Access

• Data
• Metadata

Description

• Introduction
• Source Data
• Data Coverage

Methods

• Data Integration
• Quality Control
• Bias Adjustment

Other

• Journal Articles
• Related Projects
• Status Reports
• NCDC Land-based Data

Contacts

Description - Source Data

Most nations operate at least one network of surface observing stations that collect data on a daily basis. Unfortunately, there is no central repository for all of the daily data collected from all observing systems worldwide. As a result, a major task in creating GHCN-Daily was to maximize spatial coverage by acquiring historical records for as many stations in as many national networks as possible. This was accomplished using three complementary data acquisition strategies. The first approach involved identifying relevant data sets that are already stored in NCDC's archives. The second strategy entails leveraging off of international initiatives, such as the Global Climate Observing System (GCOS) Surface Network (GSN), that facilitate the free exchange of data. The third tactic is to exploit personal contacts, particularly those at national meteorological centers around the world.

The following is a list of the sources of data currently contained in GHCN-Daily along with a brief description of each source.

• U.S. Cooperative Summary of the Day (NCDC DSI-3200) - Includes daily observations at 19,000 stations in the United States and its territories. While most measurements are taken by volunteer observers as part of the U.S. NOAA National Weather Service's Cooperative Observer (COOP) Program, manual and automated measurements from some "First Order" sites are also included. Some records extend back to the late 1800s, but most do not begin until 1948 or later. The dataset is ongoing; observations for a specific year and month are added three to four months after they were taken, and corrections to fix processing or reporting errors in data from previous months are made frequently.
• U.S. Preliminary Cooperative Summary of the Day - Provides real-time updates for over 1000 U.S. COOP stations. Updates are provided on a daily basis for stations that transmit observations electronically.
• U.S. Preliminary Cooperative Summary of the Day - Provides updates for several thousand U.S. stations as soon as the original paper forms have been keyed following the close of the data month. Updates are provided within weeks for the previous month.
• U.S. Fort data - Contains daily observations primarily from the 19th Century from over 30 Forts and Voluntary Observer sites that were keyed as part of NCDC's Climate Data Modernization Program (CDMP). Additions are made periodically.
• High Plains Regional Climate Center Cooperative Summary of the Day - Provides real-time updates to records for several thousand U.S. COOP stations. Data extend back to 2004. Updates are provided by the High Plains Regional Climate Center on a daily basis and represent observations for the previous day.
• CDMP U.S. Cooperative Summary of the Day (NCDC DSI-3206) - Contains mostly pre-1948 observations from more than 11,000 COOP stations that were keyed as part of NCDC's Climate Data Modernization Program (CDMP). Corrections are made occasionally.
• U.S. First Order Summary of the Day (NCDC DSI-3210) - Contains historical and present-day manual and automated observations from approximately 1600 sites, including U.S. First Order stations, a selection of Canadian sites, and U.S.-operated stations in other countries. Observations for a specific year and month are added two to three months after they were taken, and corrections to historical data may occasionally be applied.
• ASOS Summary of the Day, 2006-present (from NCDC DSI-3505) - Contains reports from U.S.-operated Automated Surface Observing System (ASOS) stations beginning in January 2006. Data are updated daily with observations from the previous day. In contrast to observations contained in the Global Summary of the Day, these observations apply to the 24-hour period ending at midnight local time.
• U.S. ASOS Summary of the Day, 2000-2005 (NCDC DSI-3211) - Contains observations for nearly 900 U.S. ASOS stations between October 2000 and December 2005. The data set is no longer updated, but corrections are made occasionally.
• Surface Metar Monthly Airways Extract (NCDC DSI-6407) - Contains hourly surface weather observations for 1996-2002 at major airports that include 24-hour reports at local midnight. Observations are made by automated equipment and may be augmented by a human observer.
• Governmental Exchange Data - Contains data received through GCOS and bilateral agreements and currently includes observations for several hundred GSN stations outside the United States as well as for several thousand Canadian sites. Both recent observations and historical data are added as often as once a month for stations outside North America, but the update frequency for individual locations depends on the frequency with which the corresponding countries supply their data and on the speed with which they are processed at NCDC. In contrast, observations from many Canadian stations are updated daily.
• International Collection - Contains historical records for over 13,000 locations outside the United States. These records were obtained through personal contacts in their respective countries and are not updated on a regular basis.
• Global Summary of the Day (NCDC DSI-9618) - Contains 24-hour observations derived from hourly synoptic reports exchanged on the Global Telecommunications System (GTS) and archived in NCDC's Integrated Surface Dataset (DSI-3505). The 24-hour summary period Is generally midnight-midnight UTC. Daily values derived in this fashion may differ significantly from "true" daily data, particularly for precipitation. However, they provide data for a number of locations that are not contained in In any other archive and represent the only source of daily updates for others.
• U.S. Climate Reference Network - Daily climate summaries from the U.S. Climate Reference Network. Data begin as early 2001 and are ongoing. Data are updated at least weekly. Time of observation is local midnight.

The data extracted from these sources consist of up to six GHCN-Daily elements (daily maximum and minimum temperatures, temperature at the time of observation, precipitation, snowfall, and snow depth). In order to facilitate the application of a uniform suite of quality control procedures, only "original" values are used (i.e., values identified as estimated or edited are not retained).

The data sources vary considerably in terms of spatial coverage, period of record, temporal completeness, and update frequency. Furthermore, the types of elements reported and the means by which observations were taken differ among the data sources and can also vary with station and time within a source dataset. More information on the resulting spatial and temporal coverage of GHCN-Daily can be found on the Data Coverage page.