The estuarine The estuarine parameterization problem: parameterization problem: sensitivity of ROMS to the sensitivity of ROMS to the

specifics of line source specifics of line source buoyancy input in the buoyancy input in the Coastal Gulf of AlaskaCoastal Gulf of Alaska

A. J. Hermann and E. L. DobbinsA. J. Hermann and E. L. DobbinsJISAO-UW/PMELJISAO-UW/PMEL

Nested model Sea Surface Nested model Sea Surface SalinitySalinity

Observed cross-shelf Observed cross-shelf hydrographyhydrography

A simple salt-wedge estuaryA simple salt-wedge estuary

Diagrams courtesy of Pritchard

Two-layer estuary balancesTwo-layer estuary balances

Q/R = Si/(Si-Sq)Q/R = Si/(Si-Sq)

I small, Sq~0 -> Q~RI small, Sq~0 -> Q~RI big, Sq~Si -> Q>RI big, Sq~Si -> Q>R BUT in either caseBUT in either case Q-I=R Q-I=R

RQ

I

Q*Sq

I*Si

Hq

Hi

Water Balance: Water Balance: Q = R + IQ = R + IQ - I = RQ - I = R

Salt Balance: Salt Balance: I*Si = Q*SqI*Si = Q*Sq

Partially mixed deep estuary -> Partially mixed deep estuary -> brackish Qbrackish Q

Hi >> Hq; Hi >> Hq;

Net outflow = Q at the surface with Net outflow = Q at the surface with S=SqS=Sq

I/Hi small; maybe can ignore?I/Hi small; maybe can ignore?

R QHq

Hi IROMS

Totally mixed shallow estuary -> Totally mixed shallow estuary -> brackish R!brackish R!

Hi, Hq -> 0 ; Hi, Hq -> 0 ;

Net outflow = Net outflow = R at the surfaceR at the surface withwith S S > 0> 0

Nothing happening further downNothing happening further down

R Q-I=RHqHi

ROMS

4 tests4 tests

Near-surface river Dambreak river

Partially mixed deep estuary

Totally mixed shallow estuary

SchemeScheme PROPRO CONCON

Near-surface riverNear-surface river

(tip of salt wedge)(tip of salt wedge)

S=0, Q=R S=0, Q=R

Maximal at surface (linear Maximal at surface (linear ramp)ramp)

•Model caculates Model caculates mixingmixing

•simplesimple

• Get thin bore in Get thin bore in deep watersdeep waters

• Push estuary Push estuary offshoreoffshore

Dambreak riverDambreak river

(far upstream of salt (far upstream of salt wedge)wedge)

S=0, Q=RS=0, Q=R

vertically uniformvertically uniform

•Model calculates Model calculates mixingmixing

•simplesimple

•Get thin bore in Get thin bore in deep watersdeep waters

•Push estuary Push estuary offshoreoffshore

Partially mixed deep Partially mixed deep estuaryestuary

S>0, Q>RS>0, Q>R

all at surfaceall at surface

•More like a More like a typical estuarytypical estuary

•Uncertain Uncertain parametersparameters

•We ignore return We ignore return flow at depthflow at depth

•Huge flows at Huge flows at surface!surface!

Totally mixed shallow Totally mixed shallow estuaryestuary

S>0, Q=R S>0, Q=R

all at surfaceall at surface

•SimpleSimple

•Assimilates dataAssimilates data•Highly idealizedHighly idealized

•Assimilates dataAssimilates data

Modeled Surface SalinityModeled Surface Salinity

Modeled cross-shelf salinityModeled cross-shelf salinity

Models vs data early March Models vs data early March 2001 2001

Model Model Data Data

Models vs data late July Models vs data late July 2001 2001

Model Model Data Data

Model Model Data Data

Mid-shelf salinity profile: Mid-shelf salinity profile: near-surface rivernear-surface river vs. vs.

datadata

Mid-shelf salinity profile: Mid-shelf salinity profile: tot mixed shallow estuarytot mixed shallow estuary vs. data vs. data

Model Model Data Data

•Partially-mixed estuary (yellow, green) yield excess transport compared to data (black).

•Tot mixed shallow estuary (pink) is better

•Near-surface river (blue) yields too much stratification compared to data (black).

•Tot mixed shallow estuary (pink) is better

Conclusions so farConclusions so far

• None of the solutions is ideal; there is no None of the solutions is ideal; there is no simple substitute for a real estuarysimple substitute for a real estuary

• Pure river approaches are too fresh at Pure river approaches are too fresh at surface -> Runaway estuary effect on shelfsurface -> Runaway estuary effect on shelf

• Partially mixed deep estuary yields too Partially mixed deep estuary yields too much outflow, overwhelms systemmuch outflow, overwhelms system

• Totally mixed shallow estuary is best one Totally mixed shallow estuary is best one so far!so far!