Combined processing of meteorological information for very short-range weather forecasting in central Europe

Transcription

1 Hydrologie Applications of Space Technology (Proceedings of the Cocoa Beach Workshop, Florida, August 1985). IAHS Publ. no. 160, Combined processing of meteorological information for very short-range weather forecasting in central Europe DUSAN PODHORSKY Czechoslovak Hydrometeorological Service, WMO Activity Centre for Very Short-range Forecasting, Bratislava, Czechoslovakia Abstract The geographic spatial complex (geographic landscape) is understood as the spatial dynamic system considered in the uniform cartographic projection which is optimum for the transformation of point and areal hydrometeorological data (e.g. satellite, radar, etc.) referring to the digital relief model. For the purposes of efficient data collection and processing in operational service the purpose-made technological link and the specialized data bank MBTEOTREND '85 were established in Czechoslovakia enabling hydrologist and meteorologist to analyse real-time remote sensing data and very short-range weather forecasts, and at the same time the distribution of results obtained to users with the help of nowcasting technology. The implementation of the MEIEOTREICD '85 project affects the structure of both hydrological and meteorological forecasting services in Czechoslovakia and influences in positive way several branches of the national economy. Introduction Each mathematical forecasting model in meteorology and hydrology considers the relief influence on a studied process. Therefore, we have started with the mathematical description of the physiogeographic area; when investigating micro- and meso-scales we pay attention to their links with socioeconomic factors. It follows from the work by Barrett E.G. and Curtis L-.F. "Introduction to Environmental Remote Sensing" /3/ that the ecological analysis forms a core that joins geography with geology, biology with meteorology by 59

2 60 Dusan Podhorsky means of the study of rational exploitation of natural resources, environment and its protection applying cartographic and remote sensing methods. In this connection the term "ecological monitoring" appears with its two subsystems: geophysical and biological» The monitoring here represents that part of the control and information system which includes also geophysical, hydrological, and meteorological measurements enabling to analyse, observe, to give diagnosis and to forecast relationships - interactions between relief and atmosphere or hydrosphere with regard to the study of the degree of anthropogenic environmental impacts. Considering these presumptions we define the relief by a set of morphometric quantitative parameters, e.g. relief slope, relief orientation towards cardinal points (i.e. relief exposure, normal and horizontal curvature, relief insolation depending on time, etc.) and the state of the atmosphere and hydrosphere is characterised by a complex of individual quantities measured by conventional means and remote sensing methods and they are transformed subsequently into an optimum uniform cartographic system. In other words, with regard to the fact that the relief in Central Europe is an important spatial factor of differentiation from the viewpoint of the states of the atmosphere and hydrosphere, it is very important for the relief data to be included into an information system and to model the relief by means of the so called "complex digital model." Nov/, when the efficient hardware is at our disposal, and the information system about atmosphere and hydrosphere is solved by the form of a data bank, it is possible to start with an operational processing of numerous data within separate elements of the physiogeographic sphere as the spatial complex system and in this system as a whole. Geographic landscape as the geographic spatial complex is according to the works by Krcho /1/ considered a spatial dynamic system in a given system of coordinates. In this system it is possible to express two basic subsystems i.e. the sub-system of the physiogeographic sphere and the sub-system of the socio-economic sphere. At present we load the data bank gradually with the data of the physio-

3 Combined processing of meteorological information 61 geographic sphere s sub-system, i.e. with elements of the set: atmosphere s hydrosphere, litosphere, pedosphere, and biosphere. The structure of the sub-systems is expressed by nodal diagrams, individual elements of sub-sets are expressed by vectors and matrices, and thus inputs and outputs of each element of the physiogeographic sphere as well as its states are in the area considered in a given system of coordinates characterized by a set of quantitative parameters which form the parametric basis for the given physiogeographic sub-system. The area studied is expressed in the data bank in a discrete form - its units are created by areal elements of the square net. An analysis of meteorological data in a given region of interest is needed not only in a term of observations but also in a site on the Earth s surface to which an observation is related to, i.e. it is necessary to know the territorial relevance of meteorological data. The geographical coordinates are usually used to locate meteorological stations. However, such approach is suitable for the point data only. The areal data generally require the division of the territory into areal units which correspond to the certain values of measured quantities. Since the areal units defined by the same differences of geographical coordinates have not equal areas, these coordinates are not suitable for expressing the territorial relevance of the areal data. A concrete selection of the appropriate cartographic system depends on the size and location of the given area of interest, resolution required and allowable coefficient of deformation on the boundaries of the area. Regarding the needs of the current but especially future investigations and practical use of meteorological data, the territory bounded by the following cartographic coordinates: 9^=60, ^=35, /l w =-10 and /l E =35 has been defined as the maximum area of interest. The uniform cartographic system of the mentioned area was done by the planar projection onto a truncated cone which intersects the Earth's surface in the parallels Y<-5A ^ and V 2 =42 N. The way of addressing gives the possibility to work with p 1x1 km resolution, and furthermore it is possible to select any resolution of 2 n dimensions. Special transformation

4 62 Dusan Podhorshy procedures provide data conversion from other cartographic systems into the uniform system and vice versa, and thus it is possible to process data in any of these cartographic systems. Regarding up-to-now experience it can be stated that the above mentioned requirements on the territorial relevance of areal data are satisfied if these data enter the data base in a form of rectangular sectors of a certain network. The size of the sectors is defined so that the length of respective sentences corresponds to the size of physical blocks. Respective identifiers characterizing the territorial relevance of the sectors compensate for areal data identifiers of stations - sources of the point data. It is clear from the above that while the territorial access to the point data has to be realized by the station identifiers, the territorial access to the areal data can be realized directly. The development of the technological link for nowcasting calls for a system approach as for example in proposing of automated systems in flight assistance. The basic principles of METEOTREND'85 have been formulated as follows: -reliability - the principle of failure-free meteorological observations, their collection, processing, and distribution of data and information; - continuous operation - the principle of continuous operation of all components of the technological link; - readiness - the principle of optimal terms (frequency) of recovery, collection, processing, representation and distribution of all types of meteorological observations; - efficiency - the principle of protection of results and operation of the technological link for nowcasting under real (optimal) economic conditions with the aim to serve all lasers of very short-range weather forecasts. 'The beginning of the data bank development for the purposes of very short-range forecasts of cloudiness and associated phenomena is dated back to the second half of the 1970s when the computer centre EC 1040 (equivalent to IBM 360)was put

5 Combined processing of meteorological information 63 into operation at the Regional Centre for Radar Meteorology on the Maly Javornik hill. The teams of specialists led by Dr Badikovâ, Dr Micietovâ, Dr Vitek and Dr Vlcâk have realized under the leadership of Dr Fuchs requirements and objectives stated by meteorologists at the Regional Centre (Dr Podhorsky, Dr Wolek) as the basic philosophy of combined meteorological data processing. Increasing number of meteorological data contributes to more and more tide connections among meteorological data and computing technique. Scientific research has brought complicated algorithms with many demands on input data, processing speed and flexibility in choosing methods and inputs. Substantial simplification and optimization of software can be achieved by an uniform data bank, archiving and data access. The data bank system METEOSYS/DB was built up at Slovak Hydrometeorological Institute after the preceding analysis of demands on meteorological data processing and, above all, demands on combined operational information for very shortrange forecast of dangerous phenomena and precipitation. The contents and structure of the system satisfy the principle and the most frequent demands on data processing without duplicated creation on files which depend on individual users programs. Thus a desirable reduction and unification of communication procedures with the uniform system of data archiving and protection is possible. System Description METEOSYS/DB system consists of a data base and a programming data base management system. The system is based on the IDMS (Integrated Database Management System) from Cullinane Corp., USA. Since the product was designed for applications in other spheres (economic, social), its modified version METEOSYS/DB has been created on the basis of the analysis and experimental evaluations of specific meteorological models. Data Base METEOSYS/DB The formation of the data base was preceded by an analysis of data structure and correlations among the data themselves, and by the investigation of several characteristics of

6 64 Dusan Podhorsky meteorological data. Data Types Meteorological observations at a certain time and in a certain place give us simultaneously several values of measured characteristics which belong due to their informative value and the way of observation to one logical unit. In connection with the above mentioned, the data type is an accurately defined structure in a programming language that collects coherent quantities of one type of observations, e.g. synoptic data, aerological data, etc.a record from the observation of a certain data type is done by writing one sentence with the structure of the respective data type. Kinds of Data With regard to the method of observations and territorial representation we differentiate the following kinds of data: - point data - areal data. Point data represent observations at some fixed place on the Earth s surface and they enter the data base above all from the network of ground, climatic and upper-air stations, etc. Areal data are those which belong to certain areal units of the Earth s surface. Results of spatial measurements - after their appropriate projection into the plane of the Earth s surface - are processed as the areal data, too. Such character is typical mainly for the results of remote sensing of the atmosphere, i.e. for radar and satellite data. The kinds of meteorological data are of great importance to the definition of the inner structure of respective sentence types. While the sentence structures for the point data are simple in majority, sentences for the areal data are characterized by a matrix structure depending on the way of areal reference of such data. Time Dependence A notion of time for the structural sub-division of meteorological data is very important regarding the definition

7 Combined processing of meteorological information 65 of their validity in time. Prom this point of view we differentiate : - instantaneous data - interval data - time-independent data. This division follows from the physical base of values and from methods of their measurement. Thus for example, air pressure and water temperature belong to instantaneous data^ average daily temperatures and yearly precipitation totals belong to certain time intervals. Different station characteristics, relief data, etc. belong to data independent of time. Data Base Contents In spite of its original aim - to build up the data bank only for the purposes of very short-range forecasting based on combining the data from the remote sensing of the atmosphere, the METEOSYS/DB system has become the uniform data-base system for storage of all meteorological and hydrological data types obtained at Slovak Hydrometeorological Institute which are the subject of automated data processing and storage. At present the system operates storage and processing of the following meteorological and hydrological data: synoptic data, aero logical data, radar data, satellite data, climatic data, precipitation data, soil temperature data, air pollution data, radiation data, data on surface waters, relief characteristics of the territory of Czechoslovakia, data defining administrative units on the territory of C ze cho Slovakia. From the point of view of instantaneous weather analysis and very short-range forecast especially radar and satellite data are important, together with synoptic, aerological and relief data on an investigated region. Data Inputs Into Data Base Radar data enter the data base from hourly measurements of the dual-wavelength weather radar MRL-5 situated on the Maly Javornik hill with several hours delay due to the preliminary manual coding of radar data on punched cards.

8 66 Dusan Podhorsky At present we assume that an automated real-time processing of these data could be realized, and records are done for the square-like territorial units 100x100 km, 200x200 km, 300x300 km, and 600x600 km with the centre in the MRL-5 location and with resolutions 5x5, 10x10, 15x15, and 30x30km. The automated mode offers an optional resolution up to 2x2 km with four entries into the data base per hour. Satellite data are primarily processed by the PDP computer which forms one part of the receiving system. They enter the data base once per hour via magnetic tape which is transmitted off-line to the computer EC The record of one satellite orbit consists of several records from 32x32 km regions the sum of which forms a polygon covering the Czechoslovak territory and boundary regions. Entries of the operational data from the meteorological stations are realized temporarily using punched telex tapes from the Regional Telecommunication Centre. A real-time input of these data can. be realized on the assumption that a computer network will be formed during next year. Synoptic data enter the data base from all primary and secondary terms from 90 stations situated in the square of about 650x650 km with the centre on Maly Javornik. Aerological data from five stations (Prague, Poprad, Vienna, Warsaw, Budapest) are recorded at 00 and 12 GMT. Operation of METEOSYS/DB System It is clear that a quick and optimal access to meteorological and hydrological data can be ensured in the best way by means of direct access storage media. However, such media have not capacity enough for the whole fond of meteorological and hydrological data. So it is necessary to use magnetic tapes with sequential data organization only. The data base in the METEOSYS/DB system is from this reason divided into: - operational part stored on magnetic discs; - non-operational archived part stored on magnetic tapes. Although it can be assumed that actual meteorological and hydrological data of appropriate types will be stored in the operational part of the data base, the operational utilization cannot be limited only to these data. In the case of

9 Combined processing of meteorological information 67 inevitable processing of certain data from the non-operational part of the data base, it is possible to transport these data from archives into the operational part of the data base and to control, correct, or process them. Generalization of Experience from Case Studies Technological link METEOTEEND'85 uses besides the data from the dense network of conventional hydrological and meteorological stations also information from the network of weather radars and data from the satellite receiving systems for NOAA and MEÏBOSÀT II satellites. Based on the analysed case studies it is possible to conclude : 1) recognition of clouds associated with precipitation is much more effective using a complex - combined diagnosis based on radar and satellite data. At the same time it is necessary to use data from all spectral bands of a satellite and in the case of meteorological radars it is suitable to combine classical radar data with multiwave-leng.th and Doppler radars data. Estimated rainfall intensities have to undergo a real-time calibration by radiopluviographs situated at various distances from the radar; 2) when estimating evolution of precipitation field it is not sufficient to use data on radar reflectivity measured at the boundary layer of the atmosphere (0-2 km). Of great importance from the viewpoint of very short-range precipitation forecasting is the vertical profile of radar reflectivity and its tendency depending on time, while the vertical step of measurement is recommended to be for convective cloud each two kilometers as minimum and every kilometer as optimum; for stratus clouds it is every kilometer as minimum and each 500 m as optimum (in this case, of course, the maximum range of radar observation is up to km distance); 3) with cloud systems consisting of As - Ns - Cb it is important to estimate cloud tops in each pixel from satellite data and with the help of radars it is necessary to study in Ns clouds the connection between cloudless layers and location of the line of intensive crystallization (LIC) which, must take place within the cloud mass if rainfall should be produced /2/;

10 68 Dusan Podhorsky 4) uneven micro-structure of clouds and precipitation causes also an uneven distribution of radar reflectivity in space. If we study the dependency of the average value of radar reflectivity Z" on the measured maximum values of reflectivity Z^.,,, on the distance between the cloud and the radar R and the relationship between the beam width and horizontal and vertical thickness of cloud, we can see that in some cases it is necessary to correct the basic radar equation for the measurement of radar characteristics of clouds on the radar equation for point targets which is used for air traffic control, etc. 5) for precipitation occurrence at middle latitudes the presence of intensive crystallization is inevitable and it takes place at the isothermic level (from -10 C to -15 C) depending on the vertical velocity of parcel motion in stratus clouds. The level of intensive crystallization divides Ns clouds schematically into two zones: A-zone - zone of active ice nuclei growth and formation of precipitation particles situated under LIC; I-zone - zone of the intensive formation of natural ice nuclei situated above LIC. In A-zone the natural process of cloud drops freezing almost does not occur. A-zone consists of supercooled drops, and ice crystals from I-zone quickly grow here as a result of coagulation. So it can be said that I-zone determines the number of precipitation particles and A-zone their size. Probability of precipitation falling from non-convective clouds depends on many parameters e.g., on cloud size, heights of cloud top and cloud base, etc. Intensity of the reflected signal depends on the structure and density of cloud particles. Moreover, these characteristics influence also the rate of particle growth in cloud. Weather radars operating in the?<?ave length /?<3«2 cm enable to determine with satisfying accuracy the height of cloud top AH and distribution of cloudless layers in non-convective clouds to the distance R-80 km» After changes in the inner structure of cloudiness also the radioecho parameters have to be changed. Then it is

11 Combined processing of meteorological information 69 possible to determine indirect connections between radar parameters of cloud layer and formation of precipitation in stratus clouds. In other words, it is necessary in our opinion to pay extra attention to the relationship between the values of precipitation intensities near ground and to tendencies, i.e. changes of quantities of radar reflectivity in the vertical profile above the line of intensive crystallization and, based on these new links, to give more precise methods of rainfall forecasts. References /1/ Krcho J. - Podhorsky D., 1981, Dynamic model of landscape relief and remote sensing of environment? Meteorologické zprâvy, 34, Wo.2, pp /2/ Barrett B.C. - Curtis L.P., 1976, Introduction to environmental remote sensing, London, New York. /3/ Podhorsky D., 1985, Prognosis of precipitation evolution based on remote sensing, seminar Remote sensing applications in hydrology and water resources, Czechoslovakia, 10p.

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