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Extract Mesoscale Eddy Centroids From SpatiaLite Database

Extracts eddy centroid points from the Chelton et al. (2011) mesoscale eddy database in SpatiaLite format.

In order to use this tool, you must first download the mesoscale eddy database netCDF file (usually available at http://cioss.coas.oregonstate.edu/eddies/) and convert it to a SpatiaLite database using the Convert Mesoscale Eddies NetCDF to SpatiaLite Database tool.

Because the database includes over 200,000 eddies with nearly 2.5 million centroids in total, we recommend that you use the Where Clause parameter to limit the extraction to the eddies that occured in your region and time period of interest. If you do not specify the Where Clause, all of the centroids will be extracted, which can take quite a long time and produce an output feature class that requires several hundred megabytes of disk space.

References

Chelton, D.B., M.G. Schlax, and R.M. Samelson (2011). Global observations of nonlinear mesoscale eddies. Progress in Oceanography 91: 167-216.


Command line syntax

CheltonMesocaleEddyPointsExtractArcGISPointsFromSpatiaLite_GeoEco <spatiaLiteDB> <outputFeatureClass> {tableName} {where}

Parameters
ExpressionExplanation
<spatiaLiteDB>

Mesoscale eddies SpatiaLite database to read.

This database is produced from the mesoscale eddy database netCDF file (usually available at http://cioss.coas.oregonstate.edu/eddies/) by the Convert Mesoscale Eddies NetCDF to SpatiaLite Database tool.

<outputFeatureClass>

Point feature class to create.

Each point represents the centroid of an eddy. Longitudes of the points will range from 0 to 360. The points will have the following attributes; data types are indicated in parentheses following the field name.

  • track (integer) - eddy identification number.

  • n (integer) - point number along the eddy track. Starts with 1. Points are separated by intervals of 7 days, so at point 2 the eddy is 7 days old, at point 3 it is 14 days old, and so on.

  • obsdate (date) - date of the point.

  • cyc (integer) - polarity of the eddy: -1 for cyclonic eddies and +1 for anticyclonic eddies.

  • lon, lat (float) - longitude and latitude of the centroid of the eddy. The longitudes are converted from the range used in the netCDF (260 E - 650 E) to 0 E - 360 E.

  • A (float) - eddy amplitude (cm) defined to be the magnitude of the height difference between the extremum of SSH within the eddy and the SSH around the contour defining the perimeter of the eddy.

  • L (float) - eddy radius scale (km) defined to be the radius of a circle with area equal to that enclosed by the contour of SSH within the eddy around which the circum-average speed is maximum.

  • U (float) - average speed (cm/sec) around the SSH contour that defines the scale L, i.e., the maximum circum-average speed within the eddy.

Please see Chelton et al. (2011) and http://cioss.coas.oregonstate.edu/eddies/ for more information about how these parameters were calculated.

A spatial index will be created on the output feature class.

{tableName}

Name of the table to read from the SpatiaLite database.

{where}

SQL WHERE clause expression that specifies the subset of points to extract. If this parameter is not provided, all of the points will be extracted.

The expression is evaluated by the SQLite database engine that SpatiaLite is built upon. Please see the SQLite documentation for more information about the syntax of this expression.

The following expression shows how to specify a geographic bounding box and time window to extract centroids that occurred in a region of the north Atlantic in the first three months of 2000. Note that longitude ranges from 0 to 360:

lat >= 25 and lat <= 50 and lon >= 280 and lon <= 340 and obsdate >= '2000-01-01' and obsdate <= '2000-03-31'

This example shows how to extract the centroids from the southern hemisphere that were at least 16 weeks old and that had anticyclonic polarity:

lat < 0 and n >= 17 and cyc = 1

You may use SpatiaLite's SQL functions in this expression to perform spatial comparisons. Please see the SpatiaLite documentation for more information.

Scripting syntax

CheltonMesocaleEddyPointsExtractArcGISPointsFromSpatiaLite_GeoEco (spatiaLiteDB, outputFeatureClass, tableName, where)

Parameters
ExpressionExplanation
Mesoscale eddies SpatiaLite database (Required)

Mesoscale eddies SpatiaLite database to read.

This database is produced from the mesoscale eddy database netCDF file (usually available at http://cioss.coas.oregonstate.edu/eddies/) by the Convert Mesoscale Eddies NetCDF to SpatiaLite Database tool.

Output feature class (Required)

Point feature class to create.

Each point represents the centroid of an eddy. Longitudes of the points will range from 0 to 360. The points will have the following attributes; data types are indicated in parentheses following the field name.

  • track (integer) - eddy identification number.

  • n (integer) - point number along the eddy track. Starts with 1. Points are separated by intervals of 7 days, so at point 2 the eddy is 7 days old, at point 3 it is 14 days old, and so on.

  • obsdate (date) - date of the point.

  • cyc (integer) - polarity of the eddy: -1 for cyclonic eddies and +1 for anticyclonic eddies.

  • lon, lat (float) - longitude and latitude of the centroid of the eddy. The longitudes are converted from the range used in the netCDF (260 E - 650 E) to 0 E - 360 E.

  • A (float) - eddy amplitude (cm) defined to be the magnitude of the height difference between the extremum of SSH within the eddy and the SSH around the contour defining the perimeter of the eddy.

  • L (float) - eddy radius scale (km) defined to be the radius of a circle with area equal to that enclosed by the contour of SSH within the eddy around which the circum-average speed is maximum.

  • U (float) - average speed (cm/sec) around the SSH contour that defines the scale L, i.e., the maximum circum-average speed within the eddy.

Please see Chelton et al. (2011) and http://cioss.coas.oregonstate.edu/eddies/ for more information about how these parameters were calculated.

A spatial index will be created on the output feature class.

SpatiaLite table name (Optional)

Name of the table to read from the SpatiaLite database.

Where clause (Optional)

SQL WHERE clause expression that specifies the subset of points to extract. If this parameter is not provided, all of the points will be extracted.

The expression is evaluated by the SQLite database engine that SpatiaLite is built upon. Please see the SQLite documentation for more information about the syntax of this expression.

The following expression shows how to specify a geographic bounding box and time window to extract centroids that occurred in a region of the north Atlantic in the first three months of 2000. Note that longitude ranges from 0 to 360:

lat >= 25 and lat <= 50 and lon >= 280 and lon <= 340 and obsdate >= '2000-01-01' and obsdate <= '2000-03-31'

This example shows how to extract the centroids from the southern hemisphere that were at least 16 weeks old and that had anticyclonic polarity:

lat < 0 and n >= 17 and cyc = 1

You may use SpatiaLite's SQL functions in this expression to perform spatial comparisons. Please see the SpatiaLite documentation for more information.