Environmental Engineering Reference
In-Depth Information
4.13 Improving Low-Level Wind Field Forecast over
Coastal Regions with a Mesoscale Boundary Layer
Model Forced with Local Observations and Regional
Operative Forecasts, Examples of Lagrangian
Trajectories
Guillermo J. Berri
Department of Atmospheric and Oceanic Sciences (University of Buenos Aires),
and National Research Council (CONICET) of Argentina
Abstract
A primitive equation mesoscale boundary layer model -MBLM- has
been especially developed for forecasting the low-level wind field over coastal
regions. The model high horizontal resolution allows representing the small scale
features and the land-river surface temperature contrast over coastal regions of
complex geometry. The model can be forced with observations as well as with
regional operative forecasts. The model surface wind climatology reproduces very
well the observed winds at five weather stations of the La Plata River region of
South America. A 6-month test period of 12-hour surface wind forecast obtained
by forcing the MBLM model with regional operative forecasts produces significantly
smaller errors than those of the regional forecast model itself.
The La Plata River in South America is an extended water surface −300 km long
and between 50 and 200 km wide- that creates the appropriate conditions for low-
level atmospheric circulations with sea-land breeze characteristics, which are a
dominant factor of the local weather and climate. In general, regional operative
forecast models have insufficient horizontal resolution for the appropriate represent-
ation of the small scale features of the daily cycle of low-level winds over a region
with a complex geometry of the river-land temperature contrast. A mesoscale
boundary layer model -MBLM- is used to simulate the high-resolution low-level
wind field over the La Plata River region (see
Fig. 1).
The dry and hydrostatic model has three forecast equations for the horizontal
wind components and potential temperature perturbation, respectively, and three
diagnostic equations for the vertical motion, total pressure and pressure perturbation.
For more details about the model formulation and the numerical method of
solution, please refer to Berri and Nuñez (1993). The model has been validated
over the La Plata River region during a 25-year period by comparing the low level
wind climatology calculated by model with the local surface wind observations at
five weather stations in the region. The model climatology is calculated as the
ensemble result of a series of 24-h forecasts initialized at 0900 local standard time
