Satellite Images Reveal Two Types of Ocean Eddies
West of the Hawaiian Islands
S. Yoshida (IPRC), B. Qiu (UH), P. Hacker (IPRC)
(cm)
SSH (60-day signal
Horizontal maps of
the RMS of SSH
anomaly (top) and
EKE (bottom). SSH
anomaly is
bandpassed at 60days (left) and 100days (right).
SSH (100-day signal
(cm/s)2
EKE (60-day signal)
EKE (100-day signal)
Ocean eddies with a scale of 100 km or more greatly impact ocean dynamics and marine life. Weekly satellite
data of sea surface height (SSH) reveal two kinds of eddies lee of the Hawaiian Islands: The kinetic energy
immediately in the lee of Hawaii is significantly greater than further west, and the sea surface height variation in
the region 159ºW-157ºW is greatest for a 60-day period and in 169ºW-162ºW for a 100-day period. The eddies
with the 60-day signal originate in the southwest corner of the island of Hawaii. QuikSCAT analysis shows they
are induced by the local 60-day wind stress curl associated with the trade wind’s blockage by the islands of
Maui and Hawaii. Since the 60-day SSH signal does not stretch far to the west, these wind-induced eddies are
rather short-lived and must be independent of the longer-lasting eddies further west, which are thought to be
not due to winds. Noteworthy is the finding that the 60-day SSH anomalies take 1~2 weeks to grow fully so that
real-time observed wind stress can be used to predict these high-amplitude eddies.