Comparación de resultados de este estudio con los resultados de la encuesta sobre

The following sections focus on a few selected topics. They are not really dedicated to the practical use of these models and are far from comprehensive. They primarily represent needs of the modelling community towards research, improvements and to access to input data.

7.1 Research and model improvements

Intensive research activity related to different aspects of wind field and dispersion modelling over complex terrain is still needed.

An important topic for harmonization purposes is the adequate evaluation and validation of atmospheric flow models, including a better assessment of the uncertainty of their results. Efforts are still needed within the framework of international research programmes to select or develop experimental data sets which can be suitable for wind field model evaluation over complex terrain and to define benchmark criteria and exercises. Verification is still hampered by the lack of suitable experimental data. Neither a review of existing data sets nor any experiment has been performed within our working group 4 of COST 710. Anyway, according to our knowledge, the existing experimental data sets are often incomplete and lacking of information mainly because they have been usually programmed for scopes different from complex terrain flow and dispersion model validation. A huge amount of work is generally needed just to clean, validate the data and make them finally suitable for model evaluation. Wind field models over complex terrain listed in this report are mainly research-born or research-oriented models, although they have been used for practical air pollution applications. Efforts should also be devoted towards applications, in terms of code portability, technical documentation, user's guides and recommendations. Only a few models have reached the status of guideline pre-processing models (VDI, 1992b), partly because the upgrade from rather simple and crude models to the new generation complex wind field models is a challenge for scientists, policy makers and users. Therefore cooperative implementation programmes involving them all are needed.

An obstacle to the diffusion of flow modelling use is often the lack of culture regarding atmospheric flow and pollutant dispersion, but another important reason is the difficulty to access proper input data, as e.g. meteorological data (see chapter 7.3).

An important need for improvement exists in the field of integration between atmospheric flow models and soil and vegetation models. Satisfactory flow modelling is in fact strongly conditioned by a proper description of the bottom boundary conditions and their evolution. The possibility to model surface effects is of course strongly tied to the availability of the needed terrain description (see chapter 7.2).

At last a relevant topic that needs to be investigated is the structure and evolution of turbulence over complex terrain, the comprehension and knowledge of which is still very poor. Related to this issue is the structure of the planetary boundary layer, particularly in relation to the parameterization of the nocturnal stable boundary layer (see chapter 4.3). We do not have enough verification experiments in order to show whether non-hydrostatic prognostic and mass-consistent diagnostic dispersion models can be applied over complex terrain for regulatory purposes with confidence now.

7.2 Access to orographic and physiographic data

Detailed orographic and physiographic data are needed for wind flow modelling over complex terrain, but they do not always exist at sufficient resolution. Fortunately, different programmes have addressed this question and data sets for many parts of the world with a rather good resolution can now be downloaded through Internet web servers. Improvements still remain necessary, especially for very high resolution data and multinational studies. National topographic agencies should be asked. Hereafter we give a couple of addresses of institutions delivering data sets from many parts of the globe (not always free of charge):

- NGDC = National Geophysical Data Center, USA, Information: http:// www.ngdc.noaa.gov, look "solid earth geophysics" and then "topography": GLOBE, Global Land One km Base Elevation (correctly: 30 seconds resolution). Data can be directly downloaded from the following internet address: edcwww.cr.usgs.gov/landdaac/gtopo30/gtopo30.html.

- USGS = U.S. Geophysical Survey also producing a global land cover data-set (edcwww.cr.usgs.gov/landdaac).

- NOAA = National Oceanic and Atmospheric Administration provides vegetation data with a 10 min resolution covering the entire globe.

- A European land cover database is being produced within a project called CORINE (European Environmental Agency).

- RIVM=National Institute for Public Health and Environmental Protection (NL), provides a 10 minutes Pan-European land-use database. A CD-ROM is

available asking directly to the Institute (For information: R.J. Van De Velde RIVM, P.O. Box 1, 3720 BA Bilthoven, The Netherlands, [email protected]). We are not aware of other institutions distributing Europe-wide orographic or physiographic data sets. We think that an effort should be made to produce high resolution orography, soil type, and land cover data available on the European scale on a common base. Presently those kind of data are often treated in a different way by each national agency (different projection, classification, resolution).

7.3 Access to meteorological data

In more detail, we hereafter address the question of data access from the National Weather Services (NWS). NWS play an important role in the harmonization within the field of meteorological pre-processing. Actually, they represent the main meteorological data suppliers and have practised harmonization within their measurement and communication networks for a long time. Nevertheless, in some countries, the environmental community has some difficulty with access to observations and gridded data. The following recommendations are issued to promote improvements where needed. On the other hand, it should be noted that such data rarely belong to the basic products of NWS and can only be made available under an appropriate charge, due to their high production cost and to increased financial pressure on the NWS.

Hence, the access to checked data sets (1 to several years) from surface stations (e.g SYNOP observations, but preferably automatic stations) and upper air soundings (TEMP’s and full

resolution) of the European NWS should be improved where administrative restrictions inhibit this access.

An increasing number of NWS run so-called Local Area weather prediction Models (LAM) on an operational basis, with a mesh size ranging from 10 to 30 km. Most of them are hydrostatic models. In the near future, non-hydrostatic models will be put in operation (LM: Germany, possibly the non-hydrostatic version of ARPEGE/ALADIN: France, see Steppeler, 1996, Bubnova et al., 1995, Lahore et al., 1996), with mesh size below 5 km. Their initialization with input meteorological data will also benefit from new research, introducing 3-D and Four Dimensional Data Assimilation (FDDA) with nudging techniques, improving noticeably their ability to resolve small scale features. Although their results have been in the past mainly confined to short term weather predictions, they have recently been increasingly used for wind field prediction, trajectory and dispersion calculations on regional scales. In the planetary boundary layer (PBL), they still exhibit weaknesses over complex terrain, firstly because they use the same PBL-parameterization at all grid points, regardless of the local topography, secondly because they do not use enough resolved input data. Nevertheless, their strengths compared to a lot of PBL-models are numerous:

- they reproduce the synoptic forcing well,

- they include moist convections, clouds and precipitations, - they are running on an operational basis,

- their initialization is based on numerous measurements and observations,

- they are undergoing a continuous verification process, leading to improvements, - their produce hourly predictions (full diurnal cycle),

- they predict the regional wind field rather well where the topography is resolved by their mesh size,

- their results can be efficiently used as initial and boundary conditions for smaller scale nested models.

Due to the tremendous amount of data produced, the full data sets are restricted to real-time wind/trajectory predictions and dispersion calculations. Only limited data sets are presently archived for statistical applications at the NWS running such LAMs. We recommend therefore that archive and retrieval procedures be further developed so as to make them more widely available for the smaller scale wind field models. Adequate sets of representative weather situations with the corresponding numerical data products could also be prepared by the NWS.