El Nino, the changes in ocean circulation that occasionally devastate fisheries off Peru, may seem of little concern half a world away. But atmosphere and ocean are an interconnected system in which virtually everything is somehow related to everything else. El Nino appears to be part of a large scale air-sea phenomenon that includes severe winters in North America.
It's a connection that could prove beneficial. El Nino-related effects in the South Pacific may give North American forecasters warning of hard winters half a year in advance.
Although it's not yet clear how useful a forcecasting aid this will be, it could become the most important practical upshot yet of decades of study of one of the most perplexing atmospheric phenomena -- the so-called southern oscillation. This is an intermittent but characteristic shift in cloudiness, rain, sea surface temperatures, surface winds, and sea-level air pressure that occurs irregularly at roughly 2 to 4 year intervals.
El Nino -- "The Child," so named because it often sets in around Christmas -- brings a warm current that replaces the normal cold, nutrient -rich water along Peru's coast. Fish -- and the sea birds that feed on them -- die off massively. There often is heavy rain with flooding on land. The shifts of pressure, winds, and sea currents that bring on this coastal catastrophe have global connections that have only begun to be fully appreciated.
This is reflected, for example, in slight changes in the atmosphere's carbon dioxide (CO) content that correlate with the southern oscillation. The correlation was reported recently in Science by a research team at Scripps Institution of Oceanography and the Canadian Institute of Ocean Sciences. Changing sea surface conditions apparently alter the ocean's tendency to release or absorb (CO) over a large enough area to affect the atmosphere.
The link between the southern oscillation and North American winters is more striking. Summarizing the work of several investigators, including himself, John Michael Wallace of the University of Washington described the connection in the 1980 Victor Paul Starr memorial lecture at the Massachusetts Institute of Technology.
Among other things, there is a substantial increase in rain over a large part of the equatorial and near-equatorial Pacific during the southern oscillation. Heat released as water vapor condensed in this rain appears to act as a major heating source to change patterns of air circulation and pressure -- an effect that can be traced for at least a hemisphere. Specifically, a severe winter circulation mode develops over North America. Precursors of this development are evident many months before the northern winter.
Perhaps, Wallace suggests, this will give North American forecasters an edge in anticipating hard winters -- a possibility now being explored by a number of scientists. Weather, it seems, is everyone's concern, no matter where it happens.