An atmosphere-ice-ocean reanalysis of the Arcticfor the IPY

Lars Axell and Per Kållberg

Research and Development

Swedish Meteorological and Hydrological Institute

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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)model domain and bathymetry of HIROMB

Hiromb OI coast following structure functions

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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

•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

•HIROMB’s analysis after its forecast; HIRLAM’s analysis before its forecast

Analysesperformedhere

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Number of ocean observations (2005-2007) (note the logarithmic scale)

temperature salinity

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March 2005

September 2005

hirlam-hiromb sea ice concentration % era_interim

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March 2005

September 2005

surface salinity surface temperature

Monthly mean fields

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monthly mean ocean-air net energy exchange, march 2006

hirlam/hiromb era interim

red=downwards, blue=upwards

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monthly mean ocean net energy exchange, september 2006

hirlam-hiromb era interim

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hiromb ice-driftmarch 2006

hirlam 10-metre windmarch 2006

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hiromb ice-driftMarch 2006

hirlam 10-metre windMarch 2006

hiromb ice-drift september 2006

hirlam 10-metre windseptember 2006

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hirlam wind-stressmarch 2006

hirlam wind-stressseptember 2006

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Arctic Sea Ice Extent(reanalysis updated until 200610)

Ice extent = sum of area with at least 15 % sea ice

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Transect across Fram StraitDate: 2005-09-15 (Greenland left)

Temperature (°C)

Velocity (cm/s)

Salinity (psu)

•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)

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Fluxes through Fram Strait(monthly means)

Volume flux (unit: Sverdrup) Heat flux (unit: TW) (0 deg reference)

2005 mean: +9.5 TW2006 mean: -25.4 TW2007 mean: ?

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Heat budget (fluxes in TW into the Arctic)(proper Arctic except Barents Sea)

•Large total differences between 2005 and 2006

•Largest difference in the Fram Strait

Bering Strait

Lancaster Strait +

Nares Strait

Fram Strait

Spitzbergen-

Russia

Total

2005 +3.1 -11.5 +9.5 +19.2+20.3

2006

preliminary

+1.2 -10.9-25.4

+22.1-13.0

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Changes in total ice volume(proper Arctic except Barents Sea)

2005-04-16 12:00 UTC

2005-09-18 00:00 UTC

Change:5622 km3

2006-04-24 12:00 UTC

2006-09-29 06:00 UTC

Change:8600 km3

Ice decrease 2005: 5 622 km3Ice export 2005: 482 km3 (9%)

Ice decrease 2006: 8600 km3Ice export 2006: 377 km3 (4%)

-------------------------------------------------------------------------------------------BE DA FR BS Tot

-------------------------------------------------------------------------------------------2005 73 102 273 34 4822006 56 82 241 -2 377-------------------------------------------------------------------------------------------

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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