Sensitivity Analysis of SST along NJ coast with ADROMS

Weifeng (Gordon) ZhangJohn WilkinJulia Levin

Hernan Arango

Institute of Marine and Coastal Sciences, Rutgers University

Oct. 2005

Background

Plenty of measurement in New Jersey shore area;

Ocean forecast and hind-cast with forward ROMS has been running;

To use data assimilation in these area to improve the forecast and measurement;

Adjoint sensitivity analysis with ADROMS is applied first to test the model based on our understanding of the physics in this area.

Adjoint sensitivity analysis: What causes the event?

Forward Model – Background for Adjoint model

Three idealized cases (steady low river discharge, no tide, no surface exchange):

No wind Southwestward wind Northeastward wind

Adjoint sensitivity set-up

For upwelling event:

Background state: 5 days bi-hourly forward model output.

Event time:

Adjoint forcing:

Adjoint variable:

FORWARD_MIXING: Adjoint model reads mixing coefficients from forward output

5.0 4.75t DendS DstrS days

21

2J SST dAdt

A t

SST dA dtscope

A t

, , , ,J J J J

temp salt zeta sustr

No wind case

J

SST

J

SSS

J

u

SST

Nowind case (cont’d)

Adjoint variable Magnitude of adjoint variable

Standard deviation of variable

ad_SST (0, 0.02) 5 0.1ad_SSS (-0.002, 0.002) 5 0.01ad_u/ad_v (-0.05, 0.05) 0.5 0.025ad_Akv (-100, 100) 10-4 10-2

ad_Akt (0, 60) 10-5 10-4

ad_Aks (-3, 3) 10-5 10-5

xx

J J J J JJ T S u Akt

T S u Akt

JX

X

Southward wind case

J

SST

J

sustr

J

SSS

J

SST

SST

Southward wind case (cont’d)

Adjoint variable Magnitude of adjoint variable

Standard deviation of variable

ad_SST (0, 0.02) 5 0.1ad_SSS (-0.005, 0.005) 5 0.025ad_sustr/ad_svstr (-100, 100) 0.002 0.2ad_u/ad_v (-0.05, 0.05) 0.5 0.025ad_Akv (-150, 150) 10-4 0.015ad_Akt (0, 15) 10-5 10-4

ad_Aks (-10, 5) 10-5 10-4

JX

X

xx

J J J J JJ T S u Akt

T S u Akt

Northward wind caseJ T T

Northward wind case (cont’d)

J

SSS

J

svstr

Summary

ADROMS gives physically reasonable results for sensitivity analysis on idealized application in NJ shore area

Users need to think about the definition of the measure of certain event, J

The validity of linearization to the nonlinear model has to be considered carefully and proved first

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Great appreciation goes to

John Wilkin, Hernan Arango, Julia Levin, Andrew Moore and B-J Choi!