His name was Jacob Aall Bonnevie Bjerknes. He is remembered by meteorologists around the world as Jacob, and his friends would call him Jack. And he died 25 years ago today, on July 7th, 1975. Jacob Bjerknes became famous in his early 20s as the lead author of a scientific paper, "On the Structure of Moving Cyclones". His was the meteorological genius behind the so-called Bergen school of meteorology, established in Norway by his father, Prof Vilhelm Bjerknes, in the closing years of the first World War.
Jacob Bjerknes and his colleagues introduced to meteorology the now familiar concept of warm and cold fronts - rain-bearing boundaries between masses of air with widely differing characteristics of temperature and humidity.
On an extended visit to America in 1940, Jack Bjerknes became stranded when Norway was invaded, and his stay on that continent became indefinite. Twenty-five years later he was professor of meteorology at the University of California, and it was there he made his second major contribution to his science: he unlocked the secret of El Nino.
It had been known for centuries that near the end of each calendar year, a weak, warm ocean current flows slowly southwards along the east coast of South America. Long ago, the local inhabitants gave this warm current a name: they called it El Nino, "the boy child", because it came along at Christmastime - and it played havoc with their fishing. Every so often it was noticed this current was much warmer than in other years, but no one took much notice.
In the winter of 1957-8, a series of ocean and atmosphere observations during the International Geophysical Year revealed a remarkable and unexpected ocean warming that extended westwards from South America across the entire equatorial Pacific.
Jacob Bjerknes, by meticulous study of this event and two subsequent warmings in 1963 and 1965, recognised that alternate warmings and coolings of the sea surface were a recurrent feature of the climate of equatorial regions of that ocean.
Furthermore, he noticed, these large-scale Pacific warmings coincided with exceptionally warm El Nino currents near the coasts of Peru and Ecuador.
Further study revealed to Bjerknes that these changing temperature patterns were accompanied by large shifts in the rainfall regimes of nearby regions, and that crucially, they were also intimately linked to pressure anomalies - a periodic "swaying" or "see-saw" in the average atmosphere pressure between the Indian Ocean and eastern Pacific - that had first been noticed more than a century before.
This linking of the coastal warmings near Peru to the so-called "Southern Oscillation" provided the key to our present understanding of El Nino.