improving the representation of estuarine processes in cesm · estuarine processes in cesm. sun,...

23rd Annual CESM Workshop, 2018National Center for Atmospheric Research

qiang.sun@uconn.edu

Improving the representation of estuarine processes in CESM

Qiang Sun①, Michael M. Whitney①, Frank O. Bryan②and Yu-heng Tseng③

① UCONN, Department of Marine Sciences② NCAR, Oceanography Section③ NTU, Institute of Oceanography

Improving the representation of estuarine processes in CESM

Sun, Q.; Whitney, M. M.; Bryan, F. O. and Tseng, Y. H.

CESM workshop - 2018 qiang.sun@uconn.edu Slide 2 of 14

Overview

Introduction

Development of Estuary Box Model (EBM) and results

Implementation of EBM in POP2 and results

Current work: Tracking riverine freshwater globally

Summary

Improving the representation of estuarine processes in CESM

Sun, Q.; Whitney, M. M.; Bryan, F. O. and Tseng, Y. H.

CESM workshop - 2018 qiang.sun@uconn.edu Slide 3 of 14

The role of river in global hydrological cycle

Improving the representation of estuarine processes in CESM

Sun, Q.; Whitney, M. M.; Bryan, F. O. and Tseng, Y. H.

qiang.sun@uconn.edu Slide 4 of 14

6

-6

1

-1

CESM workshop - 2018

Sea surface salinity bias: model (CESM) – climatology (WOA13)

Improving the representation ofestuarine processes in CESM

Sun, Q.; Whitney, M. M.; Bryan, F. O. and Tseng, Y. H.

CESM workshop - 2018 qiang.sun@uconn.edu Slide 5 of 14

River runoff treatment in standard CESM• Applied as extra precipitation at sea surface.• Spreading around river mouth (300KM radius).• Discharge into ocean with ZERO salinity.• Using global reference salinity for VSF formula.

Improving river runoff by:• Remapping runoff as point source.• Introducing in the estuary mixing.• Local salinity for VSF formula.

(Tseng et al, Ocean Modelling, 2016)

Improving the representation ofestuarine processes in CESM

Sun, Q.; Whitney, M. M.; Bryan, F. O. and Tseng, Y. H.

CESM workshop - 2018 qiang.sun@uconn.edu Slide 6 of 14

Estuarine mixing in nature• Salty sea water

intrusions along bottom.

• Non-ZERO outflow at shallow depth.

• Mixing depends on both of runoff and tides.

http://www.ldeo.columbia.edu/~orton/salt_intrusion.html

Columbia River high discharge season

Columbia River low discharge season

River mouth

32PSU

5 PSU

32PSU

15 PSU

Improving the representation ofestuarine processes in CESM

Sun, Q.; Whitney, M. M.; Bryan, F. O. and Tseng, Y. H.

qiang.sun@uconn.edu Slide 7 of 14CESM workshop - 2018

Estuary Box Model (EBM): Two layer box

QR[QU]

H h

[SU]

[QL] SL

Landmodel

Ocean model

(Sun et al, Ocean Modelling, 2017)High Low

Salinity (Sun et al, Ocean Modelling, 2017)

Estuary Box Model (EBM): Control equationsContinuity:

Potential energy (PE) balance:

Salinity balance:

Improving the representation ofestuarine processes in CESM

Sun, Q.; Whitney, M. M.; Bryan, F. O. and Tseng, Y. H.

qiang.sun@uconn.edu Slide 8 of 14CESM workshop - 2018

Estuary Box Model (EBM): Algebraic solutions

Estuary Box Model (EBM): Parameters and forcing2 Mixing parameters: ; 3 dimensional parameters:

with

3 Forcing terms: QR , Qt and SL

Improving the representation ofestuarine processes in CESM

Sun, Q.; Whitney, M. M.; Bryan, F. O. and Tseng, Y. H.

qiang.sun@uconn.edu Slide 9 of 14CESM workshop - 2018

EBM outflow salinity vs. observations

EBM volume fluxes vs. ROMS

EBM compared with observations and ROMS in Columbia River

RMSE=1.7PSU, R2=70%

RMSE=513m3/s, R2=89%

(Sun et al, Ocean Modelling, 2017)

Improving the representation ofestuarine processes in CESM

Sun, Q.; Whitney, M. M.; Bryan, F. O. and Tseng, Y. H.

qiang.sun@uconn.edu Slide 10 of 14CESM workshop - 2018

Estuary Box Model (EBM) global parameterization specification

Hudson

Chang Jiang

Chesapeake

Mississippi

STR

ATIF

ICAT

ION

RIVER DISCHARGE

*Geyer (2010)Sun et al, Ocean Modelling, 2017

Puget Sound

Estuary stratification-circulation diagram

Improving the representation ofestuarine processes in CESM

Sun, Q.; Whitney, M. M.; Bryan, F. O. and Tseng, Y. H.

qiang.sun@uconn.edu Slide 11 of 14CESM workshop - 2018

Result (G-case): SSS difference with EBM – control casePSU

(Sun et al, Ocean Modelling, 2017)

31st to 60th year averaged sea surface salinity differenceimproved runoff – control run without improvement

Improving the representation ofestuarine processes in CESM

Sun, Q.; Whitney, M. M.; Bryan, F. O. and Tseng, Y. H.

qiang.sun@uconn.edu Slide 12 of 14CESM workshop - 2018

Result (G-case): global assessment with salinity skill scores

Coastal ocean bands mask

Upper 150m ocean integrated salinity SS, with or without high latitude ocean.

Sun et al, JAMES, 2018 (in review)

Improving the representation ofestuarine processes in CESM

Sun, Q.; Whitney, M. M.; Bryan, F. O. and Tseng, Y. H.

qiang.sun@uconn.edu Slide 13 of 14CESM workshop - 2018

Future work: global riverine freshwater pathway and influences

Improving the representation ofestuarine processes in CESM

Sun, Q.; Whitney, M. M.; Bryan, F. O. and Tseng, Y. H.

qiang.sun@uconn.edu Slide 14 of 14CESM workshop - 2018

Summary The Estuary Box Model is a physically based parameterization of

unresolved estuarine mixing processes in the CESM.

The offline tests of EBM show very good agreement with direct observations of outflow salinity and high-resolution simulations of exchange flow volume fluxes.

A reduced set of parameters allows the parameterization to be practically applied to every river inflow point in global Earth system models at negligible cost.

The global CESM simulations with the EBM show it can have significant impacts on the salinity field of the coastal oceans, with non-negligible impacts in some open ocean areas.

The EBM can further imply in river borne nutrient and contaminants.

Improving the representation ofestuarine processes in CESM

Sun, Q.; Whitney, M. M.; Bryan, F. O. and Tseng, Y. H.

qiang.sun@uconn.eduCESM workshop - 2018

Improving the representation ofestuarine processes in CESM

Sun, Q.; Whitney, M. M.; Bryan, F. O. and Tseng, Y. H.

qiang.sun@uconn.edu Slide 16 of 14CESM workshop - 2018

Estuary Box Model (EBM): Implementation in POP2

with

and

Salt

Salt

Salt flux taken outof ocean: with local refence salinity

Salt flux taken fromdeeper to shallower:with local refence salinity