious precipitation patterns. The use of mesoscale analysis produces
a more realistic representation of precipitation patterns giving a further improvement to the forecast of precipitation. Furthermore,
when simulations are started from mesoscale analysis, some model-simulated thermodynamic indices show greater vertical instability
just in the regions where strongest precipitation occurred.
Received March 2, 1999/Revised May 30, 1999 相似文献
10.
Conclusions on the General Circulation Models (GCMs) horizontal and temporal optimum resolution for dynamical downscaling
of rainfall in Mediterranean Spain are derived based on the statistical analysis of mesoscale simulations of past events.
These events correspond to the 165 heavy rainfall days during 1984–1993, which are simulated with the HIRLAM mesoscale model.
The model is nested within the European Centre for Medium-Range Weather Forecasts atmospheric grid analyses. We represent
the spectrum of GCMs resolutions currently applied in climate change research by using varying horizontal and temporal resolutions
of these analyses. Three sets of simulations are designed using input data with 1°, 2° and 3° horizontal resolutions (available
at 6 h intervals), and three additional sets are designed using 1° horizontal resolution with less frequent boundary conditions
updated every 12, 24 and 48 h. The quality of the daily rainfall forecasts is verified against rain-gauge observations using
correlation and root mean square error analysis as well as Relative Operating Characteristic curves. Spatial distribution
of average precipitation fields are also computed and verified against observations. For the whole Mediterranean Spain, model
skill is not appreciably improved when using enhanced spatial input data, suggesting that there is no clear benefit in using
high resolution data from General Circulation Model for the regional downscaling of precipitation under the conditions tested.
However, significant differences are found in verification scores when boundary conditions are interpolated less frequently
than 12 h apart. The analysis is particularized for six major rain bearing flow regimes that affect the region, and differences
in model performance are found among the flow types, with slightly better forecasts for Atlantic and cold front passage flows.
A remarkable spatial variability in forecast quality is found in the domain, with an overall tendency for higher Relative
Operating Characteristic scores in the west and north of the region and over highlands, where the two previous flow regimes
are quite influential. The findings of this study could be of help for dynamical downscaling design applied to future precipitation
scenarios in the region, as well as to better establish confidence intervals on its results. 相似文献
11.
Summary High resolution aircraft observations made along flight tracks over inhomogeneous surface in the late wintertime boreal zone
are described and compared to 2D mesoscale model simulations with surface properties defined at 2 km resolution from maps.
All observations displayed the expected small-scale turbulence. On top of that, the near-surface wind speeds (but not directions)
showed mesoscale variations related to local topography and roughness. Upward (but not downward) SW and LW radiative fluxes
and ground temperature also displayed mesoscale variability; in SW radiation this was clearly due to local albedo changes.
In the sensible heat flux there was strong horizontal variation near the surface in correlation with surface types. The above
observed mesoscale along-track variations were reasonably well represented by the mesoscale model simulation. The track-averaged
observed sensible and latent heat flux profiles were in rough agreement with a mixing length approach, which used the track-averaged
wind, temperature and moisture profiles as input (mimicking a first-order turbulence closure scheme of a GCM).
Received September 20, 1999 Revised January 21, 2000 相似文献
12.
I. Bischoff-Gauß N. Kalthoff M. Fiebig-Wittmaack 《Theoretical and Applied Climatology》2006,85(3-4):227-241
Summary High-resolution model simulations were performed with the quadruple-nested version of the mesoscale model KAMM to investigate
the impact of the new storage lake ‘Embalse Puclaro’ on the arid environment. The storage lake covers an area of 1 to 2 km
in width and about 7 km in length. Model simulations were performed for a summer and a winter day.
Due to a change in the surface properties, the installation of the storage lake resulted in a modification of the energy balance.
Above the lake area, a stably stratified atmosphere establishes during the day and unstable stratification during the night.
During the day, the latent heat flux is similar to that of the replaced cultivated ground, but is higher at the night. The
influence of the storage lake on temperature and humidity can be seen to a height of about 300 m above ground level. During
the night, water vapour accumulation results in relative humidity values of 100%, as a result a greater number of days with
fog above the storage lake is likely when compared to the surrounding area. The storage lake does not produce its own lake
breeze during the day, because the larger-scale up-valley wind is too dominant. However, a significant modification of the
nocturnal down-valley wind above the lake area can be observed, especially in summer. As a consequence of the larger-scale
valley wind system, the influence of the storage lake on the temperature, humidity, and wind field can be identified up to
about 4 km on the downwind side. 相似文献
13.
E. V. Kuz’mina A. V. Ol’chev I. A. Rozinkina G. S. Rivin M.A. Nikitin 《Russian Meteorology and Hydrology》2017,42(9):574-581
The influence of forest cover in the west of the European part of Russia (55°–59° N, 28°–37° E) on regional weather conditions is analyzed via the climatic version of the COSMO nonhydrostatic mesoscale model (COSMO-CLM). The simulations are performed with a model grid spacing of 13.2 km for the warm season of 2010. The analysis demonstrates that the changes in forest cover in the selected model domain may lead to substantial variations in spatial precipitation and surface temperature patterns. At the same time, precipitation changes are evident within the entire area of the East European Plain. 相似文献
14.
The boundary-layer development and convection-pattern transition typically occurring in cold-air outbreaks is studied using
three-dimensional simulations. The simulations include the secondary-flow transition starting with the relatively small-scale
boundary-layer rolls developing during the initial phase and ending with mesoscale cellular convection patterns. The application
of a computational grid, whose horizontal mesh size enables the resolution of the small-scale initial patterns and whose domain
size is large enough to capture mesoscale convection patterns, overcharges even state-of-the-art supercomputers. In order
to bypass the computer storage problem, the horizontal size of the model domain and the horizontal resolution of the computational
grid are adjusted to the scale of the dominant convective structures. This enables the simulation of convection cells whose
horizontal scales increase up to values exceeding the size of the initial model domain.
The model is applied to conditions of a cold-air outbreak observed during the ARKTIS 1991 experiment. The most important characteristics
of the observed situation are revealed by the model. Sensitivity studies are performed in order to investigate the relation
between cell broadening and various physical processes. The artificial cutoff of liquid-water formation prevents the enlargement
of convective scales. Latent heating due to condensation and especially radiative cloud-top cooling are identified as processes
leading to cell broadening. We propose a conceptual model that elucidates the mechanism by which cloud-top cooling may generate
larger aspect ratios. 相似文献
15.
Kevin HAMILTON 《大气科学进展》2006,23(6):842-856
An informal review is presented of recent developments in numerical simulation of the global atmospheric circulation with very fine numerical resolution models. The focus is on results obtained recently with versions of the GFDL SKYHI model and the Atmospheric Model for the Earth Simulator (AFES) global atmospheric models. These models have been run with effective horizontal grid resolution of 10–40 km and fine vertical resolution. The results presented demonstrate the utility of such models for the study of a diverse range of phenomena. Specifically the models are shown to simulate the development of tropical cyclones with peak winds and minimum central pressures comparable to those of the most intense hurricanes actually observed. More fundamentally, the spectrum of energy content in the mesoscale in the flow can be reproduced by these models down to near the smallest explicitly-resolved horizontal scales. In the middle atmosphere it is shown that increasing horizontal resolution can lead to significantly improved overall simulation of the global-scale circulation. The application of the models to two specific problems requiring very fine resolution global will be discussed. The spatial and temporal variability of the vertical eddy flux of zonal momentum associated with gravity waves near the tropopause is evaluated in the very fine resolution AFES model. This is a subject of great importance for understanding and modelling the flow in the middle atmosphere. Then the simulation of the small scale variations of the semidiurnal surface pressure oscillation is analyzed, and the signature of significant topographic modulation of the semidiurnal atmospheric tide is identified. 相似文献
16.
Improved Representation of Land-surface Heterogeneity in a Non-hydrostatic Numerical Weather Prediction Model 总被引：2，自引：1，他引：2
This study focuses on the relevance of accurate surface parameters, in particular soil moisture, and of parameterizations for heterogeneous land surfaces, for the prediction of sensible and latent heat fluxes by a mesoscale weather forecast model with horizontal grid resolution of 7 km. The analysis is based on model integrations for a 30-day period, which are compared both to flux measurements obtained from the LITFASS-2003 field experiment and to high-resolution-model (1-km grid spacing) results. At first, the relevance of improved parameter sets and input data compared to usual operational practice for an accurate prediction of near-surface fluxes is shown and discussed. It is demonstrated that an observation-based land-surface assimilation scheme leads to an improved soil moisture analysis, which is shown to be essential for the realistic simulation of surface fluxes. Secondly, the implementation of two efficient parameterization strategies for subgrid-scale variability of the surface, the mosaic and the tile approach, is presented. Using these methods, the simulations are in better agreement with measurements than simulations with simple aggregation methods that use effective surface parameters. Integrations with the mosaic approach reproduce high resolution simulations very well and more accurately than simulations with the tile method. Finally, the high resolution simulations are analyzed to justify and discuss the approximations underlying both methods. 相似文献
17.
Cheol-Hee Kim Lim-Seok Chang Jeong-Soo Kim Fan Meng Mizuo Kajino Hiromasa Ueda Yuanhang Zhang Hye-Young Son Youjiang He Jun Xu Keiichi Sato Chang-Keun Song Soo-Jin Ban Tatsuya Sakurai Zhiwei Han Lei Duan Suk-Jo Lee Shang-Gyoo Shim Young Sunwoo Tae-Young Lee 《Asia-Pacific Journal of Atmospheric Sciences》2011,47(4):399-411
Three comprehensive acid deposition models were used to simulate the sulfur concentrations over northeast Asia over the period covering entire year of 2002, and discussed the aggregated uncertainties and discrepancies of the three models. The participating models are from the countries participating in the project of Longrange Transboundary Air Pollutants in Northeast Asia (LTP): China, Japan and Korea. The Eulerian Model-3/CMAQ (by China), Regional Air Quality Model (RAQM, by Japan), and Comprehensive Acid Deposition Model (CADM, by Korea) were employed by each country with common emissions data established by the administrative agencies of China, Japan and Korea. The episodic simulation results between 1 to 15, March 2002 are also presented, during which aircraft measurements were carried out over the Yellow sea. The episodic results show both a wide short-term variability in simulations against measurements, and maximum concentration differences of 3～5 times among the three models, requiring that further attention before confidence among the three models can be claimed for short-term simulations. However, the year-long cumulative simulations showed almost the same general features, with lower aggregated uncertainties between the three models, produced by the long term integration over northeast Asia. 相似文献
18.
In current operational numerical weather prediction models, the effect of shallow convection is parametrized. The grey zone of shallow convection is found between the horizontal resolutions of mesoscale numerical models (2–3 km) and large-eddy simulations (10–100 m or finer). At these horizontal scales the shallow convection is to some extent explicitly resolved by the model. The shallow-convection parametrization is still needed, but has to be regulated according to the model horizontal resolution. Here the behaviour of the non-hydrostatic mesoscale numerical weather prediction model Application of Research to Operations at Mesoscale is examined in the grey zone and a new scale-adaptive surface closure of its shallow-convection parametrization, dependent on horizontal resolution, is defined based on large-eddy simulation. The new closure is tested on a series of numerical experiments and validated on a 15-day-long real case period. Its impact on the development of deep convection is examined in detail. The idealized simulations show promising results, as the mean profiles of the subgrid and resolved turbulence change in the desired way. Based on the real case tests our modification has a low impact on model performance, but is part of a set of upgrades of the current parametrization that is aimed to treat the shallow convection grey zone. 相似文献
19.
Local Winds In A Valley City 总被引：1，自引：0，他引：1
Local winds were studied around a valley city, by using a high resolution two-dimensional mesoscale model forced by surface temperatures from a measurement campaign around Lanzhou City, China, during stagnant conditions. In the simulations nighttime winds are purely katabatic downslope winds without urban effects, despite the fact that the city is 6–7°C warmer than its surroundings all night. In contrast, daytime near-surface winds result from upslope flow resisted by an opposing simultaneous urban heat-island circulation (UHIC). Hence winds remain weak and variable around a city in a narrow valley during daytime. These conditions may lead to severe air quality problems day and night.The local circulations are sensitive to the widths of the valley and/or city,and also latitude, as is demonstrated by model experiments. Interestingly, in a flat and calm environment an extratropical daytime UHIC cell may turn into a weak `anti-UHIC' by the morning, due to frictional decoupling after sunset and subsequent inertial oscillation during the night, analogously tothe land breeze and nocturnal low-level jet formation. 相似文献