IGOR POLYAKOV
Igor Polyakov
This global water temperature and salinity dataset represents some modification of Steele et al. [2001] hydrography (PHC). The PHC is based on Levitus global water temperature and salinity data with refinement in the Arctic based on the EWG [1997] Atlas. Several major features differ our dataset from the PHC. First is different arctic winter (April) temperature and salinity data. For this purpose we use archive developed by Polyakov and Timokhov (P&T) [1994]. The P&T climatology contains 55-km gridded data at 29 standard oceanographic levels. The dataset is based on 1973-79 Russian winter surveys, as well as summer manned North Pole drifting camp observations combined with aircraft surveys. Compared with the EWG Atlas used by Steele et al. [2001], P&T dataset is based on original information from the 1970s only (the years of the most complete Russian oceanographic serveys covering the whole deep Arctic Ocean). In the Beaufort Sea, P&T winter sea surface salinity is below 30 psu whereas EWG climatology shows salinity >30 (Figure). P&T is in a better agreement with Gorshkov [1980] and Treshnikov [1985] Atlases. Summer P&T data are not as reliable as winter data, that is why we used winter P&T data only. The next modification of this dataset compared with the PHC is a special (tripolar) grid which has higher latitudinal resolution in the Arctic compared with the 1x1deg PHC spherical grid. The tripolar grid is a traditional spherical grid everywhere except the Arctic (>65N) where it is substituted with a bipolar circle which two poles are located at the 65N latidude inland [Murray, 1996]. Figure shows differences in representation of the surface salinity from both PHC and our hydrologies in high latitudes. Our dataset uses NetCDF format. We also modified original PHC hydrology [Steele et al.,2001] using NetCDF format and potential (relative to the surface) but not in situ temperatures. This data are also available online.
Initial information used for this dataset is:
- PHC global temperature and salinity (Steele et al., 2001) which is based on original Levitus data for the globe except for the arctic region where Levitus data are substituted with the EWG CD-ROM (1997) temperatures and salinities. The PHC dataset includes two separate files. The first one contains monthly data for 24 levels above 1500m with a vertical resolution of:
'0000','0010','0020','0030','0050','0075','0100',
'0125','0150','0200','0250','0300','0400','0500',
'0600','0700','0800','0900','1000','1100','1200',
'1300','1400','1500'
The second file contains seasonal (summer and winter) data for 33 levels with a vertical resolution of:
'0000','0010','0020','0030','0050','0075','0100','0125',
'0150','0200','0250','0300','0400','0500','0600','0700',
'0800','0900','1000','1100','1200','1300','1400','1500',
'1750','2000','2500','3000','3500','4000','4500','5000','5500'
The PHC information is recorded in regular spherical 1x1deg grid.
Arctic ocean winter data based on P&T archive. This data are based on 7 Russian March-April (mostly April) surveys conducted in 1973-79 and covering the whole deep ocean with measurements at Russian standard levels (m) of:
'0000','0005','0010','0015','0020','0025','0030',
'0040','0050','0075','0100','0150','0200','0250',
'0300','0400','0500','0600','0750','1000','1500',
'2000','2500','3000','3500','4000','4500'
These data were combined and interpolated in a 55-km grid using stereographic projection [Polyakov and Timokhov, 1994].
The procedure of substitution of PHC winter temperature and salinity with P&T data included several steps. Initially, all the PHC data were interpolated on tripolar grid using a simple non-conservative interpolation procedure. This interpolation uses weights calculated as reversed distances between the destination (tripolar) grid points and source (spherical) grid points. Maximum radius of search allows a flexibility in choosing the number of destination grid points. Potential (with surface as a reference level) but not in situ temperatures are r ecorded.
Arctic April PHC data were substituted with P&T data at overlaping vertical levels. The area of substitution matches the area where Steele et al [2001] used EWG arctic data to improve global Levitus data. Missing data at 125, 700, 800, 900, 1100, 1200, 1300, and 1400m levels were obtained by linear interpolation. The August data are used unchanged from the PHC. The interpolation in time to get arctic temperatures and salinities for the other ten months uses PHC [Steele et al., 2001] assumption about the seasonal cycle. For convenience, new dataset includes bathymetry and geographical coordinates for the center of the tripolar grid cells.
The data are available on web (download the data now: Unix tar.gz format or Windows zip format).
The file "t_s.tar.gz" is compressed. To uncompress the Unix version of the data, use the following command:
gunzip t_s.tar.gz
After this procedure the name of the file will become "t_s.tar". This file is a converted form of a directory named "t_s". The command:
tar xvf t_s.tar
will transfer this file to the directory "t_s". This directory includes also README file containing instructions for reading data and a brief description of the file structure.
Windows XP can handle the zip format internally, and there are several commercial and freeware programs (ZipCentral, StuffIt, WinZip, PKZip) for other versions of Windows.
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This data set is publicly available and its compilation was made possible
through the cooperation of scientists from the Arctic and Antarctic
Research Institute, St.Petersburg, Russia. We request that users acknowledge
the use of this data set by including a citation to the paper [Polyakov and
Timokhov, 1994] in the reference list of published work. Thank you.
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Environmental Working Group (EWG), Joint U.S. - Russian Atlas of the Arctic Ocean [CD-ROM], Natl. Snow and Ice Data Cent., Boulder, Colorado, 1997.
Gorshkov, S. G., Atlas of Oceans. Arctic Ocean. (in Russian). Moscow, Military Defense Publishing House, 199 pp., 1980.
Murray, R. J. Explicit generation of orthogonal grids for ocean models, J. Comput. Physics, 126, 251-273, 1996.
Polyakov, I. V., and L. A. Timokhov, Mean fields of temperature and salinity of the Arctic Ocean, Russian Meteorol. Hydrol., 7, 33-38, 1994.
Steele, M., R. Morfley, and W. Ermold, PHC: A global ocean hydrography with a high-quality Arctic Ocean, J. Climate, 14, 2079-2087, 2001/.
Treshnikov, A. F., Atlas of the Arctic, Moscow, 204 pp., 1985. (in Russian).
Last modified: December 10, 2004. 08:54:10 am