Mesoscale Meteorological Model Research Articles

Model based distributed water balance monitoring of the White Volta catchment in West Africa through coupled meteorological-hydrological simulations

Abstract. Sustainable water management requires the quantification of the spatial and temporal changes of water balance variables. Fully distributed hydrological simulations of these variables are especially in regions with weak infrastructure challenging, because the required meteorological input data are often not available in a sufficient spatial and temporal resolution. One possibility to deal with this limitation is to provide the required input data with a meteorological model. This combination results in a one way meteorological-hydrological coupling system. Within the framework of the GLOWA-Volta project it is investigated to what extent meteorological models are able to provide the required meteorological fields with sufficient accuracy for the hydrological modeling. For this study the mesoscale meteorological model MM5 and the fully distributed water balance simulation model WaSiM-ETH were first adapted and validated separately. The research area is the White Volta catchment in the semi-arid to sub-humid climate zone in West Africa. The meteorological simulations tend toward overestimating measured precipitation sums. The coupled meteorological-hydrological runoff simulations show similar model performances as the simulations driven by observations indicating the potential of this system for a contemporary estimation of the terrestrial water balance.

Description of the University of Auckland global Mars mesoscale meteorological model

The University of Auckland global Mars mesoscale meteorological model (GM4) is a numerical model of the martian atmosphere that has been developed through the conversion of the Penn State University/National Center for Atmospheric Research fifth generation mesoscale model (MM5). The model is initialized in this paper through the implementation of a ‘base-state’ atmosphere. Continual boundary condition input from a GCM is unnecessary as the global domains of the model are self consistent and form a continuous domain around the entire planet. A description of the model and its basic underlying physical principles as applicable to the atmosphere of Mars is outlined. Comparison between ASI/Met data collected from Mars Pathfinder during its 1997 mission and simulated conditions using GM4 is given. Diurnal temperature variation as predicted by the model shows very good correspondence with the measured surface data, to within 5 K for the majority of the diurnal cycle. Mars Viking I surface meteorological data is compared to the GM4 model, yielding similar results. To assess the vertical structure of the atmosphere, simulations have also been compared with Mars Global Surveyor Radio Science temperature–pressure profiles. As a further test for the model, various seasonal comparisons of surface and vertical atmospheric structure are performed with the European Space Agency AOPP/LMD Mars Climate Database. Agreement between the two models is reasonable, though polar regions are not very well represented by the GM4 model at present. As an experimental case study, mountain flow over Olympus Mons is simulated using this new mesoscale modeling system, showing results in good agreement with similar model simulations and observational data.

Mesoscale simulations of atmospheric flow and tracer transport in Phoenix, Arizona

AbstractLarge urban centres located within confining rugged or complex terrain can frequently experience episodes of high concentrations of lower atmospheric pollution. Metropolitan Phoenix, Arizona (United States), is a good example, as the general population is occasionally subjected to high levels of lower atmospheric ozone, carbon monoxide and suspended particulate matter. As a result of dramatic but continuous increase in population, the accompanying environmental stresses and the local atmospheric circulation that dominates the background flow, an accurate simulation of the mesoscale pollutant transport across Phoenix and similar urban areas is becoming increasingly important. This is particularly the case in an airshed, such as that of Phoenix, where the local atmospheric circulation is complicated by the complex terrain of the area.Within the study presented here, a three‐dimensional time‐dependent mesoscale meteorological model (HOTMAC) is employed for simulation of lower‐atmospheric flow in Phoenix, for both winter and summer case‐study periods in 1998. The specific purpose of the work is to test the model's ability to replicate the atmospheric flow based on the actual observations of the lower‐atmospheric wind profile and known physical principles. While a reasonable general agreement is found between the model‐produced flow and the observed one, the simulation of near‐surface wind direction produces a much less accurate representation of actual conditions, as does the simulation of wind speed over 1,000 metres above the surface. Using the wind and turbulence output from the mesoscale model, likely particle plume trajectories are simulated for the case‐study periods using a puff dispersion model (RAPTAD). Overall, the results provide encouragement for the efforts towards accurately simulating the mesoscale transport of lower‐atmospheric pollutants in environments of complex terrain. Copyright © 2006 John Wiley & Sons, Ltd.

Traffic-related particulate air pollution exposure in urban areas

In the last years, there has been an increase of scientific studies confirming that long- and short-term exposure to particulate matter (PM) pollution leads to adverse health effects. The development of a methodology for the determination of accumulated human exposure in urban areas is the main objective of the current work, combining information on concentrations at different microenvironments and population time–activity pattern data. A link between a mesoscale meteorological and dispersion model and a local scale air quality model was developed to define the boundary conditions for the local scale application. The time–activity pattern of the population was derived from statistical information for different sub-population groups and linked to digital city maps. Finally, the hourly PM 10 concentrations for indoor and outdoor microenvironments were estimated for the Lisbon city centre, which was chosen as the case-study, based on the local scale air quality model application for a selected period. This methodology is a first approach to estimate population exposure, calculated as the total daily values above the thresholds recommended for long- and short-term health effects. Obtained results reveal that in Lisbon city centre a large number of persons are exposed to PM levels exceeding the legislated limit value.

Use of a complex air pollution model to estimate dispersal and deposition of grass stem rust urediniospores at landscape scale

Dispersal and dry deposition of urediniospores of Puccinia graminis subsp. graminicola from infected perennial ryegrass was modeled with CALPUFF, a Lagrangian puff atmospheric dispersal model developed for air pollution studies. The emission rate (spores/min/m 2 field area) was back-calculated from aerial spore flux from a 6 m × 6 m source plot. Spore flux was measured by a novel approach in which the cross-section of the entire plume was sampled immediately downwind of the source. The diurnal pattern of spore release was obtained from continuous volumetric spore sampler measurements in a nearby field. Weather observations at the study site were combined with three-dimensional prognostic meteorological fields generated by the Penn State Mesoscale Meteorological Model (MM5) using CALMET to run CALPUFF. The settling velocities of single and clustered spores were measured in the laboratory. Deposition fields and mass balances from the 6 m × 6 m plots were modeled by using observations from four dates in June 2005. A deposition level of 10 spores/m 2 was estimated to reach 1.8–2.1 km downwind of the plot on different days. For three of the dates CALPUFF estimated few or no spores remaining airborne as long as an hour after release above the canopy. Modeling of spore dispersal from 5- or 50-ha fields of rust-infested perennial ryegrass indicated deposition of 10 spores/m 2 at a distance of 2.1–5.9 km from the field, depending on weather and source strength (size of field and severity of rust disease), and deposition of 0.01 spores/m 2 was indicated to extend more than 12 km from a heavily infested 50-ha field for one of the days. In this scenario 10 14 spores were released from the field in 24 h, 18 million remained airborne more than an hour and 400,000 reach the air aloft. Simulation of spore dispersal by a small dust devil showed 12.5% of the spore biomass advected horizontally beyond 200 km in the air aloft.

복잡 해안지역 해상풍 모의의 정확도 개선-II: LAPS를 사용한 자료동화

We focus on the improvement of accuracy of sea surface wind over complex coastal area doling the warm season. Local Analysis Prediction System (LAPS) was used to improve the initial values in Mesoscale Meteorological model (MM5). During the clear summer days with weak wind speed, sea surface wind simulated with LAPS was compared with the case without LAPS. The results of modeling with LAPS has a good agreement mesoscale circulation such as mountain and valley winds on land and in case of modeling without LAPS, wind speed overestimated over the sea in the daytime. And the results of simulation with LAPS indicated similar wind speed values to observational data over the sea under influence of data assimilation using BUOY, QuikSCAT, and AMEBAS. The present study suggests that MM5 modelling with LAPS showed more improved results than that of without LAPS to simulate sea surface wind over the complex coastal area.

한반도를 포함한 동아시아 영역에서 오존전량과 유해자외선의 특성과 예측

The average ratio of the daily UV-B to total solar (75) irradiance at Busan (35.23N, 129.07E) in Korea is found as 0.11%. There is also a high exponential relationship between hourly UV-B and total solar irradiance: UV-B=exp (a(75-b))(R=0.93). The daily variation of total ozone is compared with the UV-B irradiance at Pohang (36.03N, 129.40E) in Korea using the Total Ozone Mapping Spectrometer (TOMS) data during the period of May to July in 2005. The total ozone (TO) has been maintained to a decreasing trend since 1979, which leading to a negative correlation with the ground-level UV-B irradiance doting the given period of cloudless day: UV-B=239.23-0.056 TO (R=0.52). The statistical predictions of daily total ozone are analyzed by using the data of the Brewer spectrophotometer and TOMS in East Asia including the Korean peninsula. The long-term monthly averages of total ozone using the multiplicative seasonal AutoRegressive Integrated Moving Average (ARIMA) model are used to predict the hourly mean UV-B irradiance by interpolating the daily mean total ozone far the predicting period. We also can predict the next day's total ozone by using regression models based on the present day's total ozone by TOMS and the next day's predicted maximum air temperature by the Meteorological Mesoscale Model 5 (MM5). These predicted and observed total ozone amounts are used to input data of the parameterization model (PM) of hourly UV-B irradiance. The PM of UV-B irradiance is based on the main parameters such as cloudiness, solar zenith angle, total ozone, opacity of aerosols, altitude, and surface albedo. The input data for the model requires daily total ozone, hourly amount and type of cloud, visibility and air pressure. To simplify cloud effects in the model, the constant cloud transmittance are used. For example, the correlation coefficient of the PM using these cloud transmissivities is shown high in more than 0.91 for cloudy days in Busan, and the relative mean bias error (RMBE) and the relative root mean square error (RRMSE) are less than 21% and 27%, respectively. In this study, the daily variations of calculated and predicted UV-B irradiance are presented in high correlation coefficients of more than 0.86 at each monitoring site of the Korean peninsula as well as East Asia. The RMBE is within 10% of the mean measured hourly irradiance, and the RRMSE is within 15% for hourly irradiance, respectively. Although errors are present in cloud amounts and total ozone, the results are still acceptable.

Testing Brutsaert's temperature roughness parameterization for representing urban surfaces in atmospheric models

It is verified whether Brutsaert's temperature roughness parameterization, developed for surfaces composed of solid obstacles arrays, is suitable for representing urban surfaces in high‐resolution atmospheric models. In order to do so, the temperature roughness parameterization is incorporated into a land surface scheme coupled to a mesoscale meteorological model, and the latter is subsequently used to perform a simulation over the larger area of Paris on a cloud‐free day. As a main result, it is found that simulated land surface temperature compares favourably to observed values obtained from thermal infrared satellite imagery. This confirms the validity of Brutsaert's thermal roughness parameterization, thus warranting its use in regional‐scale prognostic atmospheric models employed for, e.g., weather forecasting or air pollution studies.

MM5-SMOKE-CMAQ as a modeling tool for 8-h ozone regulatory enforcement: application to the state of Arizona

The Penn State/NCAR Mesoscale Meteorological Model 5 (MM5), Sparse Matrix Operator Kernal Emissions (SMOKE), and Community Multiscale Air Quality (CMAQ) modeling systems were employed to simulate ozone concentration distribution within the State of Arizona, in particular, Phoenix air basin, as supporting information to designate nonattainment areas of the U.S. Environmental Protection Agency's new 8-h ozone standard. In general, based on statistical comparisons between predictions and available (sparsely distributed) observations, the modeling system performed reasonably well for the Phoenix basin, thus proving it to be a useful tool for both regulatory as well as research applications. Detailed inspection, however, revealed a serious problem with respect to the details of the ozone distribution in that for some days the transition from downslope flow to upslope flow in the Phoenix basin was delayed in the model, causing the ozone distribution to show an unrealistic high-ozone bias toward the west valley. Implementation of a modified subgrid parameterization improved the time of transition, and hence the prediction of ozone and its precursor distributions. This study points to possible inadequacies of commonly used subgrid parameterizations in dealing with rapidly changing flow conditions such as morning (and evening) transitions.

Influence of the PBL scheme on high-resolution photochemical simulations in an urban coastal area over the Western Mediterranean

Planetary boundary layer (PBL) and land-surface processes have critical implications for air quality simulations. This contribution analyses the influence of three different surface/PBL schemes from the MM5 mesoscale meteorological model on the predicted photochemical pollutant concentrations using high-resolution EMICAT2000 emission model and Models-3/CMAQ chemical transport model. The Gayno–Seaman (GS), the Medium Range Forecast (MRF), and the Pleim–Chang (PC) PBL schemes are considered. The simulations focus on a complex coastal urban area (Barcelona Geographical Area) located in the Western Mediterranean for a typical summertime situation characterised by the absence of large-scale forcing. The particularities of the area require high spatial (1 km) resolution. Air quality, meteorological and lidar data are used for the evaluation of the results. PBL height inputs have been considered as diagnosed by MM5 and re-diagnosed by the MCIP meteorological pre-processor of Models-3/CMAQ. Several variables playing an essential role in the concentrations of air pollutants, such as PBL height, temperature, and wind speed and direction, are analysed. Important differences are observed in GS scheme depending on the method used in the PBL height estimation. MRF and PC present similar results. Modelled daily maximum pollutants’ concentrations vary in magnitude and location in function of the PBL scheme. GS–MM5 scenario presents the lowest PBL heights, the highest surface temperatures and the weakest winds during daytime, which provokes an enhanced O 3 formation. The higher concentrations of NO x in the GS–MM5 scheme (which are caused mainly by the lower PBL height) provokes a higher depletion of O 3, which yields to the lower concentrations of this pollutant during nighttime in Barcelona downtown. For regulatory purposes, the model tends to underestimate the photochemical formation in the area of study due to an underestimation of VOCs emissions in an VOC-limited area as Barcelona. The lower PBL height shown by GS taken from MM5, as well as the increase in the temperature and the weaker winds over coastal areas (that allow the accumulation of photochemical pollutants) promotes the O 3 concentration and improves the statistical scores of GS–MM5 scenario.

Rapid ventilation of the Mexico City basin and regional fate of the urban plume

Abstract. Urban areas can be large emitters of air pollutants leading to negative health effects and environmental degradation. The rate of venting of these airsheds determines the pollutant loading for given emission levels, and also determines the regional impacts of the urban plume. Mexico City has approximately 20 million people living in a high altitude basin with air pollutant concentrations above the health limits most days of the year. A mesoscale meteorological model (MM5) and a particle trajectory model (FLEXPART) are used to simulate air flow within the Mexico City basin and the fate of the urban plume during the MCMA-2003 field campaign. The simulated trajectories are validated against pilot balloon and radiosonde trajectories. The residence time of air within the basin and the impacted areas are identified by episode type. Three specific cases are analysed to identify the meteorological processes involved. For most days, residence times in the basin are less than 12 h with little carry-over from day to day and little recirculation of air back into the basin. Very efficient vertical mixing leads to a vertically diluted plume which, in April, is transported predominantly towards the Gulf of Mexico. Regional accumulation was found to take place for some days however, with urban emissions sometimes staying over Mexico for more than 6 days. Knowledge of the residence times, recirculation patterns and venting mechanisms will be useful in guiding policies for improving the air quality of the MCMA.

The Use of Global and Mesoscale Meteorological Model Data to Predict the Transport and Dispersion of Tracer Plumes over Washington, D.C.

Abstract The data from a yearlong tracer dispersion experiment over Washington, D.C., in 1984 were used to evaluate Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) dispersion model calculations using coarse global meteorological reanalysis data [NCEP–NCAR and 40-Yr ECMWF Re-Analysis (ERA-40)] and calculations using meteorological data fields created by running a high-resolution meteorological model [fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5)]. None of the meteorological models were optimized for urban environments. The dispersion calculation using the ERA-40 data showed better performance than those using the NCEP–NCAR data and comparable performance to those using MM5 data fields. Calculations with MM5 data that used shorter-period forecasts were superior to calculations that used forecast data that extended beyond 24 h. Daytime dispersion model calculations using the MM5 data showed an underprediction bias not evident in calculations using the ERA-40 data or for nighttime calculations using either meteorological dataset. It was found that small changes in the wind direction for all meteorological model data resulted in dramatic improvements in dispersion model performance. All meteorological data modeled plume directions were biased 10°–20° clockwise to the measured plume direction. This bias was greatest when using the global meteorological data. A detailed analysis of the wind observations during the November intensive, which had the greatest difference between the model and measured plume directions, showed that only the very lowest level of observed winds could account for the transport direction of the measured plume. In the Northern Hemisphere, winds tend to turn clockwise with height resulting in positive directional transport bias if the lowest-level winds are not represented in sufficient detail by the meteorological model.

Operational mesoscale atmospheric dispersion prediction using a parallel computing cluster

An operational atmospheric dispersion prediction system is implemented on a cluster supercomputer for Online Emergency Response at the Kalpakkam nuclear site. This numerical system constitutes a parallel version of a nested grid meso-scale meteorological model MM5 coupled to a random walk particle dispersion model FLEXPART. The system provides 48-hour forecast of the local weather and radioactive plume dispersion due to hypothetical airborne releases in a range of 100 km around the site. The parallel code was implemented on different cluster configurations like distributed and shared memory systems. A 16-node dual Xeon distributed memory gigabit ethernet cluster has been found sufficient for operational applications. The runtime of a triple nested domain MM5 is about 4 h for a 24 h forecast. The system had been operated continuously for a few months and results were ported on the IMSc home page.Initial and periodic boundary condition data for MM5 are provided by NCMRWF, New Delhi. An alternative source is found to be NCEP, USA. These two sources provide the input data to the operational models at different spatial and temporal resolutions using different assimilation methods. A comparative study on the results of forecast is presented using these two data sources for present operational use. Improvement is noticed in rainfall forecasts that used NCEP data, probably because of its high spatial and temporal resolution

Relationship between VOC and NO x emissions and chemical production of tropospheric ozone in the Aburrá Valley (Colombia)

Relationship between volatile organic compounds (VOC) and nitrogen oxides (NO x ) emissions and the chemical production of tropospheric ozone is studied through mathematical simulation. The study is applied to the Aburrá Valley, in the Colombian Andes, which is a practically unknown area from the point of view of ozone formation. The model used for this application is the European modelling of atmospheric constituents (EUMAC) zooming model (EZM) which consists of a mesoscale prognostic model (MEMO, mesoscale meteorological model) and a chemical reaction model (MUSE, multiscale for the atmospheric dispersion of reactive species), coupled to the chemical mechanism EMEP (European monitoring and evaluation program). The analysis is performed for a real episode that was characterized by high ozone production and that happened during the 23rd and 24th December, 1999 in Medellín (Colombia). From this real scenario, a sensitivity analysis has been carried out in order to assess the influence of VOC and NO x amounts on ozone production and to extract some conclusions for future ozone abatement policies in Andean regions. As far as ozone air quality is concerned, it is shown that in order to keep current levels the emphasis must be put to avoid increasing NO x emissions, or alternatively, to augment VOC emissions in order to have a high VOC/NO x ratio.

Satellite-derived land surface parameters for mesoscale modelling of the Mexico City basin

Abstract. Mesoscale meteorological modelling is an important tool to help understand air pollution and heat island effects in urban areas. Accurate wind simulations are difficult to obtain in areas of weak synoptic forcing. Local factors have a dominant role in the circulation and include land surface parameters and their interaction with the atmosphere. This paper examines an episode during the MCMA-2003 field campaign held in the Mexico City Metropolitan Area (MCMA) in April of 2003. Because the episode has weak synoptic forcing, there is the potential for the surface heat budget to influence the local meteorology. High resolution satellite observations are used to specify the land use, vegetation fraction, albedo and surface temperature in the MM5 model. Making use of these readily available data leads to improved meteorological simulations in the MCMA, both for the wind circulation patterns and the urban heat island. Replacing values previously obtained from land-use tables with actual measurements removes the number of unknowns in the model and increases the accuracy of the energy budget. In addition to improving the understanding of local meteorology, this sets the stage for the use of advanced urban modules.

Distinct wind convergence patterns in the Mexico City basin due to the interaction of the gap winds with the synoptic flow

Abstract. Mexico City lies in a high altitude basin where air quality and pollutant fate is strongly influenced by local winds. The combination of high terrain with weak synoptic forcing leads to weak and variable winds with complex circulation patterns. A gap wind entering the basin in the afternoon leads to very different wind convergence lines over the city depending on the meteorological conditions. Surface and upper-air meteorological observations are analysed during the MCMA-2003 field campaign to establish the meteorological conditions and obtain an index of the strength and timing of the gap wind. A mesoscale meteorological model (MM5) is used in combination with high-resolution satellite data for the land surface parameters and soil moisture maps derived from diurnal ground temperature range. A simple method to map the lines of wind convergence both in the basin and on the regional scale is used to show the different convergence patterns according to episode types. The gap wind is found to occur on most days of the campaign and is the result of a temperature gradient across the southern basin rim which is very similar from day to day. Momentum mixing from winds aloft into the surface layer is much more variable and can determine both the strength of the flow and the pattern of the convergence zones. Northerly flows aloft lead to a weak jet with an east-west convergence line that progresses northwards in the late afternoon and early evening. Westerlies aloft lead to both stronger gap flows due to channelling and winds over the southern and western basin rim. This results in a north-south convergence line through the middle of the basin starting in the early afternoon. Improved understanding of basin meteorology will lead to better air quality forecasts for the city and better understanding of the chemical regimes in the urban atmosphere.

Ozone ensemble forecasts: 1. A new ensemble design

A new Ozone Ensemble Forecast System (OEFS) is tested as a technique to improve the accuracy of real‐time photochemical air quality modeling. The performance of 12 different forecasts along with their ensemble mean is tested against the observations during 11–15 August 2004, over five monitoring stations in the Lower Fraser Valley, British Columbia, Canada, a population center in a complex coastal mountain setting. The 12 ensemble members are obtained by driving the U.S. Environmental Protection Agency (EPA) Models‐3/Community Multiscale Air Quality Model (CMAQ) with two mesoscale meteorological models, each run at two resolutions (12‐ and 4‐km): the Mesoscale Compressible Community (MC2) model and the Penn State/NCAR mesoscale (MM5) model. Moreover, CMAQ is run for three emission scenarios: a control run, a run with 50% more NOx emissions, and a run with 50% fewer. For the locations and days used to test this new OEFS, the ensemble mean is the best forecast if ranked using correlation, gross error, and root mean square error and has average performance when evaluated with the unpaired peak prediction accuracy. Ensemble averaging removes part of the unpredictable components of the physical and chemical processes involved in the ozone fate, resulting in a more skilful forecast when compared to any deterministic ensemble member. There is not one of the 12 individual forecasts that clearly outperforms the others on the basis of the four statistical parameters considered here. A lagged‐averaged OEFS is also tested as follows. The 12‐member OEFS is expanded to an 18‐member OEFS by adding the second day from the six 12‐km “yesterday” forecasts to the “today” ensemble forecast. The 18‐member ensemble does not improve the ensemble mean forecast skill. Neither correlation nor a relationship between ensemble spread and forecast error is evident.

Ozone ensemble forecasts: 2. A Kalman filter predictor bias correction

The Kalman filter (KF) is a recursive algorithm to estimate a signal from noisy measurements. In this study it is tested in predictor mode, to postprocess ozone forecasts to remove systematic errors. The recent past forecasts and observations are used by the KF to estimate the future bias. This bias correction is calculated separately for, and applied to, 12 different air quality (AQ) forecasts for the period 11–15 August 2004, over five monitoring stations in the Lower Fraser Valley, British Columbia, Canada, a population center in a complex coastal mountain setting. The 12 AQ forecasts are obtained by driving an AQ Model (CMAQ) with two mesoscale meteorological models (each run at two resolutions) and for three emission scenarios (Delle Monache et al., 2006). From the 12 KF AQ forecasts an ensemble mean is calculated (EK). This ensemble mean is also KF bias corrected, resulting in a high‐quality estimate (KEK) of the short‐term (1‐ to 2‐day) ozone forecast. The Kalman filter predictor bias‐corrected ensemble forecasts have better forecast skill than the raw forecasts for the locations and days used here. The corrected forecasts are improved for correlation, gross error, root mean square error, and unpaired peak prediction accuracy. KEK is the best and EK is the second best forecast overall when compared with the other 12 forecasts. The reason for the success of EK and KEK is that both the systematic and unsystematic errors are reduced, the first by Kalman filtering and the second by ensemble averaging.

Numerical analysis of diffusion around a suspended expressway by a multi-scale CFD model

The diffusion of NO x around Ikegami–Shinmachi crossroads, which are among the most polluted roadside areas in Japan, was analyzed with a CFD model. This is a suspended four-lane express road with a six-lane ground-level road under the expressway and another four-lane ground-level road intersecting the two roads. Three types of boundary conditions for the CFD model were tested. In the first case, the boundary conditions were given with the results from the mesoscale meteorological model; in other words, the model was multi-scale. In the second case, the boundary conditions were given with the local one-point observation. In the third case, the conditions for the wind were given with the observation, and those for the turbulence were given with the mesoscale numerical model. All of the calculations indicated high concentrations in the morning and low ones in the afternoon, but they did not indicate high concentrations in the evening. The reasons for such time variations of NO x concentrations were investigated from the viewpoints of the wind direction, velocity, and boundary layer height. The results suggested that the extremely high concentration was generated by local sources and advection from the large source area of Tokyo. On the whole, the calculation with the boundary condition with the mesoscale model appears to be better than the other calculations.

New methods for evaluating meteorological models used in air quality applications

Meteorological models in conjunction with air quality models are being used to simulate the transport and fate of pollutants in the atmosphere. Hence, there is a need for an extensive evaluation of the entire modeling system. In this study, several new techniques to assess the performance of mesoscale meteorological models are introduced with an emphasis on evaluating the variables and processes that have the potential to influence the air quality predictions, since errors in the meteorological fields are passed on to the air quality model. Model performance was diagnosed by examining the inter-correlation of observable variables in the atmosphere on distinct time scales: intraday, diurnal, and synoptic. It was found that the Mesoscale Model version 5 (MM5) model did replicate the observed relationship between intraday wind speed and temperature, intraday surface pressure and temperature, diurnal surface pressure and temperature as well as most of the correlations between variables on the synoptic timescale. However, a negative correlation between temperature and precipitation was evident in the observations on the intraday scale, but such relationship was not evident in the model output. Furthermore, the diurnal response of increasing wind speed with temperature was strong in the observed time series, but it was much weaker in the model. The correlation between diurnal changes in temperature and cloud fraction was consistently negative in the model whereas it was slightly positive in the observations. Wind profilers were used to examine the simulated boundary layer wind structure. Of the twelve sites examined, the average distance error between the 24-h observed and modeled trajectory was approximately 150 km at height of 100 m above the surface. Errors in transport of this magnitude (100–200 km) can produce errors in air quality predictions. It is not the intent of this study to establish quantitative links between the performance of the specific meteorological simulation analyzed here and subsequent air quality simulations. Rather, the results presented here draw attention to errors and inconsistencies in the meteorology that are passed on to the air quality model which, in turn, have the potential to cause errors in air quality model predictions.