1. 1 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

2. 2  Grid  Forcing wind river SST (sea surface temperature)  Boundary  Model Sensitivity wind background diffusivity resolution Outline

3. 3 – 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 Grid

4. 4 Forcing – Wind Data Source http://www.wunderground.com 6 wind stations, hourly data – Interpolation wind speed is linearly interpolated along latitude and longitude – Wind speed to stress where – Amplification Factor (Xu et al. 2002; Wang and Johnson 2000) StationN-S compE-W comp NIA(KORF)1.371.25 PRS(KNHK)2.051.43 BWI(KBWI)1.501.00 Wind

5. 5 Forcing – River Data Source USGS monitoring stations, discharge (m 3 /s) and temperature (<monthly) salinity is set to zero – Major Tributaries Susquehanna (1) 01578310 Patapsco (3) 01583500 01586210 01586610 Patuxent (1) 01594440 Potomac (1) 01646500 Rappahannock (1) 01668000 York (2) 01673000 01674500 James (3) 02037500 02041650 02042500 Choptank (1) 01491000 – Sea Level at Riverine Boundary New CPP: PSOURCE_FSCHAPMAN allow incoming wave but avoid reflection River

6. 6 Forcing – SST Data Source Chesapeake Bay Program along-channel observation (monthly or biweekly) – Interpolation Surface temperature (<1m) is linearly interpolated along latitude – Configuration New CPP: SST_RELAXATION (must undef QCORRECTION) Nudging is performed every 6 hours. SST

7. 7 Boundary Model only has open boundary at eastern edge. – Data Sources Tides Five major components M 2, S 2, N 2, K 1, O 1 from Oregon State U. global inverse tidal model TPXO Subtidal Sea Level detided component from NOAA historical data at Duck, NC T and S linear interpolation from WOA2005, monthly Levitus climatology ubar and vbar zeros at boundary – Configuration sea level: FSCHAPMAN 2D momentum: EAST_M2FLATHER 3D momentum: EAST_M3RADIATION T and S: EAST_TRADIATION EAST_TNUDGING (1 day)

8. 8 Sensitivity 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

9. 9 Sensitivity 10 -4 m 2 /s 5x10 -5 m 2 /s 10 -5 m 2 /s 10 -6 m 2 /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 -5 m 2 /s.

10. 10 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. Sensitivity

11. 11 – 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

12. 12 Salinity, Apr 25, 1997 Sensitivity original wind amplified wind observation