On the process of upwelling: Progress from Sverdrup to Allen

Sverdrup (1938), in a paper entitled "On the process of upwelling", described observations made during three cruises off southern California in the spring of 1937 and noted that "it does not seem feasible to make the described conditions the subject of a mathematical analysis". Sverdrup expressed the hope that "in the future it will be possible to undertake special series of observations during periods of upwelling in order to obtain better knowledge of the phenomenon and to answer many questions which now must be left open". It would be more than thirty years before "special series of observations" were made to study coastal upwelling. Some thirty years ago the first session on "Upwelling and coastal oceanography" was scheduled at an AGU meeting: progress in understanding upwelling had finally picked up where Sverdrup had left off - and it continues today with GLOBEC and CoOP studies. It is not hyperbole to say that for more than 30 years John Allen has been "instrumental" in our progress in understanding the processes of coastal upwelling - in both the mathematical analysis of ideas and the quantitative analyses of observations. We nostalgically recount some steps in the development of our understanding of coastal upwelling: from coastal jets through coastal trapped waves to the coastal transition zone.