A numerical investigation of the aerosol effects on a mesoscale convective system

Description

Mesoscale convective systems (MCS) are frequent occurrences during summer months in the midwest of the United States and bring almost 30% of the rainfall to the region. This work investigates the effects of anthropogenic aerosols, like sulfate and black carbon, and natural aerosols like dust on an MCS. The coupled meteorology and chemistry Weather Research and Forecasting– Chemistry (WRF–Chem) model was employed for the numerical study of the MCS. The selected MCS case occurred on June 20, 2007, covering large parts of Kansas, Oklahoma, and northern Texas. The aerosol effects are analyzed by inputing the aerosol optical properties into the shortwave scheme and the physical properties into the microphysics scheme. The interaction of aerosols with the incoming shortwave radiation is higher due to the wavelength being similar to particulate sizes found in the atmosphere. The nested domain simulations have higher inner domain resolutions (6 and 1.5 km) and as a result resolved the MCS reasonably well. The combined aerosol effects are investigated by increasing the amount of the sulfate, black carbon, and dust aerosols and considering their dominant characteristics. Sulfates are the major constituents of the anthropogenic emissions, and they are scattering and reflecting in nature. On the other hand, black carbon and dust absorb radiation, evaporating clouds and also warming the atmosphere. The dust particulates form giant cloud condensation nuclei (CCN), which can enhance precipitation in the presence of moisture in the atmosphere. The combination of the radiative effects due to each of these aerosols has shown that scattering due to aerosols is a dominant factor for all the types of aerosols. The presence of aerosols interacting with the microphysics and radiation schemes produces a more organized MCS structure, as well as more liquid and ice clouds. The black carbon particulates do not solely warm the atmosphere, but also prevent a large amount of the solar radiation from reaching the surface. The giant CCN due to dust particles enhances the precipitation instead of suppressing it. Thus two absorbing aerosols when increased in amounts show very different effects on cloud cover and precipitation.