Using MM5 to Hindcast Ocean Surface Forcing Fields over the Gulf of Maine and Georges Bank

Changsheng Chen – U Mass-Dartmouth

Robert Beardsley – WHOI

Song Hu – U Mass-Dartmouth

Qichun Xu – U Mass-Dartmouth

Huichan Lin – U Georgia

GB GLOBEC Workshop, November 18, 2003

Outline of Talk

1. Description of MM5

2. MM5 Setup

3. 1995 Hindcasts

4. Summary

5. Next Steps

MM5 - 5th generation NCAR/Penn State mesoscale meteorological model

• Features: non-hydrostatic, terrain-following, variable domain and spatial resolution, multiple grid nesting, nudging 4-D data assimilation, several PBL modules

• Uses NCAR/NCEP or ETA weather model fields as initial and boundary conditions with two-way nesting capability

• Integrated for 3 days with 12-hr spin-up

• Model output fields used to construct 3-hr time series of surface wind, pressure, Ta, RH, wind stress and heat flux

PBL Models

• Models designed to represent turbulent mixing due to vertical eddy diffusion K and free and forced convection in unstable weather conditions.

• We considered four: Blackadar, ETA, MRF, Gayno-Seaman

Local domain MM5(resolution: 10 km)

Regional domain MM5(resolution: 30 km)

Surface winds, Ta, Pa, RH, wind stress, heat flux, water flux

NCEP (2.5 degree) or ETA (30 km)

Air stationsBuoy dataSatellite dataLand stations

SSTLocal buoy data

Assimilation

AssimilationNested

Nested

The Gulf of Maine/Georges Bank MM5 Model System

Local domain

Regional domain

40o N

50o N

70o W 60o W80o W

50o W60o W70o W80o W

40o N

50o N

Horizontal Resolution:

Regional domain = 30 km;Local domain = 10 km

Vertical Resolution:

31-sigma levels

Numbers and Labels:

Names of weather buoys

1995 Hindcasts

Experiments Buoy Winds Constant SST

Daily SST T/C Bulk

Simulation N Y Y N

Assimilation Y N Y Y

Simulated Assimilated

Simulated Assimilated

Short-wave

Long-wave

Latent

Sensible

TOGA/COARE (TC2.5) heat flux algorithm (Fairall et al.,1996)

• Computes wind stress, Qsen, Qlat using wind speed, Ta, RH, SST• Improved parameterization of surface roughness• Includes wind gustiness (most important at low wind speeds)• More realistic vertical profiles for stable and unstable weather conditions

January 1995

Summary• MM5 with assimilation of buoy wind data and daily SST

and modified PBL model can provide a reasonable hindcast wind field and long-wave, sensible, and latent heat flux components in the Gulf of Maine/Georges Bank region (=> adequate for ocean modeling)

• Method used to estimate short-wave radiation in MM5 needs improvement (=> need for in situ short-wave flux measurements or remote-sensing approach)

• QuikSCAT wind data do not resolve the wind field during frontal passages due to precipitation (=> no substitute for in situ buoy measurements)

Next Steps

• Develop better insolation method for MM5

• Convert TC2.5 to new COARE2.6 heat flux algorithm in MM5 PBL module (increased stress, Qsen,Qlat at higher wind speeds, valid to 20 m/s)

• Migrate to new NOAA/NCAR Weather Research and Forecasting (WRF) mesoscale model

QuikSCAT Wind Velocity Vectors