Pierre Pellerin

The Canadian MC2: A Semi-Lagrangian, Semi-Implicit Wideband Atmospheric Model Suited for Finescale Process Studies and Simulation

Abstract This paper attempts to document the developmental research and early mesoscale results of the new fully nonhydrostatic atmospheric model called MC2 (mesoscale compressible community). Its numerical scheme is the semi-implicit semi-Lagrangian approach conceived and demonstrated by Tanguay, Robert, and Laprise. The dominant effort required to become a full-fledged mesoscale model was to connect it properly to a full-scale and evolving physics package; the enlarged scope of a package previously dedicated to hydrostatic pressure coordinate-type models posed some new questions. The one-way nesting is reviewed and particularly the self-nesting or cascade mode; the potential implication of this mode is explored with a stand-alone forecast experiment and related to the other existing approach employing hemispheric or global variable meshes. One of the strong assets of MC2 is its growing community of users and developers. To demonstrate the wideband characteristic of MC2, that is, its applicability to a l...

On the Use of Coupled Atmospheric and Hydrologic Models at Regional Scale

Abstract. The purpose of this study is to present the possibilities offered by coupled atmospheric and hydrologic models as a new tool to validate and interpret results produced by atmospheric models. The advantages offered by streamflow observations are different from those offered by conventional precipitation observations. The dependence between basins and sub-basins can be very useful, and the integrating effect of the large basins facilitates the evaluation of stateof-the-art atmospheric models by filtering out some of the spatial and temporal variability that complicate the point-by-point verifications that are more commonly used. The streamflow predicted by the coupled atmospheric-hydrologic model versus the measured streamflow is sufficiently sensitive to clearly assess atmospheric model improvements resulting from increasing horizontal resolution and altering the treatment of precipitation processes in the model. A case study for several southern Ontario river basins is presented with the Watflood hydrologic model developed at the University of Waterloo. It is passively coupled to a nonhydrostatic mesoscale atmospheric model (mc2) that is integrated 318 HIGH PERFORMANCE COMPUTING SYSTEMS AND APPLICATIONS at horizontal resolutions of 35, 10 and 3 km. The Watflood model is also driven by radar derived precipitation amounts from King City Radar observations. It is demonstrated that the hydrological model is sufficiently sensitive and accurate to diagnose model and radar errors. This tool brings an additional degree of verification that will be very important in the improvement of technologies associated with atmospheric models, radar observations and the water resources management.

Impact of a Two-Way Coupling between an Atmospheric and an Ocean-Ice Model over the Gulf of St. Lawrence

The purpose of this study is to present the impacts of a fully interactive coupling between an atmospheric and a sea ice model over the Gulf of St. Lawrence, Canada. The impacts are assessed in terms of the atmospheric and sea ice forecasts produced by the coupled numerical system. The ocean-ice model has been developed at the Maurice Lamontagne Institute, where it runs operationally at a horizontal resolution of 5 km and is driven (one-way coupling) by atmospheric model forecasts provided by the Meteorological Service of Canada (MSC). In this paper the importance of two-way coupling is assessed by comparing the one-way coupled version with a two-way coupled version in which the atmospheric model interacts with the sea ice model during the simulation. The impacts are examined for a case in which the sea ice conditions are changing rapidly. Two atmospheric model configurations have been studied. The first one has a horizontal grid spacing of 24 km, which is the operational configuration used at the Canadian Meteorological Centre. The second one is a high-resolution configuration with a 4-km horizontal grid spacing. A 48-h forecast has been validated using satellite images for the ice and the clouds, and also using the air temperature and precipitation observations. It is shown that the two-way coupled system improves the atmospheric forecast and has a direct impact on the sea ice forecast. It is also found that forecasts are improved with a fine resolution that better resolves the physical events, fluxes, and forcing. The coupling technique is also briefly described and discussed.

A new adiabatic kernel for the MC2 model

Abstract Traditional semi‐implicit formulations of nonhydrostatic compressible models may not be stable in the presence of steep terrain when pressure gradient terms are split and lagged in time. If all pressure gradient terms and the divergence are treated implicitly, the resulting wave equation for the pressure contains off‐diagonal cross‐derivative terms leading to a highly nonsymmetric linear system of equations. In this paper we present a more implicit formulation of the Mesoscale Compressible Community (MC2) model employing a Generalized Minimal Residual (GMRES) Krylov iterative solver and a more efficient semi‐Lagrangian advection scheme. Open boundaries now permit exact upwind interpolation and the ability to reproduce simulations to machine precision is illustrated for one‐way nesting at equivalent resolution. Numerical simulations of hydrostatic and nonhydrostatic mountain waves demonstrate the stability and accuracy of the new adiabatic kernel. The computational efficiency of the model is repor...

Massively parallel implementation of mesoscale compressible community model

Abstract Computational fluid dynamics and meteorology in particular are among the major consumers of high performance computer technology. The next generation of atmospheric models will be capable of representing fluid flow phenomena at very small scales in the atmosphere. The mesoscale compressible community (MC2) model represents one of the first successful applications of a semi-implicit, semi-Lagrangian scheme to integrate the compressible governing equations for atmospheric flow in a limited area domain. A distributed-memory SPMD implementation of the MC2 model is described and the convergence rates of various parallel preconditioners for a Krylov type GMRES elliptic solver are reported. Parallel performance of the model on the Cray T3E MPP and NEC SX-4/32 SMP is also presented.

Operational Wave Prediction System at Environment Canada: Going Global to Improve Regional Forecast Skill

AbstractA global deterministic wave prediction system (GDWPS) is used to improve regional forecasts of waves off the Canadian coastline and help support the practice of safe marine activities in Canadian waters. The wave model has a grid spacing of ¼° with spectral resolution of 36 frequency bins and 36 directional bins. The wave model is driven with hourly 10-m winds generated by the operational global atmospheric prediction system. Ice conditions are updated every three hours using the ice concentration forecasts generated by the Global Ice–Ocean Prediction System. Wave forecasts are evaluated over two periods from 15 August to 31 October 2014 and from 15 December 2014 to 28 February 2015, as well as over select cases during the fall of 2012. The global system is shown to improve wave forecast skill over regions where forecasts were previously produced using limited-area models only. The usefulness of a global expansion is demonstrated for large swell events affecting the northeast Pacific. The first va...

High-Performance Modelling for the Mesoscale Alpine Programme (MAP) Field Experiment

With the development of a version of the Canadian non-hydrostatic MC2 model optimized for massively parallel processors, it has become possible to solve very large weather forecast problems in a time sufficiently short to envision a realtime daily calculation over a domain covering the entire Alps. MAP is a large multinational research program that will gather new knowledge about the heavy precipitation over steep topography; its field phase is to take place during Fall of 1999. The tentative grid dimensions are 490 − 400 − 35 at a horizontal resolution of 2 km, with possibly a need to increase the number of vertical layers. This is a very large problem to be solved with realtime constraints. The model results will be accessible to the forecasters at the MAP Operations Centre in Innsbruck, to assist in the scientific briefings to dispatch the flight plans of the research aircraft. The forecasts are planned to be performed on the NEC-SX/4 (10 PE) at the CSCS (Centro Svizzero di Calcolo Scientifico) in Manno (Canton Ticino, Switzerland), which is affiliated with the ETH. The current state of this joint effort is presented.

Modeling the Canadian southern Atlantic region oxidants: A study of a Canadian EMEFS‐1 hyperintensive period

The roles and mechanisms of transport and chemical transformation affecting surface ozone in the Canadian southern Atlantic region (SAR) are investigated using a three-dimensional Eulerian comprehensive modeling system. The investigation is focused a regional ozone episode over the eastern North America during the first week of August 1988. The model performance is evaluated with available observations during this period. The model is shown to reproduce the general features of this regional episode, with better performance for the sites with clear local photochemical activities than for those strongly influenced by complex coastal flow. It is shown from the reconstructed time history of various processes along the backward trajectories originating from a site in Nova Scotia that the elevated ground-level ozone in the SAR during the study period was associated with transport at low levels, under a strong southwesterly flow. The high ozone brought to the site was mostly produced within the stable marine boundary layer from precursors picked up earlier over the emission area on the east coast of the United States. A second transport situation was also simulated and shown to be associated with transport aloft that was never mixed to the surface. This study also shows that differential advection, due to stable stratification and vertical shear of horizontal wind, can deform surface-based plumes to produce elevated layers of pollutants over the Gulf of Maine.

Impact of Coupling with an Ice–Ocean Model on Global Medium-Range NWP Forecast Skill

AbstractThe importance of coupling between the atmosphere and the ocean for forecasting on time scales of hours to weeks has been demonstrated for a range of physical processes. Here, the authors evaluate the impact of an interactive air–sea coupling between an operational global deterministic medium-range weather forecasting system and an ice–ocean forecasting system. This system was developed in the context of an experimental forecasting system that is now running operationally at the Canadian Centre for Meteorological and Environmental Prediction. The authors show that the most significant impact is found to be associated with a decreased cyclone intensification, with a reduction in the tropical cyclone false alarm ratio. This results in a 15% decrease in standard deviation errors in geopotential height fields for 120-h forecasts in areas of active cyclone development, with commensurate benefits for wind, temperature, and humidity fields. Whereas impacts on surface fields are found locally in the vicin...

A Regional Modelling Study of Transport Affecting the Canadian Southern Atlantic Region Oxidants

Elevated ozone levels in the Canadian southern Atlantic region (SAR) are usually associated with regional ozone episodes over the northeastern US and southern Ontario/Quebec, typically under the synoptic settings of a high pressure system to the east over the Atlantic Ocean and a low pressure system to the northwest. Under this condition the southwesterly flow at the backside of the high pressure cell favours the transport of ozone and its precursors from the US northeastern seaboard to the SAR. Observations during the 1993 North Atlantic Regional Experiment field campaign indicate that high ozone observed over the Gulf and over the coast of Nova Scotia is generally related to moderate to fast transport from the Boston-New York corridor, typically in the warm sector ahead of an approaching cold front. However, due to the complicated vertical layering structure that dominates the lower atmosphere over the Gulf of Maine, especially towards the Nova Scotia side, high ozone concentrations are often observed well above the surface unaccompanied by surface ozone events.