Aerosol-radiation feedback loop based on satellite data

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Title: Aerosol-radiation feedback loop based on satellite data
Author: Khansari, Marzieh
Other contributor: Helsingin yliopisto, Matemaattis-luonnontieteellinen tiedekunta, Fysiikan laitos
University of Helsinki, Faculty of Science, Department of Physics
Helsingfors universitet, Matematisk-naturvetenskapliga fakulteten, Institutionen för fysik
Publisher: Helsingin yliopisto
Date: 2018
Language: eng
Thesis level: master's thesis
Abstract: The climate feedback is a response of the climate system to a perturbation through a number of mechanisms. Perturbations can be due to natural factors, like volcanic activity or changes in solar activity, or anthropogenic such as emissions of long-lived greenhouse gases and aerosol particles. Atmospheric aerosols affect the Earth’s radiation budget. The aerosols impact radiation directly by scattering and absorbing incoming solar radiation and indirectly by changing cloud properties via formation of cloud condensation nuclei. Here, the aerosol radiation feedback loop associated to the continental biosphere-aerosol-cloud-climate (COBACC) feedback loop, is suggested. This negative feedback loop connects increasing atmospheric CO2 concentration, rising temperatures, the formation of aerosol particles due to the emission of biogenic volatile organic compounds, changes in ratio of diffuse to global radiation in the clear sky condition, and changes in the plant gross primary production. In this study, in-situ atmospheric measurement data in Hyytiälä station, as well as satellite atmospheric measurement data (CERES (Clouds and the Earth’s Radiant Energy System) and MODIS (Moderate Resolution Imaging Spectroradiometer instrument)) around Hyytiälä station and a small area in the western plain of Siberia for clear sky conditions in June and July around noon, were used. Three methods for detecting clear-sky conditions were considered: brightness parameter, global radiation smoothing and lastly MODIS cloud mask method. Here, MODIS cloud mask method was selected as the most suitable method due to availability of data and global coverage. This study proved partly the existence of the aerosol radiation feedback loop by finding positive correlation between some of the components of the feedback loop, such as condensation sink(CS) and temperature, ratio of diffuse radiation to global radiation (R) and CS, and R and temperature. Additionally, it was shown that satellite-based data compares well with in-situ data. Hence, it is possible to use satellite-based data for the aerosol-radiation feedback loop. In addition, the impact of relative humidity on the relation between R and temperature was investigated. It was found that it is important to take into account the swelling effect in order to investigate the relation between R and temperature. In contrast, solar zenith angle does not have an impact on the relation during study period (June – July).

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