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
- Contents
Abstract
Keywords
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
4. References
Appendix A: State Numbers and abbreviations Used for the 48 States in the HCN/D Database
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.
- Areal Edited (Raw)
A quality control procedure is performed that uses trimmed means and standard deviations in comparison with surrounding stations to identify suspects (> 3.5 standard deviations away from the mean) and outliers (> 5.0 standard deviations). Until recently these suspects and outliers were hand-verified with the original records. However, with the development of more sophisticated QC procedures at NCDC, this has been found to be unnecessary.
- TOBS (Time of Observation)
The temperature data are adjusted for the time-of-observation bias (Karl, et al. 1986), which occurs when observing times are changed from midnight to some time earlier in the day. The ending time of the 24-h climatological day varies from station to station and/or over a period of years at a given station. The time of observation (TOB) introduces a non-climatic bias into the monthly means. The TOB software is an empirical model used to estimate the TOB biases associated with different observation schedules and the routine computes the TOB with respect to daily readings taken at midnight.
- MMTS (Maximum/Minimum Temperature System)
Temperature data at stations that have the Maximum/Minimum Temperature System (MMTS) are adjusted for the bias introduced when the liquid-in-glass thermometers were replaced with the MMTS (Quayle et al. 1991). The MMTS program debiases the data obtained from stations with MMTS sensors. The NWS has replaced a majority of the liquid-in-glass thermometers in wooden Cotton-Region shelters with thermistor based maximum-minimum temperature systems (MMTS) housed in smaller plastic shelters. This adjustment removes the MMTS bias for stations so equipped with this type of sensor. The adjustment factors are most appropriate for use when time series of states or larger areas are required.
- SHAP (Station History Adjustment Program)
The homogeneity adjustment scheme described in Karl and Williams (1987) is performed using the station history metadata file to account for time series discontinuities due to random station moves and other station changes. The debiased data from the MMTS adjustment are then entered into the Station History Adjustment Program or SHAP. The SHAP allows a climatological time series of temperature and precipitation adjustment for station inhomogeneities using station history information. The adjusted data retain their original scale and are not anomaly series. The methodology uses the concepts of relative homogeneity and standard parametric (temperature) and non parametric (precipitation) statistics to adjust the data. In addition, this technique provides an estimate of the confidence interval associated with each adjustment. The SHAP program debiases the data with respect to changes other than the MMTS conversion to produced the “adjusted data”. Specific details on the procedures used are given by Karl and Williams (1987).
- FILNET (Fill Missing Original Data in the Network)
- Urban (Urban Warming Adjustment)
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. |
 |
 |
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. |
 |
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. |
 |
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.
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
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.