Effects of volcanism on tropical variability Motivation Results - - PowerPoint PPT Presentation

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

Effects of volcanism on tropical variability

Nicola Maher Matthew England, Alex Sen Gupta and Shayne McGregor

Climate Change Research Centre, UNSW and ARC CoE Climate System Science

18/11/2015

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

Introduction

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

Volcanic eruptions

◮ SAT cools rapidly over 1-3 years post eruption, then

recovers over 6-7 years

Surface cooling

Impact on heterogeneous chemistry Tephra deposit Impact on vegetation Impact on SST

• cean circulation

and marine biogeochemistry Cirrus modification Impact on river runoff Removal processes Infrared Precipitation changes Increased planetary albedo More diffuse radiation Sulphate aerosol

STRATOSPHERE TROPOSPHERE Rainout H2O, HCI, Ash hν + OH SO2 SO2 H2S HCI Warming Ash

Figure: Timmreck, 2012

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

Volcanic eruptions and Pacific variability

◮ Many studies have investigated link to Pacific Ocean

variability

◮ El Ni˜

no response, hypothesised due to a dynamical thermostat (Adams et al 2003; Seager et al 1988, Clement et al 1996; Cane 1997, Mann et al 2005, Ohba et al 2013)

◮ El Ni˜

no followed by La Ni˜ na (McGregor et al 2010)

◮ El Ni˜

no response only with Pinatubo or larger eruptions (Emile-Geay et al 2008)

◮ No response (Hirono 1988; Nicholls 1990; Self et al

1997; Robock 2000; Ding et al 2014)

◮ Influences on the Pacific may then influence SST (El

Ni˜ no/La Ni˜ na associated with warm/cool SST)

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

Motivation

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

Motivation

Maher, N., Sen Gupta, A. and England , M. H. (2014), Drivers of decadal hiatus periods in the 20th and 21st centuries, Geophys.

• Res. Lett., 41, 5978-5986

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

Results

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

Tropical modes of variability

−80 −60 40 −20 20 40 60 80

Latitude

A) IOD (SST EOF) B) IOD (SSH EOF)

50 100 150 200 250 300 350 −80 −60 40 −20 20 40 60 80

Latitude Longitude

C) ENSO (SST EOF)

−0.5 0.5

50 100 150 200 250 300 350

Longitude

D) ENSO (SSH EOF)

−0.06 −0.04 −0.02 0.02 0.04

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

Volcanic forcing and SST response

−5 −4 −3 −2 −1 1 2 3 4 5−4 −3.5 −3 −2.5 −2 −1.5 −1 −0.5

B) Volcanic forcing for 5 eruptions and composite Year in relation to eruption peak Forcing (W/m2)

Krakatau Santa Maria Agung Pinatubo El Chichon Composite

−5 −4 −3 −2 −1 1 2 3 4 5 −0.5 −0.4 −0.3 −0.2 −0.1 0.1 SAT anomaly

A) SAT anomalies Year in relation to eruption peak

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

ENSO phase relative to volcanic eruption

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

IOD phase relative to volcanic eruption

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

Hovmoller of SST

50 75 100 125 150 175 200 225 250 275 −5 −4 −3 −2 −1 1 2 3 4 5

Time in relation to eruption Longitude

A) Hovmoller of SST

Pacific Ocean Indian Ocean

−0.2 −0.1 0.1 0.2

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

Hovmoller of SSH

50 75 100 125 150 175 200 225 250 275 −5 −4 −3 −2 −1 1 2 3 4 5

Time in relation to eruption Longitude

B) Hovmoller of SSH

Pacific Ocean Indian Ocean

−0.01 −0.005 0.005 0.01

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

Hovmoller of zonal wind

50 75 100 125 150 175 200 225 250 275 −5 −4 −3 −2 −1 1 2 3 4 5

Time in relation to eruption Longitude

C) Hovmoller of Zonal wind

Pacific Ocean Indian Ocean

−3 −2 −1 1 2 3 x 10

−3

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

Change in probability of ENSO phase

At 95% significance level in the multi-volcano mean there is:

◮ 20-25% increase in probability of a positive IOD in 6-18

months after eruption

◮ 30% chance of El Ni˜

no- like response at same time (seen in SSH field)

◮ 50% increase in chance of La Ni˜

na 18months - 3.5 years after the eruption (in SST field)

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

Conclusions

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

Conclusions

• 1. Large tropical eruptions consistently result in cooling in

the CMIP5 models

• 2. Large tropical eruptions cause a increase in probability
• f the following sequence of events

◮ Positive IOD and El Ni˜

no-like event in the austral spring/summer post eruption

◮ La Ni˜

na in the third austral summer after the eruption

◮ Increased persistence of volcanic cooling due to La Ni˜

na state of the ocean

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

Questions? Thank you for your attention!

n.maher@unsw.edu.au

◮ Maher, N., McGregor, S., England, M. H, and Sen Gupta, A.

(2015), Effects of volcanism on tropical variability, Geophys.

• Res. Lett., 42, 6024 - 6033

Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions

Key questions

◮ Do the results differ if we subset for models that

represent ENSO well?

◮ Kim et al. [2014] have used ENSO magnitude to subset

the best 9 CMIP5 models

◮ These models have a noticeably reduced cold tongue

bias when compared to the remaining models

◮ We find no difference in result when subsetting for the

best 7 models

◮ Does it matter which forcing dataset is used?

◮ Each model uses one of the following volcanic forcing

datasets: Sato et al. [1993], Ammann et al. [2003], Ammann et al. [2007], Stenchikov et al. [1998] or Andres and Kasgnoc [1998]

◮ Different models also treat volcanic aerosols differently