1. a Department of Fisheries and Oceans, Physical and Chemical Sciences Branch , Bedford Institute of Oceanography , Dartmouth, Nova Scotia, B2Y 4A2, Canada
2. b Remote Sensing Group , James Rennell Centre for Ocean Circulation , Chilworth Research Park, Chilworth, Southampton, SOI 7NS, U.K
3. c Consiglio Nazionale Delle Richerche , Istituto Di Fisica Dell' Atmosfera , Piazzale Luigi Sturzo, 31, Roma, 00144, Italy