NOCN03 CWAO 162035 GENOT NO. 007 VERSION FRANCAISE DANS LE GENOT NO. 008 BILINGUAL MESSAGE - FRENCH TEXT TO FOLLOW ENGLISH TEXT MESSAGE BILINGUE - LE TEXTE FRANCAIS SUIT LE TEXTE ANGLAIS GEM-MACH15 AIR QUALITY FORECAST MODEL TO REPLACE CHRONOS AT THE CANADIAN METEOROLOGICAL CENTRE ON NOVEMBER 18 2009 STARTING WITH THE 1200 UTC RUN, THE CANADIAN METEOROLOGICAL CENTRE (CMC) WILL IMPLEMENT GEM-MACH15, A 15-KM CONFIGURATION OF THE NEW ON-LINE OPERATIONAL AIR QUALITY FORECAST MODEL CALLED GEM-MACH (GLOBAL ENVIRONMENTAL MULTI-SCALE MODEL - MODELLING AIR QUALITY AND CHEMISTRY). GEM-MACH15 WILL REPLACE THE CURRENT MODEL CHRONOS (CANADIAN HEMISPHERIC AND REGIONAL OZONE AND NOX SYSTEM), WHICH HAS BEEN IN SERVICE SINCE 1999. THE NEW MODEL, WHICH FEATURES A MORE SOPHISTICATED REPRESENTATION OF CHEMICAL PROCESSES AND AN IMPROVED SET OF EMISSIONS, WILL IMMEDIATELY PROVIDE IMPROVEMENTS TO THE AIR QUALITY FORECAST SYSTEM, WHILE ENABLING MORE SIGNIFICANT ADVANCEMENTS IN THE YEARS TO COME. 1. OVERVIEW OF CHANGES 1.1 ON-LINE VERSUS OFF-LINE CHRONOS IS AN OFF-LINE CHEMICAL TRANSPORT MODEL. THE METEOROLOGY USED IN ITS INTEGRATION IS PROVIDED BY AN INDEPENDENT WEATHER FORECAST MODEL (CURRENTLY, THE GEM-REGIONAL MODEL). SINCE THE TWO MODELS DO NOT SHARE THE SAME GRID, AN INTERPOLATION OF THE METEOROLOGICAL OUTPUT FIELDS FROM THE WEATHER MODEL GRID TO THE CHRONOS GRID IS REQUIRED, WHICH INTRODUCES ERRORS AND IS TIME-CONSUMING. GEM-MACH, ON THE OTHER HAND, IS AN ON-LINE MODEL IN WHICH THE CHEMISTRY IS INTEGRATED IN-STEP WITH THE DYNAMICAL AND PHYSICAL WEATHER PROCESSES. THE ELIMINATION OF THE INTERPOLATION STEP REDUCES ERRORS AND INCREASES COMPUTATIONAL EFFICIENCY. GEM-MACH15 SHARES SIMILAR PHYSICAL AND DYNAMICAL LIBRARIES WITH THE REGIONAL OPERATIONAL WEATHER FORECAST MODEL, GEM-REGIONAL. 1.2 MORE SOPHISTICATED CHEMISTRY PROCESSES SIGNIFICANT IMPROVEMENTS HAVE BEEN MADE WITH RESPECT TO THE PROCESSING OF AEROSOLS IN GEM-MACH. FIRST THE NUMBER OF CHEMICAL SPECIES IN THE TREATMENT OF PARTICULATE MATTER (PM) COMPOSITION HAS BEEN INCREASED FROM 4 TO 8. IMPROVEMENTS HAVE ALSO BEEN MADE TO PARAMETERIZATIONS OF AEROSOL DYNAMICS, SECONDARY ORGANIC AEROSOL YIELDS, AND WET DEPOSITION. THE CHEMICAL INITIAL AND BOUNDARY CONDITIONS HAVE ALSO BEEN MODIFIED TO BE MORE REPRESENTATIVE OF TRUE CLIMATOLOGICAL LEVELS OF THE BASIC POLLUTANTS. AQUEOUS-PHASE CHEMISTRY PROCESSES HAVE BEEN ADDED TO GEM-MACH, WHEREAS NONE WERE INCLUDED IN CHRONOS. ANTHROPOGENIC EMISSIONS FOR GEM-MACH15 ARE NOW BASED ON THE 2006 AND 2005 EMISSIONS INVENTORIES FOR CANADA AND THE UNITED STATES, RESPECTIVELY, WHEREAS EMISSIONS FOR CHRONOS WERE BASED ON UPDATED VERSIONS OF THE 2000 AND 2001 INVENTORIES, RESPECTIVELY. BOTH SPATIAL AND TEMPORAL ALLOCATIONS OF ANTHROPOGENIC AND BIOGENIC EMISSIONS HAVE BEEN IMPROVED AND PRIMARY PM EMISSIONS ARE NOW SPECIATED CHEMICALLY. 1.3 MODEL DOMAIN, HORIZONTAL RESOLUTION, AND TIME STEP GEM-MACH15 IS A LIMITED AREA MODEL (LAM) CONFIGURATION OF THE NEW GEM-MACH MODEL WITH 15-KM HORIZONTAL GRID SPACING. ITS MODEL DOMAIN PROVIDES A BETTER COVERAGE OF THE CANADIAN LANDMASS THAN WAS AVAILABLE FROM CHRONOS. HORIZONTAL MODEL RESOLUTION HAS BEEN INCREASED FROM THE 21-KM HORIZONTAL GRID SPACING OF CHRONOS. THE GEM-MACH15 GRID POINTS ARE COLOCATED WITH A SUBSET OF THE GRID POINTS OF THE UNIFORM-RESOLUTION CORE GRID OF THE GEM-REGIONAL WEATHER MODEL. THEREFORE, GEM-MACH15 IS ABLE TO MAKE DIRECT USE OF THE METEOROLOGICAL INITIAL AND BOUNDARY CONDITIONS FROM THE REGIONAL WEATHER FORECAST MODEL WITHOUT THE NEED FOR INTERPOLATION. THE WEATHER PROCESSES IN GEM-MACH15 ARE EXECUTED WITH THE SAME TIME STEP OF 450 S AS IS USED FOR THE WEATHER MODEL. THE CHEMISTRY PROCESSES ARE NOW EXECUTED WITH A TIME STEP OF 900 S FOR GEM-MACH15 VERSUS 3600 S FOR CHRONOS. 1.4 MODEL LID RAISED TO 0.1 HPA (64 KM) THE MODIFIED GAL-CHEN VERTICAL COORDINATE OF THE CHRONOS MODEL IS REPLACED BY A NEW HYBRID COORDINATE WITHIN GEM-MACH15, WHICH IS SIMILAR TO THE NEW COORDINATE OF THE GEM-REGIONAL WEATHER MODEL. THE NUMBER OF MODEL LEVELS HAS BEEN INCREASED FROM 24 TO 58 AND THE MODEL LID HAS BEEN RAISED FROM 6 TO 64 KM (0.1 HPA), MATCHING THE TOP OF GEM-REGIONAL. RAISING THE MODEL LID ALLOWS FOR A MORE REALISTIC REPRESENTATION OF METEOROLOGICAL PROCESSES. 1.5 PARALLEL PROCESSING CHRONOS IS CODED IN SUCH A WAY THAT IT CANNOT TAKE FULL ADVANTAGE OF THE SUPERCOMPUTER RESOURCES AVAILABLE AT THE CMC. BY CONTRAST, GEM-MACH HAS BEEN CODED TO RUN OPTIMALLY IN THE CURRENT AND FUTURE COMPUTING ENVIRONMENT, ALLOWING THE MODEL TO DRAW UPON THE FULL RESOURCES OF THE SUPERCOMPUTER. IN THE FUTURE, THIS WILL ALSO PERMIT THE DEVELOPMENT OF A MORE SOPHISTICATED AIR QUALITY MODEL WHILE MAINTAINING OR REDUCING THE EXECUTION TIME. 2. PERFORMANCE EVALUATION GEM-MACH15 HAS BEEN TESTED EXTENSIVELY OVER SUMMER AND WINTER SEASONS SINCE 2007. MOST RECENTLY, THE MODEL HAS BEEN RUN IN PARALLEL WITH CHRONOS DURING THE SUMMER OF 2009. DURING THIS PERIOD, A COORDINATED EVALUATION OF THE MODEL BY OPERATIONAL FORECASTERS AT REGIONAL WEATHER OFFICES AND AT CMC, BY MODEL DEVELOPERS, AND BY ENVIRONMENT CANADA AIR QUALITY SCIENCE UNITS HAS GREATLY BENEFITED THE DEVELOPMENT OF GEM-MACH15. 2.1 OBJECTIVE EVALUATION OBJECTIVE EVALUATION SCORES GENERALLY INDICATE A SMALL IMPROVEMENT IN THE FORECASTS GENERATED BY GEM-MACH15, PARTICULARLY FOR O3 AND NO2. THE CORRELATION AND UNBIASED RMSE SCORES ARE GENERALLY IMPROVED, WHEREAS THE MODEL MEAN BIAS HAS DETERIORATED SOMEWHAT FOR O3 AND PM2.5. 2.2 SUBJECTIVE EVALUATION SUBJECTIVE EVALUATIONS DURING THE DEVELOPMENT AND PARALLEL RUNS INDICATE AN OVERALL SLIGHT IMPROVEMENT IN MODEL PERFORMANCE FOR GEM-MACH15 OVER CHRONOS. IN SUMMER, O3 AND NO2 ARE GENERALLY BETTER HANDLED BY GEM-MACH15. PM2.5 IS GENERALLY SLIGHTLY OVER-PREDICTED BY GEM-MACH15, WHEREAS IT IS REGULARLY UNDER-PREDICTED BY CHRONOS. IN WINTER, A MARKED IMPROVEMENT IS VISIBLE IN THE PREDICTION OF O3 FIELDS AS A RESULT OF THE NEW BOUNDARY CONDITIONS PROVIDING MORE REALISTIC BACKGROUND LEVELS OF O3. OTHER SIGNIFICANT, BUT ISOLATED IMPROVEMENTS HAVE BEEN NOTED IN WESTERN CANADIAN CITES, WHICH ARE ATTRIBUTED TO IMPROVED EMISSIONS. 2.3 EVALUATION OF METEOROLOGY METEOROLOGICAL FIELDS PRODUCED FROM GEM-MACH15 WERE COMPARED WITH THOSE OF THE GEM-REGIONAL WEATHER FORECAST MODEL. A STUDY OF MASS FIELDS INDICATES NO SIGNIFICANT DEPARTURES IN THE TROPOSPHERE, WHERE THE VERTICAL RESOLUTION IS IDENTICAL. A SMALL DETERIORATION WAS FOUND IN THE STRATOSPHERE, WHICH CAN BE PRIMARILY ATTRIBUTED TO A REDUCTION IN VERTICAL RESOLUTION IN GEM-MACH15. A COMPARISON OF PRECIPITATION FIELDS DURING THE DEVELOPMENT RUNS SHOWED NO APPRECIABLE DIFFERENCES BETWEEN THE MODELS. THESE RESULTS ARE NOT UNEXPECTED AS THE MODELS SHARE SIMILAR DYNAMICS AND PHYSICS LIBRARIES. 3. IMPACT ON OPERATIONAL PRODUCTS AND OTHER FORECAST SYSTEMS AFTER IMPLEMENTATION, SCRIBE MATRICES WILL CONTAIN GEM-MACH15 OUTPUT RATHER THAN THE CURRENT CHRONOS OUTPUT. IMAGE PRODUCTS FROM GEM-MACH15 WILL REPLACE THE EQUIVALENT PRODUCTS FOR CHRONOS CURRENTLY AVAILABLE AT HTTP://WWW.WEATHEROFFICE.GC.CA/CHRONOS/INDEX_E.HTML. A REVIEW OF THIS WEB PAGE IS PRESENTLY UNDERWAY TO REMOVE REFERENCES TO CHRONOS AND ADD THE PROPER REFERENCES TO GEM-MACH15. ALSO, A THOROUGH REVIEW OF THESE PRODUCTS WILL BE UNDERTAKEN TO MAKE USE OF IMPROVED METHODS OF DISSEMINATING MODEL OUTPUT FROM GEM-MACH15. 4. AVAILABILITY OF PRODUCTS PRODUCTS FROM GEM-MACH15 ARE EXPECTED TO BE AVAILABLE 45 TO 80 MINUTES SOONER THAN EQUIVALENT PRODUCTS PREVIOUSLY PRODUCED FROM THE CHRONOS MODEL. A TECHNICAL NOTE DESCRIBING THE GEM-MACH15 MODEL IN MORE DETAIL WILL SOON BE AVAILABLE AT: HTTP://WWW.SMC-MSC.EC.GC.CA/CMC/OP_SYSTEMS/RECENT_E.HTML FOR SPECIFIC QUESTIONS CONCERNING THIS IMPLEMENTATION, PLEASE WRITE TO: PRODUCTION-INFO(AT)CMC.EC.GC.CA GRIMES ADMA - MSC / SMA - SMC TORONTO