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The new revision 3 (Easterling et al. 1996) data represent the best available data from the United States for analyzing long-term climate trends on a regional scale and may be used for studies attempting to determine the climatic impacts of increased concentrations of greenhouse gases. The data for most stations extend through December, 1994, and a majority of the station records are complete for at least 80 years. Unlike many data sets that have been used in past climate studies, these data have been adjusted to remove biases introduced by station moves, instrument changes, time-of-observation differences, and urbanization effects.
At this revision (Revision 3) the data set has been extended through the end of 1994 and several stations have been added (54) and deleted (52). Twenty-five of these additions/deletions involved stations who's official station name and number changed, but who did not actually move. These revisions have resulted in a network with 1221 stations (Figure 1).
The 1221 station U.S. HCN database contains station histories, monthly temperature (maximum, minimum, and mean) data, and total monthly precipitation data that were compiled by NCDC after being extracted from digital and nondigital data sets archived at NCDC. These data sets originated from a variety of sources, including climatological publications, universities, federal agencies, individuals, and data archives. All stations were quality controlled by NCDC with the use of outlier and areal edits, and each station in the network was corrected for time-of-observation differences, instrument changes, instrument moves, station relocations, and urbanization effects (Karl et al. 1986; Karl and Williams 1987; and Karl et al. 1988). A unique feature of the data set is that, within most temperature and precipitation data files, both original and adjusted estimates are given, along with confidence factors for each adjusted estimate. Another unique feature of the database is that in relation to the long periods of record, a small portion of the data are represented as missing. In order to make the U.S. HCN record as serially complete as possible, missing data have been estimated by using data from neighboring stations. The majority of the 1221 stations have had data records that are serially complete since 1900; where serially complete is defined as having original or adjusted data available for all months after the reported serially complete date for a given station.
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