The impact of biomass burning aerosols on isotope ratios of stratocumulus clouds
Abstract
Stratocumulus clouds over the eastern side of ocean of basins form in regions of locally low surface temperature and an overlying stable atmosphere. These clouds play a central role in the radiative balance of the atmosphere because of their high reflectivity and their capacity to absorb longwave radiation. Aerosols from biomass burning, industrial activity and other natural sources influence the behavior of stratiform cloud decks because of the differing roles that the aerosols can have on the cloud environment. Key to understanding the interplay between aerosols and liquid cloud behavior is evaluating the rates with which dry air dilutes the cloudy layers and how aerosols influence the condensation and evaporation rates, which are assessed using the disequilibrium state of isotope ratios in clouds. The three-year NASA ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) Earth Ventures aircraft mission aims to evaluate the impact of continental agricultural biomass burning on the stratocumulus clouds of the southeastern Atlantic. Isotope ratios of cloud water and vapor were both measured with the Water Isotope System for precipitation and Entrainment Research (WISPER) system. Oxygen and hydrogen stable isotope ratios are compared with simulations from the NCAR Community Atmosphere Model that has isotopic tracers (iCAM). The model shows significant limitations in the capacity to simulate the mean thermodynamic profiles even when constrained by observed meteorology. A parameter sensitivity study is performed to use the isotope ratio information to evaluate the microphysical simulation of clouds and shows excessive cloud top entrainment. Aerosol impacts on nucleation, drizzle production and cloud evaporation are simulated in improper proportion. These limitations have significant consequence on the distribution of clouds, and cloud feedbacks.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMPP13B..02N
- Keywords:
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- 3344 Paleoclimatology;
- ATMOSPHERIC PROCESSESDE: 1041 Stable isotope geochemistry;
- GEOCHEMISTRYDE: 1655 Water cycles;
- GLOBAL CHANGEDE: 1833 Hydroclimatology;
- HYDROLOGY