+ NASA Portal + Goddard Space Flight Center + GSFC Earth Sciences Division



## GISS Surface Temperature Analysis

Sources

GHCN = Global Historical Climate Network (NOAA) USHCN = US Historical Climate Network (NOAA)
SCAR = Scientific Committee on Arctic Research

Basic data set: GHCN - ftp://ftp.ncdc.noaa.gov/pub/ data/ghcn/v2 v2.mean.Z (data file) v2.temperature.inv.Z (stat ion information file)

For US: USHCN - ftp://ftp.ncdc.noaa.gov/pub/ data/ushcn/v2/monthly 9641C_yyyymm_F52.avg.gz wher e yyyy/mm is related to the date

that file was created
ushcn-v2-stations.txt

For Antarctica: SCAR - http://www.antarctica.ac.uk/ met/READER/surface/stationpt.html http://www.antarctica.ac.uk/ met/READER/temperature.html http://www.antarctica.ac.uk/ met/READER/aws/awspt.html

For Hohenpeissenberg - http://members.lycos.nl/Erre nWijlens/co2/t_hohenpeissenberg_200306.txt complete record for this rur al station (thanks to Hans Erren who re ported it to GISS on July 16, 2003)

USHCN stations are part of GHCN; but the data are a djusted for various recording and protocol errors and discontinuities; this set i s particularly relevant if studies of US temperatures are made, whereas the co rrections have little impact on the GLOBAL temperature trend, the US covering le ss than 2% of the globe.

Step 0 : Merging of sources (do_comb_step0.sh)

--------------------------- GHCN contains reports from several sources, so ther e often are multiple records for the same location. Occasionally, a single recor d was divided up by NOAA into several pieces, e.g. if suspicious discontinui ties were discovered.

USHCN and SCAR contain single source reports but in different formats/units
and with different or no identification numbers. Fo r USHCN, the table "ushcn2.tbl" gives a translation key, for SCAR we e xtended the WMO number if it existed or created a new ID if it did not (2 cases) . SCAR stations are treated

as new sources.

Adding SCAR data to GHCN:

The tables were reformatted and the data rescaled t o fit the GHCN format; the new stations were added to the inventory file. The site temperature.html has not been updated for several years; we found an d corrected a few typos in that file. (Any SCAR data marked "preliminary" a re skipped)

Replacing USHCN-unmodified by USHCN-corrected data: The reports were converted from F to C and reformat ted; data marked as being filled in using interpolation methods were removed. USHCN-IDs were replaced by the corresponding GHCN-ID. The latest common 10 years for each station were used to compare corrected and uncorrected data . The offset so obtained was subtracted from the corrected USHCN reports to match any new incoming GHCN reports for that station (GHCN reports are upd ated monthly; in the past, USHCN data used to lag by 1-5 years).

Filling in missing data for Hohenpeissenberg: This is a version of a GHCN report with missing dat a filled in, so it is used to fill the gaps of the corresponding GHCN series.

Result: v2.mean_comb

Step 1 : Simplifications, elimination of dubious re cords, 2 adjustments (do_comb_step1.sh)

--------------------------------------------------- -------------------- The various sources at a single location are combin ed into one record, if possible, using a version of the reference station method. The adjustments are determined in this case using series of estimat ed annual means.

Non-overlapping records are viewed as a single reco rd, unless this would result introducing a discontinuity; in the document ed case of St.Helena 

# Page 1 of 3 Data @ NASA GISS: GISTEMP: Sources Documentation

7/19/2010 http://data.giss.nasa.gov/gistemp/sources/gistemp.htmlthe discontinuity is eliminated by adding 1C to the early part.

After noticing an unusual warming trend in Hawaii, closer investigation showed its origin to be in the Lihue record; it had a discontinuity around 1950 not present in any neighboring station. Based on those data, we added 0.8C to the part before the discontinuity.

Some unphysical looking segments were eliminated af ter manual inspection of unusual looking annual mean graphs and comparing th em to the corresponding graphs of all neighboring stations. See CLEANING NOTES for further details.

Result: Ts.txt

Step 2 : Splitting into zonal sections and homogeni zation (do_comb_step2.sh)

--------------------------------------------------- ------- To speed up processing, Ts.txt is converted to a bi nary file and split into 6 files, each covering a latitudinal zone of a width of 30 degrees. At the same time, stations with less than 20 years of data are dropped, since in the subsequent gridding step we require overlaps of at least 20 years
to combine station records.

The goal of the homogenization effort is to avoid a ny impact (warming or cooling) of the changing environment that some s tations experienced by changing the long term trend of any non-rural st ation to match the long term trend of their rural neighbors, while ret aining the short term monthly and annual variations. If no such neighbors exist or the overlap
of the rural combination and the non-rural record i s less than 20 years, the station is completely dropped; if the rural records are shorter, part of the non-rural record is dropped.

Result: Ts.GHCN.CL.1-6 - before peri-urban ad justment Ts.GHCN.CL.PA.1-6 - after peri-urban ad justment

Step 3 : Gridding and computation of zonal means (d o_comb_step3.sh)

------------------------------------------------ A grid of 8000 grid boxes of equal area is used. Ti me series are changed to series of anomalies. For each grid box, the stat ions within that grid box and also any station within 1200km of the cente r of that box are combined using the reference station method.

A similar method is also used to find a series of a nomalies for 80 regions consisting of 100 boxes from the series for those b oxes, and again to find the series for 6 latitudinal zones from those regio nal series, and finally to find the hemispheric and global series from the zonal series.

WARNING: It should be noted that the base period fo r any of these anomalies is not necessarily the same for each grid box, region, zone. This is irrelevant when computing trend maps; howe ver, when used to compute anomalies, we always have to subtract the base period data from the series of the selected time period to get a consistent anomaly map.

Result: SBBX1880.Ts.GHCN.CL.PA.1200 and tables (GLB .Ts.GHCN.CL.PA.txt,...)

Step 4 : Reformat sea surface temperature anomalies

--------------------------------------------------- Sources: http://www.hadobs.org HadISST1: 1870-present ftp.emc.ncep.noaa.gov cmb/sst/oimonth_v2 Reynolds 11/1981-present

For both sources, we compute the anomalies with res pect to 1982-1992, use the Hadley data for the period 1880-11/1981 and Rey nolds data for 12/1981-present. Since these data sets are complete, creating 1982-9 2 climatologies is simple. These data are replicated on the 8000-box qual-area grid and stored in the same way
as the surface data to be able to use the same util ities for surface and ocean data.

Areas covered occasionally by sea ice are masked us ing a time-independent mask. The Reynolds climatology is included, since it also may be used to find that mask. Programs are included to show how to regrid t hese anomaly maps: do_comb_step4.sh adds a single or several successiv e months for the same year to an existing ocean file SBBX.HadR2; a program to add several years is also
included.

Result: update of SBBX.HadR2

Step 5 : Computation of LOTI zonal means

---------------------------------------- The same method as in step3 is used, except that fo r a particular grid box the anomaly or trend is computed twice, first based on surface data, then based on ocean data. Depending on the location of t he grid box, one or the other is used with priority given to the surfac e data, if available.

Result: tables (GLB.Tsho2.GHCN.CL.PA.txt,...) 

# Page 2 of 3 Data @ NASA GISS: GISTEMP: Sources Documentation

7/19/2010 http://data.giss.nasa.gov/gistemp/sources/gistemp.htmlFinal Notes

----------- A program that can read the two basic files SBBX188 0.Ts.GHCN.CL.PA.1200 and SBBX.HadR2 in order to compute anomaly and trend ma ps etc was available on our web site for many years and still is.

For a better overview of the structure, the program s and files for the various steps are put into separate directories with their own input_files, work_files, temp_files directories. If used in this way, files created by step0 and put into the temp_files directory will ha ve to be manually moved to the temp_files directory of the step1. To avoid that, you could consolidate all sources in a single directory and m erge all input_files directories into a single subdirectory.

The reason to call the first step "Step 0" is histo rical: For our 1999 paper "GISS analysis of surface temperature change", we s tarted with "Step 1", i.e. we used GHCN's v2.mean as our only source for stati on temperature data. The USHCN data were used for the 2001 paper "A closer l ook at United States and global surface temperature change", the other parts of "Step 0" were added later.

+ NASA Privacy Policy and Important Notices GISS Website Curator: Robert B. Schmunk Responsible NASA Official: James E. Hansen Page updated: 2010-07-02 

# Page 3 of 3 Data @ NASA GISS: GISTEMP: Sources Documentation

7/19/2010 http://data.giss.nasa.gov/gistemp/sources/gistemp.html