Mechanisms of Multidecadal Variability in the CM2.1

Transcription

1 Mechanisms of Multidecadal Variability in the CM2.1 Preliminary results from analysis of atmosphere and ocean processes associated with the leading pattern of the CM2.1 multi-decadal SST variability Y. Kushnir and N. Naik / GloDecH meeting, 8 Feb 2011

2 RMS of 5m Temperature 2

3 RMS of 5m Temperature 2

4 PCA of 5m Temperature PC1 = 18% PC2 = 10% smoothed with 1 pass of 121 Patterns appear in quadrature in time. Does this imply propagation? 3

5 Vertical Structure (Atl x-average) PC1 T o (5m) PC2 T o (5m) Regression Correlation 4

6 Time Scales of Variability Auto Corr PC1 Autocorrelation implies ~15 year period Time series are in quadrature with PC2 lagging PC1 by 3-4 years X-Corr PC1 & PC2 Auto Corr PC2 PC2 Leads PC1 Leads Lag (years) 5

7 SST evolution PC1 lags by 4 years Damped oscillations with transition between two states. Impression of southward propagation PC1 T o (5m) corr lag 0 PC2 T o (5m) corr PC1 leads by 4 years 6

8 SLP EOF1 - models NAO SLP EOF1 SLP variability dominated by annular mode pattern (NAO) explaining 36% of total variance. SST footprint similar to observed, NAO forced, SST tripole, somewhat different from SST PC1 Autocorrelation implies a very weak oscillation of about the same period as that of SST. SST corr with SLP PC1 Auto Corr SLP PC1 PC1 & T o (5m) corr 7

9 SLP EOF1 - models NAO SLP EOF1 SST corr with SLP PC1 SLP variability dominated by annular mode pattern (NAO) explaining 36% of total variance. SST footprint similar to observed, NAO forced, SST tripole, somewhat different from SST PC1 Autocorrelation implies a very weak oscillation of about the same period as that of SST. Auto Corr SLP PC1 7

10 SLP EOF1 - models NAO SLP EOF1 SST corr with SLP PC1 SLP variability dominated by annular mode pattern (NAO) explaining 36% of total variance. SST footprint similar to observed, NAO forced, SST tripole, somewhat different from SST PC1 Autocorrelation implies a very weak oscillation of about the same period as that of SST. Auto Auto Corr Corr SLP of PC1 Lowpass SLP PC1 7

11 Corr SLP PC1 & SST PC1 SLP EOF1 NAO forcing SLP variability dominated by annular mode pattern (NAO) explaining 36% of total variance. PC has very weak oscillation of about the same period as that of SST. SLP lags SLP Leads Auto Corr PC1 8

12 Corr SLP PC1 & SST PC1 SLP EOF1 SLP lags NAO forcing SLP Leads SLP variability dominated by annular mode pattern (NAO) explaining 36% of total variance. PC has very weak oscillation of about the same period as that of SST. Corr SST PC1 yrs & SLP PC1 yrs Auto Corr PC1 SLP Leads SST Leads 8

13 T 5 T5 PC1 correlation with T 5 & SLP PC1 lags by 4 years SLP leads by 4 years SLP PC1 lags by 1 year SLP leads by 1 year lag 0 lag 0 9

14 PC1 of T 5 - SLP correlation PC1 lags by 4 years PC1 lags by 4 years lag 0 lag 0 PC1 leads by 4 years PC1 leads by 4 years SLP from YEARS SLP from YEARS

15 SST & Heat transport H-trans leads by 4 years PC1 lags by 4 years lag 0 lag 0 PC1 leads by 4 years H-trans lags by 4 years 11

16 m H-content & H-ytrans Contours = SST Corr SST PC1 & 50 N SST Lags SST Leads 12

17 m H-content & H-ytrans Contours = SST Corr SST PC1 & 50 N SST Lags SST Leads 12

18 NAO & Heat transport H-trans leads by 2 years Corr SLP PC1 - H-ytrans lag 0 Corr SLP PC1 - curl τ NAO leads by 2 years 13

19 NAO & AMV relationships Auto Corr SST PC1 (Warm SPG) 14

20 NAO & AMV relationships Auto Corr SST PC1 (Warm SPG) Corr SST PC1 & PC2 (Warm SPG & warm STG) PC1 Lags PC1 Leads 14

21 NAO & AMV relationships Auto Corr SST PC1 (Warm SPG) Corr SST PC1 & PC2 (Warm SPG & warm STG) PC1 Lags PC1 Leads Corr SLP PC1 & SST PC1 (Neg NAO & Warm SPG) SLP lags SLP Leads 14

22 NAO & AMV relationships Auto Corr SST PC1 (Warm SPG) Corr SST PC1 & PC2 (Warm SPG & warm STG) PC1 Lags PC1 Leads Corr SLP PC1 & SST PC1 (Neg NAO & Warm SPG) Corr SLP PC1 (Neg NAO) & H- 50 N SLP lags SLP Leads SLP Lags SLP Leads 14

23 References Bjerknes (1964), Kushnir (1994), Curry and McCartney (1998 (with Joyce) and 2001) Delworth et al. (1993), Delworth and Greatbatch (2001) Eden and Willebrand (2001), Eden and Junge (2001), Eden and Greatbatch (2003) Dong and Sutton (2005), Knight et al. (2005 and 2006), Danabasoglu (2008)... 15

24 Observed SST PC1 18% PC2 15% 16

25 Observed SST PC1 18% PC2 15% 16

26 Questions? What is the role of salt? Sea ice? What is the relation to convection? How does the atmosphere feel the ocean? What determines the time scale? Is the mode realistic? What are the impacts on land? the tropics (SST & ITCZ)? 17