A Numerical Study Of Aerosol Effects As CCN On Microphysical Process And Electrification In Thunderstorms

A two-dimensional?2-D?cumulus model with electrification and lightning processes is implemented to investigate aerosol effects as CCN on microphysical process and electrification in thunderstorms.The 2-D cumulus model coupled with a droplet freezing module to better describe the microphysical process and electrification in thunderstorms.Eleven experiments with aerosol concentration changing from 100 cm^-3to 5000 cm^-3have been simulated a SEET case by the improved model.Aerosols effects on the content and distribution of hydrometeors in thunderstorms are analyzed in depth,and the electrification and charge structure are discussed.On this basis,The effects under different convective conditions?weak convection,medium convection,and strong convection?have been compared by changing perturbed temperature and perturbed humidity of the damp heat bubbles.The main conclusions are as follows.The results show that aerosol concentration has significant effects on the microphysical process and electrification in thunderstorms.1)The number concentration of cloud droplets increases and its scale decreases with increasing aerosol concentration,but the content of raindrops reduces.Ice crystals grow rapidly in the low-temperature region,which is attributed to droplets freezing,and the number concentration of ice crystals increases but the scale decreases.The number concentration of graupels increases first and then decreases sharply because ice crystals are difficult to grow into graupels with larger scale when the aerosol concentration exceeds 1000 cm^-3.2)In addition,the charge structure of thunderstorms is not affected by aerosol concentration,but there is a significant effect on the strength of electrification:when the aerosol concentration is lower,more ice crystals and graupels collision enhances the non-inductive charging process and increases the charge density as the aerosol concentration increases;however,the non-inductive charging rate starts to decrease when the aerosol concentration exceeds 1000 cm^-33 due to the appearance of small ice crystals and little graupels,and the charge density is reduced.Aerosol has a more pronounced effect on electrification in thunderstorms under strong convection conditions.1)The convective intensity increases with increasing perturbed temperature and perturbed humidity.The hydrometeors formed earlier and its content are higher in strong convection conditions.With the increase of aerosol concentration,the scale of cloud droplets and ice crystals decreases rapidly caused to the inhibition of raindrops and graupel particles is more pronounced than weak convection conditions.2)The start-up of the electrification process is very rapidly,which is attributed to ice crystals and graupels appeared earlier when increasing the convection intensity.Enhanced the thunderstorm electrification intensity,and its spatial distribution is wider.With the increase of aerosol concentration,more ice crystals and graupels colliding lead to an obvious increase of the non-inductive charging rate.3)The charge structure is more complex under strong convection conditions as the aerosol concentration increases.More ice phase particles collision caused these ice particles to carry different polarity charges in different regions.In addition,the charges are redistributed after discharge,which makes there is a significant stratification of the charge structure results in an extremely complex four polarity charge structure when the aerosol concentration is 3000 cm^-3.