LEVITUS94 Ocean Climatology

The data are here.

This multivolume atlas presents global, objectively analyzed fields of major ocean parameters on a one-degree latitude-longitude grid for selected standard depth levels from the sea surface to 5500 m depth. Work to date includes quality control of historical in situ temperature , salinity, oxygen, phosphate, nitrate, and silicate data and the preparation of one-degree latitude-longitude mean fields for each of these parameters. Two technical reports describing the data analysis and quality control procedures are also available (listed below as TR-79 and TR-81). World Ocean Atlas 1994 and the atlas data sets were produced by the NODC Ocean Climate Laboratory using NODC's data holdings as of the first quarter of 1993.

The Ocean Climate Laboratory (OCL) at the National Oceanographic Data Center (NODC) is supported by the NOAA Climate and Global Change program to produce scientifically quality controlled oceanographic databases. Work to date includes quality control of historical in situ temperature, salinity, oxygen, phosphate, nitrate, and silicate data and the preparation of one-degree latitude-longitude mean fields for each of these parameters using objective analysis techniques. Specifically, this project has produced four ocean atlases describing the global distributions of these parameters and two technical reports describing the quality control and processing procedures (see section 6 of this documentation for a listing of these publications). Observed and standard level profile data (along with quality control flags) used in the production of these atlases are being made available to the international oceanographic community on the World Ocean Atlas 1994 CD-ROM series (referred to herein as WOA94). In addition, the CD-ROM series contains the objectively analyzed one-degree latitude-longitude mean fields for each of the measured parameters, and two derived parameters (Apparent Oxygen Utilization and oxygen saturation), and five-degree square statistics of standard level values.

Profile data on the CD-ROM series are recorded in ASCII format and sorted geographically, so they are easy to access and manipulate. The CD-ROMs are formatted in the ISO 9660 standard.

The Ocean Climate Laboratory expresses its thanks to all those who provided us with their comments and helped us develop an improved product.

National Oceanographic Data Center
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Silver Spring, Maryland 20910-3282

Telephone: 301-713-3277 (Andy Allegra)
Fax: 301-713-3302
Internet: services@nodc.noaa.gov

http://www.nodc.noaa.gov/NODC-pub.html

DlSC CONTENTS

The gridded fields of these parameters and the ocean profile data sets from which they were derived--a total of 4.8 gigabytes of data--are available on a set of nine CD-ROMs or on a single Exabyte tape.

A. DATA SOURCES

The data used in this project are all the data found in the NODC archives as of the first quarter of 1993. Levitus and Gelfeld (1992) show global distribution maps of the data held in these files for all years (1900-1992). In addition, data gathered as a result of the NODC's National Oceanographic Data Archaeology and Rescue (NODAR) and the IOC/IODE Global Oceanographic Data Archaeology and Rescue (GODAR) projects, not yet incorporated into the NODC master archives, were included in this study. A description of the NODAR and GODAR projects can be found in Levitus et al. (1994e). The NODAR and GODAR data sets are in separate files (since they have not yet been archived at the NODC).

Data on the CD-ROM series includes the following flagged data:

1. BOTTLE - NODC Station Data

Parameters: Station data profiles may have one or more of the following parameters: Source: NODC Station Data

2. BOTTLE2 - Station Data not incorporated in the NODC archives as of the first quarter of 1993

Sources:

3. CTD - NODC CTD/STD (Conductivity/Salinity, Temperature, Depth probe)

Parameters: Temperature and/or salinity

Source: All data from NODC's low resolution CTD file (CTD profiles from the NODC Station Data file were transferred to this file)

4. CTD2 - CTD data not incorporated in the NODC archives as of the first quarter of 1993

Sources:

5. MBT - NODC Mechanical Bathythermograph data

Parameter: Temperature

Source: NODC MBT file (Includes NODC MBT data from the NODC Selected Bathythermograph (SBT) data file that contains data at selected depths)

6. MBT2 - MBT data not incorporated in the NODC archives as of the first quarter of 1993

Sources: Argentine MBT data French Salinobathythermograph data Japanese Fisheries MBT data Canadian (MEDS) MBT data Miscellaneous ship of opportunity MBT data Russian MBT data Declassified Russian Navy MBT data and Russian NODC MBT data MBT data from Woods Hole Oceanographic Institution

7. XBT - NODC Expendable Bathythermograph data

Parameter: Temperature Source: NODC XBT file. (Includes XBT data from NODC SBT (Selected Bathythermograph) file) [NOTE: XBT standard level values were interpolated using observed level measurements corrected for a drop rate error for T4, T6, and T7 probes. T5 depths were not recalculated (any measurement at a depth greater than 725 m was assumed to be from a T5 probe).]

The drop rate correction applied was:

zc = 6.733t - 0.00254t2

where

zc = the corrected depth

"t", the elapsed time since the instrument entered the ocean, is determined by:

t = 1498.14 - (2244447.430 - 462.963z0)1/2

where

z0 = originally calculated depth (Szabados, personal communication).

8. XBT2 - XBT data not incorporated in the NODC archives as of the first quarter of 1993

Sources: [NOTE: XBT standard level values were interpolated using observed level measurements corrected for a drop rate error for T4, T6, and T7 probes. T5 depths were not recalculated.]

9. DBT2 - Digital Bathythermograph data

Parameter: Temperature Sources: Canadian (MEDS) DBT data Japanese DBT data

10. ISD - Station data from India (data set received too late to incorporate into BOTTLE2 file)

Parameters: Temperature and/or salinity

B. PARAMETER INFORMATION

Table 1 shows the units, precision, and number of profiles for each parameter. 
Table 1.  Precision and number of profiles for each parameter.
----------------------------------------------------------------                                       
                                        Maximum 
                                        stored          # of
Parameter            Unit               precision     Profiles
----------------------------------------------------------------
Temperature         degrees C             xx.xxx      4,553,426
Salinity            p.s.u.                xx.xxx      1,254,771
Oxygen              ml/l                   xx.xx        367,635
Phosphate           micromolar             xx.xx        184,153
Silicate            micromolar             xxx.x        110,413
Nitrate             micromolar              xx.x         75,403
----------------------------------------------------------------
Each parameter is identified in the data by a numeric code. The parameters and their associated codes are listed in Table 2. 
Table 2.  Numeric codes associated with each parameter

--------------------------------------
Code            Parameter
--------------------------------------
 0              Depth
 1              Temperature (in-situ)
 2              Salinity
 3              Oxygen
 4              Phosphate
 6              Silicate
 8              Nitrate
--------------------------------------

C. QUALITY CONTROL PROCEDURES

Observed level data were checked for quality prior to interpolation to standard levels. We call the actual measured value of an oceanographic parameter at some depth an "observed level" datum. The value interpolated to a standard level depth is referred to as a "standard level" datum.

For many analysis purposes, it is necessary to interpolate from observed level to standard depth levels. The standard depth analysis levels selected for this study are listed in Table 3 and include the 30 NODC standard depths and three additional levels at 3500, 4500, and 5500 meters. There are additional standard level depth data in some of the standard level profiles (i.e., 6000, 6500, 7000, 7500, 8000, 8500, 9000 meters, numbered 34 through 40). 

Table 3.  Standard levels and depths (in meters)
------------------------------------------------
 Level       Depth       Level       Depth
     1           0          18         900
     2          10          19        1000
     3          20          20        1100
     4          30          21        1200
     5          50          22        1300
     6          75          23        1400
     7         100          24        1500
     8         125          25        1750
     9         150          26        2000
    10         200          27        2500
    11         250          28        3000
    12         300          29        3500
    13         400          30        4000
    14         500          31        4500
    15         600          32        5000
    16         700          33        5500
    17         800
------------------------------------------------
The quality of the observed and standard level data were checked using the following procedures:

At the NODC:

1.
NODC Data Processing Branch checks - date/time fields (valid values, ship speed between stations). It also performs broad range checks, compares each station to an NODC T-S climatology, and checks for large density inversions.
At the NODC/Ocean Climate Laboratory:
2.
Preliminary checks - checks for duplicate profiles, depth inversions;
3.
Range check of the observed level data for each major basin as a function of depth; [Note: some temperature values reported in the XBT2 observed level file exceeded 999.999 and therefore were set to the missing value -99.999. These values are flagged with a 1 (failed range check).]
4.
Large temperature inversion and gradient checks;
5.
Density inversion check on the standard level data;
6.
XBT drop rate correction before interpolation of observed level to standard level data for T4, T6, and T7 probes;
7.
Standard deviation check;
8.
Check for unrealistic features after an initial computation of the objective analysis.

Data were flagged for each quality control check. A datum or profile flagged as an outlier was excluded from further checks. A description of the flags can be found in Appendix 1. The quality control procedures have been documented in two NOAA Technical Reports (Boyer and Levitus, 1994; Conkright et al., 1994).

D. AVAILABLE OBJECTIVELY ANALYZED FIELDS

Table 4 lists the mean objectively analyzed fields for each parameter. 
Table 4.  Available objectively analyzed fields for each parameter.
----------------------------------------------------------------------
PARAMETER                      ANNUAL*     SEASON**     MONTH***

Temperature                          X          X           X 
Salinity                             X          X           X 
Dissolved oxygen                     X          X
Apparent Oxygen Utilization          X          X
Oxygen saturation                    X          X 
Phosphate                            X 
Nitrate                              X         
Silicate                             X

  *ANNUAL - composite of all data regardless of season or year
 **SEASON - data composite based on seasons following the Northern 
            Hemisphere convention.  The seasons are defined as:
                  Winter (January - March)
                  Spring (April - June)
                  Summer (July - September)
                  Fall (October - December)
*** MONTH - data composite for each month.  January through December 
            analysis for 19 depth levels only (0-1000 m)
----------------------------------------------------------------------
For all the files in Table 4, there are accompanying mask files. The mask file contains the number of grid points which contain data within the radius of influence surrounding each grid box. If a grid box contains three or fewer observations within its radius of influence, the mask value for that one-degree square will be zero. This file is used in plotting routines to "mask" or cover up areas with three or less observations (see maps in the World Ocean Atlases for fields plotted using these masks).

6. REFERENCES ASSOCIATED WITH THE DATA


A.  DOCUMENTATION DESCRIBING THE QUALITY CONTROL PROCEDURES:

    (a)  Boyer, T.P. and S. Levitus.  1994.  Quality control and processing of 
         historical temperature, salinity and oxygen data.  NOAA 
         Technical Report NESDIS 81.  U.S. Department of Commerce. Washington,
         D.C.  65 pp.

    (b)  Conkright, M.E., T.P. Boyer and S. Levitus.  1994.  Quality control 
         and processing of historical nutrient data.  NOAA Technical Report 
         NESDIS 79.  U.S. Departement of Commerce, Washington, D.C. 75 pp.



B.  DOCUMENTATION DESCRIBING THE ANALYSIS PROCEDURES AND THE DATA 
    DISTRIBUTION AND ANALYSIS:

    (a)  Conkright, M.E., S. Levitus and T.P. Boyer.  1994. World Ocean Atlas 
         1994 Volume 1: Nutrients.  NOAA Atlas NESDIS 1.  U.S. Department of
         Commerce, Washington, D.C.  150 pp.

    (b)  Levitus S. and T.P. Boyer.  1994a. World Ocean Atlas 1994 Volume 2: 
         Oxygen. NOAA Atlas NESDIS 2.  U.S. Department of Commerce, Washington,
         D.C.  186 pp.

    (c)  Levitus S., R. Burgett and T.P. Boyer.  1994b. World Ocean Atlas 1994 
         Volume 3: Salinity. NOAA Atlas NESDIS 3.  U.S. Department of Commerce,
         Washington, D.C.  99 pp.

    (d)  Levitus S. and T.P. Boyer.  1994c. World Ocean Atlas 1994 Volume 4:                   
                               
         Temperature.  NOAA Atlas NESDIS 4.  U.S. Department of Commerce, 
         Washington, D.C. 117 pp.
 

C.  DOCUMENTATION DESCRIBING THE NON-ARCHIVED NODC DATA USED:

    Levitus, S., R. Gelfeld, T. Boyer and D. Johnson.  1994e.  Results of the
    NODC and IOC Oceanographic Data Archaeology and Rescue Projects.  Key
    to Oceanographic Records Documentation No. 19, NODC, Washington, D.C.


D.  DOCUMENTATION DESCRIBING THE NODC ARCHIVED DATA USED:

    Levitus, S. and R. Gelfeld.  1992.  NODC Inventory of Physical
    Oceanographic Profiles.  Key to Oceanographic Records Documentation No. 18,  
    NODC, Washington, D.C.



Appendix 1.  Description of flags used in the quality check of observed and
             standard level                                                                        data.

ERROR FLAGS
         
WHOLE-PROFILE FLAGS (AS A FUNCTION OF PARAMETER)
              0 - accepted profile
              1 - failed annual standard deviation check
              2 - two or more density inversions (Levitus 1982 criteria)
              3 - flagged cruise
              4 - failed seasonal standard deviation check
              5 - failed monthly standard deviation check
              6 - failed annual and seasonal standard deviation check
              7 - failed annual and monthly standard deviation check
              8 - failed seasonal and monthly standard deviation check
              9 - failed annual, seasonal, and monthly standard deviation 
                  check

FLAGS ON INDIVIDUAL DEPTHS AND OBSERVATIONS

Depth Flags:
              0 - accepted value
              1 - error in recorded depth (same or less than previous depth)
              2 - temperature inversion of magnitude > 0.3 degrees/meter
              3 - temperature gradient of magnitude  > 0.7 degrees/meter 
              4 - temperature gradient (of > 0.7 degrees/meter) followed 
                  closely by a temperature inversion (of > 0.3 degrees/meter) 
                  or vice versa
    
Observed Level Flags:
              0 - accepted value
              1 - range outlier (outside of range check)
              2 - density inversion
              3 - failed range check and density inversion check

Standard Level Flags:
              0 - accepted value
              1 - bullseye marker
              2 - density inversion
              3 - failed annual standard deviation check
              4 - failed seasonal standard deviation check
              5 - failed monthly standard deviation check
              6 - failed annual and seasonal standard deviation check
              7 - failed annual and monthly standard deviation check
              8 - failed seasonal and monthly standard deviation check
              9 - failed annual, seasonal and monthly standard deviation check

EXPLANATION OF ERROR FLAGS


A.  CHECK FOR DEPTH INVERSIONS AND DUPLICATE DEPTHS

Depth error flags:

(1)  If the second of two successive depths is shallower than the first (a
     depth inversion), the second depth will be marked with a flag value = 1.  

(2)  If two successive depths are shallower than the first depth, every depth
     reading following the first will be marked with a flag value = 1.

(3)  If two successive depth readings are equal, the second reading will be
     marked with a flag value = 1.

(4)  All correct depths are marked with a flag value = 0.


B.   STANDARD DEVIATION CHECK ON STANDARD LEVEL DATA

This check calculates the mean and standard deviation of five-degree square
latitude-longitude boxes for annual (all parameters), seasonal (temperature,
salinity, and oxygen), and monthly (temperature and salinity) periods.

Data are flagged if

(1)  a value is five standard deviations away from the mean in coastal waters
     (defined as any five-degree grid box adjacent to a land grid point or any
     five-degree grid box with a bottom depth of less than 200 m);

(2)  a value is four standard deviations away from the mean in near coastal
     waters or near the ocean floor (defined as any one-degree grid point
     where the depth is equal to or less than the depth in an adjacent 
     one-degree box) or any adjacent five-degree grid box is designated 
     coastal;

(3)  a value is three standard deviations away from the mean in open ocean;

(4)  if a profile contains two or more standard deviation failures, the
     whole profile is flagged. 




C.   DENSITY CHECKS FOR TEMPERATURE AND SALINITY PROFILES

The criteria for an instability are described by Levitus (1982).  


Flags are assigned 

(1)  for density inversions at the depths where they occur in the observed and
     standard level profiles;

(2)   when two or more density inversions (or instabilities) occur in a
      standard level profile. The entire profile is then flagged.

[Note: Stability checks were performed on observed as well as standard level
data.  Observed level flags are included for information only, since they were
not used to exclude any data from the profile data sets.  Whole-profile flags
for stability and standard deviation checks are for standard level data only. 
For informational purposes, if a standard level profile includes a whole
profile density flag (or standard deviation flag), the observed level data
will also include a whole profile flag.]


D.   CRUISE FLAGS 

Indicates all profiles from a cruise have anomalous data.  


E.   BULLSEYE FLAGS 

Flags individual depths with anomalous data which cause ripple effects or
"bullseyes" in the contoured objectively analyzed data.

benno@ldeo.columbia.edu