SUPPLEMENTARY INFORMATION

Transcription

1 SUPPLEMENTARY INFORMATION DOI: /NGEO2571 Mechanisms of change in ENSO-induced tropical Pacific rainfall variability in a warming climate Ping Huang and Shang-Ping Xie Comparison with the results in Power et al and Chung et al. 2014: In Power et al and Chung et al (P13C14), the moisture budget associated with the changes in ENSO-driven rainfall variability is decomposed into the thermodynamic and dynamic components in a similar way. In P13C14, the ENSO-driven thermodynamic anomaly is defined as δ TH = 1 ρg δ MCD = 1 ρg p s ( ) ( u 0 [ δ q] ) 0 p s ( ) ( [ δ u]q 0 ) 0 dp and the dynamic anomaly as dp, in which δ indicating the ENSO-driven anomaly is equivalent to the prime in the equations of the present study. Therefore, the change in the two components in P13C14 can be presented in the present symbols as ΔT H Δ ω q ΔMC D Δ ( ) ( Δω q + ω Δ q ) and ( ω q) ( Δ ω q + ω Δq). As discussed in the main text and shown in Supplementary Fig. 1, the ratio of q to q is much smaller than the ratio of ω to ω, i.e. the ENSO-driven variability of moisture is relatively small. Thus, the thermodynamic change in P13C14 ΔT H should be small and the dynamic change should be dominant. This derivation applied to simplify Eq. 1 to Eq. 2 in the present study is consistent with the results in P13C14. For the dynamic change in P13C14, the present study further decomposes it into two components Δ ω q and ω Δq, which are induced by circulation variability change and mean moisture change, respectively. Different from the terminology in P13C14, the change contributed by circulation variability change Δ ω q is named as "dynamic component" and the change by mean moisture change ω Δq as "thermodynamic component", and their relative roles and attributions are discussed. NATURE GEOSCIENCE 1

2 In summary, although the "thermodynamic" change is demonstrated to be a comparable component to the "dynamic" change in the present study while the "thermodynamic" change is relatively small in P13C14, these "different" results do not conflict with each other because of the different terminologies. The present study further clarifies the mechanisms for the "dynamic component" in P13C14. 2

3 Supplementary Figure S1 Simulated historical ENSO-related SST variability in the 18 CMIP5 models. 3

4 Supplementary Figure S2 Simulated historical ENSO-driven rainfall variability in the 18 CMIP5 models. 4

5 Changes in ENSO-driven rainfall variability (Fig. 1d) ( ) Δ P ~ Δq ω + q Δ ω + Δω q + ω Δ q Thermodynamic component (Fig. 2a) Δq ω + Dynamic component (Fig. 2c) q Δ ω Two negligible terms related to ENSO-driven moisture variability (Supp. Fig. S5) Increases in mean moisture (Supp. Fig. S4) Historical ENSOdriven circulation variability (Fig. 2b) Historical mean moisture (Supp. Fig. S4) Changes in ENSO-driven circulation variability (Fig. 2d) Δ ω = Δ ω a + Δ ω s Absolute increases in background SST Amplitude changes in ENSO-driven circulation variability (Fig. 3b) + Structural changes in ENSO-driven circulation variability (Fig. 4b) Amplitude changes in ENSO-driven SST variability (Fig. 3a) { Changes in ENSOdriven SST variability (Fig. 1c) Structural changes in ENSO-driven SST variability (Fig. 4a) Spatially relative changes in background SST (Fig. 4d) Supplementary Figure S3 Diagram illustrating the formation mechanisms of the changes in ENSO-driven rainfall variability. 5

6 Supplementary Figure S4 Historical climatologies (a, b), climatology changes (c, d), historical ENSO-driven anomalies (e, f), and changes in ENSO-driven anomalies (g, h) in surface specific humidity (left) and 500-hPa vertical pressure velocity (right) in multi-model ensemble mean. Regional root-mean-square (RMS) shown at the upper right corner is calculated to represent the magnitude. 6

7 Supplementary Figure S5 The two terms related to ENSO-driven specific humidity variability in Eq. 1. They are both much weaker than the thermodynamic and dynamic components shown in Fig. 2a,b. 7

8 Supplementary Figure S6 The sum of the thermodynamic and dynamic components (shaded) and the changes in ENSO rainfall (contours with interval 0.05 mm day 1 and dashed negative contours) in the individual models. The pattern correlation coefficient between the sum of the thermodynamic and dynamic components and the ENSO rainfall changes in each model is shown in the bottom-left corner. 8

9 Supplementary Figure S7 The four components consisted of changes in ENSO-driven rainfall variability and their sum. 9

10 Supplementary Figure S8 (left) Inter-model EOF modes (1 6) of the structural changes in ENSO SST Δ T s. The percentage of the variance explained by each mode and the expansion coefficient ( e i ) for the multi-model ensemble structural changes in ENSO SST is shown at the top-right corner of each left panel. (Right) Regression patterns of the structural changes in ENSO circulation ( Δ ω s1 ) onto the principal components (PCs) associated with the inter-model EOF modes of 10

11 the structural changes in ENSO SST. The percentage of the variance of Δ ω s1 explained by each PC is shown at the upper right corner of each panel. The product of the root-mean-square (RMS) of each regression pattern and the expansion coefficient e i is shown at the upper right corner of each panel. Supplementary Figure S9 As in Supplementary Figure S8, but for the modes

12 Supplementary Figure S10 Reconstruction (left) of the multi-model ensemble structural changes in ENSO SST using the truncated EOF modes and the residual (right) related to the reconstruction. 12

13 Supplementary Figure S11 The structural changes in ENSO circulation induced by the structural changes in ENSO SST estimated by the EOF modes ( Δ ω s1, left) and the related residuals ( Δ ω s2, right). 13