COREII studies in Kiel

1
CORE-II studies in Kiel

• General aim mechanisms of interannual-decadal
  variability of oceanic phenomena
• atmospheric forcing vs. internal dynamics
• wind stress vs. buoyancy forcing
• propagation of anomaly signals
• Experiments building on DRAKKAR hierarchy, based
  on NEMO (Madec, 2008) ORCA05 025

2
ORCA05 Experiments under CORE v1 Forcing (Subset)
(1) Strong polar SSS, weak elsewhere (2) weak
polar 3D salinity, weak SSS
3
Topics

• Subpolar North Atlantic dynamics of gyre
  variability? Can it be observed by altimetry?
• Changes in freshwater and heat content trend or
  variability? Cause? Effect on MOC?
• MOC role of buoyancy fluxes, wind stress?
  intrinsic variability? Agulhas? how detect
  long-term changes?
• Tropical Pacific decline of subtropical-tropical
  cells?
• Tropical Atlantic Atlantic Ninos Benguela
  Ninos?
• SW Pacific what caused recent warming trend?
• Leeuwin Current heat budget role of advection
  (ITF)
• Agulhas role of upstream perturbations effects
  on MOC

4
Examples

• Subpolar North Atlantic dynamics of gyre
  variability? Can it be observed by altimetry?
• Changes in freshwater and heat content trend or
  variability? Cause? Effect on MOC?
• MOC role of buoyancy fluxes, wind stress?
  intrinsic variability? Agulhas? how detect
  long-term changes?
• Tropical Pacific decline of subtropical-tropical
  cells?
• Tropical Atlantic Atlantic Ninos Benguela
  Ninos?
• SW Pacific what caused recent warming trend?
• Leeuwin Current heat budget role of advection
  (ITF)
• Agulhas role of upstream perturbations effects
  on MOC

5
Australia
Tasmania
6
Observed T (1991 2005) surface
average 0-800m
7
Model simulation (Mean 0-800m)
8
Long term context
9
SSH (and heat content) Propagating signal in
Pacific Ocean
SSH increase in the last years and signal
propagation is reproduced in the model Trend
is part of variability and propagating westward
10
Hemispheric scale SSH signal
Linear SSH-Trend from 1993 to 2002 SSH anomaly
at 35S for REF05 and REF025 ? no trend but
variability

• SSH at 35S
• - No trend
• westward signal
• propagation gt Rossby wave

11
Sensitivity experiment PAC05
Interannual wind forcing over Pacific Ocean only
12
Comparison REF05 vs. PAC05 upper ocean heat
content
Upper ocean heat content (0-450m) Rossby wave
signal in the Indian Ocean similar in both
experiments
13
(2) Subpolar North Atlantic Changes in the
freshwater and heat budget Background
observed freshening trend
between the late 1960s and mid-1990s
reversal after the mid-1990s
correlated with changes in heat content
14
(No Transcript)
15
(No Transcript)
16

Issues (I)
Initialization and spin-up
absolute
relative to time-mean
Atlantic MOC strength at 45N in climatological
and interannual (ensemble runs)
17
(II) Salinity restoring

• Alternative approach for polar regions
• strong (20d) surface SSS-restoring
• OR-
• - weak (180d) full-depth restoring (T and S)

18
(No Transcript)
19
Publications using Kiel CORE CIAF runs
Biastoch, Böning, Lutjeharms, 2008 Agulhas
leakage dynamics affects decadal variability in
Atlantic overturning circulation, Nature, 456,
489-492 Biastoch, Lutjeharms, Böning, Scheinert,
2008 Mesoscale perturbations control inter-ocean
exchange south of Africa, Geophys. Res. Lett.,
35 Biastoch, Böning, Getzlaff, Molines, Madec,
2008 Mechanisms of interannual - decadal
variability in the meridional overturning
circulation of the mid-latitude North Atlantic
Ocean, J. Climate, 21, 65996615. Biastoch, Beal,
Lutjeharms, Casal, 2009 Variability and
coherence of the Agulhas Undercurrent in a
high-resolution OGCM, J. Phys. Oc., 39, in
press Van Sebille, Biastoch, van Leeuwen, de
Ruijter, 2009 A weaker Agulhas Current leads to
more Agulhas leakage, Geophys. Res. Lett.,
36 Siedler, Rouault, Biastoch, Backeberg, Reason,
Lutjeharms, 2009 Modes of the southern extension
of the East Madagascar Current, JGR, 114 Feng,
Biastoch, Böning, Caputi, Meyers, 2008
Seasonal-interannual variations of upper ocean
heat balance off the west coast of Australia,
JGR, 113 Alvarez-Garcia, F., M. Latif, and A.
Biastoch, 2008 On multidecadal and quasi-decadal
North Atlantic variability, J. Climate, 21,
3433-3452 Durgadoo, Lutjeharms, Biastoch,
Ansorge, 2008 The Conrad Rise as an obstruction
to the Antarctic Circumpolar Current, Geophys.
Res. Lett., 35 Lübbecke, Böning, Biastoch, 2008
Variability in the subtropical-tropical cells and
its effect on near-surface temperature of the
equatorial Pacific a model study, Ocean Sci., 4,
73-88, 2008 Latif, Böning, Willebrand, Biastoch,
Alvarez, Keenlyside, Pohlmann, 2007 Decadal to
multidecadal variability of the Atlantic MOC
Mechanisms and Predictability, in Schmittner, A.
et al. (Eds.) Ocean Circulation Mechanisms and
Impacts, AGU Monograph 173. Submitted
Lorbacher, Dengg, Böning, Biastoch Regional
patterns of sea level change related to
variability and trends in the MOC. In
preparation Scheinert, Böning, Biastoch
Changes in subarctic freshwater and heat content
orchestrated by the wind-driven circulation.
Schwarzkopf, Böning,
Biastoch Decadal variability of heat content in
the Southern Hemisphere subtropical thermocline.
Behrens, Böning,
Biastoch Interannual decadal variability of
the Indonesian Throughflow Mechanisms and
pathways.