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?