Winter hazes in East Asia have attracted much attention from researchers. The extremely high concentration of particle matter not only affects people’s health, but also has a strong impact on weather and climate. The NASA Unified-Weather Research and Forecasting model (NU-WRF) is a modeling system that can represent aerosol, cloud, precipitation and land processes, and is a great tool to evaluate the aerosol-weather-climate interactions.
To better understand the uncertainties within the model, two applications with different resolutions (45km and 15km) are used for simulations during a haze event in Beijing-Tianjin-Hebei (BTH) area in January 2010. The daily-averaged results of both simulations can estimate the meteorological variables well, with an overestimation in wind speed at 10m. Application with coarser resolution performs better in predicting the temperature at 2m. Hourly-averaged results show that simulation with a coarser resolution does not present obvious diurnal change of meteorology. The rapid change in the simulations for meteorological variables during the “cleaning” stage after the severe haze pollution show a delay in the finer resolution simulation. The simulations of various air pollutants of both resolutions at urban and suburban sites are evaluated. The model performance is not very sensitive to the type of areas, but there are some differences shown between air pollutant species. Simulations of both resolutions can capture the overall trend of PM2.5 concentration, but fail to capture the daily peak of PM2.5 in urban/suburban sites, and the PM2.5 concentration in the mountain site is overestimated.
During the same haze event, simulations with options related to aerosol direct/indirect feedbacks are compared in this thesis as well. Aerosols have a negative impact in temperature, water vapor mixing ratio and AOD. The direct feedbacks play the dominant part in decreasing these variables. Both direct and indirect feedbacks have positive forcing at the top of atmosphere. The effect of total feedbacks on the ground is negative, with direct feedbacks having a great negative forcing and indirect feedbacks having a small positive forcing. The meteorological conditions become more stable because of the aerosol radiative feedback. This situation makes it harder for pollutants to disperse, so the PM2.5 concentration increase by over 16 μg/m3 in the southern part of BTH area. The aerosol radiative forcing also causes a smaller diurnal variation of PM2.5 concentration.