 Okay, so I'm Nicola, and I'm going to talk today about some work I've done as part of my PhD on the effects of volcanism on tropical variability with Matt England, Alex St. Gupta and Shane McGregor. Okay, so as we saw on the first day, volcanic eruptions are known to influence climate, and studies have shown with observations that surface air temperature cools over the time scale of about one to three years after a large tropical volcanic eruption and then tends to recover over the next six to seven years. And this figure illustrates exactly what happens. So you have a large tropical volcanic eruption, and that puts a whole bunch of stuff into the atmosphere. And what's really important is the sulfur dioxide, which turns into sulfate aerosols and acts to reflect and scatter solar radiation particles and act to cool the surface of the earth. Many studies have previously investigated a link between the Pacific Ocean variability, particularly looking at El Nino and the Southern Oscillation. Some studies have found that there's an El Nino that occurs after a large tropical eruption, and this tends to be hypothesized to be due to what's known as a dynamical thermostat. So if you think about the tropical Pacific Ocean, the Western Pacific, if you have a volcanic eruption, the Western Pacific tends to cool, whereas the East and Pacific cools, but is also influenced by upwelling waters. So it cools less than the West and Pacific. So when you have more cooling in the West and less cooling in the East, you get something that looks more El Nino-like. However, there is, I'll mention that there is a lot of debate around this dynamical thermostat hypothesis. Other studies have found that you get an El Nino followed by a La Nina. Some have found that you get an El Nino only in a Pinatubo-sized eruption or larger, and a whole bunch of studies have found that there's no real statistical significant response. So it seems to be a bit of an open question as to what's really going on here. While we're interested in this, among other reasons, is that influences on the Pacific Ocean might influence the sea surface temperatures. So if you have an El Nino-like state of the ocean, it tends to be warmer or a La Nina tends to be cooler. OK, so the motivation for this study came from the first section of my PhD work, and in these figures, you can see four different large eruptions that have occurred since the 1800s. And what I've shown here is the composite from 31 different Seymour 5 models of 10-year trends in surface air temperature around the volcanic eruption. So as you'd expect, there tends to be cooling after a volcanic eruption. And this has some structure. The first sort of thing that the first thing that really jumps out at you is that Pinatubo in the bottom right here really doesn't look quite the same as the other eruptions. And we think this is just because Pinatubo occurs in 1991. The climate's warmer than in the 1800s, so you get less cooling because it's already warmer or the same amount of cooling but on a already warmer base state. You can see in these plots that the trend in surface air temperature has a whole bunch of structure, as you might expect. The land tends to cool more than the oceans. But what we're really interested in is this response in the Pacific Ocean that it's difficult to see, but is highly stippled. So the models really agree in this region. And it looks really La Nina-like. So we wanted to know what was going on. OK, so to look at this, we used a whole bunch of Seymour 5 models. I have 33 different models and 122 different ensemble members. And we looked at both ENSO and the Indian Ocean Dipole because many studies have shown that they've been linked. So these panels show the EOFs for the Indian Ocean Dipole and the El Nino-Southern Oscillation calculated using both sea surface temperature and sea surface height. And the reason we've used sea surface height is because the sea surface temperature EOFs can be affected by the volcanic cooling, whereas the sea surface height EOFs tend to give you a more dynamic response about what's going on in the ocean. So the top left shows the positive mode of the Indian Ocean Dipole, which is characterized by warming in the Western Indian Ocean, which you can see here, cooling over the Indonesian region. And that corresponds with an increase in sea surface height over the Western Indian Ocean and a decrease over the Indonesian region. The bottom panel show the positive phase of the El Nino-Southern Oscillation or the El Nino. And you can see a characteristic El Nino with this warming in the East and Pacific. And you can see that the EOFs for the sea surface height tend to show an increase in sea surface height in the East and Pacific and a decrease in the Western Pacific. OK, so in this study, we looked at five volcanoes and they're the five large tropical volcanoes that occurred in the historical period. I mean, you can see them in the right hand panel. These plots show the year in relation to the eruption peak on the X-axis with the volcanoes composited around the eruption peak. And that's shown in the solid vertical line and the average eruption start times in the dash vertical line. I mean, if you look at the left panel, these are the surface air temperature anomalies around the eruption composited over all of the cement five models and the red lines, the multi-model multi-volcano composite. And these anomalies are in relation to the five years before the eruption peak. And that was just done because the eruptions occur in different warm states of the climate. So it's to put them on a similar baseline. You can see here that after the eruption start, you tend to get a cooling in surface air temperature as you'd expect, and that occurs over about a two-year time scale, which agrees well with observations. And then you have a recovery over a longer time scale of those surface air temperatures. This plot here shows Enso. And again, I'll just reiterate, the solid vertical line is the eruption peak and the dash vertical line is the average eruption start time. And here the horizontal black lines show the 95% significant level just for the multi-volcano multi-model mean composite, which is the red line. And so what you can see here is if you look at the left panel in the blue, centered around about two and a half years after the eruption, you have a really significant La Nina-like pattern. And that's what was showing up in the plots that motivated this study. However, what we found is that the volcanic cooling tends to project on this mode and enhance that La Nina-like signal. And if you look at the sea surface height variable on the right, you actually see something quite different. You see about straight after the eruption, you tend to have an El Nino-like response. And you don't really see that La Nina signal the same way. If you move on and look at the Indian Ocean Dipole, you can see it's less affected by the volcanic cooling. So the sea surface temperature and the sea surface height plots tend to agree. And you can see a positive phase of the Indian Ocean Dipole that's significant in the shaded red regions after the eruption. And so these results are much more easily seen in Hovmola plots. And the first one here shows sea surface temperature. And so you can see the Indian Ocean on the left of the figure, the Pacific Ocean on the right. And the sea surface temperatures have again been normalized in relation to the five years before the eruption. And again, this is the multi-model, multi-volcano mean. So five years before the eruption starts down here and five years after the eruption up here. So you can see when you look at sea surface temperatures that around the eruption peak, the band of five north to five south tends to cool. But what's really interesting is what happens after this. So you can see that the Indian Ocean is cooling and the Western Pacific is cooling, but the Eastern Pacific isn't cooling nearly as much as the Western Pacific. And this is what looks like the El Nino lack response. So we hesitate to call it an El Nino because there's not warming in the Eastern Pacific and cooling in the Western Pacific, but cooling and less cooling. And you can see that this pattern flips a bit later. And this is the sort of El Nino type pattern that we saw earlier. If you move on to look at the sea surface height variable, you can really see what's happening in the Indian Ocean as well as the Pacific. You can see right after the eruption, you get an increase in sea surface height in the Western Indian, a decrease in the Eastern Indian and the Western Pacific and an increase in the Eastern Pacific. And this really looks a lot like a positive Indian Ocean dipole event corresponding with an El Nino like event. And then you can see a weaker, I guess, change in this phase towards the drop in sea surface height in the East and an increase in the West, which looks more landing your like. So if you were having and so type anomalies, you'd expect to see some sort of zonal wind changes in the Pacific region. And so this figure here shows the same plot, but for the zonal wind. And keep in mind that the winds in the Pacific go from East to West. So the red color isn't actually an increase in the winds. It's a decrease in the winds and a blue color is an increase in the winds. And you can see after the eruption or around the after the eruption peak, you get this decrease in the winds in the Pacific. And that corresponds with what you'd expect if you have an El Nino like pattern. And then you can see you get an increase in the winds shown in the blue around when you see these more landing your like anomalies. Okay, so if we look at the probability of these events happening, what we actually find is a change in the probability of getting IOD and El Nino type events after an eruption. And so at the 95% significant level, you get about a 20 to 25% increase in the probability of getting a positive IOD in the six to 18 months after an eruption. And that corresponds with a 30% chance of an El Nino like pattern occurring. And that's seen just in the sea surface height field because it's really damped out in the sea surface temperature field by that volcanic cooling. And we do see about a 50% chance of an increase in the La Nina, but this is again enhanced by the volcanic cooling, but it explains what we were seeing in the motivation plots at the beginning, that when you composite decadal trends around a volcano, you tend to get a La Nina like pattern in the Pacific. Okay, so if you've zoned out till now, I'm gonna illustrate what we found using pictures. This here is your volcano that goes off. And what you tend to get is that volcanic cooling that occurs on the globe. You could hypothesize that due to the dynamical thermostat that I talked about before or other people have hypothesized other mechanisms, you get what looks like. A positive Indian Ocean Dipole event corresponding with an El Nino like event that isn't warming in the East and Pacific and cooling in the West and Pacific, but cooling in the West and Pacific and less cooling in the East and Pacific. And many studies have shown that a pattern like this tends to lead to a La Nina type pattern occurring on these sort of time scales that we see the La Nina occurring after. And this is interesting because when you look at 10 year trend plots around an eruption, you tend to get sort of persistent cooling and a La Nina like pattern in the Pacific Ocean. Okay, so to summarize, what have we found? We found that large tropical eruptions consistently result in cooling in the CMF5 models. Large tropical eruptions tend to cause an increase in the probability of the following sequence of events, which are a positive IOD and an El Nino like event occurring in the Austral Spring or Summer after the eruption. I'm an El La Nina type event occurring in the third Austral Summer after the eruption that's really enhanced by this volcanic cooling signal. And we find this interesting because it might lead to increased persistence of cooling due to the La Nina state of the ocean. Thanks.