Assessment of the effects of acid‐coated ice nuclei on the Arctic cloud microstructure, atmospheric dehydration, radiation and temperature during winter

Abstract

ABSTRACT:Owing to the large-scale transport of pollution-derived aerosols from the mid-latitudes to the Arctic, most of the aerosols are coated with acidic sulfate during winter in the Arctic. Recent laboratory experiments have shown that acid coating on dust particles substantially reduces the ability of these particles to nucleate ice crystals. Simulations performed using the Limited Area version of the Global Multiscale Environmental Model (GEM-LAM) are used to assess the potential effect of acid-coated ice nuclei on the Arctic cloud and radiation processes during January and February 2007. Ice nucleation is treated using a new parameterization based on laboratory experiments of ice nucleation on sulphuric acid-coated and uncoated kaolinite particles. Results show that acid coating on dust particles has an important effect on cloud microstructure, atmospheric dehydration, radiation and temperature over the Central Arctic, which is the coldest part of the Arctic. Mid and upper ice clouds are optically thinner while low-level mixed-phase clouds are more frequent and persistent. These changes in the cloud microstructures affect the radiation at the top of the atmosphere with longwave negative cloud forcing values ranging between 0 and −6 W m −2 over the region covered by the Arctic air mass.

Thin ice clouds in the Arctic: cloud optical depth and particle size retrieved from ground-based thermal infrared radiometry

“…The DGF impact of the TIC2 particles (meaning their progressive removal by precipitation) would accordingly be that their radiative forcing influence would progressively decrease with an attendant cooling due to a reduction in thermal interaction with the remaining TIC1 particles (and the unprecipitated TIC2 particles). A long-term analysis would help to support modeling conclusions on the impact of acid-coated ice nuclei on Arctic cloud as reported by Girard et al (2013). These authors reported Radiometer TIC1 6 9 TIC2 1 68 Overall accuracy = 88 % err.…”

On the relationship between Arctic ice clouds and polluted air masses over the North Slope of Alaska in April 2008

“…The ice crystal growth rate in very cold conditions impinges on the precipitation efficiency, dehydration and radiation balance. A regional climate model evaluating the impact of the IN deactivation effect by acid coating on the cloud microstructure, precipitation and radiation have also been performed by Girard et al (2013). Results show that acid coating on dust particles has an important effect on cloud microstructure, atmospheric dehydration, radiation and temperature over the Central Arctic, which is the coldest part of the Arctic.…”

Relative importance of acid coating on ice nuclei in the deposition and contact modes for wintertime Arctic clouds and radiation

“…No modifications have been made to the original scheme for the parameterization of contact freezing. Deposition ice nucleation on uncoated IN and immersion freezing of sulphuric acid-coated IN are parameterized following Girard et al (2013). These parameterizations are based on the classical nucleation theory (CNT) of Fletcher (1962).…”

“…1) and their spatial and temporal variabilities. Following Girard et al (2013), a constant value in time and space (0.38 cm -3 ) for N dust is assumed since the model does not simulate aerosol transport and physics. This means that there are no sources and sinks of dust particles.…”

“…Previous modeling studies have shown that acid coating on deposition IN can have a substantial effect on ice and mixed-phase cloud microstructure and radiative forcing over the Arctic during the cold season Du et al 2011;Girard et al 2013). Acid coating on deposition IN leads to the formation of fewer and larger ice crystals.…”