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A brief introduction to
UMCES Chesapeake Bay Model
Yun Li and Ming Li
University of Maryland Center for Environmental Science
VIMS, SURA Meeting
Oct-1-2010
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Grid
Forcingwind
river
SST (sea surface temperature)
Boundary
Model Sensitivitywind
background diffusivity
resolution
Outline
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– Model domain includes mainstem, 8 major tributaries a piece of coastal ocean
– Curvilinear orthogonal grid
– 20 stretched layers
– Resolution Low (80x120) <1km in cross-channel 2~3km in along-channel deepest point is 26m.
High (160x240) <500m in cross-channel 0.5~2km in along-channel deepest point is 40.5m.
Deep channel is well resolved in the high-resolution model
Gri
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Fo
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– Wind Data Sourcehttp://www.wunderground.com
6 wind stations, hourly data
– Interpolationwind speed is linearly interpolated along latitude and longitude
– Wind speed to stress
where
– Amplification Factor (Xu et al. 2002; Wang and Johnson 2000)
UUCdair
310063.061.0 UCd
Station N-S comp E-W comp
NIA(KORF) 1.37 1.25
PRS(KNHK) 2.05 1.43
BWI(KBWI) 1.50 1.00
Wind
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– River Data SourceUSGS monitoring stations, discharge (m3/s) and temperature (<monthly)
salinity is set to zero
– Major TributariesSusquehanna (1) 01578310Patapsco (3) 01583500 01586210 01586610Patuxent (1) 01594440Potomac (1) 01646500Rappahannock (1) 01668000York (2) 01673000 01674500James (3) 02037500 02041650 02042500Choptank (1) 01491000
– Sea Level at Riverine Boundary
New CPP: PSOURCE_FSCHAPMAN allow incoming wave but avoid reflection
River
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Fo
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– SST Data SourceChesapeake Bay Program along-channel observation (monthly or biweekly)
– InterpolationSurface temperature (<1m) is linearly interpolated along latitude
– ConfigurationNew CPP: SST_RELAXATION (must undef QCORRECTION)Nudging is performed every 6 hours.
SST
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Bo
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ryModel only has open boundary at eastern edge.
– Data SourcesTidesFive major components M2, S2, N2, K1, O1 from Oregon State U. global inverse tidal model TPXO
Subtidal Sea Leveldetided component from NOAA historical data at Duck, NC
T and Slinear interpolation from WOA2005, monthly Levitus climatology
ubar and vbarzeros at boundary
– Configuration sea level: FSCHAPMAN 2D momentum: EAST_M2FLATHER 3D momentum: EAST_M3RADIATION T and S: EAST_TRADIATION EAST_TNUDGING (1 day)
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Se
ns
itiv
ity
original wind
amplified wind
observation
Salinity, Nov 11, 1996
Wind
Along channel distribution in a low-runoff period.
Using the amplification factors, the model produces a well-mixed surface layer in better agreement with the observation
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Se
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itiv
ity
10-4m2/s
5x10-5m2/s
10-5m2/s
10-6m2/s
Vertical Diffusivity
A comparison of along-channel salinity distribution between four model runs with different vertical diffusivity (Ks) shows that
– the stratification increases as Ks decreases.
– the along-channel salinity gradient increases as Ks decreases.
– model prediction becomes less sensitive when Ks is reduced below 10-5m2/s.
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k-kl,80x120
k-kl,160x240
observation
Salinity, April 23, 1997
Resolution
Increasing model resolution is important to resolve the narrow deep channel, which is the main conduit for the landward salt transport.
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– Special features in UMCES Chesapeake Bay Model
1. Both low- and high-resolution configurations are available
2. Apply Chapman’s condition for sea level elevation at Riverine boundary to avoid wave reflection.
3. SST nudging to observation with a time scale of 6hr.
4. Using wind amplification factors, the model produces a well-mixed surface layer
– Areas of Improvement
1. Model resolution in the deep channel
2. Turbulent mixing near the pycnocline (Li et al. 2005)
3. Adjustment of observational wind (Xu et al. 2002; Li et al. 2005)
Summary
Recommended