The primary swell period identifies the
period (the time between waves) of the dominant wave system (swell) that is
Note on the viewer:
versions 6-8. Alternative browsers in which the viewer does perform
correctly include Firefox, Opera, Safari, Chrome, Konqueror, Omniweb,
Seamonkey, Camino, others. If you encounter difficulties with the viewer in
Internet Explorer, we suggest trying one of the other browsers.