Rory Bingham, Peter Clarke & Phil Moore

Transcription

1 The physical processes underlying interannual variations in global mean sea level as revealed by Argo and their representation in ocean models Rory Bingham, Peter Clarke & Phil Moore Newcastle University

2 The steric component of global mean sea level from Argo Steric component of global mean sea level (66S-66N; 0-900m) from Argo

3 The steric component of global mean sea level from Argo Steric component of global mean sea level from Argo

4 Comparing total and steric global mean sea level Argo GMSH Altimetry GMSL (detrended)

5 A decomposition of global mean steric height into 100m layers Interannual GMSH from Argo Interannual GMSH per 100m layer from Argo Cross correlation array

6 Global mean steric height from 0-100m and m layers Layer 1 (0-100 m) Layer 2 ( m) clear anti-correlation between 0-100m and m layers variability below 300m much weaker, but is cumulative

7 Global mean steric height from 0-100m and m layers Layer 1 (0-100 m) Layer 2 ( m) clear anti-correlation between 0-100m and m layers variability below 300m much weaker, but is cumulative

8 Contribution to GMSH from upper layer (0-100 m) GMSH (0-900m) Layer 1 (0-100 m)

9 Contribution to GMSH from upper layer (0-100 m) GMSH (0-900m) Layer 1 (0-100 m)

10 EOF analysis of steric height from 0-100m and m layers Leading EOF from layer 1 (0-100m) Principal Components Layer 1 (0-100 m) Layer 2 ( m) Leading EOF from layer 2 ( m)

11 Global mean steric height from 0-100m and m layers Layer 1 (0-100 m) Layer 2 ( m) GMSH (solid) PCs (dashed)

12 mm; SST ºC Global mean steric height from layer 1 (0-100m) and NIN03.4 GMSH Layer 1 (0-900m) (0-100 m) Layer NIN (0-100 m)

13 mm; SST ºC Global mean steric height and NIN03.4 GMSH (0-900m) GMSH (0-900 m) Layer 1 (0-100 m) NIN03.4

14 mm; SST ºC Global mean steric height and NIN03.4 GMSH (0-900m) GMSH (0-900 m) Layer 1 (0-100 m) NIN03.4

15 Steric height analysis for HadCM3 GMSH Layer 1 (0-100 m) Global mean steric height in HadCM3 (green) largely determined by the upper 100m (red)

16 Steric height analysis for HadCM3 GMSH NINO3 Consequently interannual global mean steric height fluctuations in HadCM3 (green) are largely driven by ENSO (NINO3 index - magenta)

17 Steric height EOF analysis for HadCM3 EOF1: layer 1 (0-100m) EOF1: layer 2 ( m) EOF Principal components (dashed) and corresponding layer global means (solid) Layer 1 (0-100 m) Layer 2 ( m) EOF1 layer 1 EOF1 layer 2 Nino4 index

18 The vertical structure of Argo steric height variability Standard dev. of interannual steric height variability Standard dev. of interannual steric height variability function of reference depth H Argo HadCM3 OCCAM

19 Conclusions: GMSH and ENSO Depth decomposition shows ENSO to be dominant mode of interannual steric sea level Responsible for the global means of the 0-100m and m layers 0-100m and m layers compensatory ENSO leaves small direct trace in GMSL The strong El Nino/La Nina events of 2009/2010 are seen in GMSH upper layer signal larger relative to lower ENSO dominant steric signal in models Upper layer GMSH not compensated by lower layer: ENSO dominates GMSH Over-estimation of interannual GMSH fluctuations

20 The contribution to GMSH from below 300m Interannual GMSH from Argo Interannual GMSH per 100m layer from Argo Cross correlation array

21 Global mean steric height from 0-300m and m layers 0-300m and m layers contrib. equally 0-300m layer dominates GMSH (0-900m) Layer 1+2 (0-300 m) Layer 3 ( m)

22 Global mean steric height: equatorial vs. mid-latitude contributions GMSH Equatorial (20S-20N) contribution Total solid 0-300m dashed m dotted GMSH Mid-high lat. contribution Total solid 0-300m dashed m dotted

23 EOF analysis of steric height from m layer Leading EOF Principal component GMSH ( m)

24 Area mean steric height timeseries from m layer North Atlantic South Atlantic North Pacific

25 Global mean steric height from m layer Principal component GMSH ( m) Area mean ( m) steric height over 3 key regions

26 Area mean steric height timeseries from 0-900m layer North Atlantic South Atlantic North Pacific

27 Area mean 0-900m steric height (solid) and sea level (dashed) North Atlantic South Atlantic North Pacific

28 Global mean steric height from m layer Principal component GMSH excluding equator (0-900 m) Area means over 3 key regions (steric solid; total - dashed)

29 Leading EOF of interannual atmospheric surface pressure Principal component Area means steric solid total dashed

30 Leading EOF of interannual atmospheric surface pressure GMSH Principal component

31 Global mean steric height: Northern vs. Southern hemispheres GMSH (exc. eq.) N. Hemisphere (>20N) contribution Total solid 0-300m dashed m dotted GMSH (exc. eq.) S. Hemisphere (>20S) contribution Total solid 0-300m dashed m dotted

32 Conclusions ENSO dominates IA density variations First period ( ): Net equatorial (ENSO) contribution to GMSH is small Mid-high latitude contribution dominates Spread equally between 0-300m and m layers Part of global atmospherically teleconnected mode which sees a slow fall/rise in total/steric sea level in three basins (10 cm in North Pacific) Primarily from Southern Ocean 4 mm drop in GMSL Second period ( ): Net mid-high latitude contribution to GMSH is weak Equatorial ENSO response dominates (strong event) Confined to upper 300 m layer Longer record required!