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Southwest North Atlantic (SWNA) Regional Climatology

Overview: Since publication of the Climatological Atlas of the World Ocean (Levitus, 1982), objectively analyzed fields of essential oceanographic parameters, such as temperature, salinity and oxygen have been traditionally referred to as ocean climatologies. The Southwest North Atlantic Regional Climatology (SWNA RC) based on the updated 2018 edition of the World Ocean Atlas (WOA18). The SWNA RC is comprised of the objectively analyzed temperature and salinity fields as well as some additional parameters, which include simple statistical means, data distributions, standard deviations, standard errors of the mean, observed minus analyzed, and seasonal minus annual distributions for both temperature and salinity. These parameters may be useful for applied climate studies and other applications. All SWNA RC parameters were computed using all data from 1955 to 2017 available in the World Ocean Database. The maps and data for the SWNA are available for viewing and downloading.

The seasonal and annual fields are computed after completion of all monthly analyses on all three horizontal grids (1°x1°, a 1/4°x1/4°, and 1/10°x1/10°). Annual and seasonal fields above 1500 m are calculated using the monthly fields. The monthly fields are computed by taking the average of six decadal monthly analyses from 1955 to 2017 (the last "decade" includes the years from 2005 to 2017 thus containing thirteen years instead of ten). Above 1500 m, the seasonal fields are built at all depths by averaging the three months comprising each season (e.g., January, February and March for winter) and the annual mean fields are calculated by averaging the four seasonal fields at all depths. Below 1500 m depth an annual analysis is defined as the mean of the four seasonal analyses and only annual and seasonal fields are shown (the monthly fields are not shown).

It is important to note that the high-resolution monthly temperature and salinity data coverage on the 1/10°x1/10° grid have more gaps than seasonal and annual fields computed from the monthly fields. In general, all high-resolution analyzed fields should be reviewed carefully before using them in critical mission applications. It is especially important when working with the high-resolution monthly fields. Users are advised to review the data distribution and statistical mean arrays before deciding whether to use the high-resolution analyzed temperature and salinity fields or their climatological means. Moreover, the monthly maps of objectively analyzed data on 1/10°x1/10° may show some too strong eddy-like irregularities in some data-sparse regions due to interpolation and plotting combined (Seidov et al., 2019). Although such cases are relatively few, more careful review of the fields with such occurrences is needed before using analyzed variables in research or applications.

Temperature and salinity climatologies are calculated separately. There are many more temperature data than salinity data. Even when there are salinity measurements, there are not always concurrent temperature measurements. As a result, when density is calculated from standard level climatologies of temperature and salinity, instabilities may result in the vertical density field. Appendices A and B in (Locarnini et al., 2018) describe a method employed to minimally alter climatological temperature and salinity profiles to achieve a stable water column everywhere in the world ocean. However, in the SWNA region, such instabilities are very uncommon.

Area: The SWNA domain is encompassed between 85.0°W and 60.0°W longitudes and between 10.0°N and 35.0°N latitudes.

Temporal resolution:

  1. All data from the WOD18 for the SWNA domain were used to calculate six decadal climatologies within the following time periods: 1955-1964; 1965-1974; 1975-1984; 1985-1994; 1995-2004; 2005-2017. The all averaged decadal climatology was calculated by averaging six individual decades listed above (see World Ocean Database 2018 Introduction).
  2. Each decadal climatology consists of
    1. Annual (computed as 12-months averages);
    2. Seasonal: Winter (Jan.-Mar.), Spring (Apr.-Jun.), Summer (Jul.-Sep.), Fall (Oct.-Dec.) computed as 3-months averages;
    3. Monthly fields (above 1500 m).

Spatial resolution:

  1. Annual, seasonal and monthly fields are available on a 1°x1°, a 1/4°x1/4°, and a 1/10°x1/10° latitude/longitude grids.
  2. Monthly fields are available only above 1500 m on all grids.

Vertical resolution:

  1. All annual and seasonal fields were calculated from 0 to 5500 m depth on 102 standard levels;
  2. All monthly fields were calculated from 0 to 1500 m on 57 standard levels.
Standard depth levels in the NWA regional climatology are the same as in the WOA18 (see Table 3 in the WOA18 documentation).

Objectives: Higher spatial resolutions – here the 1/10°x1/10° grid – provide major advantages in the areas where such resolutions are feasible and supported by data availability. The quality control on a higher-resolution grid reveals more outliers than an analysis on coarser grids. More importantly, with the significantly shorter radius of influence in the objective analysis procedure, the structure of the gridded fields is far better sustained, especially in regions with sharp gradients of the essential oceanographic parameter (temperature and salinity). Residual effect of quasi-stationary meanders and transient mesoscale eddies on climatological fields is clearly seen at 1/10°x1/10° resolution. They are better preserved in high-resolution climatological fields, which make them more valuable for ocean modeling and other applications.

Units: Temperature units are °C. Salinity is unitless on the Practical Salinity Scale-1978.

Data: All data from WOD18 were used to generate the SWNA mean and decadal climatologies. The description of employed datasets can be found in World Ocean Database 2018 Introduction Boyer et al., 2018.

Bathymetry: For all three grid resolutions, mean depth values at the center of a grid square with the respective resolution were extracted from the ETOPO2 World Ocean bathymetry.

Methods: The methods of calculating mean climatological fields are described in details in the following publications: Temperature: Locarnini et al., 2018, Salinity: Zweng et al., 2018.

Additional details on high-resolution climatological calculations can be found in Boyer et al., 2005.

The updated table from (Boyer et al., 2005), including the 1/10° grid resolution, provides radii of influence for the analysis procedure as:

Pass1° radius of influence1/4° radius of influence1/10° radius of influence
1892 km321 km253 km
2669 km267 km198 km
3446 km214 km154 km

Data formats:
Data are distributed in several formats:

  1. Comma Separated Values (CSV) format which gives latitudes and longitudes of the center of a grid box and the value at each depth in that grid box;
  2. ArcGIS shape-file format;
  3. netCDF format.

Most of the procedures used for generating all NCEI regional climatologies are similar to those used in generating WOA18, e.g., (Locarnini et al., 2018; Zweng et al., 2018). Several recently published studies of long-term ocean climate change are based on SWNARC (Seidov et al., 2015; Seidov et al., 2017; Seidov et al., 2018).

References:

Boyer, T., S. Levitus, H. Garcia, R. A. Locarnini, C. Stephens, J. Antonov, 2005: Objective analyses of annual, seasonal, and monthly temperature and salinity for the world ocean on a 0.25 degree grid. Int. J. Clim., 25, 931-945.

Boyer, T. P., O. K. Baranova, C. Coleman, H. E. . Garcia, A. Grodsky, R. A. Locarnini, A. V. Mishonov, C. R. Paver, J. R. Reagan, D. Seidov , I. V. Smolyar, K. Weathers, M. M. Zweng, 2018: World Ocean Database 2018. A. V. Mishonov, Technical Ed.; NOAA Atlas NESDIS 87, 209 pp.

Levitus, S., 1982: Climatological Atlas of the World Ocean, NOAA Professional Paper 13, U.S. Gov. Printing Office, Rockville, M.D., 190 pp.

Locarnini, R. A., A. V. Mishonov, O. K. Baranova, T. P. Boyer, M. M. Zweng, H. E. Garcia, J. R. Reagan, D. Seidov, K. Weathers, C. R. Paver, I. Smolyar, 2018: World Ocean Atlas 2018, Volume 1: Temperature. A. V. Mishonov Technical Ed.; NOAA Atlas NESDIS 81, 40 pp.

Seidov, D., O. K. Baranova, T. Boyer, S. L. Cross, A. V. Mishonov, and A. R. Parsons, 2016: Northwest Atlantic Regional Ocean Climatology, in NOAA Atlas NESDIS 80, edited, p. 56, NOAA/NESDIS, Washington, DC, i https://repository.library.noaa.gov/view/noaa/12209">doi:10.7289/V5/ATLAS-NESDIS-80; https://repository.library.noaa.gov/view/noaa/12209.

Seidov, D., A. Mishonov, J. Reagan, and R. Parsons, 2017: Multidecadal variability and climate shift in the North Atlantic Ocean, Geophys. Res. Let., 44(10), 4985-4993, doi:10.1002/2017GL073644.

Seidov, D., A. Mishonov, J. Reagan, O. Baranova, S. Cross, and R. Parsons, 2018: Regional climatology of the Northwest Atlantic Oceanhigh-resolution mapping of ocean structure and change, Bulletin of the American Meteorological Society, 9(10), doi:doi:10.1175/BAMS-D-17-0205.1.

Seidov, D., Mishonov, A., Reagan, J., Parsons, R., 2019: Eddy-Resolving In Situ Ocean Climatologies of Temperature and Salinity in the Northwest Atlantic Ocean. Journal of Geophysical Research: Oceans, 124, 41-58, doi:10.1029/2018JC014548

Zweng, M. M, J. R. Reagan, D. Seidov, T. P. Boyer, R. Locarnini, H. E. Garcia, A. V. Mishonov, O. K. Baranova, K. Weathers, C. R. Paver, I. Smolyar, 2018: World Ocean Atlas 2018, Volume 2: Salinity. A.Mishonov, technical editor, NOAA Atlas NESDIS 82, 39 pp.