Interview with Klaus Wyrtki
213
wind-induced seiches of the Baltic. There were southwest winds ahead of a cold front.
Twelve hours later there were northeast winds, very strong behind the cold front, and
the Baltic was excited; seiches were introduced, and the Baltic schwabberte, mit
der bekannten 24h-Periode.
19 Seit diesem Tage, wo ich diese seiches in der Ostsee
beobachtet und gesehen habe, habe ich mich gewundert, ob der große weite, offene
Ozean nicht mehr schwabbert. Das war eine Fragestellung.
20
The other thing was related to Peru. I made a current chart for the eastern
tropical Pacific and I was amazed that certain currents start nearly out of nothing
and end somewhere in a very diffuse way: the huge South Equatorial Current that
transports fifty Sverdrups, starts of this little Peru current that transports 10 Sv—
where is all the water coming from? And the South Equatorial Current ends near New
Guinea in the Coral Sea and you cannot see how it ends, it disappears. Where does
all the water go? This was the next question.
When making the Indian Ocean Atlas we drew maps for every month of the
topography of the 20
◦ isotherms, i.e., of the thermocline, in the Indian Ocean. It was
obvious that in certain parts of the ocean the thermocline was seasonally going down
and in other parts it was seasonally going up. So the idea came, if the thermocline goes
down by 20 or 30 m, how much water does it really transport out of an area? I made
the rough calculation and it showed that a substantial amount—10 to 20 Sverdrups—
leaves Somalia and goes over to Sumatra. And so I was looking at current charts
and there was the equatorial jet in the Indian Ocean, going from one area where the
thermocline lifts up to the other site of the ocean where the thermocline goes down.
That was really the next step on the road to El Ni˜ no.
Did you make your own measurements in the Indian Ocean?
No, that was the International Indian Ocean Expedition on which I did not participate,
because at that time I was working in the Tasman and Coral Sea. But, David Rochefort,
my colleague in Australia, was one of the main participants in the International Indian
Ocean Expedition.
Those were the years from 1966 to 1970, when I was working on the Indian
Ocean Atlas
21 . In 1971 I spent half a year at Kiel with Dietrich on a sabbatical and
when I came back, climate research started. This was the International Decade of
Ocean Exploration and the National Science Foundation started to fund big projects.
There was GEOSECS, MODE, the Southern Ocean, NORPAX. In the beginning I
participated in the NORPAX project. After having seen in the Indian Ocean, how
important annual variability is, and having known from my tuna research years that
year-to-year changes are quite important, I looked at the data from Hawaii and I found
19 The Baltic wobbled with the known 24-hour period.
20 Since that day, when I had observed the seiches in the Baltic, I was wondering whether something like
that happens in the big ocean, and why the wide open ocean is not wobbling more. That was the question.
21 Wyrtki, K., 1971: Oceanographic Atlas of the International Indian Ocean Expedition. National Science
Foundation Publication, OCE/NSF 86-00-001Washington, DC, 531 pp.
213
wind-induced seiches of the Baltic. There were southwest winds ahead of a cold front.
Twelve hours later there were northeast winds, very strong behind the cold front, and
the Baltic was excited; seiches were introduced, and the Baltic schwabberte, mit
der bekannten 24h-Periode.
19 Seit diesem Tage, wo ich diese seiches in der Ostsee
beobachtet und gesehen habe, habe ich mich gewundert, ob der große weite, offene
Ozean nicht mehr schwabbert. Das war eine Fragestellung.
20
The other thing was related to Peru. I made a current chart for the eastern
tropical Pacific and I was amazed that certain currents start nearly out of nothing
and end somewhere in a very diffuse way: the huge South Equatorial Current that
transports fifty Sverdrups, starts of this little Peru current that transports 10 Sv—
where is all the water coming from? And the South Equatorial Current ends near New
Guinea in the Coral Sea and you cannot see how it ends, it disappears. Where does
all the water go? This was the next question.
When making the Indian Ocean Atlas we drew maps for every month of the
topography of the 20
◦ isotherms, i.e., of the thermocline, in the Indian Ocean. It was
obvious that in certain parts of the ocean the thermocline was seasonally going down
and in other parts it was seasonally going up. So the idea came, if the thermocline goes
down by 20 or 30 m, how much water does it really transport out of an area? I made
the rough calculation and it showed that a substantial amount—10 to 20 Sverdrups—
leaves Somalia and goes over to Sumatra. And so I was looking at current charts
and there was the equatorial jet in the Indian Ocean, going from one area where the
thermocline lifts up to the other site of the ocean where the thermocline goes down.
That was really the next step on the road to El Ni˜ no.
Did you make your own measurements in the Indian Ocean?
No, that was the International Indian Ocean Expedition on which I did not participate,
because at that time I was working in the Tasman and Coral Sea. But, David Rochefort,
my colleague in Australia, was one of the main participants in the International Indian
Ocean Expedition.
Those were the years from 1966 to 1970, when I was working on the Indian
Ocean Atlas
21 . In 1971 I spent half a year at Kiel with Dietrich on a sabbatical and
when I came back, climate research started. This was the International Decade of
Ocean Exploration and the National Science Foundation started to fund big projects.
There was GEOSECS, MODE, the Southern Ocean, NORPAX. In the beginning I
participated in the NORPAX project. After having seen in the Indian Ocean, how
important annual variability is, and having known from my tuna research years that
year-to-year changes are quite important, I looked at the data from Hawaii and I found
19 The Baltic wobbled with the known 24-hour period.
20 Since that day, when I had observed the seiches in the Baltic, I was wondering whether something like
that happens in the big ocean, and why the wide open ocean is not wobbling more. That was the question.
21 Wyrtki, K., 1971: Oceanographic Atlas of the International Indian Ocean Expedition. National Science
Foundation Publication, OCE/NSF 86-00-001Washington, DC, 531 pp.