The effect of aerosol composition and concentration on the development and anvil properties of a continental deep convective cloud

A 3-D cloud-resolving model including an explicit aerosol module is used to examine the influence of a range of hygroscopic (CCN) and hydrophobic (IN) aerosol concentrations on the development of a mid-latitude, continental deep convective cloud. The model reproduces a response to changes in CCN which is in agreement with previous studies of continental convection, i.e. lower precipitation rates and a later onset of deep convection for high CCN concentrations. However, the response is non-linear and for low increments of CCN, coalescence and graupel formation becomes more efficient, which increases the total precipitation, i.e. a response similar to what has been obtained for oceanic deep convection. This result indicates the importance of using a range of CCN concentrations when examining aerosol influence on deep convection. The simulations show that an increased IN concentration has a substantial influence on the convective cloud development. Higher IN concentrations generally result in higher updraught velocities, a prolonged precipitation event and larger total precipitation amounts. The radiative forcing exerted by the cloud is determined by the anvil extent and ice crystal size. The anvil area is linked to the average updraught velocity which in turn is found to be correlated with the IN concentration. Homogeneously nucleated ice crystals dominate the total anvil ice mass formed, but heterogeneously formed ice crystals may significantly alter the homogeneous freezing process. For the simulated case, a key parameter for determining whether the number of homogeneously nucleated ice crystals will decrease or increase with increasing IN concentration is the initial updraught velocity. This dependence makes the results sensitive to the amount of heterogeneously formed ice crystals. Copyright (C) 2007 Royal Meteorological Society.