P49 WRF model resolution impacts on a hydrodynamic model in near-shore environments.
Watson, Campbell D., Guillaume Auger, Harry R. Kolar, and Lloyd A. Treinish, IBM Research, TJ Watson Research Center
The increasingly
urgent problem of harmful algal blooms (HABs) in lake and near-shore coastal
environments has placed renewed focus on the coupled simulation of weather,
hydrology and hydrodynamics. To date, modeling efforts at the Great Lakes and
elsewhere have provided results generally consistent with observations,
however, hydrodynamics closer to the shoreline – where HABs commonly originate
– are often not well simulated. The poor near-shore hydrodynamic simulation can
often be attributed to a weather model running at a resolution too coarse to
properly resolve airflow dynamics at the land-water interface. To interrogate
this issue, the present study uses Lake George, NY, a medium sized lake (55 x 3
km) in the eastern Adirondacks, as a testbed to quantify and understand the
impact of weather model resolution on near-shore hydrodynamics. Lake George is
the subject of The Jefferson Project, a collaborative effort between IBM
Research, Rensselaer Polytechnic Institute and The FUND for Lake George.
The WRF-ARW V3 model is used to simulate the weather down to 0.33 km, and the
SUNTANS Community Model is used to simulate the hydrodynamics with a variable
horizontal grid of around 40 m. WRF and SUNTANS are coupled one-way. Results
from a one-month case study in June 2017 examine the impact of WRF resolution
on the simulated hydrodynamics of Lake George across three experiments: WRF at
3 km, 1 km and 0.33 km. Model results are compared to a lake-wide observation
network. It reveals SUNTANS driven by WRF at 0.33 km provides much better
representation of the lake temperature field and dynamics. For example, at the
north end of the lake, the depth of the thermocline is more accurately
simulated when using WRF at 0.33 km across the entire month, which results in a
thicker mixed layer and thereby larger volume of water that is more conducive
to phytoplankton growth. An observed downwelling event at the south of the lake
is also better captured when using WRF at 0.33 km; this event is of importance
to HABs-related research because immediately after the relaxation of the
downwelling, the observed chlorophyll-a profiles show an increased
concentration within the mixed layer. Reasons why these differences emerge
across experiments is explained via an energy budget that shows increasing the
resolution of WRF modifies the transfer of energy between the atmosphere and
lake surface.