The GHCN data base contains mean monthly sea level pressure data (in tenths of millibars) for 1883 stations throughout the world. The majority (89%) have records for fewer than 50 years, and only a small proportion (2%) have records in excess of 100 years. The longest period of record for any given station is 216 years (1755-1970 for Basel/Binningen, Switzerland). Most records (72%) end in the 1980s. No data are available for any station after 1988.
The density of stations in central Europe is extremely high, and moderately high in much of the rest of the world. Significant data gaps are evident in northern North America, the Amazon basin, the Sahara desert, southern Africa, the Arabian peninsula, the Gobi desert, the East Indies, and all of Antarctica. The global distribution of stations with 50 years or more of data is characterized by a low density of stations in all areas. There are very few stations with 100 years or more of data.
In general, the number of stations has increased over the past 250 years, particularly in third-world countries. The rate of increase has accelerated since the nineteenth century, owing to the widespread availability of reliable instrumentation and the increased habitation of areas that were previously less populated. The sharp increase in the number of stations in 1921, 1931, 1941, 1951, and 1961 is due to the inclusion of various versions of the WWR data set in the WMSSC. The decrease in the number of stations after 1971 results from the inclusion of only three of the six volumes of the 1971-1980 WWR publication (i.e., three volumes have yet to be prepared and thus could not be included).
Nearly 66% of all stations are missing less than 10% of their data. Typically, these are the same stations in central North America and central Europe with the longest periods of record. In contrast, the data sparse areas of South America, Africa, and Asia are characterized by higher proportions of missing data.
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