[1] Aerosols are a critical factor in the atmospheric hydrological cycle and radiation budget. As a major agent for clouds to form and a significant attenuator of solar radiation, aerosols affect climate in several ways. Current research suggests that aerosol effects on clouds could further extend to precipitation, both through the formation of cloud particles and by exerting persistent radiative forcing on the climate system that disturbs dynamics. However, the various mechanisms behind these effects, in particular, the ones connected to precipitation, are not yet well understood. The atmospheric and climate communities have long been working to gain a better grasp of these critical effects and hence to reduce the significant uncertainties in climate prediction resulting from such a lack of adequate knowledge. Here we review past efforts and summarize our current understanding of the effect of aerosols on convective precipitation processes from theoretical analysis of microphysics, observational evidence, and a range of numerical model simulations. In addition, the discrepancies between results simulated by models, as well as those between simulations and observations, are presented. Specifically, this paper addresses the following topics: (1) fundamental theories of aerosol effects on microphysics and precipitation processes, (2) observational evidence of the effect of aerosols on precipitation processes, (3) signatures of the aerosol impact on precipitation from large-scale analyses, (4) results from cloud-resolving model simulations, and (5) results from large-scale numerical model simulations. Finally, several future research directions for gaining a better understanding of aerosol-cloud-precipitation interactions are suggested.

A series of large mesoscale convective systems that occurred during the Brazilian phase of GTE/TRACE A (Transport and Atmospheric Chemistry near the Equator‐Atlantic) provided an opportunity to observe deep convective transport of trace gases from biomass burning. This paper reports a detailed analysis of flight 6, on September 27, 1992, which sampled cloud‐ and biomass‐burning‐perturbed regions north of Brasilia. High‐frequency sampling of cloud outflow at 9–12 km from the NASA DC‐8 showed enhancement of CO mixing ratios typically a factor of 3 above background (200–300 parts per billion by volume (ppbv) versus 90 ppbv) and significant increases in NOx and hydrocarbons. Clear signals of lightning‐generated NO were detected; we estimate that at least 40% of NOx at the 9.5‐km level and 32% at 11.3 km originated from lightning. Four types of model studies have been performed to analyze the dynamical and photochemical characteristics of the series of convective events. (1) Regional simulations for the period have been performed with the NCAR/Penn State mesoscale model (MM5), including tracer transport of carbon monoxide, initialized with observations. Middle‐upper tropospheric enhancements of a factor of 3 above background are reproduced. (2) A cloud‐resolving model (the Goddard cumulus ensemble (GCE) model) has been run for one representative convective cell during the September 26–27 episode. (3) Photochemical calculations (the Goddard tropospheric chemical model), initialized with trace gas observations (e.g., CO, NOx, hydrocarbons, O3) observed in cloud outflow, show appreciable O3 formation postconvection, initially up to 7–8 ppbv O3/d. (4) Forward trajectories from cloud outflow levels (postconvective conditions) put the ozone‐producing air masses in eastern Brazil and the tropical Atlantic within 2–4 days and over the Atlantic, Africa, and the Indian Ocean in 6–8 days. Indeed, 3–4 days after the convective episode (September 30, 1992), upper tropospheric levels in the Natal ozone sounding show an average increase of ∼30 ppbv (3 Dobson units (DU) integrated) compared to the September 28 sounding. Our simulated net O3 production rates in cloud outflow are a factor of 3 or more greater than those in air undisturbed by the storms. Integrated over the 8‐ to 16‐km cloud outflow layer, the postconvection net O3 production (∼5–6 DU over 8 days) accounts for ∼25% of the excess O3 (15–25 DU) over the South Atlantic. Comparison of TRACE A Brazilian ozonesondes and the frequency of deep convection with climatology [Kirchhoff et al., this issue] suggests that the late September 1992 conditions represented an unusually active period for both convection and upper tropospheric ozone formation.

The adsorption of lysozyme onto a polyethylene (PE) surface in an aqueous environment was investigated with molecular dynamics (MD) simulation. The adsorption can be divided into three processes: diffusion to the surface, dehydration induced by hydrophobic surface-protein interactions followed by denaturation. The dehydration process is very long and takes around 70ns. Structural deformations start soon after the protein reaches the surface and continue during the whole trajectory. The hydrophobic residues are slowly driven toward the surface, inducing changes in the protein’s secondary structure. The protein secondary structural components near the surface are more disturbed than those farther away from the surface. The lysozyme is adsorbed with its long axis parallel to the surface and displays an anisotropic mobility on the surface probably due to the intrinsic structure of the PE surface. Our study demonstrates the need of long-time atomistic simulation in order to gain a complete understanding of the adsorption process.

SUMMARYThis paper reports an intercomparison study of midlatitude continental cumulus convection simulated by eight two-dimensional and two three-dimensional cloud-resolving models (CRMs), driven by observed large-scale advective temperature and moisture tendencies, surface turbulent uxes, and radiative-heating pro les during three sub-periods of the summer 1997 Intensive Observation Period of the US Department of Energy's Atmospheric Radiation Measurement (ARM) program. Each sub-period includes two or three precipitation events of various intensities over a span of 4 or 5 days. The results can be summarized as follows.CRMs can reasonably simulate midlatitude continental summer convection observed at the ARM Cloud and Radiation Testbed site in terms of the intensity of convective activity, and the temperature and speci c-humidity evolution. Delayed occurrences of the initial precipitation events are a common feature for all three sub-cases among the models. Cloud mass uxes, condensate mixing ratios and hydrometeor fractions produced by all CRMs are similar. Some of the simulated cloud properties such as cloud liquid-water path and hydrometeor fraction are rather similar to available observations. All CRMs produce large downdraught mass uxes with magnitudes similar to those of updraughts, in contrast to CRM results for tropical convection. Some inter-model differences in cloud properties are likely to be related to those in the parametrizations of microphysical processes.There is generally a good agreement between the CRMs and observations with CRMs being signi cantly better than single-column models (SCMs), suggesting that current results are suitable for use in improving parametrizations in SCMs. However, improvements can still be made in the CRM simulations; these include the proper initialization of the CRMs and a more proper method of diagnosing cloud boundaries in model outputs for comparison with satellite and radar cloud observations.

Population migration has upgraded the direct energy consumption with remarkable benefits on air quality and health in China.