Chlorophyll Based Shortwave Absorption in POP Bruce Briegleb Bill Large Steve Yeager Gokhan...
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Transcript of Chlorophyll Based Shortwave Absorption in POP Bruce Briegleb Bill Large Steve Yeager Gokhan...
Chlorophyll Based Shortwave Absorption in
POP
Bruce Briegleb
Bill Large
Steve Yeager
Gokhan Danabasoglu
Keith Lindsay
Peter Gent
Chlorophyll Based Absorption
Why?
• Present absorption based on Jerlov water type IA Constant in space and time
• Vertical distribution of shortwave absorption important to ocean modeling (as shown in 1D boundary layer models)
• Chlorophyll data available (we used SeaWIFS over September 1997 to November 2001)
• Transmission parameterization available (Carter Ohlmann’s chlorophyll-dependent)
Chlorophyll Transmission from Carter Ohlmann
• A_1 exp(-B_1 z) + A_2 exp(-B_2 z)• A,B chlorophyll dependent: range of chl from .001
mg/m^3 to 10 mg/m^3• A,B from empirical fits to atmosphere-ocean radiative
transfer calculations• Solar zenith angle and cloud effects ignored• Overall precision of transmission about .005• Transmission compared well to EPIC and TOGA-
COARE observations
Implementation
• Controlled by namelist input. Default transmission available, as well as top layer
• Monthly climatology of chlorophyll data• Chlorophyll assumed uniformly mixed
vertically through column• Chlorophyll based transmission computed
once a month and stored in a look-up table• New sw_absorb.F module
Testing
• Control from Keith Lindsay
• Ocean only
• gx3 with1991-1993 NCEP/ISCCP forcing
• 350 years accelerated; 50 years synchronous
• Chlorophyll absorption run from year 400 to 423. Years 421-423 compared to control
Absorbed Shortwave Fluxes (W/m^2)Global Mean Ocean Year 400
Chlorophyll Jerlov IA Diff
Total 172.3 172.3 0.0
Top Layer 132.2 144.2 -12.0
Bnd Layer minus top
12.4 6.9 +5.5
Deep below bnd layer
27.7 21.2 +6.5
Test Results: Ocean Only
• SST cools in subtropics about .1C to .2C• SST warms along equator about 0.5C,
coasts 1C• Only small changes in SST seasonal cycle• Tropical and sub-tropical waters between
~40m and ~200m depth warm about 0.5C• Significant response in Pacific Equatorial
Undercurrent
Future Work
• Combine with Gokhan’s mods
• Run coupled test (with, without Gokhan’s?)
• Implement for IPCC?