" El Nino refers to the extensive warming of the central and eastern Pacific that leads to a major shift in weather patterns across the Pacific, including an increased probability of drier conditions.
Presenter: Geraldine Coutts
Speaker: Dr. Kevin E. Trenberth,Head of the Climate Analysis Section, National Center for Atmospheric Research in Boulder, Colorado
TRENBERTH: I think that's true by at least some of the measures. It's certainly nowhere near as strong as the big 1997/98 El Nino, and that along with the 1982/83 El Nino. Those are the two really big El Ninos and then everything else is in a category a notch down.
COUTTS: What are the differences between the earlier ones and this one?
TRENBERTH: Well, the great big El Ninos have very extensive warming of the tropical Pacific Ocean in terms of the sea temperatures all the way across the Pacific and are much more disruptive of the weather patterns all around the world. So much bigger impacts, a longer duration, much more distinctive and somewhat different patterns also than the sort of the run of the mill El Nino, and this is sort of a category that's really a moderate to strong event but much more in the run of the mill category. The warmest sea temperatures at the moment are, or the warmest anomalous aspects of the sea temperatures, are about 170 west just east of the dateline in the equatorial region of the tropical Pacific, and that's where a lot of the convection is occurring, a lot of the activity that then runs to the south-east down towards Tahiti and so on. And so that's also the area where there's a lot more tropical storm activity that tends to occur in El Nino conditions.
COUTTS: Well it sounds like we know quite a bit about El Ninos but how much do we know about them, their behaviour and their impact?
TRENBERTH: Well we've been, the information has really developed from a project we had called TOGA, Tropical Oceans Global Atmosphere, from 1985 to 1995, and that set up an operational system where we have a whole bunch of something like 90 moored buoys along the equator now that can track the sub-surface ocean heat content and the sea surface temperatures and how they are developing in time. And this has led to some predictive capability and so we can certainly predict that this El Nino is going to continue for the next say six months or something like that, and after that it's much less certain. But it will continue to have disruptive influences, or make differences from normal should I say, in terms of the weather patterns that will influence Australia and other parts of the world.
COUTTS: Well El Ninos are supposed to be dry and yet we're having lots of cyclones if you've just heard with the weather forecast leading into you, which is bringing lots of rain to some parts, and if you even look at Australia, we've got some parts that are flooding and other parts that are as dry as?
TRENBERTH: Yes so it depends where you are of course. The places that are supposed to be dry are Southeast Asia, the Indonesian region and especially the northern parts of Australia and that does not seem to have been the case quite as much as we would have expected. Instead the pattern seems to have been more that it's been drier in the western half of Australia, but other parts of Australia have gotten a lot more rain someone would normally expect with El Nino conditions. And so part of that relates to what we call intransient disturbances, there's a phenomenon called the Madden-Julian Oscilation that has some large patterns that are embedded within the El Nino pattern that are sufficient to produce some of these disturbances. And some of the tropical disturbances tend to align with that as well. In general there's less tropical storm activity under El Nino conditions in the Australian sector and across to about the dateline, and there's a lot more east of the dateline in the South Pacific under El Nino conditions.
COUTTS: We read this week as a matter of fact that scientists are now saying that they think they've got a clue as to how they can predict an El Nino more accurately now by following what's happening in the Indian Ocean, and so they'd be able to warn farmers and weather forecasters more accurately because of the conditions there. Is that something you've been looking at?
TRENBERTH: Well certainly the Indian Ocean is something that is worth paying attention to as well, but exactly how the Indian Ocean and the Pacific relate to one another and whether the Indian Ocean can be used in a predictive sense I'm less sure about that. The more established pattern is that the Indian Ocean gets affected by the El Nino pattern and there is a subsequent warming of the Indian Ocean, so that would occur more in your fall, and even going into next winter. And that also has big effects on East Africa, and so there can be substantial rains in the Rift Valley in Kenya, they've had drought conditions in that region, and so that's the sort of thing that tends to follow from an El Nino, but maybe there's some new information, certainly the Indian Ocean is rearing its head because of global warming in some sense. The Indian Ocean has warmed up more than other oceans, and in particular it's warmed more than the Pacific Ocean, and so some of these relationships are changing over time.