Microscale Numerical Prediction over Montreal with the Canadian External Urban Modeling System

Abstract

The Canadian urban and land surface external modeling system (known as urban GEM-SURF) has been developed to provide surface and near-surface meteorological variables to improve numerical weather prediction and to become a tool for environmental applications. The system is based on the Town Energy Balance model for the built-up covers and on the Interactions between the Surface, Biosphere, and Atmosphere land surface model for the natural covers. It is driven by coarse-resolution forecasts from the 15-km Canadian regional operational model. This new system was tested for a 120-m grid-size computational domain covering the Montreal metropolitan region from 1 May to 30 September 2008. The numerical results were first evaluated against local observations of the surface energy budgets, air temperature, and humidity taken at the Environmental Prediction in Canadian Cities (EPiCC) field experiment tower sites. As compared with the regional deterministic 15-km model, important improvements have been achieved with this system over urban and suburban sites. GEM-SURF’s ability to simulate the Montreal surface urban heat island was also investigated, and the radiative surface temperatures from this system and from two systems operational at the Meteorological Service of Canada were compared, that is, the 15-km regional deterministic model and the so-called limited-area model with 2.5-km grid size. Comparison of urban GEM-SURF outputs with remotely sensed observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) reveals relatively good agreement for urban and natural areas.

A parametrization of 3‐D subgrid‐scale clouds for conventional GCMs: Assessment using A‐Train satellite data and solar radiative transfer characteristics

“…Nevertheless, there are important advantages that a 3‐D MC treatment has over 1‐D parametrizations: full separation of the RT model from descriptions of attenuating media: descriptions of subgrid‐scale variations of the Earth‐atmosphere system rest with stochastic generators that are relatively easy to alter and adjust [cf. Räisänen et al ., ]; account of 3‐D RT effects: assuming that regime‐dependent 3‐D RT effects are important, their biases and accuracies are limited only by the credibility of the stochastic generator; handling of scattering properties: MC RT solutions are effectively infinite‐stream models that can faithfully include arbitrarily detailed descriptions of particle scattering phase functions that vary throughout arbitrarily complex atmospheres [see Barker et al ., ]; measurement simulation: if the local estimation method is used for the MC solution [ Marchuk et al ., ], fluxes and radiances can be computed straightforwardly, and efficiently, thereby ensuring consistency between modeled and diagnostic radiative quantities; scale independence I: MC RT models are scale independent so as the sizes of a GCM's grid‐spacings change, only the stochastic generator needs to be altered, not the RT model; scale independence II: as GCM horizontal grid‐spacings rival typical cloud cell sizes, such as in high‐resolution domains of weather prediction models [e.g., Leroyer et al ., ; Vionnet et al ., ], subgrid‐scale cloud generators can be jettisoned leaving the 3‐D MC RT model that operated on stochastically generated atmospheres to operate on domains provided by the host GCM. …”

How can we use MODIS land surface temperature to validate long-term urban model simulations?

“…Land surface temperature (LST) products from satellite remote‐sensing platforms are widely available and are potential sources for model validation, having comprehensive spatial coverage, comparable scale with models, and constant periodicity. There are many ways to apply satellite LST data to evaluate and improve atmospheric model simulations at multiple temporal and spatial scales [ Jin et al , ; Sohrabinia et al , ; Miao et al , ; Leroyer et al , ]. For example, Jin et al [] compared skin temperatures simulated with NCAR Community Climate Model (CCM2) coupled with a biosphere‐atmosphere transfer scheme with satellite‐derived radiative temperature to evaluate model performance globally.…”

Role and Impact of the Urban Environment in a Numerical Forecast of an Intense Summertime Precipitation Event over Tokyo

“…The TEB scheme has been extensively tested since its early development over a wide variety of cities and climate conditions (e.g., Lemonsu and Masson 2002, Hamdi et al 2012. Several of these studies have been performed with GEM or its offline component GEM-Surf, as described in Lemonsu et al (2009) and Leroyer et al (2011).…”