C. N. Williams, Jr., M. J. Menne,
Dale P. Kaiser and Thomas A. Boden
1. Background Information
2. Descriptions and Formats of USHCN Data Files and Supporting Files
2.1 USHCN Temperature Data Files
2.2 USHCN Precipitation Data File
2.3 USHCN Supporting Files
Station Inventory File
Station History File
Station Area Land Use/Land Cover File
Population Metadata Files for USHCN Stations
3. Obtaining USHCN Data Files
Appendix A: State Numbers and abbreviations Used for the 48 States in the HCN/D Database
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
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
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.
2.1 USHCN Temperature Data FilesThe 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.
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.ZThese 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.
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.
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),
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.
011084-07 31.07 -87.05 85 AL BREWTON 3SSEThe 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
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
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.
Carbon Dioxide Information Analysis Center
Oak Ridge National Laboratory
P.O. Box 2008
Oak Ridge, Tennessee 37831-6335, U.S.A.
(865) 574-3645 (Voice)
(865) 574-2232 (Fax)
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.