Meteorology sometimes runs in families. "But rarely," declared Homer, no doubt as he nodded over his Odyssey thinking of anything but weather, "rarely are sons similar to their fathers; most are worse, and a very few are considerably better." For the Bjerknes, pere et fils, however, such was not the case; as meteorological achievers they must rate ex aequo.
Villem Bjerknes was Norwegian, and established the so-called Bergen school of meteorology in the years immediately after the first World War. With a small but dedicated team, including his son Jacob, Bjerknes remade one of the great discoveries in weather history: he introduced the concept of warm and cold fronts, separating masses of air with differing characteristics of temperature and humidity, and thereby brought order to the apparent chaos of our daily weather.
A quarter of a century later Jacob Bjerknes was professor of meteorology at the University of California, and it was there that he made his great contribution: he unlocked for us the secret of El Nino.
Now 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. It played havoc with their fishing.
Every so often it was noticed that this current was much warmer than in other years, but no one took much notice.
Then, in the winter of 1957'58, 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 - which 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.