Explicit simulation of aerosol physics in a cloud-resolving model

A. M. L. Ekman, C. Wang, J. Wilson, J. Ström
2004 Atmospheric Chemistry and Physics Discussions  
The role of convection in introducing aerosols and promoting the formation of new particles to the upper troposphere has been examined using a cloud-resolving model coupled with an interactive explicit aerosol module. A baseline simulation suggests good agreement in the upper troposphere between modeled and observed results includ-5 ing concentrations of aerosols in different size ranges, mole fractions of key chemical species, and concentrations of ice particles. In addition, a set of 34
more » ... , a set of 34 sensitivity simulations has been carried out to investigate the sensitivity of modeled results to the treatment of various aerosol physical and chemical processes in the model. The size distribution of aerosols is proved to be an important factor in determining the aerosols' 10 fate within the convective cloud. Nucleation mode aerosols (0≤d≤5.84 nm) are quickly transferred to the larger modes as they grow through coagulation and condensation of H 2 SO 4 . Accumulation mode aerosols (d≥31.0 nm) are almost completely removed by nucleation (activation of cloud droplets) and impact scavenging. However, a substantial part (up to 10% of the boundary layer concentration) of the Aitken mode aerosol pop-15 ulation (5.84 nm≤d≤31.0 nm) reaches the top of the cloud and the free troposphere. These particles may continually survive in the upper troposphere, or over time form ice crystals, both that could impact the atmospheric radiative budget. The sensitivity simulations performed indicate that critical processes in the model causing a substantial change in the upper tropospheric Aitken mode number concentration are coagula-20 tion, condensation, nucleation scavenging, nucleation of aerosols and the transfer of aerosol mass and number between different aerosol bins. In particular, for aerosols in the Aitken mode to grow to CCN size, coagulation appears to be more important than condensation. Less important processes are dry deposition, impact scavenging and the initial vertical distribution and concentration of aerosols. It is interesting to note that 25 in order to sustain a vigorous storm cloud, the supply of CCN must be continuous over a considerably long time period of the simulation. Hence, the treatment of the growth of particles is in general much more important than the initial aerosol concentration itself. 754 ACPD Abstract Introduction Conclusions References Tables Figures Back Close Full Screen / Esc Print Version Interactive Discussion © EGU 2004 and spatial scales that need to be considered in simulating the cloud development; the physical and chemical properties including the size distributions of aerosols and cloud droplets, as well as the interactions among these particles. Given this broad range of conditions, most previous model studies of aerosol-cloud interactions have used simplified descriptions of the cloud processing, usually by considering adiabatic ACPD 4, 2004 Abstract 25 of thunderstorms were formed along the cold front, and the aircraft measurements were conducted along a cross-section through the center of one of these storm clouds. 762 ACPD CO and SO 2 in the upper troposphere (where observations of aerosol number and CO are available), and surface precipitation, representing several aspects of interest dealing with aerosol microphysics, convective transport of important trace gases, as well as cloud dynamics and microphysics. It is worthwhile noting that our sensitivity simulations are carried out using a "real" atmospheric case rather than an idealized 5 4, 2004 The results of series B (dry deposition, Fig. 7) suggest that the modeled Aitken MNC at 10.4 km is not particularly sensitive to the formulation of dry deposition of aerosols. 5 4, 2004
doi:10.5194/acpd-4-753-2004 fatcat:4h47jszhjbdmre7vxeimown3z4