APPENDIX About weather data

Weather data is something we take for granted, but few meteorologists know exactly where it comes from.  This section helps clarify how it works.

Every day, nearly ten thousand weather stations across the world disseminate weather observations. These observations are taken according to standards and formats laid out by the World Meteorological Organization (WMO), a United Nations organization based in Geneva that facilitates international cooperation in meteorology and hydrology. In 1961 the WMO developed the concept of the World Weather Watch (WWW), whose goal is to keep the entire atmosphere under continuous surveillance. The nuts and bolts of the WWW are laid out in its Global Observation System (GOS), and data is used, reprocessed, and shared according to the WWW Global Data Processing System (GDPS). However the technical breakthrough that makes this all possible is the Global Telecommunications System (GTS). This is a permanent communications network that facilitates the flow of global weather information.

The GTS's main link is the Main Telecommunications Network (MTN), which links Melbourne, Moscow, and Washington. Connected to the MTN is a series of regional networks, known as Regional Meteorological Telecommunications Networks (RMTNs), located at Algiers, Beijing, Bracknell, Brasilia, Buenos Aires, Cairo, Dakar, Jeddah, Maracay (Venezuela), Nairobi, New Delhi, Norrkoping (Sweden), Offenbach, Prague, Rome, Sofia, Tokyo, Toulouse (France), and Wellington. Within each country is its own National Meteorological Telecommunications Network (NMTN). There are also specialized networks connected to the GTS, such as the U.S. Air Force's Global Weather Intercept Program, which uses powerful receivers to collect and share weather data from politically and economically isolated regions.

The weather data is shared among WMO member states, who in turn set policy and procedures for sharing data with the private sector. In the United States, the data is distributed to the public through the National Weather Service's NOAAPORT and FOS data feeds. Much of this data reaches the Internet and is available free of charge. This puts affordable forecasting in the hands of millions of American citizens and business owners, boosting economic productivity and earnings on a national scale. Unfortunately in Europe, Asia, South America, and even Canada, long-standing ultra-conservative government policies make the data available only to pilots, mariners, and big spenders (i.e. large corporations). The Internet is the ultimate GTS, though, and its presence has done much to break down these economic barriers.

Surface weather data is transmitted in one of two main formats: METAR and SYNOP. The METAR format is used primarily at airports, and has an hourly observation cycle. It gives us the best picture of weather conditions in North America, Europe, and the Pacific Rim. The METAR format is fairly readable and uses station identifiers prescribed by the International Civil Aeronautical Organization (ICAO). The SYNOP format is more detailed and uses extensive numerical coding, using numerical station identifiers prescribed by the WMO, and typically has a 6-hour cycle. It gives us the best picture of weather in South America, Africa, Asia, Australia, and Antarctica, where "meteorological observatories" tend to be bona fide weather offices rather than control towers or flight service stations.

Upper air data from balloon launches is taken worldwide twice a day. It is transmitted in TEMP format, also known as "TTAA", "TTBB", "PPBB format", and "radiosonde format". This format uses extensive numerical coding. Availability of upper air data is fairly good across much of the northern hemisphere, but is seriously lacking in the southern hemisphere where satellite-based sensors are widely used to initialize computer model forecasts.

Since much of this data is freely available from a variety of sources, Digital Atmosphere gives users a flexible tool for graphically importing and displaying all of the different weather data formats provided by the GTS.