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Modelling Near-Surface Low Winds over Land under Stable Conditions: Sensitivity Tests,Flux-Gradient Relationships,and Stability Parameters 总被引:1,自引:1,他引:0
Low or weak wind-speed conditions, roughly defined as the periods when the mean wind speed at 10 m above the ground is 2 ms−1 or less, are of considerable practical interest. However, they are not readily amenable to treatment within prognostic meteorological
models and, consequently, difficult to predict, especially when the ambient stability is strong. In this paper, we apply an
E − ε prognostic meteorological model to simulate near-surface meteorology and, focusing on low wind speeds, compare the predictions
with measurements from two independent datasets. A sensitivity analysis is performed to investigate the possible reasons for
the relatively inferior model performance for low winds when the atmosphere is stably stratified. A comprehensive data analysis
is carried out to study low wind stable conditions, concentrating on the validity of various forms of flux–gradient relationships
for momentum and heat within the framework of the Monin-Obukhov similarity theory, which models employ for calculating surface
fluxes. The observed behaviour of various stability parameters, such as the Richardson number, is investigated. The results
point to inadequacies of the current flux–gradient relationships, especially regarding momentum, under strongly stable conditions
as being a dominant reason for the poor low wind predictions. The modelling issues identified are not just restricted to the
present model, but are general in nature. The use of an alternative stability function for momentum under strongly stable
conditions is explored. It results in improved model performance for low winds; however, further research is needed to better
understand strongly stable flows in the lower atmosphere and to develop methods that can translate that understanding to operational
meteorological modelling. 相似文献
2.
The meteorology at the Cabauw tower site in the Netherlands has been modelled for 2005 using a local scale prognostic meteorological
and air pollution model called TAPM. A number of performance measures have been used to assess model accuracy, including comparison
statistics such as root-mean-square error (RMSE) and index of agreement (IOA). Results show that the model performs very well
for prediction of wind and temperature at the six tower levels that range from 10 to 200 m above the ground, as well as performing
well for radiation and surface fluxes. The model simulation shows almost no bias in mean and standard deviations of wind and
temperature at each tower height level, with small RMSE (e.g. RMSE of 1.2 m s−1 for 10-m wind speed, and 1.6°C for 10-m temperature) and high correlation and IOA (e.g. IOA of 0.92 for 10-m wind speed and
0.98 for 10-m temperature). Results for radiation and surface fluxes also show good performance, although some biases were
seen for these variables, and possibilities for future model development were identified. An examination of model sensitivity
also explored several aspects of the model configuration and input. 相似文献
3.
Peter Hurley 《Boundary-Layer Meteorology》2007,125(3):525-536
The treatment of turbulence closure in atmospheric models is examined in the context of the dry convective boundary layer
(CBL) and the eddy-diffusivity/mass-flux (EDMF) approach. The EDMF approach is implemented into a model called TAPM to use
a coupled two-equation prognostic turbulence closure and the mass-flux approach to represent turbulence in the CBL. This work
also extends the range of turbulence variables that can be derived from the mass-flux component of the model and uses these
along with their values from the prognostic scheme to provide total turbulence fields that can be used to compare to data
and/or to feed into other components of TAPM, including those needed to drive Eulerian and Lagrangian air pollution dispersion
modules. Model results are presented for the afternoon of a simulated summer day and are compared to both laboratory and field
observations in a mixed-layer scaled framework. The results show that the EDMF approach works well within TAPM and can provide
good predictions of mean and turbulence fields, including in the upper levels of the CBL. The EDMF approach has several attractive
features, including the potential to be one approach to unify the treatment of turbulence and dry and moist convection in
atmospheric models. 相似文献
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