Aerosol-Cloud-Precipitation Interactions - Studied using combinations of remote sensing and in-situ data
Summary, in English
Cloud droplets were found to be smaller in low-level clouds formed in air with higher aerosol number concentrations over the ocean north of Scandinavia. This was also true for low-level and convective clouds over land in Sweden and Finland. The results regarding cloud optical thickness (COT), which is a measure of how much light a cloud reflects, was not as conclusive. For the low-level clouds over the ocean, the COT was higher in air masses with higher aerosol number concentrations. Differences in meteorological conditions in the clean and polluted air masses may however explain some of the differences in COT. The low-level and convective clouds over land did not show any significant changes in COT with varying aerosol number concentrations. This may be caused by changes in cloud dynamics due to the smaller droplets in the clouds. Hence, the indirect aerosol effect could not be observed for clouds studied over land.
The precipitation intensity from the clouds over land and how this varied with changing aerosol loading was also investigated. For both low-level and convective clouds, the precipitation was found to decrease somewhat with increasing aerosol number concentrations. However, for the convective clouds, this relationship only appeared when the clouds were sorted according to vertical extent, as higher convective clouds tend to produce heavier precipitation.
How cirrus clouds at midlatitudes in the northern hemisphere are affected by the mass concentration of particulate sulphate present in the lowermost stratosphere (LMS) was investigated using satellite data. Changes in the LMS particle levels were caused by explosive volcanos that emit gases and particles into the stratosphere. Due to subsidence in the stratosphere at midlatitudes, the volcanic sulphate eventually enters the upper troposphere, increasing its sulphate concentration. The reflectance of the cirrus clouds decreased when there were more sulphate particles present in the LMS. Cirrus clouds warm the climate and a decrease in their reflectance hence cools the climate.
- Meteorology and Atmospheric Sciences
- aerosol particles
- satellite data
- Fysicumarkivet A:2016:Sporre
- Aerosol, Nuclear Physics-lup-obsolete
- ISBN: 978-91-7623-589-8
- ISBN: 978-91-7623-590-4
19 February 2016
Lecture hall Rydbergsalen, Physics Department, Professorsgatan 1, Lund University, Faculty of Engineering