27 Gulf Stream Index
Description: Annual time series of the Gulf Stream index
Indicator category: Published method
Found in: State of the Ecosystem - New England (2019 (Different Methods), 2020+), State of the Ecosystem - Mid-Atlantic (2019 (Different Methods), 2020+)
Contributor(s): Zhuomin Chen, Young-oh Kwon
Data steward: Vincent Saba, vincent.saba@noaa.gov
Point of contact: Vincent Saba, vincent.saba@noaa.gov
Public availability statement: Source data are publicly available at CMEMS. Index data are NOT publicly available so please email vincent.saba@noaa.gov for further information and queries of GSI indicator data.
27.1 Methods
The methods used to calculate the Gulf Stream Index changed between 2019 and 2020 SOEs. The most recent methods and at the top with older methods below those.
This gulf stream index is a position anomaly meaning the larger the value of the index the further north the northern wall of the Gulf Stream is for that year.
27.1.1 Data sources
Data used in this analysis come from Compernicus Marine Environment Monitoring Service CMEMS - GLOBAL OCEAN GRIDDED L4 SEA SURFACE HEIGHTS AND DERIVED VARIABLES REPROCESSED (1993-ONGOING).
27.1.2 Data analysis
The GSI is calculated based on the method presented by Pérez-Hernández and Joyce (2014). It is a simple 16-point GS index constructed by selecting grid points following the maximum Standard deviation of sea level height anomalies every 1.33° longitude between 52° and 72°W and averaging them. The value of 1.33° is based on the resolution of satellite dataset from AVISO. We followed the same method, except using the dataset from CMEMS, which has a 0.25°x0.25° resolution. Therefore we select points every 1° between 52° and 72° and average them, and there are 21 points in total.
27.1.3 Data Processing
The Gulf Stream index data set was formatted for inclusion in the ecodata R package with the code found here.
27.2 2019 Methods
Summarized from Joyce et al. (2019), ocean temperature data from NOAA NODC were sorted by latitude, longitude, and time using a resolution of 1° of longitude, latitude, and 3 months of time, respectively, with a Gaussian squared weighting from the selected desired point in a window twice the size of the desired resolution. Editing was used to reject duplicate samples and 3\(\sigma\) outliers from each selected sample point prior to performing the weighting and averaging; the latter was only carried out when there were at least three data points in the selected interval for each sample point. Typically, 50 or more data values were available. The resulting temperature field was therefore smoothed. Data along the Gulf Stream north wall at nine data points were used to assemble a spatial/temporal sampling of the temperature at 200m data along the north wall from 75°W to 55°W. The leading mode of temperature variability of the Gulf Stream is equivalent to a north‐south shift of 50–100 km, which is zonally of one sign and amounts to 50% of the seasonal‐interannual variance between 75°W and 55°W. The temporal behavior of this mode (PC1) shows the temporal shift of the Gulf Stream path with a dominant approximately 8‐ to 10‐year periodicity over much of the period.
27.2.1 Data Sources
Ocean temperatures at 200 m are available at https://www.nodc.noaa.gov/OC5/3M_HEAT_CONTENT/.
27.2.2 Data analysis
For detailed analytical methods, see Joyce et al. (2019).
27.2.3 Data processing and plotting
Data processing and plotting remained the same between years.
catalog link https://noaa-edab.github.io/catalog/gsi.html