JOURNAL OF GEOPHYSICAL RESEARCH, VOL. ???, XXXX, DOI:10.1002/,

12

3

Reconciling the Observed and Modeled SouthernHemisphere Circulation Response to Volcanic
Eruptions–Supplemental Material
112Marie C. McGraw , Elizabeth A. Barnes , and Clara Deser

4Contents:

56

1. Selection of CMIP5 Models (Figure S1)7

2. Eddy-Driven Jet Results (Figure S2)8

3. Combined CMIP5-CESM1 Results for ENSO Analysis (Figure S3)9

4. List of CMIP5 Models and simulations used (Table S1)Corresponding author: Marie C. McGraw (mmcgraw@atmos.colostate.edu)
1

Department of Atmospheric Science,

Colorado State University, Fort Collins,
Colorado, USA.
2

Climate and Global Dynamics Division,

National Center for Atmospheric Research,Boulder, Colorado, USA.

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MCGRAW ET AL.: RECONCILING SH RESPONSE TO VOLCANOES

1. Selection of CMIP5 Models (Figure S1 and Table S1)
10

Not all of the CMIP5 ‘historical’ forcing simulations include volcanic forcing. Following

11

previous studies (e.g. Santer et al. [2013]), we use a lower stratospheric temperature

12

anomaly (TLS) to determine whether or not a model demonstrates a strong enough re-13

sponse to volcanic forcing. Similar to Santer et al. [2013], we define the TLS as the zonal

14

mean temperature anomaly at 50 hPa from 82.5◦ S-82.5◦ N. For each model, the ensem-

15

ble mean TLS must exceed 0.5◦ C in at least one of the twelve months following the El

16

Chichón and Pinatubo eruptions for the to be included in our analysis. The mean TLS of17

the models that did exhibit a sufficient forced response, as well as the TLS of the models

18that were excluded, can be seen in Figure S1. This selection process is not sensitive to19

where we set the threshold; the same models were excluded if the threshold temperature20

was set at 0.25◦ C or at 0.75◦ C.

21

Figure S1 demonstrates that the 9 models that were excluded–the three CMCC mod-22els (CMCC-CM, CMCC-CMS, CMCC-CESM), FGOALS-g2, FIO-ESM, the three IPSL

23models (IPSL-CM5B-LR, IPSL-CM5A-MR, IPSL-CM5A-LR), and inmcm4–lack the clear

24

lower stratospheric temperature increase that is a hallmark of volcanic forcing. Other

25

studies (e.g. Santer et al. [2013], Lehner et al. [2016]) exclude the same models for simi-

26

lar reasons. Ultimately, a total of 37 models and 155 simulations are used in the CMIP5

27

analysis; a full list of these models and simulations is given in Table S1.

2. Midlatitude Jet Results (Figure S2)
28

In addition to analyzing changes in the circulation using the Southern Annular Mode

29(SAM), we also analyze changes in the midlatitude jet explicitly by calculating changes in

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the 10-meter zonal mean zonal winds. An advantage of using the 10-meter zonal winds is31that changes in these winds can be directly connected to changes in ocean surface stress,

32

thus linking atmospheric to potential oceanic changes. The results at 700 hPa and 10-m

33

are similar (not shown). The Southern Hemisphere midlatitude jet is calculated using the34zonal wind anomalies at all longitudes between 20-80◦ S, from 1970-2004 (1979-2004 for35

the MERRA reanalysis data). The jet position is defined by identifying the maximum

36of the zonal-mean zonal wind at the level of interest (in this case, 10 meters above the37surface), and then fitting a second-order polynomial through the wind maximum. The

38

midlatitude jet position and strength are defined as the location and the magnitude of39

the maximum of this polynomial. 10-meter zonal winds were not available for the CESM-40

Pacemaker simulations, so only the CESM1 Large Ensemble (CESM-LE) and MERRA

41

reanalysis were analyzed.

42

Figure S2 shows the histogram of anomalous NDJ jet position (Figure S2a) and jet

43strength (Figure S2b). Years following El Chichón (1982-1983) and Pinatubo (1991-441992) are in red, while all other years are in blue; the observed responses to El Chichón

45(dashed line) and Pinatubo (solid line) are shown in black. The eddy-driven jet results

46

present a similar picture to the SAM results (Figure 2), showing a poleward shift and a47

strengthening of the 10-m zonal winds following eruptions. In both cases, the internal

48

variability remains considerable, with equatorward shifts and weakening of the 10-meter

49

zonal mean zonal winds occurring after volcanoes in some simulations. The distributions

50for years following eruptions and for all other years for both jet position and jet strength51

are significantly different at 95% confidence using a two-sample K-S test. As with the52

SAM indices, the MERRA reanalysis results fall within the range of internal variability,

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53

indicating that, while the forced response to a volcanic eruption is that of a positive54

SAM/poleward shift/strengthening of the eddy-driven jet, internal variability is great55

enough that a negative SAM/equatorward shift/weakening of the eddy-driven jet can all

56

occur following a volcanic eruption.

57

The relationship between the eddy-driven jet and the state of the El Niño-Southern

58

Oscillation (ENSO) is less clear than the relationship between the SAM and ENSO (see59

Figure 4 and discussion). While the eddy-driven jet shifts poleward and strengthens

60

regardless of ENSO state, these changes are generally not significant, and do not exhibit61

a clear relationship with ENSO state (not shown). The eddy-driven jet is inherently more62

variable than the SAM–the eddy-driven jet is a maximum, while the SAM is a large-scale63

pattern calculated over 60◦ of latitude. Therefore, while the eddy-driven jet results support64

the conclusions drawn using the SAM, the effect of ENSO state on the eddy-driven jet

65

response to volcanoes is not as clear.

3. Combined CMIP5-CESM1 Results for ENSO State Analysis (Figure S3)
66

In addition to analyzing the CESM1 and CMIP5 results separately, we also combined all

67

simulations from CESM1 and CMIP5 and analyzed the relationship between the ENSO

68

state and the volcanically-forced SAM response. By combining the CESM1 and CMIP5

69

runs, we are able to analyze over 200 simulations across 2 eruptions, thereby giving us

70over 400 volcanically-influenced circulation anomalies. Figure S3 shows the results of71

the combined analysis. A significant forced positive SAM is seen following a volcanic

72

eruption for all three ENSO states, and is significant at 95% confidence using a one-sided

73

signed rank test. Additionally, the volcanically-forced SAM response during negative74

ENSO events is significantly more positive than the SAM response following negative

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MCGRAW ET AL.: RECONCILING SH RESPONSE TO VOLCANOES
75

ENSO events, with this significance improved to the 95% confidence level (again, using a76one-sided signed rank test).

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MCGRAW ET AL.: RECONCILING SH RESPONSE TO VOLCANOES

CMIP5 50 hPa Temperature Anomaly, 82.5S − 82.5N
6T Response
T Response, MMM
MERRA
No Response°C

420−2
CMCC−CESM
CMCC−CMS
CMCC−CMFGOALS−g2
FIO−ESMIPSL−CM5A−LR
IPSL−CM5A−MR
IPSL−CM5B−LR
inmcm41970 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004

YearFigure 1. 50 hPa zonal mean temperature anomalies for the CMIP5 models. The gray shading
indicates the range of temperature anomalies across the 37 CMIP5 models that demonstrated astrong enough temperature response to volcanic forcing (at least 0.5◦ C, denoted by the red line),
and the black line is the multi-model mean of these 37 models. The observed changes in 50 hPa
zonal mean temperature anomalies are shown in green. The 9 models that did not exhibit anadequate 50 hPa temperature response are shown in blue.

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X-7(a) Change in 10−m Zonal Wind Position
0.4
No Volcano
Volcano
MERRA, El Chichon
MERRA, Pinatubo

0.35

0.3

Frequency

0.25

0.2

0.15

0.1

0.05

0−8−6−4−20246

Change in Jet Position (°S)(b) Change in 10−m Zonal Wind Strength
0.4
No Volcano
Volcano
MERRA, El Chichon
MERRA, Pinatubo

0.35

0.3

Frequency

0.25

0.2

0.15

0.1

0.05

0−2−1.5−1−0.5

00.5

11.5

2

Change in Jet Strength (m/s)

Figure 2.

The distribution of NDJ changes in near-surface (10 meter) (a) jet position and(b) jet strength for years without volcanoes (blue lines) and years with volcanoes (red lines) for
the CESM-LE. The observed changes in jet position and strength following El Chichón (dashedlines) and Pinatubo (solid lines) are in black.

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MCGRAW ET AL.: RECONCILING SH RESPONSE TO VOLCANOESCESM1 and CMIP5No Volcano
Volcano21

SAM Index

126021442186

132

136
1974−1−2−3

Negative

NeutralPositive

ENSO StateFigure 3.

Mean NDJ SAM index as a function of ENSO state for all CESM-LE and CMIP5simulations. Years following volcanoes are in red, while all other years are in blue. Shaded boxes
indicate that the median value of the SAM index in years with volcanoes is significantly different
from that in years without volcanoes at 95% confidence. The numbers inside the boxes list thenumber of simulations in each ENSO state. The whiskers show the 95th percentile range acrossthe simulations.

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MCGRAW ET AL.: RECONCILING SH RESPONSE TO VOLCANOES

Table 1. CMIP5 ‘historical’ simulations used to calculate the circulation response to volcanicforcing.
Model
ACCESS 1-0
ACCESS 1-3
bcc-csm1-1
bcc-csm1-1
bcc-csm1-1
bcc-csm1-1-m
bcc-csm1-1-m
bcc-csm1-1-m
BNU-ESM
CanCM4CanCM4CanCM4CanCM4CanCM4CanCM4CanCM4CanCM4CanCM4CanCM4CanESM2
CanESM2
CanESM2
CanESM2
CanESM2
CCSM4
CCSM4
CCSM4
CCSM4
CCSM4
CCSM4
CESM1-BCG
CESM1-CAM5
CESM1-CAM5
CESM1-CAM5
CESM1-CAM5-1-FV2
CESM1-CAM5-1-FV2
CESM1-CAM5-1-FV2
CESM1-CAM5-1-FV2
CESM1-FASTCHEM
CESM1-FASTCHEM
CESM1-FASTCHEM
D R A F T

Ensemble
Memberr1i1p1
r1i1p1
r1i1p1r2i1p1
r3i1p1
r1i1p1r2i1p1
r3i1p1
r1i1p1
r1i1p1r2i1p1
r3i1p1
r4i1p1
r5i1p1
r6i1p1
r7i1p1
r8i1p1
r9i1p1
r10i1p1
r1i1p1r2i1p1
r3i1p1
r4i1p1
r5i1p1
r1i1p1r2i1p1
r3i1p1
r4i1p1
r5i1p1
r6i1p1
r1i1p1
r1i1p1r2i1p1
r3i1p1
r1i1p1r2i1p1
r3i1p1
r4i1p1
r1i1p1r2i1p1
r3i1p1

Model
CESM1-WACCM
CESM1-WACCM
CESM1-WACCM
CESM1-WACCM
CNRM-CM5CNRM-CM5CNRM-CM5CNRM-CM5CNRM-CM5CNRM-CM5CNRM-CM5CNRM-CM5CNRM-CM5CNRM-CM5CNRM-CM5-2
CSIRO-Mk3-6-0
CSIRO-Mk3-6-0
CSIRO-Mk3-6-0
CSIRO-Mk3-6-0
CSIRO-Mk3-6-0
CSIRO-Mk3-6-0
CSIRO-Mk3-6-0
CSIRO-Mk3-6-0
CSIRO-Mk3-6-0
CSIRO-Mk3-6-0
FGOALS-s2
FGOALS-s2
FGOALS-s2
GFDL-CM2p1
GFDL-CM2p1
GFDL-CM2p1
GFDL-CM2p1
GFDL-CM2p1
GFDL-CM2p1
GFDL-CM2p1
GFDL-CM2p1
GFDL-CM2p1
GFDL-CM2p1
GFDL-CM3
GFDL-CM3
GFDL-CM3

June 21, 2016, 9:44am

Ensemble
Memberr1i1p1r2i1p1
r3i1p1
r4i1p1
r1i1p1r2i1p1
r3i1p1
r4i1p1
r5i1p1
r6i1p1
r7i1p1
r8i1p1
r9i1p1
r10i1p1
r1i1p1
r1i1p1r2i1p1
r3i1p1
r4i1p1
r5i1p1
r6i1p1
r7i1p1
r8i1p1
r9i1p1
r10i1p1
r1i1p1r2i1p1
r3i1p1
r1i1p1r2i1p1
r3i1p1
r4i1p1
r5i1p1
r6i1p1
r7i1p1
r8i1p1
r9i1p1
r10i1p1
r1i1p1r2i1p1
r3i1p1
D R A F T

X - 10Model
GFDL-CM3
GFDL-CM3
GFDL-ESM2G
GFDL-ESM2M
GISS-E2-H
GISS-E2-H
GISS-E2-H
GISS-E2-H
GISS-E2-H
GISS-E2-H
GISS-E2-H
GISS-E2-H
GISS-E2-H
GISS-E2-H
GISS-ED-H-CC
GISS-E2-H
GISS-E2-R
GISS-E2-R
GISS-E2-R
GISS-E2-R
GISS-E2-R
GISS-E2-R
GISS-E2-R
GISS-E2-R
GISS-E2-R
GISS-E2-R
GISS-E2-R
GISS-E2-R
GISS-E2-R
GISS-E2-R
GISS-E2-R
GISS-E2-R-CC
HADCM3
HADCM3
HADCM3
HADCM3
HADCM3

D R A F T

MCGRAW ET AL.: RECONCILING SH RESPONSE TO VOLCANOES

Ensemble
Member
r4i1p1
r5i1p1
r1i1p1
r1i1p1
r1i1p1
r1i1p2r2i1p1r2i1p2r3i1p1
r3i1p2
r4i1p1
r4i1p2
r5i1p1
r5i1p2
r1i1p1
r1i1p1
r1i1p2
r1i1p3r2i1p1r2i1p2r2i1p3r3i1p1
r3i1p2r3i1p3r4i1p1
r4i1p2
r4i1p3r5i1p1
r5i1p2
r5i1p3r6i1p1
r1i1p1
r1i1p1r2i1p1
r3i1p1
r4i1p1
r5i1p1Model
HADCM3
HADCM3
HADCM3
HADCM3
HADCM3
HadGEM2-CC
HadGEM2-CC
HadGEM2-CC
HadGEM2-ES
HadGEM2-ES
HadGEM2-ES
HadGEM2-ES
MIROC5
MIROC5
MIROC5
MIROC5
MIROC5
MIROC-ESM
MIROC-ESM
MIROC-ESM
MIROC-ESM-CHEM
MPI-ESM-LR
MPI-ESM-LR
MPI-ESM-LR
MPI-ESM-MR
MPI-ESM-MR
MPI-ESM-MR
MPI-ESM-P
MRI-CGCM3
MRI-CGCM3
MRI-CGCM3
MRI-CGCM3
MRI-ESM1
NorESM1-M
NorESM1-M
NorESM1-M
NorESM1-ME

June 21, 2016, 9:44am

Ensemble
Member
r6i1p1
r7i1p1
r8i1p1
r9i1p1
r10i1p1
r1i1p1r2i1p1
r3i1p1
r1i1p1r2i1p1
r3i1p1
r4i1p1
r1i1p1r2i1p1
r3i1p1
r4i1p1
r5i1p1
r1i1p1r2i1p1
r3i1p1
r1i1p1
r1i1p1r2i1p1
r3i1p1
r1i1p1r2i1p1
r3i1p1
r1i1p1
r1i1p1r2i1p1
r3i1p1
r4i1p1
r1i1p1
r1i1p1r2i1p1
r3i1p1
r1i1p1

D R A F T