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

Effects of volcanism Nicola Maher Introduction Effects of volcanism on tropical variability Motivation Results Conclusions 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

Volcanic eruptions Effects of volcanism Nicola Maher ◮ SAT cools rapidly over 1-3 years post eruption, then Introduction Motivation recovers over 6-7 years Results Conclusions Impact on Increased heterogeneous STRATOSPHERE planetary chemistry albedo h ν + OH SO 2 H 2 S HCI Sulphate SO 2 Ash aerosol Warming Removal More processes diffuse radiation Cirrus modification TROPOSPHERE Rainout Precipitation Infrared changes H 2 O, HCI, Ash Surface cooling Impact on Impact on SST river runoff Tephra ocean circulation deposit and marine biogeochemistry Impact on vegetation Figure: Timmreck, 2012

Volcanic eruptions and Pacific variability Effects of volcanism Nicola Maher ◮ Many studies have investigated link to Pacific Ocean Introduction variability Motivation ◮ El Ni˜ Results no response, hypothesised due to a dynamical Conclusions 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

Motivation Effects of volcanism Nicola Maher Introduction Motivation Results Conclusions 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

Tropical modes of variability Effects of volcanism Nicola Maher A) IOD (SST EOF) B) IOD (SSH EOF) Introduction 80 60 Motivation 40 Results 20 Latitude 0 Conclusions −20 40 −60 −80 C) ENSO (SST EOF) D) ENSO (SSH EOF) 80 60 40 20 Latitude 0 −20 40 −60 −80 50 100 150 200 250 300 350 50 100 150 200 250 300 350 Longitude Longitude −0.5 0 0.5 −0.06 −0.04 −0.02 0 0.02 0.04

Volcanic forcing and SST response Effects of volcanism Nicola Maher Introduction Motivation A) SAT anomalies B) Volcanic forcing for 5 eruptions and composite 0 Results 0.1 Conclusions −0.5 −1 0 Forcing (W/m2) SAT anomaly −1.5 −0.1 −2 −0.2 −2.5 −0.3 −3 Krakatau Santa Maria −0.4 Agung −3.5 Pinatubo El Chichon Composite −0.5 5−4 −5 −4 −3 −2 −1 0 1 2 3 4 5 −5 −4 −3 −2 −1 0 1 2 3 4 Year in relation to eruption peak Year in relation to eruption peak

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 Effects of volcanism Nicola Maher Introduction A) Hovmoller of SST Motivation 5 0.2 Results 4 Time in relation to eruption Conclusions 3 0.1 2 1 0 0 −1 −0.1 −2 −3 −0.2 −4 −5 50 75 100 125 150 175 200 225 250 275 Longitude Indian Ocean Pacific Ocean

Hovmoller of SSH Effects of volcanism Nicola Maher Introduction B) Hovmoller of SSH Motivation 5 0.01 Results 4 Time in relation to eruption Conclusions 3 0.005 2 1 0 0 −1 −0.005 −2 −3 −0.01 −4 −5 50 75 100 125 150 175 200 225 250 275 Longitude Indian Ocean Pacific Ocean

Hovmoller of zonal wind Effects of volcanism Nicola Maher Introduction C) Hovmoller of Zonal wind Motivation 5 −3 x 10 3 Results 4 Time in relation to eruption Conclusions 2 3 2 1 1 0 0 −1 −1 −2 −2 −3 −3 −4 −5 50 75 100 125 150 175 200 225 250 275 Longitude Indian Ocean Pacific Ocean

Change in probability of ENSO phase Effects of volcanism Nicola Maher Introduction Motivation At 95% significance level in the multi-volcano mean there is: Results Conclusions ◮ 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

Conclusions Effects of volcanism Nicola Maher Introduction Motivation 1. Large tropical eruptions consistently result in cooling in Results the CMIP5 models Conclusions 2. Large tropical eruptions cause a increase in probability of 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

Questions? Effects of volcanism Nicola Maher Introduction Motivation Results Thank you for your attention! Conclusions 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

Key questions Effects of volcanism Nicola Maher ◮ Do the results differ if we subset for models that Introduction represent ENSO well? Motivation ◮ Kim et al. [2014] have used ENSO magnitude to subset Results the best 9 CMIP5 models Conclusions ◮ 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