Implementation of a thermodynamic sea ice module in COSMO … · 2016-12-20 · Implementation of a...
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Implementation of a thermodynamic sea ice
module in COSMO and its impact on polynya studies in
the Laptev Sea
D. Schröder, G. Heinemann, and D. Mironov1
1 DWD, Offenbach am Main
10 March 2009
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Umweltmeteorologie, Fachbereich VI 2
Laptev Sea
(AMSR, 9 April 2007)
Net annual ice production: 1000 km3 (Dimitrenko et al., 2009)
Total sea ice in N-Hemi:
5000-10000 km3 (min)
20000-30000 km3 (max)
Annual ice export (FramStrait): 3000 km3
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Umweltmeteorologie, Fachbereich VI 3
→Version 4.0, →35 (42) layers, →dlon=dlat=0.05°, →dt=20s,→hincrad=1h, →itype_tran=2 (TKE-based scheme), →7 soil layers, →&INICT: ndfi=2, tspan=600s, taus=600s, dtbak=15s,
dtfwd=15s
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Umweltmeteorologie, Fachbereich VI 4
COSMO-05km Run
GME 20-24 April 2008, 6-hourly
COSMO-15km 20-24 April, 1-hourly
Sea Ice: AMSR 22 April 2008
T_sfc (Sea Ice) = 250 K (const.)
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Umweltmeteorologie, Fachbereich VI 5
after 60h: T2m over sea ice close fixed Tsfc, ~ -13°C over polynyas
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Umweltmeteorologie, Fachbereich VI 6
Time series at Station 1 (position marked by a cross in above figure)
=> Diurnal cycle of T2m can naturally not be modelled if Tsfc is constant
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Umweltmeteorologie, Fachbereich VI 7
COSMO-05km seaice Run
GME 20-24 April 2008, 6-hourly
COSMO-15km 20-24 April, 1-hourly
AMSR 22 April 2008
T_sfc (Sea Ice) = 250 K (initial value)
Thermodynamic Sea Ice Model
1m ice thickness (initial value)
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Umweltmeteorologie, Fachbereich VI 8
Thermodynamic Sea Ice Model (Mironov and Ritter)
Prognostic Equations for T_sfc and h_ice
Heat budget of the ice slab (one layer)
Shape function for temperature profile
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Umweltmeteorologie, Fachbereich VI 9
Thermodynamic Sea Ice Model
⎟⎟⎠
⎞⎜⎜⎝
⎛ −⋅−
⋅⋅
⋅Δ
=ΔhTT
cQ
htT frA )(
5.0λ
ρ
c
λ
= 2100 J/(kg K) ice heat capacity (same value for snow)
= 1.2E-06 m2/s ice heat conductivity
ρ = 910 kg/m3 ice density (100-600 kg/m**3 for snow)
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Umweltmeteorologie, Fachbereich VI 10
=> Tsfc too warm, diurnal cycle too weak and delayed => T2m even poorer!
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Umweltmeteorologie, Fachbereich VI 11
Location of the 4 weather stations and the GME grid cells (0.5°).
Nearest and surrounding grid cells are compared with weather stations.
Why are results even poorer? Comparison of GME and in-situ data
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Umweltmeteorologie, Fachbereich VI 12
Good agreement re wind speed
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Umweltmeteorologie, Fachbereich VI 13
MSLP comparison for all 4 stations
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Umweltmeteorologie, Fachbereich VI 14
daily means daily means
6-hourly values 6-hourly values
2m temperature: diurnal cycle missing => Surface temperature!
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Umweltmeteorologie, Fachbereich VI 15
Btw NCEP analyses are pretty good regarding temperature over sea ice...
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Umweltmeteorologie, Fachbereich VI 16
Diurnal cycle of Tsfc/T2m missing in GME Ana and GME forecast over sea ice!
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Umweltmeteorologie, Fachbereich VI 17
=> The GME seaice module is not able to produce realistic Tsfc changes on short timescale
=> The GME soil model would produce more realistic Tsfc over sea ice
=> Sea ice surface temperature over thick ice (>50cm) behaves very similar to land ice surface temperature
- Potential reason: snow on top of sea-ice has to be included (low density)
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Umweltmeteorologie, Fachbereich VI 18
COSMO-05km snow Run
GME 20-24 April 2008, 6-hourly
COSMO-15km 20-24 April, 1-hourly
AMSR 22 April 2008
T_sfc (Sea Ice) = 250 K (at start)
Thermodynamic Sea Ice Model
5cm snow layer (ρ=100kg/m*3)
T under the snow layer const (250K)
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Umweltmeteorologie, Fachbereich VI 19
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Umweltmeteorologie, Fachbereich VI 20
No trendin GME
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Umweltmeteorologie, Fachbereich VI 21
Difference between both runs: up to 200 Wm-2 over polynyas
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Umweltmeteorologie, Fachbereich VI 22
Conclusions
Ice surface temperature is critical for energy balance and thermodynamic sea ice changes
Sea ice module implemented in COSMO
Realistic changes of ice surface temperature on short timescale only in the case with a snow layer
Positive trend has to be investigated
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Umweltmeteorologie, Fachbereich VI 23
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Umweltmeteorologie, Fachbereich VI 24
Wind direction
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Umweltmeteorologie, Fachbereich VI 25
COSMO run (with const. Tsfc): energy loss over ice, gain over polynyas
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Umweltmeteorologie, Fachbereich VI 26
COSMO run snow: small energy gain over ice, strong gain over polynyas