Aerosol effects on the anvil characteristics, cold pool forcing and stratiform-convective precipitation partitioning and latent heating of mesoscale convective systems
- Colorado State Univ., Fort Collins, CO (United States)
The overarching science goal of this project has been to assess the impacts of aerosols on mesoscale convective systems (MCSs). More specifically we have investigated the impacts of (a) aerosol types, (b) aerosol concentrations, and (c) the vertical and horizontal location of aerosols on the (1) anvil cloud characteristics and feedbacks; (2) total precipitation and the partitioning between convective and stratiform precipitation; (3) the vertical heating structure; (4) hydrometeor size distributions; and (5) the strength and intensity of the cold pools and updrafts. These have been achieved both through observational analyses and high-resolution cloud-resolving model simulations of three MCSs that were observed during the MC3E field campaign (25 April, 20 May and 23 May 2011). The primary findings of these research are the following: Condensation and deposition are the primary contributors to MCS latent warming, when compared to riming and nucleation processes. In terms of MCS latent cooling, sublimation, melting, and evaporation all play significant roles. Throughout the MCS lifecycle, convective regions demonstrate an approximately linear decrease in the magnitudes of latent heating rates, while latent heating within stratiform regions is associated with transitions between MCS flow regimes including the rear inflow jet. Such information regarding the temporal evolution of latent heating within convective and stratiform MCS regions could be useful in developing parameterizations representing convective organization. Increasing aerosol concentration from a clean continental to a highly polluted state produces an increase in the riming rates of cloud water, which results in less lofted cloud water in polluted environments. Aerosol-induced trends in the cloud mixing ratio profiles are, however, nonmonotonic in the mixed phase region, such that a moderate increase in aerosol concentration produces the greatest reduction in cloud water. Less lofted cloud water due to enhanced riming rates leads to reduced anvil ice mixing ratios but to greater numbers of small ice crystals within the anvil. In spite of reduced anvil ice mixing ratio, the anvil clouds exhibit greater areal coverage, increased albedo, reduced cloud top cooling, and reduced net radiative flux, which produces an aerosol-induced warming (reduced cooling) effect in these MCSs. Lower-tropospheric aerosol particles largely influence the MCS precipitation response directly rearward of the leading cold pool boundary. However, further backward in the MCS, the relative impact of lower- versus mid-tropospheric aerosol particles is strongly dependent on the MCS structure and differences in the line-normal wind shear. Mid-tropospheric aerosol particles are able to activate new cloud droplets in the mid-tropospheric levels of convective updrafts and thereby enhance mixed-phase precipitation through increased cloud riming.
- Research Organization:
- Colorado State Univ., Fort Collins, CO (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- SC0010569
- OSTI ID:
- 1482383
- Report Number(s):
- DOE-CSU-10569
- Country of Publication:
- United States
- Language:
- English
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