Impact of water constituents on radiative heat transfer in the ...

Coastal Ocean Modelling Workshop, Hamburg, 22 – 23 February 2018

Bronwyn CahillInstitute for Space Science, Freie Universität Berlin

Impact of water constituents on radiative heat transfer in the open

ocean and shelf seas

Collaborators:Jürgen Fischer (WEW-FUB)

Hans Burchard, Ulf Gräwe (Leibniz Institut für Ostseeforschung Warnemünde)John Wilkin (IMCS, Rutgers University, USA)

John Warner, Neil Gangu (USGS-Woods Hole, USA)

2 of 16Coastal Ocean Modelling Workshop, Hamburg, 22 – 23 February 2018

MotivationHow important is the temporal and spatial variability in underwater light feld to modelling biogeochemical and physical processes in coastal and shelf seas?

A number of feedback mechanisms determine biogeochemical dynamics in upper ocean layer (light, heat, photosynthesis) - especially complex in shelf and coastal waters (organic and inorganic particulate matter, CDOM).

Attenuation of underwater light interaction of absorption and scattering of optically active constituents, i.e. water molecules, phytoplankton, CDOM and detritus.

Different parameterizations of downward irradiance (I(z)) can lead to different upper ocean water masses, e.g. Cahill et al., 2008. Dynamics of turbid buoyant plumes and the feedbacks on near-shore biogeochemistry and physics


Hudson River Plume

RGB MODIS - Acqua, New York / New Jersey Bight, 6th April 2005 - distinct

regions of highly turbid water, differing optical properties associated with the

Hudson River plume.

OSRP

RP

RP RP

RP

RP

Open Shelf: <0.1 m-1

River Plume: >0.2 m-1

RP

(Schofield et al., 2004)


Hudson River PlumeHudson River Freshwater Transport 2005

East Wind Speed Component 2005

North Wind Speed Component 2005

Year Day

LaTTE Project (2004 - 2008)● Extensive Field Campaign● Model Study (ROMS)


Hudson River PlumeImpact of different water types on surface radiant heating, stratifcation & circulation:

● Warmer surface temperatures● Deeper, warmer surface mixed layer● Colder bottom water● Sharper temperature gradient● Greater velocity shear● Narrow, southward buoyancy driven

coastal current along New Jersey coast

● Anti-cyclonic circulation around freshwater bulge at head of Hudson River Canyon

River Plume (RP) – Open Shelf (OS)


Hudson River Plume● Causality between light attenuation,

transport of river plume properties & biogeochemical transformations.

● Phytoplankton biomass tracks fresh water anomaly.

● Light attenuation impacts growth of phytoplankton which subsequently modifies evolution of attenuation fields & feeds back into overall heat budget.

● Coupled ecosystem-circulation models rarely share same parameterization or source of radiative forcing to drive hydrodynamics & fuel photosynthesis.

RP - OS

Phytoplankton AnomalyFreshwater Anomaly

River Plume Attenuation (1/m) 2005 April 18

2m


Study Objectives

Water constituents, heating rates, shelf seas● Contribution of optically active water constituents

(phytoplankton, CDOM, inorganic suspended sediment) to energy fluxes in upper ocean and across air-sea interface.

● How heterogeneity in water constituents impacts characteristics of sub-mesoscale vertical turbulent mixing and advective fluxes.

● How variability in CDOM attenuation is reflected by environmental conditions and phytoplankton community structure.


Bio-Optic

aDET(λ,z)

Adaptation of EcoSim (Bissett et al., 1999)


Absorption & Scatter

Water constituent spectra used in daylight calculations

+ b_phy+ a_det+ b_det


Bio-Optic

Rate of radiant energy converted into heat (horizontally homogeneous water body) ~ divergence of net radiative flux:

Bio-Optic calculates in-water spectrally resolved (400 - 700nm; 5nm):

● Absorption, scattering, backscatter coefficients● Average cosine zenith angle● Downwelling irradiance attenuation coefficient, Kd

● Scalar and downward irradiance fields, E0 and Ed

(Morel, 1988)


1D Experiment Different Water Types


Regional COAWST 1D Simulations

● Site specific comparative simulations of coupled 1D COAWST, with and without feedback of biological and sediment heating rates:– Regional configuration of CDOM specific absorption and spectral

slope (e.g. Kowalczuk et al., 2006; Stedmon et al., 2000; Mannino et al., 2014)

– Calculate PAR and annual heating rates– Analyse impact on marine atmospheric boundary layer heat

fluxes– Extract absorption and scattering profiles (for radiative transfer

calculations)


Regional MOMO (RadTran) Simulations

● Comparative 1D simulations using MOMO – heating rates:– downward, upward and scalar irradiances– absorption, scattering and attenuation coefficients– volume scattering functions and radiance distributions– surface refectances

● Evaluate regional implications MOMO vs. Bio-Optic underwater light field characteristics and heating rates:

– including upward irradiance in heat flux calculations– direction evaluation of MOMO output with satellite reflectances -

MERIS 10 year archive time series● Optimise Bio-Optic heat flux algorithms


3D Western Baltic Sea Assessment● Temporal, spatial distribution of

optically active water constituents, upper ocean heating rates, air-sea heat fluxes

● Characteristics of sub-mesoscale vertical mixing and advective fluxes

● Relationship between ocean state, variability in CDOM attenuation, mixing processes and phytoplankton community structure.

● Consequences for transport and transformation of phytoplankton biomass, accumulative effect on upper ocean heat budget.

BCs / ICs:GETM/ERGOM 600nm

(Graewe/Friedland)


Thank you!Acknowledgements:

German Research Foundation (DFG Grant No. CA 1347/2-1), 2018 – 2021

Impact of water constituents on radiative heat transfer in the ...

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