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GHCN-Monthly Version 3

Overview

The Global Historical Climatology Network-Monthly (GHCN-M) temperature dataset was first developed in the early 1990s (Vose et al. 1992). A second version was released in 1997 following extensive efforts to increase the number of stations and length of the data record (Peterson and Vose, 1997). Methods for removing inhomogeneities from the data record associated with non-climatic influences such as changes in instrumentation, station environment, and observing practices that occur over time were also included in the version 2 release (Peterson and Easterling, 1994; Easterling and Peterson 1995). Since that time efforts have focused on continued improvements in dataset development methods including new quality control processes and advanced techniques for removing data inhomogeneities (Menne and Williams, 2009). Effective May 2, 2011, the Global Historical Climatology Network-Monthly (GHCN-M) version 3 dataset of monthly mean temperature has replaced GHCN-M version 2 as the dataset for operational climate monitoring activities. The dataset is available at ftp://ftp.ncdc.noaa.gov/pub/data/ghcn/v3/. The formal designation is ghcnm.x.y.z[optionally -betan].yyyymmdd

where

  • x = major upgrades of unspecified nature to either qc, adjustments, or station configurations and accompanied by a peer reviewed manuscript
  • y = substantial modifications to the dataset, including a new set of stations or additional quality control algorithms. Accompanied by a technical note.
  • z = minor revisions to both data and processing software that are tracked in "status and errata".
  • yyyy = year in which the update to the dataset occurred.
  • mm = month in which the update to the dataset occurred.
  • dd = day in which the update to the dataset occurred.

Each evening as part of the GHCN-M update process, the output files will be labeled with the current version number and date and time stamped to indicate when the update occurred. For example, the filename for the dataset produced on April 28, 2011 will include the string "v3.0.0.20110428" to indicate the data were developed using version 3.0.0 station data and quality control and homogeneity adjustment methods. This notation also will indicate the most recent update occurred in the year 2011, in the 4th month (April) and the 28th day of the month. The data will be placed on line at the conclusion of each update process and available via the link noted above. This versioning format facilitates documentation and communication of updates and modifications that occur as a normal part of the life of this climate dataset.

Information on Version 3 quality control and homogeneity adjustment processes is also available.

Data Access

Unadjusted and Adjusted GHCN-Monthly Data

Unadjusted and adjusted GHCN-Monthly data and inventory files:
ftp://ftp.ncdc.noaa.gov/pub/data/ghcn/v3/

Directions on Uncompressing and Extracting Files (Includes description of inventory file and format of data files [measurement, quality, and source flags])

Station-Level Information

Detailed station-level information on monthly mean temperatures and trends for unadjusted and adjusted station data is provided in graphical form:
ftp://ftp.ncdc.noaa.gov/pub/data/ghcn/v3/products/stnplots/

Explanation of Figures

Station Vs. Neighbor Comparison Graphs

Graphs of station versus neighbor comparisons (with additional information on station-level bias adjustments):
ftp://ftp.ncdc.noaa.gov/pub/data/ghcn/v3/products/stn-vs-net/

Explanation of Graphs

Quality Assurance

With the development of GHCN-M v3, new quality control (QC) procedures were instituted using methods established as part of other dataset development efforts during the past five years. The QC algorithms are based on methods used for the GHCN-Daily temperature dataset and subsequently applied to USHCN-Monthly Version 2 data (Menne et al. 2009). The QC process used in GHCN-M v3 consists of the seven checks listed in Table 1. They are performed in the order listed. The thresholds shown in column two were selected and their performance evaluated based on the method outlined in Durre et al. (2008).

Table 1. Quality Assurance Checks Applied to GHCN-Monthly Version 3 Temperature
Data Problem Description of Check
Consecutive month duplication Used to identify duplicate retransmission and mislabeling of previous month's temperature for current month. Occurs in GTS transmitted CLIMAT bulletins
Series Duplication Identifies duplication of data between years
Streak Identifies runs of the same value in four or more consecutive months
Isolated value Identifies months that are isolated in time. One to three consecutive months that are separated from other non-missing months by 36 or more consecutive months of missing values
Climatological Outlier Identifies temperatures that exceed their respective climatological means for the corresponding station and calendar month by at least five standard deviations
Spatial inconsistency 1 Compares z scores (relative to their respective climatological means) to concurrent z scores at the nearest 20 neighbors located within 500 km of the target; a temperature fails if (i) its z score differs from the regional (target and neighbor) mean z score by at least 3.5 standard deviations and (ii) the target's temperature anomaly differs by at least 2.5°C from all concurrent temperature anomalies at the neighbors
Spatial inconsistency 2 Identifies temperatures whose anomalies differ by more than 4°C from concurrent anomalies at the five nearest neighboring stations whose temperature anomalies are well correlated with the target (correlation >0.7 for the corresponding calendar month)

Homogeneity Adjustment

Many surface weather stations undergo minor relocations through their history of observation. Stations may also be subject to changes in instrumentation as measurement technology evolves. Further, the land use/land cover in the vicinity of an observing site may also change with time. Such modifications to an observing site have the potential to alter a thermometer's microclimate exposure characteristics and/or change the bias of measurements, the impact of which can be a systematic shift in the mean level of temperature readings that is unrelated to true climate variations. The process of removing such "non-climatic" artifacts in a climate time series is called homogenization.

In version 3 of the GHCN-Monthly temperature data, the apparent impacts of documented and undocumented inhomogeneities are detected and removed through automated pairwise comparisons of mean monthly temperature series as detailed in Menne and Williams [2009]. In this approach, comparisons are made between numerous combinations of temperature series in a region to identify cases in which there is an abrupt shift in one station series relative to many others. The algorithm starts by forming a large number of pairwise difference series between serial monthly temperature values from a region. Each difference series is then statistically evaluated for abrupt shifts, and the station series responsible for a particular break is identified in an automated and reproducible way. After all of the shifts that are detectable by the algorithm are attributed to the appropriate station within the network, an adjustment is made for each target shift. Adjustments are determined by estimating the magnitude of change in pairwise difference series form between the target series and highly correlated neighboring series that have no apparent shifts at the same time as the target.

References

  • Durre, I., M.J. Menne, and R.S. Vose, 2008: Strategies for evaluating quality assurance procedures. Journal of Applied Meteorology and Climatology, 47(6), 1785-1791.
  • Easterling, D.R., and T.C. Peterson, 1995: A new method for detecting undocumented discontinuities in climatological time series. International journal of climatology, 15 (4), 369-377.
  • Lawrimore, J. H., M. J. Menne, B. E. Gleason, C. N. Williams, D. B. Wuertz, R. S. Vose, and J. Rennie (2011), An overview of the Global Historical Climatology Network monthly mean temperature data set, version 3, J. Geophys. Res., 116, D19121, doi:10.1029/2011JD016187.
  • Menne, M.J., and C.N. Williams Jr., 2009: Homogenization of temperature series via pairwise comparisons. Journal of Climate, 22(7), 1700-1717.
  • Peterson, T.C., and D.R. Easterling, 1994: Creation of homogeneous composite climatological reference series. International journal of climatology, 14 (6), 671-679.
  • Peterson, T.C., and R.S. Vose, 1997: An overview of the Global Historical Climatology Network temperature database. Bulletin of the American Meteorological Society, 78 (12), 2837-2849.

Contact

For questions specific to GHCNM, please email NCDC.GHCNM@noaa.gov.

How to Cite

Please provide acknowledgement to NOAA's National Climatic Data Center and the version 3 publication:

  • J. H. Lawrimore, M. J. Menne, B. E. Gleason, C. N. Williams, D. B. Wuertz, R. S. Vose, and J. Rennie (2011), An overview of the Global Historical Climatology Network monthly mean temperature data set, version 3, J. Geophys. Res., 116, D19121, doi:10.1029/2011JD016187.