The ChesROMS Community Model

Raleigh Hood, Wen Long, Jiangtao Xu, Jerry Wiggert, Lyon Lanerolle, and Christopher Brown

Funded by the NOAA Ecological Forecasting and MERHAB programs

Motivation:

• Provide T, S and biogeochemical forcing for empirical Sea Nettle, HAB and pathogen nowcasts and short-term forecasts that we are generating as part of our NOAA funded projects.

• Provide nowcasts and short-term forecasts of 3D hydrodynamic circulation, temperature and salinity, sediment transport, and biogeochemical properties for research, management and public uses in Chesapeake Bay.

ChesROMS Grid and Implementation

Chesapeake Bay implementation of ROMS

Curvilinear horizontal grid

Horizontal Grid (100 * 150)

Includes all major tributaries

Diffuse freshwater inputs estimated

C and D canal: treated as a river

Hindcast and operational implementations

(chief architects, Dr. Jiangtao Xu and Dr. Wen Long)

ChesROMS Grid and Implementation

Sigma-coordinate vertically

20 levels

Increased resolution at surface and bottom boundaries

Turbulence closure: κ-ω

ChesROMS Forcing

• Tides --- ADCIRC 9 harmonics • River discharge – USGS daily mean data • Surface Wind and Heat Flux (NAM/NARR)• Open BC non-tidal water level (NWLON)• Open BC T and S (WOA2001)• All forcing data compiled for 1991-2005 (14 yr time-series) • Operational forcing for nowcast and 3-day forecast

ADCIRC: Advanced Circulation Model

NAM: North American Mesoscale Model

NARR: North American Regional Reanalysis

NWLON: National Water Level Observation Network

WOA: World Ocean Atlas

NAM/NARR Wind and Surface Fluxes

• Surface wind, air pressure, heat flux and long wave radiation • Surface temperature is NOT relaxed to observations

Effects of OBC Temp. and Salinity

• Do not have results yet for WOA01 vs. WOA05 but have compared WOA01 to GODAS during model development

• GODAS OBC TS gives less stratified system in lower bay compared to data

• WOA OBC TS gives stratification of lower bay closer to measured data

Effects of C & D Canal flux

• Inflow brings low salinity water into upper bay

• Important to incorporate C & D canal in model for upper bay physical structure and dynamics

• Gives better upper bay salinity structure prediction

Effects of Turbulence ClosuresCompared the four closures:

1. Mellor-Yamada 2.5

2. KPP

3. Generic Length Scale (GLS) Mellor-Yamada

4. Generic Length Scale (GLS) K-omega

Results:

• Mellor Yamada (MY) 2.5 similar to KPP

• GLS K-omega similar to GLS MY 2.5

• GLS K-omega gives best comparison to data in terms of vertical mixing/stratification

ChesROMS Available through SourceForgehttp://sourceforge.net/projects/chesroms/

Retrospective Run (1991 - 2005)

(chief architect, Dr. Jiangtao Xu) 15 year retrospective validation run

Large variations in freshwater discharge

Lets focus on 2003 as an example

Temperature and salinity (2003)• CB5.3

Mid Bay

Temperature simulation excellent

Salinity simulation not as good

2003 Model Skill for Temperature

Correlations on the order of 0.99

Normalized standard deviation close to 1

2003 Model Skill for Salinity

Correlations on the order of 0.75-0.85

Normalized standard deviation generally > 1

The model tends to underestimate the salinity variabiliy in most regions, though there are some exceptions, like in some of the flank (shallow stations)

Why the Reduced Skill for Salinity? At least partially due to smoothed topography

It has also been suggested that ROMS tends underestimate stratification (is this true?)

The fact that the model tends to underestimate the standard deviation is consistent with over mixing

Thank You

ChesROMS Biogeochemical Model - Work in Progress (chief architect Dr. Jerry Wiggert)

Based on Fennel et al. core model bundled with ROMS NPZD type model with oxic sediment denitrification Adding DON ISS loading Atmospheric N deposition Anoxic benthic denitrification Water column denitrification,