Environmental Engineering Reference
In-Depth Information
Chapter 10
Sensitivity Tests in the Dynamical and Thermal
Part of the MRF-Urban PBL Scheme
in the MM5 Model
Aggeliki Dandou and Maria Tombrou
Abstract
In the present study, sensitivity tests were carried out in the 'dynamical'
and 'thermal' part of a meteorological model in urban environment. The numeri-
cal simulations were performed by the PSU/NCAR Mesoscale Model (MM5), by
applying the non-local Medium-Range Forecast (MRF) Planetary Boundary Layer
(PBL) parameterisation scheme, plus the MRF-urban scheme, whereby urban fea-
tures are considered. An unrealistic run was also performed by the MRF scheme,
where the city of Athens was replaced by dry cropland and pasture surface, as in the
surrounding area. The model results were compared with sonic anemometer mea-
surements of turbulence and routine meteorological data. Modifications in both the
'dynamical' and 'thermal' parts seem to play an important role and improve the
model's results. In addition, a delay in the sea breeze front was found, and a reason-
able frictional retard concerning its penetration, as well as an inland displacement
of the heat island, as the air moved over the city of Athens.
10.1 Introduction
Urbanization leads to the replacement of natural surfaces with buildings and paved
surfaces. This change in surface characteristics together with human activities in
urban environments alters heat, moisture and momentum exchange processes in
the atmospheric boundary layer (ABL) and distinguishes the urban climate from
that of surrounding rural areas (Fan and Sailor, 2005). Land-surface parameteriza-
tions in nearly all advanced meteorological models are built around a prognostic
energy budget equation for the earth's surface temperature and they may include
a prognostic equation for soil moisture, as well (Seaman, 2000). The urban areas
usually appear as bare soil with different classifications of surface characteristics
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