Vast, strong and with unusual storm characteristics, Hurricane Sandy is posing some new problems for climate scientists to debate. Rhiannon Elston speaks to Steve Sherwood, Co-Director of the Climate Change Research Centre at the University of New South Wales about what scientists could learn from the latest major weather event.
RE: Steve, thanks for joining us. Why is Hurricane Sandy being called a superstorm?
SS: It's really the combination of a tropical cyclone interacting with a mid-latitude cyclone or a disturbance on the polar jet stream. It's unusual, this is a very unusual thing to have happened.
RE: And there are some confusing elements, for example, it's called a post-tropical storm and yet it's also causing snow. Can you explain why that is?
SS: It's late Autumn in the northern hemisphere so it's starting to get cold up there and it's possible to get temperatures well below freezing aloft where your precipitation forms so in fact you can even get hail in the summertime.
So it's not crazy to get frozen precipitation even when it's fairly warm but up until recently this has been a tropical storm. I noticed it was just changed to an extra-tropical storm.
They're calling it a downgrade but it doesn't mean the storm is any weaker at all, it's just that it's so far north, you can't call it a tropical cyclone anymore.
RE: One of the things we've been hearing about this particular storm is the sheer size of it is the thing that's really putting fear into people. How does it compare to other cyclones and tropical storms that we've seen both here in Australia and abroad?
SS: It's much larger than a typical tropical cyclone, depends how you measure it. By some measures its double the size of a typical tropical cyclone but that's because when these storms move out the tropics they do tend to basically spread out, they usually weaken and they get bigger.
So a typical cyclone outside the tropics is larger but doesn't normally generate anything like the kind of winds and damage that you see near the centre, near the eye or the eye wall of a tropical cyclone.
But what's happening with this one is that it's actually staying pretty strong, it's still got hurricane-force winds over a large area, but it's also growing in size.
RE: What are some of the biggest risks to those living in the affected areas?
SS: Well people are talking about storm surges being a really scary part of this but I think the high winds are also dangerously getting above 140km/h and in a lot of places it sounds like a lot of things are blowing off of rooftops and I just got a report from Yale University where I used to work – things have fallen off of some roofs and caused a lot of damage and they're telling everyone to stay indoors. So there's that and there's the storm surge that will probably be what causes the most damage by the end of the day.
RE: This storm has reignited concern over climate change, but is it possible to tell whether there's a direct link between this storm and changes in our global weather patterns?
SS: Every time a weird storm or some extreme weather happens, people ask this question and it's always hard to answer because storms like this are not unprecedented, I'm sure, but what climate change does is it gives them a little bit more fuel, a bit more power, and that's true for any cyclone.
They're all a bit stronger now than they would have been without global warming. But what's really interesting about this storm is that it's showing something that I personally haven't thought of as possible impact for climate change, which is we know that the tropics have been expanding out away from the equator for the last few decades and nobody's quite sure how to explain it.
It seems like it's consistent with what we expect from global warming but happening faster than we would have thought.
And one of the things, now that we've watched the storm evolve that could be a result of this, is that you actually can move the tropical cyclones closer potentially to the jets, the main jet and the polar jet, and also by having a lot more water vapour in the atmosphere, particularly in the mid latitudes and higher latitudes, it may be that this sort of weird interaction could start to happen a lot more often, and I never actually thought of that, but it's quite possible.
RE: And just in the longer term, what kind of effects will a storm like this have on the atmosphere? Does it have a long tail?
SS: These storms tend to hang around in some form for a week. It takes a long time for everything to get completely back to normal so there's going to be a lot of rain around there and this storm will inevitably get carried over and dump a lot of rain on Europe. But if you mean very long term effects, no, this is just one of those fluctuations that comes and goes in the atmosphere.
