1. Chlorophyll Based Shortwave Absorption in POP Bruce Briegleb Bill Large Steve Yeager Gokhan Danabasoglu Keith Lindsay Peter Gent

2. 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)

4. 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

7. 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

8. 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

9. Absorbed Shortwave Fluxes (W/m^2) Global Mean Ocean Year 400 ChlorophyllJerlov IA Diff Total 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

20. 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

21. Future Work Combine with Gokhan’s mods Run coupled test (with, without Gokhan’s?) Implement for IPCC?