G - I
The U.S. Historical Climatology Network (U.S. HCN) was compiled in response to the need for an accurate, unbiased, modern historical climate record for climate change research. The Carbon Dioxide Research Program of the U. S. Department of Energy and the National Climatic Data Center (NCDC) of the National Oceanic and Atmospheric Administration (NOAA) established a network of 1219 stations in the contiguous United States for the specific purpose of compiling a data set suitable for detecting and monitoring climate change over the past two centuries. This network, known as the U.S. Historical Climatology Network (U.S. HCN), and the resulting data set were initially documented by Quinlan et al. (1987) and made available free of charge through the Carbon Dioxide Information Analysis Center (CDIAC). The data presented in Quinlan et al. (1987) extended only through 1984. In 1990 NCDC and CDIAC revised and updated the HCN data records through 1987 (Karl et al. 1990). In addition, ! using the techniques of Karl et al. (1988), NCDC generated temperature files in which the biases introduced by urbanization effects were removed. 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. Source and Scope of the Data: One of the objectives in establishing the U.S. HCN was to detect secular changes of regional rather than local climate. Therefore, only those stations that were not believed to be influenced to any substantial degree by artificial changes of local environments were included in the network. Some of the stations in the U.S. HCN are first order weather stations, but the majority were selected from U.S. cooperative weather stations (approximately 5000 in the United States). To be included in the U.S. HCN, a station had to be active (in 1987), have at least 80 years of mean monthly temperature and total monthly precipitation data, and have experienced few station changes. An additional criterion that was used in selecting the 1221 U.S. HCN stations, which sometimes compromised the preceding criteria, was the desire to have a uniform distribution of stations across the United States. 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 r! elation 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. Applications of the Data: The U.S. HCN database represents the best monthly temperature and precipitation data set available for the contiguous United States. It provides an accurate, serially complete, modern historical climate record that is suitable for detecting and monitoring longterm climatic changes on a regional scale and may be used for studies attempting to determine the climatic impacts of increased concentrations of greenhouse gases. The U.S. HCN climate record may also be used by dendrochronologists and paleoclimatologists for calibrating tree ring growth, pollen, and marine plankton data or by those studying the climatic impacts of periodic events such as El Nino/Southern Oscillation or volcanic eruptions. Those studying longterm climatic changes on smaller scales, may want to review the information given in the appendices in order to identify the stations most suitable for their research needs. For more information, link to "http://cdiac.esd.ornl.gov/epubs/ndp019/ndp019.html"
HCN