Transcript An atmosphere-ice-ocean reanalysis of the Arctic for the IPY Lars Axell and Per Kållberg Research and Development Swedish Meteorological and Hydrological Institute.

An atmosphere-ice-ocean reanalysis of the Arctic
for the IPY
Lars Axell and Per Kållberg
Research and Development
Swedish Meteorological and Hydrological Institute
Outline
•Description of the coupled model system
•Results from the Arctic reanalysis
•Conclusions so far
•Outlook
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Description of the coupled model system
•Atmosphere:
–Circulation model: HIRLAM version 7.2
–Data assimilation: 4D-Var 6-hour cycle
–Observations: TEMP, PILOT, AIREP, SYNOP, SHIP,
AMSU-A over sea and ice – from ECMWF MARS archive
–40 hybrid levels (top at 10 hPa)
–lateral boundary conditions – from ERA-interim
•Ocean:
–Circulation model: HIROMB version 4.1
–Data assimilation: Optimal Interpolation (OI)
–Observations: NCEP SST, AMSR-E SIC, S/T profiles
(ships, buoys, gliders, moorings, Ice-Tethered Profilers)
–208 z-levels (5-25 m resolution)
•Horizontal grid: 306x306, ~12 nm resolution (both HIRLAM
and HIROMB)
•Rotated coordinate system: South pole at 4ºS, 0ºW (both
HIRLAM and HIROMB)
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model domain and bathymetry of HIROMB
Hiromb OI coast following structure functions
Description of the coupled model system
(cont.)
•Exactly the same horizontal grid as HIRLAM (no separate coupler)
•Bathymetry data:
– International Bathymetric Chart of the Arctic Ocean (IBCAO)
– Regional data from the Baltic Sea
– Scripps Institution of Oceanography, UCSD (satellite altimetry and depth soundings)
•47 rivers (annual means)
•Open boundaries:
– Salinity and temperature from World Ocean Atlas 2005, monthly means
– Sea levels: inverse barometer effect
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The coupling
Analyses
performed
here
•Coupling time step: 6 hours
•HIROMB is forced by HIRLAM-fields (winds, air temperature, air pressure, cloudiness, etc.)
•HIRLAM reads fields of ice concentration and SST from HIROMB
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•HIROMB’s analysis after its forecast; HIRLAM’s analysis before its forecast
Number of ocean observations (2005-2007)
(note the logarithmic scale)
temperature
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salinity
March 2005
hirlam-hiromb
sea ice concentration %
September 2005
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era_interim
Monthly mean fields
March 2005
surface salinity
surface temperature
September 2005
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monthly mean ocean-air net energy exchange, march 2006
red=downwards, blue=upwards
hirlam/hiromb
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era interim
monthly mean ocean net energy exchange, september 2006
hirlam-hiromb
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era interim
hiromb ice-drift
march 2006
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hirlam 10-metre wind
march 2006
hiromb ice-drift
september 2006
hiromb ice-drift
March 2006
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hirlam 10-metre wind
september 2006
hirlam 10-metre wind
March 2006
hirlam wind-stress
march 2006
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hirlam wind-stress
september 2006
Arctic Sea Ice Extent
(reanalysis updated until 200610)
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Ice extent = sum of area with at least 15 % sea ice
Transect across Fram Strait
Date: 2005-09-15 (Greenland left)
•Northward transport of high-saline, warm
water west of Svalbard
•Southward transport of low-saline, cold water
off Greenland’s shelf
•Data assimilation of mooring data (S/T)
•Net southward volume transport: 1 Sverdrup
(mean 2005)
•Net northward heat transport: 10 TW
(mean 2005)
Velocity (cm/s)
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Salinity (psu)
Temperature (°C)
Fluxes through Fram Strait
(monthly means)
2005 mean: +9.5 TW
2006 mean: -25.4 TW
2007 mean: ?
Volume flux (unit: Sverdrup)
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Heat flux (unit: TW) (0 deg reference)
Heat budget (fluxes in TW into the Arctic)
(proper Arctic except Barents Sea)
Bering
Strait
Lancaster Strait
+
Fram
Strait
Nares Strait
2005
SpitzbergenTotal
Russia
+3.1
-11.5
+9.5
+19.2
+20.3
+1.2
-10.9
-25.4
+22.1
-13.0
2006
preliminary
•Large total differences between 2005 and 2006
•Largest difference in the Fram Strait
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Changes in total ice volume
(proper Arctic except Barents Sea)
2005-04-16 12:00 UTC
2006-04-24 12:00 UTC
2005-09-18 00:00 UTC
2006-09-29 06:00 UTC
Change:
8600 km3
Change:
5622 km3
Ice decrease 2005:
Ice export 2005:
5 622 km3
482 km3 (9%)
Ice decrease 2006:
Ice export 2006:
8600 km3
377 km3 (4%)
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------------------------------------------------------------------------------------------BE
DA
FR
BS
Tot
------------------------------------------------------------------------------------------2005
73
102
273
34
482
2006
56
82
241
-2
377
-------------------------------------------------------------------------------------------
Conclusions
•Common horizontal grid – simplifies coupling
•23 months reanalysed so far (Jan. 2005 to Nov. 2006)
•Ice decrease in 2005 and 2006 due to regional melting, not ice export
•Lateral oceanic heat flows into the Arctic Larger in 2005 than in 2006
•Compared to ERA-interim, our analysis has
– consistent air-sea energy exchanges between the ‘spheres’
– more detailed sea ice analyses
– an ocean component!
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Outlook
•Complete three years, 2005-2007
•Replace HIROMB bulk formulae with HIRLAM fluxes
•Re-calculate lateral oceanic budgets (volume, heat, freshwater)
•Write a report and a paper
END
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