Simulation of Surface Ozone Pollution in the Central Gulf Coast Region Using WRF/Chem Model: Sensitivity to PBL and Land Surface Physics

The fully coupled WRF/Chem (Weather Research and Forecasting/Chemistry) model is used to simulate air quality in the Mississippi Gulf coastal region at a high resolution (4 km) for a moderately severe summer ozone episode between 18 CST 7 and 18 CST 10 June 2006. The model sensitivity is studied for meteorological and gaseous criteria pollutants (O3, NO2) using three Planetary Boundary Layer (PBL) and four land surface model (LSM) schemes and comparison of model results with monitoring station observations. Results indicated that a few combinations of PBL and LSMs could reasonably produce realistic meteorological fields and that the combination of Yonsei University (YSU) PBL and NOAH LSM provides best predictions for winds, temperature, humidity and mixed layer depth in the study region for the period of study. The diurnal range in ozone concentration is better estimated by the YSU PBL in association with either 5-layer or NOAH land surface model. The model seems to underestimate the ozone concentrations in the study domain because of underestimation of temperatures and overestimation of winds. The underestimation of NO2 by model suggests the necessity of examining the emission data in respect of its accurate representation at model resolution. Quantitative analysis for most monitoring stations indicates that the combination of YSU PBL with NOAH LSM provides the best results for various chemical species with minimum BIAS, RMSE, and high correlation values

Simulation of surface ozone pollution in the Central Gulf Coast region during summer synoptic condition using WRF/Chem air quality model

AbstractWRF/Chem, a fully coupled meteorology–chemistry model, was used for the simulation of surface ozone pollution over the Central Gulf Coast region in Southeast United States of America (USA). Two ozone episodes during June 8–11, 2006 and July 18–22, 2006 characterized with hourly mixing ratios of 60–100ppbv, were selected for the study. Suite of sensitivity experiments were conducted with three different planetary boundary layer (PBL) schemes and three land surface models (LSM). The results indicate that Yonsei–University (YSU) PBL scheme in combination with NOAH and SOIL LSMs produce better simulations of both the meteorological and chemical species than others. YSU PBL scheme in combination with NOAH LSM had slightly better simulation than with SOIL scheme. Spatial comparison with observations showed that YSUNOAH experiment well simulated the diurnal mean ozone mixing ratio, timing of diurnal cycle as well as range in ozone mixing ratio at most monitoring stations with an overall correlation of 0.726, bias of –1.55ppbv, mean absolute error of 8.11ppbv and root mean square error of 14.5ppbv; and with an underestimation of 7ppbv in the daytime peak ozone and about 8% in the daily average ozone. Model produced 1–hr, and 8–hr average ozone values were well correlated with corresponding observed means. The minor underestimation of daytime ozone is attributed to the slight underestimation of air temperature which tend to slow–down the ozone production and overestimation of wind speeds which transport the produced ozone at a faster rate. Simulated mean horizontal and vertical flow patterns suggest the role of the horizontal transport and the PBL diffusion in the development of high ozone during the episode. Overall, the model is found to perform reasonably well to simulate the ozone and other precursor pollutants with good correlations and low error metrics. Thus the study demonstrates the potential of WRF/Chem model for air quality prediction in coastal environments

Mesoscale characteristics and prediction of an unusual extreme heavy precipitation event over India using a high resolution mesoscale model

Numerical prediction experiments using a high resolution mesoscale model NCAR MM5 were performed to simulate an unusual extreme precipitation event that occurred over west coast region of India on 26 July 2005. During this event, unprecedented precipitation of 90–100 cm was recorded over northeast parts of Mumbai City, India causing enormous losses while southern parts received only 10 cm. Model prediction with analysis nudging for 12 h followed by 36 h of integration produced the best simulation with 55 cm of precipitation in 24 h and with the location over north Mumbai agreeing with the observations. Model diagnostics of the vorticity, divergence, vertical velocity and lower tropospheric moisture convergence show the mesoscale characteristics of the convective system with a horizontal extent of 50 km2 and of a sudden cloud burst for 3–6 h followed by few shorter rain spells. The model simulates the veering of the wind with height due to warm air advection to favor convection but a moist layer at lower levels capped by dry air inhibited convection. The simulated circulation features indicate that a mesoscale convective system formed in the monsoon westerlies due to passage of a synoptic disturbance across the east coast strengthening the monsoon flow, and dry air incursion at middle levels suppressed convection and contributing to increase of potential instability at lower levels. All this helped the sudden initiation of deep convection and cloud burst with heavy precipitation rate. Stretching term associated with vorticity contributes most for the increase of cyclonic vorticity indicating the interaction of convection with mesoscale circulation

Regional scale prediction of the onset phase of the Indian southwest monsoon with a high-resolution atmospheric model

A nonhydrostatic atmospheric model with a resolution of 30 km is used to make predictions of the rainfall during the onset phase of the southwest monsoon (SWM) of 2003. Model predictions of the pentad rainfall time series indicate good predictions up to lead time of 5 days. The correlation coefficients (CCs) between the model-predicted and observed rainfall at different locations, representative of the five homogeneous regions of SWM rainfall, over the Indian subcontinent show correlations significant at 90% level up to 5 days lead time with values above 0.32. The spatial distribution of the model-predicted pentad rainfall show an advancement of the Arabian Sea and the Bay of Bengal branches of SWM over the Indian subcontinent up to 5 days lead time. Copyright © 2008 Royal Meteorological Societ

An assessment of cumulus parameterization schemes in the short range prediction of rainfall during the onset phase of the Indian Southwest Monsoon using MM5 Model

The performance of cumulus parameterization schemes in the short range prediction of rainfall during onset phase of the Indian Southwest Monsoon (ISM) was evaluated using Fifth-Generation Pennsylvania State University / National Center for Atmospheric Research Mesoscale Model (MM5). MM5 model was used to predict rainfall at 30 km resolution up to 72 h over the Indian subcontinent for each day during the period 1–30 June 2002, which corresponds to the onset phase of the ISM. Experiments were performed with 5 different cumulus parameterization schemes of Anthes–Kuo (AK), Grell (GR), Betts–Miller (BM), Kain–Fritsch (KF) and Kain–Fritsch2 (KF2). Rainfall prediction assessment was made over five zones through comparison with corresponding APHRODITE gridded precipitation data and for selected location with station observations by analyzing the statistical parameters of correlation coefficient, mean absolute error and Hanssen–Kuipers score. Monthly mean zone-wise rainfall was well predicted by GR and AK schemes up to 48 hours and slight overestimation beyond. GR scheme predicted higher rainfall over west coast, central parts of India and low rainfall over southeast peninsula. BM and KF schemes showed overestimation with prediction of rainfall over dry southeast peninsula. All the schemes underestimated the coefficient of variability (CV) over all the five zones. AK and GR schemes had the mean and CV nearer to the APHRODITE observations, with AK scheme slightly better than GR scheme over Zones 1, 2 and 3 while GR scheme had the best agreement over Zones 4 and 5. GR scheme had also shown higher CC values and lower MAE over most of the zones up to 72 h, while BM had the least predictability with lower CC and HK scores and higher MAE over most of the zones. Over Western Ghats, the uncertainty limits could be higher than shown due to dominant heavy rains. Of the ten stations selected for verification, GR scheme had shown better prediction with significant positive CC values at nine of the ten stations and consistently lower MAE values and higher HK scores. Further analysis has shown that GR scheme predicted higher grid-scale and nighttime rainfall agreeing with earlier studies concerning monsoon rainfall. All other schemes predicted the features contrarily with higher convective and daytime rainfall. GR scheme alone was found to have provided the best prediction considering the mean monthly, daily zone-wise and station rainfall predictions. The present study concludes that GR cumulus parameterization scheme is the most suitable at 30 km resolution