Meteorological data from ground stations
The stations are limited to those that regularly collect data and can supply the data in near real time (Burrill and Vossen, 1992). Relevant information of stations includes station number, station name, latitude, longitude and altitude. This data is available in the table WEATHER_STATION.
Some of the historic meteorological data are purchased directly from National Meteorological Services. Others are acquired via the Global Telecommunication System (GTS). As the data are obtained from a variety of different sources, considerable preprocessing is necessary to convert them to a standard format. Two different procedures are applied for distinct subsets of the data. Around 1992 the historic meteorological data represented approximately 380 stations in the EU, Switzerland, Poland and Slovenia with data from 1949 to 1991 (Burrill and Vossen, 1992). Later the historic sets have been extended with stations in eastern Europe, western Russia, Maghreb and Turkey.
The historic data are converted into consistent units and checked on realistic values. The database was also scanned for inconsistencies, such as successive days with the same value for a variable, or minimum temperatures higher than maximum temperatures (Burrill and Vossen, 1992).
From 1991 to present, meteorological data are received in near real time from the GTS network for different hours within one day. The data are pre-processed and quality checked using the AMDAC software package (MeteoConsult, 1991) which extracts, decodes and processes the GTS data.
The station database stored in table WEATHER_STATION holds over 7100 stations distributed over 74 countries. In near real time over 3000 stations provide weather data. All weather data is stored in the stations weather database (METDATA) that currently counts over 33.8 million records.
|Meteodata delivery reports of number of stations by country|
The figures on the right illustrate the increase of available number of stations for the temperature indicator between 1975 and 2009. In general the stations density in the monitored areas is considered sufficiently high for the purpose of the project. Raw station data are collected from various sources:
- Economic interest grouping of the National Meteorological Services of the European Economic Area (ECOMET)
- National oceanic and atmospheric administartion (NOAA USA)
- Meteorological Aviation Reports (METAR)
Observations of maximum and minimum temperatures, precipitation amounts and sunshine duration (when available) are contained in the main hours synoptic. METAR data provide temperature, dew point, visibility and cloud amount. As far as available, they can be used for intermediate or even non-standard (i.e. all but main and intermediate) hours. From most countries outside Europe, 3-hourly synoptic data are exchanged world wide and can be made available through Meteo Consult.
Data from outside the ECOMET area are transmitted from the 'Royal Netherlands Meteorological Institute' (KNMI) as if WMO essential. A number of countries in Europe, especially in the east, are aiming to become a member of ECOMET. This might lead to a reduction in the amount of data freely available.
Meteorological stations selected in priority are those located in the agricultural zones and equally distributed over the mainland (instead of over islands - for Portugal, Spain or Greece in particular). In particular, for western Russia (western of Urals) the main areas covered are the agricultural districts.
Early March 2009 an updated station list became available with changes for 117 stations and 54 new stations. The lists will be compared with the WEATHER_STATION table and if consistent the changes and additions will be updated.
Data quality check
For the data quality check specific software has been developed (AMDAC). The software performs the following actions:
- Decode intermediate-hour and main-hour SYNOP reports and METAR reports from weather stations circulating on the GTS;
- Check the quality and correct the obvious errors in the received weather reports;
- Perform time consistency checks to compare the values of reported parameters with those previously or subsequently reported for the same station;
- Correct automatically obvious errors detected while performing consistency checks;
- Fill up automatically gaps in the database through interpolation based on time consistency criteria. This implies that observations from 18 UTC of the previous day until 12 UTC of the next day are available in order to compute an interpolation in time if missing values occurred;
- Flag errors and dubious observations and write these to a log file;
- Finally the data are converted into daily values. It comprises the selection of minimum and maximum temperature, the aggregation of the rainfall, cloud cover and sunshine duration, the calculation of mean vapor pressure etc.
The values of the following observation elements are checked:
- air temperature
- dew-point temperature
- pressure at sea level
- wind speed
- amount of precipitation
- amount of clouds
- duration of sunshine
Obvious errors in the observations are automatically corrected and a message is written to a log file. Dubious observations which can not automatically be corrected are also written to a log file. The operational meteorologist who has the possibility of modifying the data can read these latter messages. After the observations of a station are checked (and if necessary corrected) the derived parameters are recalculated and the data are written back to the database.
Once the database has been filled using the previous module, a final check is performed on the daily file before storing it in table METDATA. This automated quality check consists in verifying the following conditions:
|Daily mean of total cloud cover : N||0 to 8 octas|
|Measured sunshine duration: Msun||0 to 24 hours|
|Minimum temperature: Tn||-15 to 25°C|
|Maximum temperature: Tx||0 to 40°C|
|Maximum temperature - Minimum temperature||0< Tx-Tn <30°C|
|Daily mean vapor pressure: e||0 to 30 hPa|
|Daily mean wind speed at 10 metres: ff10||0 to 15 m/s|
|Amount of precipitation from 6 UTC-6 UTC: RRR||0 to 75 mm|
|Air temperature: TT||-15 to 40°C|
|Relative humidity: RH||20 to 100%|
|Daily mean vapor pressure deficit: vpd||0 to 40 hPa|
|Daily mean slope of saturation vapor pressure vs. temperature curve: slope||0 to 3 hPa/°C|
|Daytime mean of total cloud cover: N||0 to 8 octas|
|Penman evaporation: ETP||0 to 10 mm/day|