Seasonal Sea Surface Temperature Averages, 1985-2001

Title: Seasonal Sea Surface Temperature Averages, 1985-2001

Abstract:

This data set consists of four images showing seasonal sea surface temperature (SST) averages for the entire earth. Data for the years 1985-2001 are averaged to produce each seasonal image. The seasons are January-March (sst001i4km.tif), April-June (sst002i4km.tif), July-September (sst003i4km.tif), and October-December (sst004i4km.tif).

These SST data are the result of the 4 km Pathfinder effort at the National Oceanic and Atmospheric Administration (NOAA) National Oceanographic Data Center (NODC) and the University of Miami's Rosenstiel School of Marine and Atmospheric Science (RSMAS), which uses data from the NOAA-9, NOAA-11, NOAA-14, and NOAA-16 satellites. The 4 km Pathfinder effort at NODC is an improvement to the original Pathfinder program, which was jointly developed by the National Aeronautics and Space Administration (NASA) and NOAA to provide long-term, consistently calibrated global change data sets to Earth scientists. One of the data sets selected for the Pathfinder project was collected by the Advanced Very High Resolution Radiometer (AVHRR), a scanning radiometer flying onboard polar orbiters operated by NOAA. The original AVHRR Pathfinder Program involved four separate elements: Atmosphere, Land, Oceans, and Calibration. The objective of the AVHRR Oceans Pathfinder was to develop a long and consistent time series of global sea surface temperature (SST) fields. The Pathfinder Project at NODC carries on this objective.

The files for each season, also known as seasonal climatologies, are available both as 16-bit (pixel values from 0 to 65535) Hierarchical Data Format (.HDF) data files and as 8-bit (pixel values from 0 to 255) GeoTIFF images.

This data set is also referred to as 4 km NODC/RSMAS AVHRR Pathfinder v.5.0 Seasonal Climatologies (1985-2001).

Supplemental_Information:

The data displayed in the Map Maker of the National Atlas of the United States <http://nationalatlas.gov/natlas/Natlasstart.asp> have been clipped to the standard National Atlas extent, masked using a National Atlas land/water mask, and projected to a Lambert Azimuthal Equal Area projection. The distributed data represent the global data set rather than the clipped and projected version available for viewing through the National Atlas.

SST is a difficult parameter to define exactly because the upper ocean (~10 m) has a complex and variable vertical temperature structure that is related to ocean turbulence and the air-sea fluxes of heat, moisture and momentum. Definitions of SST provide a necessary theoretical framework that can be used to understand the information content and relationships between measurements of SST made by different instruments. The following explanatory statements attempt to provide this framework and encapsulate the effects of the dominant heat transport processes and time scale of variability associated with distinct vertical and volume regimes within a vertical element of the water column (horizontal and temporal variability is implicitly assumed):

 The interface SST, SSTint, is the temperature of an infinitely thin layer at the
 exact air-sea interface.  It represents the temperature at the top of the SSTskin
 temperature gradient (layer) and cannot be measured using current technology.
 It is important to note that it is the SSTint that interacts with the atmosphere.
 The skin SST, SSTskin, is a temperature measured within a thin water layer (<500
 micrometer) adjacent to the air-sea interface.  It is where conductive, diffusive
 and molecular heat transfer processes dominate.  A strong vertical temperature
 gradient is characteristically maintained in this thin layer sustained by the
 magnitude and direction of the ocean-atmosphere heat flux.  Thus, SSTskin varies
 according to the actual measurement depth within the layer.  This layer provides
 the connectivity between a turbulent ocean and a turbulent atmosphere.
 The sub-skin SST, SSTsub-skin, is representative of the SST at the bottom of the
 surface layer where the dominance of molecular and conductive processes gives way
 to turbulent heat transfer.  It varies on a time scale of minutes and is
 influenced by solar warming in a manner strongly dependent on the turbulent
 energy density in the layer below.
 The near surface ocean temperature (~10 m) is significantly influenced by local
 solar heating and typically varies with depth over a time scale of hours.
 Consequently "SST" measurements should always be referenced against a specific
 depth or an average over a depth range.  The notation SSTdepth  refers to any
 temperature within the water column beneath the SSTsub-skin where turbulent heat
 transfer processes dominate.  The traditional "bulk" SST is related to this
 measure.  SSTdepth should always be quoted at a specific depth in the water
 column; e.g., SST1m refers to the SST at a depth of 1m.
 The SSTskin is the closest parameter actually measured by the AVHRR satellite
 radiometer.  However, because the Pathfinder algorithm regresses the satellite-
 observed radiances against buoy temperatures to determine a "bulk" SST, the
 actual SST is akin to the SSTdepth where depth is about 1 m.

The current 4 km data set is an extension of and improvement on the SST fields from the AVHRR Oceans 9 km Pathfinder data set (<http://www.rsmas.miami.edu/groups/rrsl/pathfinder/index.html>). Some important shortcomings in the original 9 km data have been corrected, and the entire time series has been reprocessed at the 4 km Global Area Coverage (GAC) level, currently the highest resolution possible globally. In addition, several enhancements have been made that increase the usefulness of the SST fields, including the use of sea ice in the quality level determination scheme, inclusion of many inland water bodies, and the use of a greatly improved land mask. The greatest improvements are seen in coastal zones, marginal seas, and boundary current regions where SST gradients are often large and their impact on operational or research products is greatest.

The data set was produced from 1985-2001 data using the Version 5.0 Pathfinder algorithm. Version 5.0 is an improved version of the previously-most-successful of the many methods used to derive SST from AVHRR observations. For more detail on this version of the Pathfinder data, a description of the processing algorithm, and a comparison of version 5 and version 4, please see the 4 km Pathfinder Version 5.0 User Guide at <http://www.nodc.noaa.gov/sog/pathfinder4km/userguide.html>.

Relative to the older 9 km v4.2 Pathfinder data, the new, ~4 km-resolution Pathfinder Version 5.0 global SSTs increase detail roughly by a factor of four simply by virtue of the increased resolution. The increase in detail over widely used but relatively coarse SST datasets such as Optimally Interpolated SST Version 2 (Reynolds et al., 2002, <http://ams.allenpress.com/amsonline/> ?request=get-abstract&issn=1520-0442&volume=015&issue=13&page=1609>) and the Hadley Centre's Global Sea Ice and SST (Rayner et al., 2003, <http://www.agu.org/pubs/crossref/2003/2002JD002670.shtml>) is far greater.

The University of Miami Pathfinder version v4.2 SST algorithm is fully described in Kilpatrick et al., (2001). <http://www.agu.org/pubs/crossref/2001/1999JC000065.shtml>. The v4.2 algorithm offered marked improvement over operational retrieval algorithms such as multi- channel sea surface temperature (MCSST) and was applied to AVHRR data to maximize accuracy and to minimize artificial fluctuations arising from the sequence of AVHRR instruments flown on NOAA's polar-orbiting satellites during the past 2 decades. The 9 km v4.2 Pathfinder SSTs were shown to be the highest quality product then available for the construction of global climatologies (Casey and Cornillon, 1999, <http://ams.allenpress.com/amsonline/?request=get-abstract&issn=1520-0442&volume>= 12&issue=6&page=1848>) and longer-term SST trend determination (Casey and Cornillon, 2001, <http://ams.allenpress.com/amsonline/?request=get-abstract&issn>= 1520-0442&volume=14&issue=18&page=3801>), and have been demonstrated to be accurate within about 0.3 degrees C under optimal conditions (Kearns et al., 2000, <http://ams.allenpress.com/pdfserv/i1520-0477-081-07-1525.pdf>).

For a detailed description of the Version 4.0 Pathfinder SST algorithm, please see <http://www.rsmas.miami.edu/groups/rrsl/pathfinder/Algorithm/algo_index.html>.

For a review of earlier techniques, see Barton (1995). <http://www.agu.org/pubs/crossref/1995/95JC00365.shtml>

For more information on AVHRR, see <http://eros.usgs.gov/guides/avhrr.html> and <http://nationalatlas.gov/articles/mapping/a_avhrr.html>.

The NOAA Polar Orbiter Data User's Guide describes the orbital and spacecraft characteristics, instruments, data formats, etc. of the TIROS-N, and NOAA-6 through NOAA-14 polar orbiter series of satellites. See <http://www2.ncdc.noaa.gov/docs/podug/> for more information.

A text file containing a complete source bibliography for this data set and suggested additional reading is bundled with the downloadable data. The file is called sstalli_biblio.txt.

The following parameters are used for the GeoTIFF:

Version: 1
Key_Revision: 1.0

Tagged_Information:
ModelTiepointTag (2,3):
0                0                0
-180             90               0
ModelPixelScaleTag (1,3):
0.0439453      0.0439453      0
End_Of_Tags.

Keyed_Information:
GTModelTypeGeoKey (Short,1): ModelTypeGeographic
GTRasterTypeGeoKey (Short,1): RasterPixelIsArea
GTCitationGeoKey (Ascii,17): "LONG/LAT    E005"
GeographicTypeGeoKey (Short,1): GCS_WGS_84
GeogAngularUnitsGeoKey (Short,1): Angular_Degree
ProjLinearUnitsGeoKey (Short,1): Linear_Meter
End_Of_Keys.
End_Of_Geotiff.

GCS: 4326/WGS 84
Datum: 6326/World Geodetic System 1984
Ellipsoid: 7030/WGS 84 (6378137.00,6356752.31)
Prime Meridian: 8901/Greenwich (0.000000/  0d 0' 0.00"E)

Projection Linear Units: 9001/metre (1.000000m)
Corner Coordinates:
Upper Left    (180d 0' 0.00"W, 90d 0' 0.00"N)
Lower Left    (180d 0' 0.00"W, 90d 0' 0.00"S)
Upper Right   (180d 0' 0.00"E, 90d 0' 0.00"N)
Lower Right   (180d 0' 0.00"E, 90d 0' 0.00"S)
Center        (  0d 0' 0.00"E,  0d 0' 0.00"N)

The associated world file is included as part of the GeoTIFF. The contents of the world file are:

in the HDF files, SST in deg C = 0.075 x pixel value - 3. Temperatures are represented in 0.075 degree C increments, and land has a value of 1. While pixel values can range from 0 to 65535, realistic pixel values for SST will always be less than 600. in the GeoTIFF files, SST in deg C = 0.15 x pixel value - 3. Temperatures are represented in 0.15 degree C increments, and land has a value of 255. Pixel values can range from 0 to 255.

Range of values

Minimum:

Maximum:

500

Data format:

GeoTIFF

Network links:

<http://nationalatlas.gov/atlasftp.html?openChapters=chpclim#chpclim>

Data format:

Four .HDF files comprising seasonal climatologies 1985-2001 (seasons as defined by periods Jan-Mar, Apr-Jun, Jul-Sept, Oct-Dec). Four 8-bit GeoTIFF files of the same climatologies are bundled with the .HDF files. in format HDF (version 4) NCSA Hierarchical Data Format (HDF 4), Scientific Data Set (HDF-SDS) Size: 30000000

Network links:

<http://www.nodc.noaa.gov/search/prod/>
<ftp://ftp.nodc.noaa.gov/pub/pathfinder/seasonal_climatology>

Data format:

Four 8-bit GeoTIFF representations of seasonal climatologies 1985-2001 (seasons as defined by periods Jan-Mar, Apr-Jun, Jul-Sept, Oct-Dec). Four 16-bit .HDFD files of the same climatologies are bundled with the GeoTIFF files. Although the data are represented using 16-bit in the .HDF files, 8-bit GeoTIFF files were developed to facilitate access and use of these data by the widest variety of users; as such the GeoTIFF representations of the .HDF files are not a complete representation of the data in the .HDF files. in format TIFF (version 1) GeoTIFF Size: 36000000

Network links:

<http://www.nodc.noaa.gov/search/prod/>
<ftp://ftp.nodc.noaa.gov/pub/pathfinder/seasonal_climatology>

Seasonal Sea Surface Temperature Averages, 1985-2001

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