Review High Resolution Modeling of Steric Sea-level Rise Tatsuo Suzuki (FRCGC,JAMSTEC)

1
Review High Resolution Modeling of Steric
Sea-level RiseTatsuo Suzuki (FRCGC,JAMSTEC)

• Understanding Sea-level Rise and Variability
• 6-9 June, 2006
• Paris, France

2
Introduction

• Sea level change under global warming in medium
  and low resolution AOGCMs in the IPCC TAR
  (Resolution of the ocean component lt 1º?1º)
• The models projections show a considerable
  spread. (Different models predict different
  distributions of sea level change.)

3

• Some simulations show common features of sea
  level change under global warming
• Sea level rise in the Arctic Ocean
• Dipole pattern in the North Atlantic
• Sea level rise along the northern boundary of the
  ACC
• Reduced sea level rise in the Southern Ocean
• Sea level rise in the Kuroshio extension

Sea level change in high resolution model
4
Model for Interdisciplinary Research on Climate
(MIROC) version 3.2

• MIROC_hi
• Atmosphere T106, 56 vertical levels
• Ocean 0.28125º?0.1875º, 48 vertical levels
• MIROC_med
• Atmosphere T42, 20 vertical levels
• Ocean 1.4º?0.56º(near equator), 44 vertical
  levels

In both models, the same physics have been used.
5
Sea surface height (SSH) averaged between
1981-2000(20C3M)
MIROC_hi
MIROC_med

Sea level patterns corresponding to major ocean
gyres are well reproduced.
6
Changes in SSH under global warming (A1B
20C3M difference between the last two decades of
the 21st century and 20th century )
MIROC_hi
MIROC_med
The regions with large sea level changes are more
restricted to specific areas and the magnitudes
are more pronounced in MIROC_hi than
MIROC_med. These differences are caused by
representation of the detailed ocean structure.
7
SSH averaged between 1981-2000 (20C3M)
MIROC_hi
MIROC_med
Sea level distribution associated with the
subpolar Gyre is realistically represented in
MIROC_hi
8
SSH averaged between 1981-2000 (20C3M)
MIROC_hi
MIROC_med
Sea level distribution associated with the
subpolar Gyre is realistically represented in
MIROC_hi. MIROC_hi represents the sea level
distribution associated with the current system
east of the Philippines.
9
Changes in SSH under global warming (A1B 20C3M)
MIROC_hi
MIROC_med
Color difference of sea surface height between
last two decades of 21st century and 20th
century (cm) Contour sea surface height during
last two decades of 20th century (cm)
MIROC_hi exhibits a region of reduced sea level
rise in the North Pacific Gyre.
10
Changes in SSH under global warming (A1B 20C3M)
MIROC_hi
MIROC_med
MIROC_hi exhibits a region of reduced sea level
rise in the North Pacific Gyre. In MIROC_hi,
there is a reduced sea level rise east of the
Philippines.
11
SSH averaged between 1981-2000 (20C3M)
MIROC_hi
MIROC_med
12
SSH and Surface current vector averaged between
1981-2000 (20c3m)
MIROC_med
MIROC_hi
The Kuroshio and the Kuroshio extension in
MIROC_hi is realistically represented.
13
Changes in SSH under global warming (A1B 20c3m)
MIROC_hi
MIROC_med
There was a reduced sea level rise north of the
Kuroshio Current and an enhanced sea level rise
to the south in MIROC_hi.
Kuroshio acceleration is caused by changes in
wind stress and the consequential spin-up of the
Kuroshio recirculation (Sakamoto et al., 2005).
14
Extreme sea level rise caused by warm ocean eddies

• Warm ocean eddies increase the risk of flooding
  in the coastal areas.

Okinawa Island had flood-damage on the 22nd of
July 2001 without the passage of atmospheric low.
The temporal high sea level is responsible for
the warm eddy above 15 cm (Tokeshi and Yanagi,
2003 Nozaki et al 2003, etc.).
15
RMS of sea level variability (eddy component)
during the 20th century(cm)
TOPEX/POSEIDON 1991-2001
MIROC_hi (20C3M)
The regional distribution of sea level
variability is well represented in MIROC_hi.
16
Changes in RMS of sea level variability (eddy
component)under global warming (A1B -20C3M)
Globally averaged RMS of sea level variability
(cm)
0.3cm
-12 -3 3 12cm
The enhanced eddy activities are confined to
specific areas. Those area are overlapped with
the enhanced sea level rise around some coastal
regions and Islands.
Flood risk increases.
17
Summary

• Sea level changes in MIROC_hi are similar to
  that in MIROC_med on a large scale.
• High resolution model presents more detailed
  ocean structure changes under global warming.
• High resolution model can estimate changes in
  extreme sea level variability associated with
  ocean eddies.

18
Experiments

• Spin-up
• 109-years integration forced by fixed external
  condition for 1900 for MIROC_hi
• 560-years integration forced by fixed external
  condition for 1850 for MIROC_med
• Control-run
• 100-years integration for MIROC_hi
• 400-years integration for MIROC_med
• 20C3M-run
• Forced by historical data during the 20th century
• A1B-run
• IPCC SRES A1B scenario
• B1-run
• IPCC SRES B1 scenario

Some trends are shown in control runs. So, we
subtract these control trends from 20C3M run and
scenario runs.
19
1. Steric contribution (thermal expansion and
haline contraction) to Globally averaged sea
level rise

• estimated indirectly from density changes as the
  equivalent volume change under mass conservation
  as the Boussinesq approximation was adapted in
  the ocean model
• ?H globally averaged sea level rise,
• S surface area of the ocean,
• Z ocean depth, ? in situ density,
• ?? difference from the reference state

2. Contributions of ice-sheet melt estimated
using the methods of Wild et al. 2003
20
Global averaged heat content
Can 20th Century Sea Level changes be Explained?
Model (20C3M-run) vs. observation (Levitus-data)
21
Decadal variation of Sea Level (mm/year) during
1950-1998Regression (Sea level vs. NAO index)
Can 20th Century Sea Level changes be Explained?
Observation (Ishii-data)
Model (20C3M-run)
North Atlantic Oscillation Index

• Distribution is reproduced.
• Phase is different.

22
Decadal variation of Sea Level (mm/year) during
1950-1998Regression (Sea level vs. NP index)
Can 20th Century Sea Level changes be Explained?
Observation (Ishii-data)
Model (20C3M-run)
North Pacific Index

• Distribution is reproduced.
• Phase is different.

23
Sea level trend (mm/year) during 1993-2003Model
vs. Observation (TOPEX/POSEIDON)
Can 20th Century Sea Level changes be Explained?

• Sea level rise along North boundary ACC and
  Kuroshio-extension is reproduced.
• Decadal pattern of sea level is overlapped. (NAO
  etc.)

24
Heat content
Levitus vs. MIROC(Hi and Mid resolution)
25
Globally averaged sea level rise

• The steric contribution during 21st century in
  MIROC_hi is similar to that in MIROC_med.
• The contributions of the Greenland and Antarctic
  ice-sheet exhibited opposite tendencies in both
  models, as in previous estimations Church et
  al., 2001
• The amplitude of ice-sheet melt in MIROC_hi was
  larger than that in MIROC_med

Different sensitivity
A1B run induced global warming of about 4.0?C in
MIROC_hi and 3.4?C in MIROC_med at the end of the
21st century, respectively.
26
Why steric contribution in MIROC_hi is similar to
that in MIROC_med in spite of the different
sensitivity?

• Total heat flux into the ocean for the 21st
  century is similar in the both models
• The upper ocean in MIROC_hi warms up more
  than that in MIROC_med (different heat uptake?).

The reasons for these differences are current
problems.
27
difference of sea level distribution between
2080-2100 in A1B run and 1980-2000 in 20C3M run
Spatial standard deviation of the decadal-mean
field of sea level change with respect to the
control run
28
Sea level rise trend (thermo-steric
contribution) CO2 1 increase run
total
upper 450m
lower 450m
29
Sea level rise trend (halo-steric contribution)
CO2 1 increase run
total
upper 450m
lower 450m
30
Zonal averaged sea level rise (A1B-run)
Future projection of the sea level change
20812100
20612080
cm
20412060
20212040
20012020
Latitude