A195-03
Polluted cloud tracks across spatial and temporal scales
Tuesday, 15 December 2020: 10:08
Virtual
Velle Toll1, Nicolas Bellouin2, Matthew Christensen3, Johannes Quaas4, Heido Trofimov1, Jorma Rahu1 and Michael S Diamond5, (1)University of Tartu, Tartu, Estonia, (2)University of Reading, Department of Meteorology, Reading, United Kingdom, (3)University of Oxford, Oxford, United Kingdom, (4)University of Leipzig, Leipzig Institute for Meteorology, Leipzig, Germany, (5)University of Washington, Atmospheric Sciences, Seattle, WA, United States
Abstract:
Anthropogenic aerosols off-set an unknown fraction of greenhouse gas warming, whereas the aerosol impact on clouds is the most uncertain mechanism of anthropogenic radiative forcing of the Earth's climate. In this research, we analyze satellite observations of polluted tracks in low-level liquid-water clouds. Polluted cloud tracks (examples in Fig 1) serve as natural laboratories of aerosol impacts on clouds as properties of polluted clouds can be directly compared to the properties of nearby unpolluted clouds. Ship-track-like tens of kilometers wide polluted cloud lines are induced by aerosols from oil refineries, smelters, coal-fired power plants, smaller industry towns, ships, and volcanoes (
Toll et al 2019; Nature). Hundreds by hundreds of kilometers wide polluted cloud areas are induced by very strong pollution sources like Norilsk nickel smelters and larger industrial regions (
Trofimov et al 2020; JGR Atmospheres). Polluted cloud areas similar to the South-East Atlantic shipping corridor (
Diamond et al 2020; AGU Advances) are detected around aerosol hot spots based on the long-term average cloud properties derived from MODIS and AVHRR observations.
Increases in cloud droplet number concentrations are observed in the polluted cloud tracks in all major global industrial regions. The amount of cloud water can both increase and decrease in the polluted clouds depending on meteorological conditions. On average, there is a relatively weak decrease in cloud water in the polluted cloud tracks, off-setting part of the cloud albedo enhancement caused by the increased cloud droplet numbers. Polluted cloud tracks show that cloud fraction can sometimes increase and sometimes decrease compared to the nearby unpolluted clouds. Preliminary results on the temporal evolution of cloud responses in pollution tracks and meteorological conditions favorable for pollution track occurrence are presented. Observations of polluted cloud tracks help to improve process-level understanding of aerosol impacts on clouds and help to better constrain radiative forcing by aerosol-cloud interactions.
