UNITED STATES HISTORICAL CLIMATOLOGY NETWORK
MONTHLY TEMPERATURE AND PRECIPITATION DATA




Contributed by:

C. N. Williams, Jr., M. J. Menne,
R. S. Vose, and D. R. Easterling
National Oceanic and Atmospheric Administration
National Climatic Data Center
Asheville, North Carolina



Documentation Prepared by:

Dale P. Kaiser and Thomas A. Boden
Carbon Dioxide Information Analysis Center
Environmental Sciences Division
OAK RIDGE NATIONAL LABORATORY (ORNL)
Oak Ridge, Tennessee 37831-6335
managed by
UT-Battelle, LLC
for the U.S. DEPARTMENT OF ENERGY
under contract DE-AC05-00OR22725

May 2008

DOI: 10.3334/CDIAC/cli.ndp019




    Abstract

    Williams, C. N., M. J. Menne, R. S. Vose, and D. R. Easterling, 2007. United States Historical Climatology Network Monthly Temperature and Precipitation Data. ORNL/CDIAC-87, NDP-019. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee. doi: 10.3334/CDIAC/cli.ndp019

    The U.S. Historical Climatology Network (USHCN) is a high-quality, moderate-sized data set of monthly averaged maximum, minimum, and mean temperature and total monthly precipitation. The USHCN was developed to assist in the detection of regional climate change; it is comprised of 1221 high-quality stations from the U.S. Cooperative Observing Network within the 48 contiguous United States. The period of record varies for each station, especially in the case of the first year of the record. Most station records extend through 2006. The stations were chosen using a number of criteria including length of record, percent missing data, number of station moves and other station changes that may affect the data homogeneity, and spatial coverage. Included with the data set are metadata files that contain station history information about station moves, instrumentation, observing times, and elevation. This document describes the USHCN station network and gives details of the format and content of all files. The USHCN was developed and is maintained at the National Climatic Data Center (NCDC) and the Carbon Dioxide Information and Analysis Center (CDIAC) of Oak Ridge National Laboratory through a cooperative agreement between the NCDC and the U.S. Department of Energy.


    1. Background Information

    Over the past few decades, numerous global, hemispheric, and regional meteorological databases have been assembled for use in studying the nature and variability of the earth's climate. This work has been largely inspired by growing international concern over the potential climatic impacts of increasing atmospheric concentrations of greenhouse gases. While the parameters important in the study of climate change are myriad, those that seem to have received the most attention are near-surface air temperature (herein referred to as temperature) and precipitation. There are many reasons for this, including (1) the spatial and temporal variability of these parameters affects ecosystems, agriculture, water resources, human health, and energy needs and consumption; (2) instrumental records of these variables are relatively long, beginning in the 1800s in many regions of the northern hemisphere; and (3) analyses of temperature data from around the globe show an increase in global mean surface temperature of 0.74°C ± 0.18°C over the period 1906-2005 (IPCC 2007).

    The suitability of modern historical temperature and precipitation data for climate change studies depends on their reliability and accuracy. Most records of significant length, regardless of source, are likely to contain biases or inhomogeneities resulting from changes in the environment or operation of individual observing sites (e.g., urbanization, station moves, and instrument and time of observation changes). The process of identifying and removing these nonclimatic effects is complex and tedious, and has been undertaken on large scales in such studies as Jones (1994), Jones et al. (1986; 1997), Vinnikov et al. (1990), Peterson and Vose (1997), and Quinlan et al. (1987). The work of Quinlan et al. (1987) involved the compilation of a database containing monthly temperature and precipitation data from a network of 1219 U.S. stations — the first version of the USHCN. The compilation was performed at the National Climatic Data Center (NCDC) of the National Oceanic and Atmospheric Administration (NOAA) in Asheville, North Carolina, and sponsored by the Carbon Dioxide Research Program of the U.S. Department of Energy. The project arose from the need for an accurate, unbiased, and modern historical climate record suitable for detecting and monitoring secular changes in regional climate in the contiguous United States. The quality of the HCN data was enhanced with the use of outlier and areal edits, and the data were corrected for time of observation differences, instrument changes, instrument moves, station relocations, and urbanization effects (Karl et al. 1986; Karl and Williams 1987). The USHCN was formally updated (i.e, accompanied by printed documents) several times since its inception and before the advent of the Word Wide Web, most recently by Easterling et al. (1996). It is now updated online each year and currently consists of 1221 stations. Some of the stations in the HCN are first-order weather stations, but the majority were selected from approximately 5000 U.S. cooperative weather stations.


    2. Descriptions and Formats of USHCN Data Files and Supporting Files

    The section describes the various USHCN temperature and precipitation data files and several supporting files that contain information about the USHCN stations. Temperature and precipitation data files will be described first, followed by descriptions of all other files.

    The data for each station in the USHCN are subjected to several quality control tests, homogeneity tests, and adjustment procedures. These steps are applied so as to sequentially produce six different types of data records, with each successive record type using the preceding record type as input. Each data record type is listed below with a description of the tests and/or adjustments that go into making each of them.

    The Areal Edited, TOBS, FILNET, and Urban data files are available in this version of the USHCN. The MMTS and SHAP iterations of the data are also available (email D. Kaiser at CDIAC), but are used less often in favor of the FILNET data files, which incorporate both the MMTS and SHAP adjustments.

    Currently all data adjustments in the USHCN are based on the use of metadata. However, station histories are often incomplete, or changes that can cause a time series discontinuity (such as replacing a broken thermometer with one that is calibrated differently) are not routinely entered into station history files. Because of this, NCDC is currently developing another step in the processing that will apply a time series discontinuity adjustment scheme described in Peterson and Easterling (1994) and Easterling and Peterson (1995). This methodology does not use station histories and identifies discontinuities in a station's time series using a homogeneous reference series developed from surrounding stations.

    To illustrate the effects of each adjustment scheme, we produced annual time series from each data set using the Climate Analysis System (CAS), a software package developed at NCDC that provides a wide-array of analysis options. Athough various grid sizes can be used in the analyis of USHCN data, we determined the optimum grid size to be 2.5 degrees X 3.5 degrees. We calculated all anomalies with respect to the base period 1961-1990 and adjusted the time series to the period 1900 - 1910 to simplify the comparison of the different data sets. The following graphs depict the time series resulting from each USHCN data set.

    The adjacent plot shows the annual time series calculated from each of the six USHCN data sets. The USHCN adjustment procedures are applied in stepwise fashion so that the effects from each adjustment have a cumulative effect. The data set containing the final adjustment procedure (urbanization adjustments) also contains all of the previous adjustments. Each series contains data from 1900-1999. Data Set Comparison
    larger image

    Differences Due to Adjustments
    larger image
    It is much easier to evaluate the effects of each adjustment by plotting stepwise differences between USHCN time series. The effect of each successive adjustment is clearly evident in the adjacent plot that shows the differences in the above time series.
    Applying the Time of Observation adjustment (black line) resulted in approximately a 0.3F warming from the late 1960's to the 1990's. The shift from Cotton Region Shelters to the Maximum/Minimum Thermometer System in the mid-1980's is clearly evident in the difference between the TOBS and the MMTS time series (red line). This adjustment created a small warming in the US annual time series during the mid to late 1980's. Application of the Station History Adjustment Procedure (yellow line) resulted in an average increase in US temperatures, especially from 1950 to 1980. During this time, many sites were relocated from city locations to airports and from roof tops to grassy areas. This often resulted in cooler readings than were observed at the previous sites. When adjustments were applied to correct for these artificial changes, average US temperature anomalies were cooler in the first half of the 20th century and effectively warmed throughout the later half. Filling in missing data (blue line) produced cooler temperatures prior to 1915. Adjustments to account for warming due to the effects of urbanization (purple line) cooled the time series an average of 0.1F throughout the period of record.
    Areal vs Final
    larger image
    The adjacent graph shows how the annual raw (areal edited) mean temperature anomalies compare with the anomalies from the data set containing all adjustments (final). The difference of these two time series is shown below.
    The cumulative effect of all adjustments is approximately a one-half degree Fahrenheit warming in the annual time series over a 50-year period from the 1940's until the last decade of the century. Areal vs Final Difference
    larger image

    2.1 USHCN Temperature Data Files

    The USHCN data base contains monthly maximum (Tmax), minimum (Tmin), and mean temperature (Tmean) data (expressed to the nearest hundredth of a degree fahrenheit) for each of the of the four types of adjusted data records. There is also a FILNET mean data set that is the mean monthly temperature calculated from the FILNET-adjusted maximum temperature and the FILNET adjusted minimum temperature data sets. A listing of the various filenames is given at the end of this section.

    Four types of data records - the Areal Edited, TOBS, and FILNET data records, along with " Confidence" records - are all contained in the FILNET Tmax, Tmin, and Tmean files; the record type being identified by the character in column 14 of each file. Confidence records contain confidence factors/estimates for each FILNET data value. These factors are also expressed to the nearest hundredth of a degree fahrenheit (with -99.99 being the missing indicator for both temperatures and confidence factors). Temperature confidence intervals are calculated by subtracting the temperature confidence factor from the FILNET value to obtain the lower end of the confidence interval (16%, -1 standard deviation). The upper end of the confidence interval (84%, +1 standard deviation) is obtained by adding the confidence factor to the FILNET value. The FILNET temperature files have record lengths of 144 characters according to the following format.

    Position     Data Field
    
     01 - 06     STATION ID
       01-02       State Code
       03-06       Coop Station Number
     08 - 11     YEAR OF DATA
     13          DATA ELEMENT
                 (1 = maximum temperature;
                  2 = minimum temperature;
                  3 = mean temperature)
     14          DATA TYPE
                 (" " = Areal Edited Value;
                  "+" = Time of Observation Value;
                  "A" = Filnet Value;
                  "C" = Confidence Factor Value)
    
     15 - 144    MONTHLY DATA VALUES AND FLAGS
                 [13 data values (12 months and 1 annual) with flags] as follows:
    
       15 - 20     January Data Value
       21 - 24     Flags for January Data Value
    
       25 - 30     February Data Value
       31 - 34     Flags for February Data Value
          .
          .
          .
      125 - 130    December Data Value
      131 - 134    Flags for December Data Value
    
      135 - 140    Annual Data Value
      141 - 144    Flags for Annual Data Value
    
    
    Monthly Data Flags
    
    The following describes the meanings of the four types of flags for the monthly
    data values. The flags vary depending on record type (i.e., Areal Edited, TOBS, FILNET, or Confidence).
    
    
    Flag 1
    
          For the Areal Edited, TOBS, and FILNET data:
    
          Flag 1 is the code for the number of daily values not available in
          computing the monthly value ("A" = 1, "B" = 2, "C" = 3,..."H" = 8); or the
          code "I" for interpolated or "." for estimated.
          [NOTE:  for values from digital sources (e.g., flag 2 = "0" or
          "1"), the days missing code will be an "I" to indicate between 1 to 9 days were
          missing from the monthly value; whereas, for non-digital sources, a days
          missing code of "I" means 9 days missing.]
    
          For the Confidence data, Flag 1 is left blank.
    
    
    Flag 2
    
          For the Areal Edited, TOBS, and FILNET data,
          Flag 1 is the code for the data source, as follows:
    
          0 =  NCDC Tape Deck 3200, Summary of the Day Element Digital File
          1 =  NCDC Tape Deck 3220, Summary of the Month Element Digital File
          2 =  Means Book - Smithsonian Institute, C.A. Schott (1876, 1881 thru 1931)
          3 =  Manuscript - Original Records, National Climatic Data Center 
          4 =  Climatological Data (CD), monthly NCDC publication 
          5 =  Climate Record Book, as described in History of Climatological Record
               Books, U.S. Department of Commerce, Weather Bureau, USGPO (1960)
          6 =  Bulletin W - Summary of the Climatological Data for the United States (by
               section), F.H. Bigelow, U.S. Weather Bureau (1912); and, Bulletin W -
               Summary of the Climatological Data for the United Sta
    
          For the Confidence data, Flag 2 is a code representing the number of the move,
          counting back from 1994:
    
          0 = no move;
          1 = first move;
          2 = second move;
          .
          .
          9 = ninth move;
          A = tenth move;
          B = eleventh move;
    
    
    Flag 3
    
          For Areal Edited data, Flag 3 is left blank.
    
          For TOBS data, Flag 3> is the code for the quality of the available observation
          times for a given station:
    
          F = information concerning the observation times for the station during that
              year was suspect or "flaky";
          G = information concerning the observation times for the station during that
              year was "good" and the information was judged to be accurate;
      Blank = information concerning the observation times was not available for the
              station during that year and the data are represented as missing.
    
          For FILNET data, Flag 3 is the code for the temperature indicator for the Time of
          Observation bias correction:
    
          O = corrected;
      Blank = no observation time correction (treated as a station move).
    
          For Confidence data, Flag 3 is the code for representing the significance level
          at which the initial adjustment was made:
    
          1 = sigma of 1.0 and confidence interval of 16% to 84%;
          2 = sigma of 2.0 and confidence interval of 5% to 95%;
          3 = sigma of 2.57 and confidence interval of 1% to 99%;
          5 = sigma of 3.75 and confidence interval of 0.01% to 99.99%;
          C = closed station value; the station has missing values at the end of the 
              period of record for at least one calendar year;
          U = the algorithm was unable to adjust the entire series due to the station
              density of the network, but an estimate for the missing data is given by
              using neighboring stations;
          X = the algorithm was unable to adjust the data.
    
    
    Flag 4
    
          For Areal Edited and TOBS data, Flag 4
          is the code that indicates whether the monthly value is an outlier:
    
          S = between 3 to 5 standard deviations.
          X = greater than 5 standard deviations from period of record mean of the
              element;
    
          For FILNET data, Flag 4 is the code that indicates outliers,
          closed station values, and missing data estimates:
    
          C = station has closed; the station has missing values at the end of the
              period of record for at least one calendar year;
          E = original data available are available, but data were estimated using
              nearest neighbors because:
              (1) the data were between 3.5 and 5.0 standard deviations from their mean
                  offset and 1 or more days in the month were missing, or
              (2) adjustments of original data were inappropriate (less than 5 years between
                  potential inhomogeneities) so nearest neighbors were used to estimate
                  the data consistent with its 1994 location or most recent location
                  with at least 5 years without potential station discontinuities.)
          M = no original data are available, but an estimate is provided that is
              consistent with the data adjusted by using nearest neighboring stations;
              or, the data were in excess of 5.0 standard deviations from their mean
              offset with respect to the station's nearest neighbors;
          S = between 3 to 5 standard deviations.
    
          For Confidence data, Flag 4 is left blank.
    
    
    Annual Data Flags
    
    The following describes the meanings of the four types of flags for the annual
    data values. The flags vary depending on record type (i.e., Areal Edited, TOBS, FILNET, or Confidence).
    
    Flag 1
    
          For Areal Edited data, Flag 1 is the code for days missing:
    
          I = indicates "incomplete", if any monthly values had days missing.
    
          For TOBS, FILNET, and Confidence data, Flag 1 is left blank. 
    
    Flag 2
    
          For Areal Edited data, Flag 2 is the code for the data source (same codes
          as for the monthly data).
    
    
          For the TOBS, FILNET, and Confidence data
          Flag2 is left blank.
    
    Flag 3
    
          For the Areal Edited, TOBS, FILNET, and Confidence data, Flag 3 is left blank. 
    
    Flag 4
    
          For the Areal Edited, TOBS, FILNET, and Confidence data, Flag 4 is left blank. 
    


    USHCN Urban Heat-Adjusted Temperature Data Files

    The USHCN data base contains urban heat-adjusted (hereafter referred to as "urban") monthly maximum (Tmax), minimum (Tmin), and mean temperature (Tmean) data (degrees fahrenheit). There is also an urban mean data set that is the mean monthly temperature calculated from the urban Tmax and Tmin data. Along with monthly values, these files contain seasonal (winter = December, January, and February; spring = March, April, and May; etc.) mean urban-adjusted temperatures and annual means (January - December). There are no data flags in these files.

    The urban temperature files have record lengths of 130 characters according to the following format:

    Position      Data Field
    
     01 -  06     STATION ID
        01-02     State ID
        03-06     Coop ID
     08 -  11     YEAR OF DATA
     13 -  18     JANUARY MONTHLY VALUE
     20 -  25     FEBRUARY MONTHLY VALUE
        .
        .
     90 -  95     DECEMBER MONTHLY VALUE
     97 - 102     WINTER SEASONAL VALUE (December of Prior Year,
                  January and February of Current Year)
    104 - 109     SPRING SEASONAL VALUE (March, April, and May of Current Year)
    111 - 116     SUMMER SEASONAL VALUE (June, July, and August of Current Year)
    118 - 123     FALL SEASONAL VALUE (September, October, and November of Current Year)
    125 - 130     ANNUAL VALUE (January - December of Current Year)
    
    The following is a list of the USHCN temperature files with a description of each file's
    contents:
    
         hcn_doe_max_data.Z      Areal Edited, TOBS, and FILNET Tmax data
    
         hcn_doe_min_data.Z      Areal Edited, TOBS, and FILNET Tmin data
    
         hcn_doe_mean_data.Z     Areal Edited, TOBS, and FILNET Tmean data
    
         hcn_calc_mean_data.Z    TOBS and FILNET Tmean data calculated using
                                 hcn_doe_max_data.Z and hcn_doe_min_data.Z
    
         urban_max_fahr.Z        Urban Heat-Adjusted Tmax data
     
         urban_min_fahr.Z        Urban Heat-Adjusted Tmin data 
    
         urban_mean_fahr.Z       Urban Heat-Adjusted Tmean data
    
         urban_calc_mean_fahr.Z  Urban Heat-Adjusted Tmean data calculated using 
                                 urban.max.fahr.Z and urban.min.fahr.Z
    
    These files have been compressed using the UNIX compression utility compress. If this utility is not available, leave off the .Z extension and the files will uncompress on the fly through ftp.


    2.2 USHCN Precipitation Data File

    The USHCN data base contains total monthly precipitation data (expressed to the nearest hundredth of an inch) in the file hcn_doe_pcp_data.Z, which contains Areal Edited, TOBS, and FILNET data. The data is in the same format as the temperature data (records are 144 characters in length), with the following flag code differences:

    Monthly Flag Codes

    For the Areal Edited and TOBS data, Flag 3 is the code for indicating trace amounts of precipitation:

          T = trace amount of precipitation; data value = 0.00.
    
    For the FILNET data, Flag 3 is blank.

    For the Confidence data Flag 3 represents how the data was adjusted:

          A = annual values were used to adjust the data;
          S = seasonal values were used to adjust the data;
          U = the algorithm was unable to adjust the entire series due to the station
              density of the network, but an estimate for the missing data is given by
              using neighboring stations;
          X = the algorithm was unable to adjust the data.
    
    Annual Flag Codes

    For the Areal Edited and TOBS data, Flag 3 is the code for indicating trace amounts of precipitation:

          T = trace amount of precipitation during at least one month of the year; all
              monthly and annual data values = 0.00.
    
    For the FILNET data, Flag 3 is blank.

    2.3 USHCN Supporting Files

    Station Inventory File (station_inventory)

    The station inventory file for the USHCN contains one 64-character record per station. It is sorted by two-digit state code (see Table 2 for a list of these codes) and four-digit Cooperative Network Index (CNI), followed by two-digit state climate division number, a one-character station operating status flag, latitude and longitude (both in decimal degrees), elevation (ft), two-letter state abbreviation, and station name. Forty-one stations out of the 1221 USHCN stations stopped observing after 1995. These are indicated by a "*" in column 10 of that station's record in the inventory file. The first record of the file looks like:

    011084-07  31.07  -87.05    85 AL BREWTON 3SSE
    
    The format of the file is as follows:
                                                              
    Position    Data Field
    
    01 - 09     STATION ID
      01 - 02     State ID
      03 - 06     CNI
      07          "-"
      08 - 09     State Climate Division No.
    10          OPERATING STATUS FLAG (" "=open station "*"=closed station)
    11 - 16     LATITUDE (decimal degrees)
    18 - 24     LONGITUDE (decimal degrees)
    26 - 30     ELEVATION (ft)
    32 - 33     STATE ABBREVIATION
    35 - 64     STATION NAME AND QUALIFIER
    


    Station History File (station_history)

    The station history file provides valuable information concerning each station in the USHCN. This file documents station moves and instrument changes, lists station observers and observation times, and identifies suspect fields. For each station in the file there is a 236-character header record (blank-filled from column 87-236) followed by multiple 236-character data records describing station observing details over its period of record.

    The format of the file is as follows:

    HEADER RECORD:
    
     RECORD   # OF
    POSITION  CHAR CONFIGURATION            DEFINITIONS & REMARKS
    
    01-06       6  NUMERIC                  STATE & STATION NUMBER
                                            [First two positions indicate the state
                                            code (see Table 2); last four indicate
                                            the NCDC Cooperative substation ID number]
    
    08-09       2  ALPHA                    STATE ABBREVIATION
                                            (see Table 2)
    10          1  ALPHA                    " " (blank) indicates station currently open
                                            "*" Indicates station currently closed or Inactive
    11-12       2  NUMERIC                  DIVISION NUMBER
    
    14-43      30  ALPHA-NUMERIC            MOST CURRENT STATION NAME
                                            [condensed form of the station name and
                                            qualifier (see Positions 84-122 of Data
                                            Record)]
    
    45-60      16  ALPHA                    COUNTY NAME
                                            [if a prior county location was known, the
                                            earlier name and date of change is given in
                                            the X-REFERENCE (Positions 62-86 of the
                                            Header Record)]
    
    62-86      25  ALPHA-NUMERIC            X-REFERENCE
                                            [Station number for another location to/from
                                            which the current station has moved or gives
                                            change in county name (e.g. "To 2337";
                                            "From 2335"; "Cty = Buncombe, 9/1897") or
                                            Blank, if not applicable]
    
    87-236    150                           BLANK
    
    
    DATA RECORD:
    
    01-06       6  NUMERIC                  STATE & STATION NUMBER
                                            [First two positions indicate the state
                                            code (see Table 2); last four indicate
                                            the NCDC Cooperative substation ID number]
    
    08-17      10  NUMERIC (mm dd yyyy)     BEGIN DATE
    08-09       2                           comprised of:  Month (mm = 01-12, 99)
    11-12       2                                          Day   (dd = 01-31, 99)
    14-17       4                                          Year  (yyyy = 1738-1994, 9999)
    
    NOTE:  Values are separated by blanks.  "99" or "9999" are used for unknown
           component(s) of the date.
    
    19-28      10  NUMERIC (mm dd yyyy)     END DATE
    19-20       2                           comprised of:  Month (mm = 01-12, 99)
    22-23       2                                          Day   (dd = 01-31, 99)
    25-28       4                                          Year  (yyyy = 1738-1994, 9999)
    
    NOTE:  Values are separated by blanks.  "99" or "9999" are used for unknown
           components of the date.  An end date of "99 99 9999" indicates the station
           is still presently active. 
    
    30-44      15  NUMERIC (0,1)            SUSPECT FIELDS
                                            Positions equal to "1" indicate the data
                                            field(s) flagged by pre-key editor as
                                            suspect
    
                   POSITION       DATA FIELD
    
    30                1           Latitude
    31                2           Longitude
    32                3           Distance from Previous Location
    33                4           Elevation
    34                5           Distance from Post Office Location
    35                6           Station Name
    36                7           Qualifier
    37                8           Instruments
    38                9           Observation Times
    39               10           Instrument Heights
    40               11           Publications
    41               12           Begin Date
    42               13           End Date
    43               14           Observer
    44               15           Other Observers
    
    46-51     6    NUMERIC                  LATITUDE (DEGREES/MINUTES)
    46-48     3    S00-S90                  Degrees, where "S" denotes sign:
                                            S= " " indicates North;
                                            S= "-" indicates South
    50-51     2     00-59                   Minutes
    
    53-59     7    NUMERIC                  LONGITUDE (DEGREES/MINUTES)
    53-56     4    S000-S180                Degrees, where "S" denotes sign:
                                            S= " " indicates West;
                                            S= "-" indicates East
    58-59     2     00-59                   Minutes
    
    NOTE:  In the context of the USHCN, the location of temperature instrument defines
           official station location.
    
    61-63     3    NUMERIC                  DISTANCE FROM PREVIOUS
                                            LOCATION (DPL)
                                            units in tenths of miles unless Position
                                            64 = "B"; then the units are in "Blocks";
                                            "999" = unknown distance
    
    (NOTE:  Distances > 80 miles are flagged as suspect [refer to Position 32 of Data
            Record]; "9xx" codes indicate distance value is exclusively for the
            temperature instrument; "8xx" codes indicate distance value exclusively for
            precipitation.)
    
    64        1    ALPHA (" ",B)            UNITS INDICATOR FOR DPL
                                            "B" for Blocks; " " for tenths of miles
    
    65-67     3    ALPHA-NUMERIC            DIRECTION FOR DPL
                                            codes for the 16-points are used:
                                            N, NNE, NE, ENE, E, ESE, SE, SSE, S, SSW,
                                            SW, WSW, W, WNW, NW, NNW;
                                            "999" indicates direction unknown;
                                            "000" indicates no change in direction
                                            except for some instances of precipitation
                                            only moves [see "8xx 000" example below]
    
                   Examples of DPL Codes:
    
                   CODE      DEFINITION
    
                   999 999   Distance & direction unknown (the DPL is always missing in
                             the first record for a new station)
                   015 NW    Station moved 1.5 miles NW of previous location
                   000 000   No change in either station or instrument location
                   902 ESE   Temperature instrument moved 0.2 miles ESE and
                             precipitation instrument did not move; or the
                             precipitation instrument move was not equal to that of the
                             temperature instrument
                   800 000   Precipitation instrument moved, but temperature instrument
                             did not move (in more recent history entries the direction
                             may be given rather than encoded as zeroes)
                   000 ESE   Station moved < 0.1 mi ESE of previous location
                   999 NW    Moved an unknown distance to a location NW of the previous
                             location
    
    69-73     5    NUMERIC                  ELEVATION
                                            (of ground at temperature site) given in
                                            whole feet above or below mean sea level
    
    75-78     4    NUMERIC                  DISTANCE FROM POST OFFICE (DPO)
                                            units are in tenths of miles unless Position
                                            79 = "B"; then units are given in "Blocks";
                                            "9999" = unknown distance
    
    79        1    ALPHA (" ",B)            UNITS INDICATOR FOR DPO
                                            "B" for Blocks; " " for tenths of miles
    
    80-82     3    ALPHA-NUMERIC            DIRECTION FOR DPO
                                            codes for the 16-points are used:
                                            N, NNE, NE, ENE, E, ESE, SE, SSE, S, SSW,
                                            SW, WSW, W, WNW, NW, NNW;
                                            "999" indicates direction unknown;
                                            "000" indicates a location at the PO
    
                   Examples of DPO Codes:
    
                   CODE      DEFINITION
    
                   9999 999  Distance & direction unknown
                   0015 NW   Station 1.5 Miles NW of PO
                   0000 NW   Station < 0.1 Mile NW of PO
                   0000 999  Station < 0.1 Mile from PO; direction unknown
                   9999 NW   Station located an unknown distance to the NW of the PO
                   0000 000  Station located at PO
    
    84-111    28   ALPHA                    STATION NAME
                                            (may include previous state/station number
                                            contained in parentheses, e.g., 4 to 6
                                            characters)
    
    113-122   10   ALPHA-NUMERIC            QUALIFIER
                                            description added to primary station name;
                                            e.g., ASHEVILLE 2N
    
    124-159   36   NUMERIC (0,1)            INSTRUMENT INDICATOR
                                            Positions set equal to "1" indicate which
                                            instruments are on-site; otherwise "0"
    
         Position  Instrument                                 Mnemonic
    
    124         1  Additional Instruments (wind, pressure,      AI
                   psychrometer, etc.) (see position 158)
    125         2  Cotton Region Shelter (official)             CRS
    126         3  Dry-Bulb Thermometer                         DT
    127         4  Class 'A' Evaporation Station                EVA
    128         5  Fischer-Porter Gage                          FP
    129         6  Hygrothermograph                             HYTHG
    130         7  Minimum Thermometer                          MN
    131         8  Maximum Thermometer                          MX
    132         9  Non-Recording River Gage                     NRIG
    133        10  Non-Standard Rain Gage                       NSRG
    134        11  Non-Standard Shelter                         NSS
    135        12  Recording River Gage                         RRIG
    136        13  Recording Rain Gage                          RRNG
    137        14  Snow Density Gage                            SDE
    138        15  Storage Gage                                 SG
    139        16  Standard Rain Gage                           SRG
    140        17  Standard Shelter (official)                  SS
    141        18  Thermograph                                  TG
    142        19  Digital Thermometer                          DGT
    143        20  Tipping Bucket Gage                          TB
    144        21  Other than Class 'A' Evaporation station     EVO
    145        22  Maximum/Minimum Temperature System           MMTS
    146        23  Telemetry System                             TELSY
    147        24  Hygrothermometer (type unknown)              HYGRO
    148        25  Hygrothermometer - H06x series               HY6
    149        26  Hygrothermometer - H08x series               HY8
    150        27  Shielded Fischer-Porter Gage                 SFP
    151        28  Shielded Recording Rain Gage                 SRRNG
    152        29  Shielded Storage Gage                        SSG
    153        30  Shielded Standard Rain Gage                  SSRG
    154        31  Shielded Tipping Bucket                      STB
    155        32  Automated Meteorological Observing System    AMOS
    156        33  Automated Observing Station                  AUTOB
    157        34  Psychrometer (official, AK only)             PSY
    158-159 35-36  Not assigned at present time
    
    (NOTE: Mnemonics are not included in the metadata; however, these abbreviations are
           commonly used in USHCN printed products.)
    
    161-164   4    ALPHA-NUMERIC            OBSERVATION TIMES (OT)
    161-162   2                             Precipitation OT
    163-164   2                             Temperature OT
    
                   The observation times are encoded to the nearest whole hour where
                   known; in some instances, the observation may have been taken at a
                   variable hour (e.g., sunrise or sunset) or according to a rotating
                   seasonal schedule based upon agricultural needs.
    
                   Examples:
                   01-24,99  Nearest Whole Hour; "99" for unknown
                   SR        Sunrise
                   SS        Sunset
                   RS        Rotating Schedule (in general, evening observations were
                             taken during the winter months [Oct/Nov thru Apr/May] and
                             morning observations taken during summer months or
                             "crop season".)
    
                             In "RS" instances, often two observations were taken during
                             the summer; usually between 5-7 AM and again between 5-7
                             PM.  In such 2 obs/day instances, it's unclear whether both
                             elements are read twice, but recorded for a single hour; or
                             (a more likely practice), the precipitation is recorded in
                             the morning and temperature in the evening.
    
                   At some sites (usually airports) a uniform schedule was in use, but
                   the particular hour at which a particular element was observed was
                   not specified.  In these instances, the number of hours per day for
                   which observations were taken is given.  (NOTE:  the number of hours
                   must not be confused with synoptic observing schedules such as
                   3-hourly, 6-hourly, etc. ones at which observations are taken at
                   intervals of every 3 hours, 6 hours, etc.)
     
                   xxHR      where xx indicates the number of hours for which the site
                             took observations;
    
                   An early practice regarding the observation times of temperature
                   involved taking three readings (morning, afternoon, and evening or
                   "tri-daily").  These readings were usually made at 7 AM, 2 PM, and
                   9 PM.  A weighted average was computed in which the 9 PM observation
                   was summed twice and the total sum divided by 4 [e.g.,
                   (7 AM + 2 PM + 9 PM + 9 PM )/ 4  ].  Note, in these instances, no
                   precipitation observation time has been encoded.
    
                   TRID      indicates "tri-daily" temperature average
    
                   The early editions of the Weather Bureau's reporting forms allowed
                   space only for a single observing time to be entered.  Later on,
                   revised forms specifically identified whether the observation time
                   was for temperature or precipitation.  In the instances where the
                   forms were ambiguous with regard to the observing times of these
                   elements, the OT is encoded as follows:
    
                   9xx9      where xx indicates the hour as listed for the observations;
                             whether it's accurate for both temperature and precipitation
                             is unknown
    
                   Examples of OT codes:
    
                   SRSS      Precipitation reading made at sunrise; temperature read at
                             sunset
    
                   SS99      Precipitation read at sunset; temperature read at an
                             unknown hour or there is no temperature data available for
                             that period of record
    
                   0718      Precipitation read at 0700 (i.e., 7 AM); temperature read
                             at 1800 (i.e., 6 PM)
    
                   9079      Ambiguous form:  0700 was the only listed hour of
                             observation; unknown whether for both temperature and
                             precipitation
    
                   06HR      Station observed 6 hours/day; whether the average of these
                             6 observations is what was recorded or only a single hour
                             was used is unclear
    
                   RSSS      Precipitation readings made on a rotating schedule;
                             temperatures read at sunset
    
                   TRID      "Tri-daily" readings of temperature; no OT encoded for
                             precipitation
    
                   9918      Precipitation readings made at an unknown hour or there is
                             no precipitation data available for that period of record;
                             temperature read at 1800
    
    166-167        2    ALPHA-NUMERIC       HEIGHT OF PRECIPITATION INSTRUMENT ABOVE
                        (00-99, RF)         GROUND
                                            given in whole feet;
                                            "99" indicates missing;
                                            "98" indicates heights of 98 feet or greater;
                                            "RF" indicates a roof-top exposure
    
    168-169        2    ALPHA-NUMERIC       HEIGHT OF TEMPERATURE INSTRUMENT ABOVE
                        (00-99, RF)         GROUND
                                            given in whole feet;
                                            "99" indicates missing;
                                            "98" indicates heights of 98 feet or greater;
                                            "RF" indicates a roof-top exposure
    
                   Examples of Instrument Height Codes:
    
                   0305      For a standard rain gage, the opening at top of the gage
                             is mounted at 3 feet above the ground; and the thermometer
                             (inside the shelter) is located at 5 feet above the ground
    
                   RF99      Precipitation gage is located on roof; thermometer height
                             is unknown or there is no temperature data available for
                             that period of record
    
                   9805      Precipitation gage is at least 98 feet above the ground;
                             thermometer is mounted 5 feet above the ground
    
    171-186        16   NUMERIC (0,1)       PUBLICATION INDICATOR
                                            Positions equal to "1" indicate where
                                            station's data are published (see below)
                                            except when a "1" occurs in position 178 to
                                            indicate the data are unpublished; else is
                                            "0"
    
                   Position  Publication                                    Mnemonic
    
    171                  1   Bulletin W                                       BW
    172                  2   Combined Bulletin                                CB
    173                  3   Climatological Data                              CD
    174                  4   Daily River Stages                               DRS
    175                  5   Hydrologic Bulletin                              HB
    176                  6   Hourly Precipitation Data                        HPD
    177                  7   Snow Bulletin                                    SB
    178                  8   NOT PUBLISHED                                    NP
    179                  9   Report to the Chief of US Weather Bureau         CWB
    180                 10   Monthly Weather Review                           MWR
    181                 11   State Publication                                SP
    182                 12   Local Climatological Data                        LCD
    183                 13   Bulletin Q (1870-1903)                           BQ
    184                 14   Storage Gage Precipitation Data (Western US)     SGPD
    185                 15   Weekly Weather Review                            WWR
    186                 16   US Meteorological Yearbook                       MYB
    
    (NOTE: Mnemonics are not included in the metadata; however, these abbreviations are
           commonly used in the USHCN printed products.)
    
    188-233   46   ALPHA                    OBSERVERS NAME(S)
    
    235-236    2   NUMERIC                  NUMBER OF OBSERVERS
                                            this number gives either the number of
                                            observers used as observers by the listed
                                            agency or "corporate" observer (that is, "US
                                            Forest Service" may have actually been 5
                                            different observers during the particular
                                            period of record) or the number of additional
                                            known observers where to individually list
                                            multiple names would exceed the allotted
                                            space
    
    
                     Table 1. Distance Conversions
    
            FEET   = MILE        FEET   = MILE   FRACTION = DECIMAL
             < 264   0.0      2376-2903   0.5      1/8        0.1
           265-791   0.1      2904-3431   0.6      1/4        0.3
          792-1319   0.2      3432-3959   0.7      3/8        0.4
         1320-1847   0.3      3960-4487   0.8      1/2        0.5
         1848-2375   0.4      4488-5015   0.9      3/4        0.8
    
                         (One city block = 0.1 MILE)
    


    Station Area Land Use/Land Cover File (station_landuse)

    NCDC implemented a Global Baseline Data Project in 1990. The purpose of this international project was to gather long-term climatological data for research in global climate change. Some 1300 first-order stations, airports (city/rural), cooperative weather observation stations, and all stations of the USHCN were included. Each station was assigned a code of 0-9 (listed below) which best described the current predominant land use within circles around their station at radii of 100 m, 1 km, and 10 km. More than one code could be used if necessary to describe several predominant characteristics within each circle. The intent was to code the predominant types of land use; not all types.

    Codes:
    
    O    UNKNOWN
    1    NON-VEGETATED (barren, desert)
    2    COASTAL OR ISLAND
    3    FOREST
    4    OPEN FARMLAND, GRASSLAND OR TUNDRA
    5    SMALL TOWN, LESS THAN 1000 POPULATION
    6    TOWN 1000 TO 10,000 POPULATION
    7    CITY AREA WITH BUILDINGS LESS THAN 10 METERS*
    8    CITY AREA WITH BUILDINGS GREATER THAN 10 METERS*
    9    AIRPORT
    
      *30 feet or 3 stories tall
    

    Each record of the land use/cover file is 80 characters in length and is formatted as follows.
    Position	Data Field
    
    01-02		STATE 
    04-32		STATION NAME         
    34-35		STATE NUMBER
    37-40		STATION NUMBER
    48-57		LAND USE: 100 M RADIUS AROUND STATION
    59-69		LAND USE: 1 KM RADIUS AROUND STATION
    71-80           LAND USE: 10 KM RADIUS AROUND STATION
    

    The first record of the land use/cover file looks like this:

    AL BREWTON 3SSE                 01 1084       357        39         3
    	

    Population Metadata Files for USHCN Stations

    The USHCN database includes population-based temperature modifications to adjust urban temperature for the "heat-island" effect (Owen and Gallo, 2000). Unfortunately, the decennial population metadata file is not complete, as missing values are present for 17.6% of the 12,210 population values associated with the 1221 individual stations during the 1900-90 interval. Retrospective grid-based populations, within a fixed distance of an HCN station, were estimated through the use of a gridded population density dataset and historically available U.S. Census county data. The grid-based populations for the HCN stations provide values derived from a consistent methodology compared to the current HCN populations that can vary as definitions of the area associated with a city change over time. The use of grid-based populations may minimally be appropriate to augment populations for HCN climate stations that lack any population data, and are recommended when consistent and complete population data are required. The recommended urban temperature adjustments based on the HCN and grid-based methods of estimating station population can be significantly different for individual stations within the HCN dataset.

    Three population metadata files are provided:

    metrof_orig: The original population data file used in USHCN

    metrof_grid: Grid-based population estimates for all stations

    metrof_hybrid: Original population for all stations, gridded population for stations with NO original population values

    Missing population values represent over 17% of the decennial population values available for the HCN stations. By replacing the 128 stations that fully lack population values in the original file, the hybrid file provides grid-based estimates for fully 60% of all missing values in the original file.

    The population metadata files have record lengths of 107 characters and are formatted as follows:

    Column      Description
      1:8       USHCN Station ID
     10:17      1890 Population 
     19:26      1900 Population
     28:35      1910 Population
     37:44      1920 Population
     46:53      1930 Population
     55:62      1940 Population
     64:71      1950 Population
     73:80      1960 Population
     82:89      1970 Population
     91:98      1980 Population
    100:107     1990 Population
    

    3. Obtaining USHCN Data Files

    The USHCN data files are available from CDIAC's FTP site, and have been compressed using the UNIX compression utility compress. If this utility is not available, leave off the .Z extension and the files will uncompress on the fly through ftp. For non-internet data acquisitions (e.g., 8mm tape, CD-ROM, etc.), users should contact CDIAC directly.

    Address:
    Carbon Dioxide Information Analysis Center
    Oak Ridge National Laboratory
    P.O. Box 2008
    Oak Ridge, Tennessee 37831-6335, U.S.A.

    Telephone:
    (865) 574-3645 (Voice)
    (865) 574-2232 (Fax)

    email: cdiac@ornl.gov

    4. References

    Easterling, D. R., T. R. Karl, E. H. Mason, P. Y. Hughes, and D. P. Bowman. 1996. United States Historical Climatology Network (U.S. HCN) Monthly Temperature and Precipitation Data. ORNL/CDIAC-87, NDP-019/R3. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee. 280 pp.

    Easterling, D. R., and T. C. Peterson, 1995: A new method of detecting undocumented discontinuities in climatological time series. Int. J. of Climatol. 15:369-377.

    IPCC. 2007. Climate Change 2007: The Physical Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. [Soloman, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor, and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 996 pp.

    Jones, P. D. 1994. Northern Hemisphere surface air temperature variations: a reanalysis and an update to 1993. J. Climate 7:2548-2568.

    Jones, P. D., S. C. B. Raper, R. S. Bradley, H. F. Diaz, P. M. Kelly, and T. M. L. Wigley. 1986. Northern Hemisphere surface air temperature variations 1851-1984. J. Clim. Appl. Meteor. 25:161-79.

    Jones, P. D., T. J. Osborn, and K. R. Briffa. 1997. Estimating sampling errors in large-scale temperature averages. J. Climate 10:1794-1802.

    Karl, T. R., C. N. Williams, Jr., P. J. Young, and W. M. Wendland. 1986. A model to estimate the time of observation bias associated with monthly mean maximum, minimum and mean temperatures for the United States. J. Clim. Appl. Meteor. 25:145-60.

    Karl, T. R., and C. N. Williams, Jr. 1987. An approach to adjusting climatological time series for discontinuous inhomogeneities. J. Clim. Appl. Meteor. 26:1744-63.

    Karl, T. R., H. F. Diaz, and G. Kukla. 1988. Urbanization: Its detection and effect in the United States climate record. J. Climate 1:1099-1123.

    Owen, T. W., and K. P. Gallo. 2000. Updated Population Metadata for United States Historical Climatology Network Stations. J. Climate 13:4028-4033.

    Peterson, T. C., and D. R. Easterling. 1994. Creation of homogeneous composite climatological reference series. Int. J. Climatol. 14:671-680.

    Peterson, T. C., and R. S. Vose. 1997. An Overview of the Global Historical Climatology Network Temperature Database. Bull. Amer. Meteor. Soc. 78:2837-49.

    Quayle, R. G., D. R. Easterling, T. R. Karl, and P. J. Hughes. 1991. Effects of recent thermometer changes in the cooperative station network. Bull. Amer. Meteor. Soc. 72:1718-23.

    Quinlan, F. T., T. R. Karl, and C. N. Williams, Jr. 1987. United States Historical Climatology Network (HCN) serial temperature and precipitation data. NDP-019. Carbon Dioxide Information Analysis Center. Oak Ridge National Laboratory, Oak Ridge, Tennessee.

    Vinnikov, K. Ya., P. Ya. Groisman, and K. M. Lugina. 1990. Empirical data on contemporary global climate changes (temperature and precipitation). J. Climate 3:662-67.



        
    Appendix A. State Numbers and Abbreviations used for the 48 states
                          in the USHCN Database 
        
    
       01                          AL                   Alabama
       02                          AZ                   Arizona
       03                          AR                   Arkansas
       04                          CA                   California
       05                          CO                   Colorado
       06                          CT                   Connecticut
       07                          DE                   Delaware
       08                          FL                   Florida
       09                          GA                   Georgia
       10                          ID                   Idaho
       11                          IL                   Illinois
       12                          IN                   Indiana
       13                          IA                   Iowa
       14                          KS                   Kansas
       15                          KY                   Kentucky
       16                          LA                   Louisiana
       17                          ME                   Maine
       18                          MD                   Maryland
       19                          MA                   Massachusetts
       20                          MI                   Michigan
       21                          MN                   Minnesota
       22                          MS                   Mississippi
       23                          MO                   Missouri
       24                          MT                   Montana
       25                          NE                   Nebraska
       26                          NV                   Nevada
       27                          NH                   New Hampshire
       28                          NJ                   New Jersey
       29                          NM                   New Mexico
       30                          NY                   New York
       31                          NC                   North Carolina
       32                          ND                   North Dakota
       33                          OH                   Ohio
       34                          OK                   Oklahoma
       35                          OR                   Oregon
       36                          PA                   Pennsylvania
       37                          RI                   Rhode Island
       38                          SC                   South Carolina
       39                          SD                   South Dakota
       40                          TN                   Tennessee
       41                          TX                   Texas
       42                          UT                   Utah
       43                          VT                   Vermont
       44                          VA                   Virginia
       45                          WA                   Washington
       46                          WV                   West Virginia
       47                          WI                   Wisconsin
       48                          WY                   Wyoming
    


    CITE AS: Williams, C. N., M. J. Menne, R. S. Vose, and D. R. Easterling, 2007. United States Historical Climatology Network Monthly Temperature and Precipitation Data. ORNL/CDIAC-187, NDP-019. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee.
    Last updated May 2008.

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