Assessment of the dehydration‐greenhouse feedback over the Arctic during February 1990

Abstract

Abstract:The effect of pollution-derived sulfuric acid aerosols on the aerosol-cloud-radiation interactions is investigated over the Arctic for February 1990. Observations suggest that acidic aerosols can decrease the heterogeneous nucleation rate of ice crystals and lower the homogeneous freezing temperature of haze droplets. On the basis of these observations, we hypothesize that the cloud thermodynamic phase is modified in polluted air mass (Arctic haze). Cloud ice number concentration is reduced, thus promoting further ice crystal growth by the Bergeron-Findeisen process. Hence, ice crystals reach larger sizes and low-levkel ice crystal precipitation from mixed-phase clouds increases. Enhanced dehydration of the lower troposphere contributes to decreased water vapour greenhouse effect and cools the surface. A positive feedback is created between surface cooling and air dehydration, accelerating cold air production. This process is referred to as the dehydration-greenhouse feedback (DGF).Simulations performed using an Arctic regional climate model for February 1990 are used to assess the potential effect of the DGF on the Arctic climate during February. Results show that the DGF has an important effect on cloud, atmospheric dehydration, and temperature over the Central and Eurasian Arctic, which is the coldest part of the Arctic. Cloud ice is significantly reduced and the total atmospheric water path is decreased by as much as 12%. This results in a surface cooling ranging between 0 and −3 K. Moreover, the lower tropospheric cooling over the Eurasian and Central Arctic strengthens the atmospheric circulation at the upper level, thus increasing the aerosol transport from the mid-latitudes and enhancing the DGF. Over warmer areas, the increased aerosol concentration (caused by the DGF) leads to longer cloud lifetime, which contributes to warm these areas.

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

“…Using a refined treatment of the IN de‐activation effect based on laboratory experiment, this research has confirmed the results obtained in previous modeling investigations (Girard et al , 2005; Girard and Stefanof, 2007) on the effect of acid coating on the Arctic clouds and radiative budget during winter. This indirect effect of acid aerosols on arctic clouds and the resulting atmospheric cooling could explain, at least in part, the unexpected observed cooling trend of surface air temperature over the Arctic Ocean during winter in the period 1979–1999 as observed by boys (Rigor et al , 2000) and by satellite remote sensing (Wang and Key, 2003).…”

“…The acid aerosol scenario shows a tropospheric cooling ranging between 0 and 2 K when compared to an uncoated aerosol scenario. Girard and Stefanof (2007) have used a regional climate model with prognostic aerosols to evaluate the effect of acid aerosols on the Arctic surface radiative budget for February 1990. They have assumed two aerosol scenarios: (1) an acid scenario in which the reduction of the IN concentration depends on the sulphate concentration and (2) a natural aerosol scenario in which the IN concentration is unaltered.…”

“…Furthermore, it was assumed that all ice nucleation modes were altered equally by the presence of acid coatings. Finally, the one‐moment microphysics scheme used in the Girard and Stefanof (2007) investigation was relatively simple with no detailed representation of the ice crystal sedimentation process.…”

Modeling of observed mineral dust aerosols in the arctic and the impact on winter season low‐level clouds

“…Field measurements show that Arctic haze aerosol had lower ice nucleus (IN)‐to‐particle ratios and slower ice nucleation rates than aerosol in unpolluted troposphere, which is hypothesized to be caused by sulfuric acid coating on existing IN in Arctic haze [ Borys , ]. Several large‐scale modeling studies have been conducted on potential effects of acid‐coated IN in clouds; these include a reduced ice number promoting further ice crystal growth and precipitation [ Girard and Stefanof , ], a less frequent glaciation of mixed‐phase clouds leading to longer cloud lifetimes and higher cloud albedos [ Hoose et al ., ; Storelvmo et al ., ; Du et al ., ], and an increased occurrence of Arctic mixed‐phase clouds leading to more atmospheric cooling in winter [ Girard et al ., ]. Arctic clouds and their radiative forcing in climate models are sensitive to parameterizations of IN, especially in winter [ Du et al ., ; Xie et al ., ].…”

Investigation of the sulphate‐induced freezing inhibition effect from CloudSat and CALIPSO measurements

“…Moreover, the SIFI effect can also not be tested directly from the satellite measurements alone, because we can hardly design a credible proxy for in‐cloud sulphate concentrations. Hence, in this paper, we test the SIFI potential consequence according to which higher sulphate concentrations favor cloud populations made of larger ice crystals, caused by a reduction in the competition for water vapor when fewer IFN may operate [ Girard and Stefanof , 2007]. To achieve this task we have developed the Arctic Winter Aerosol and Cloud Classification from CloudSat and CALIPSO (AWAC4) algorithm.…”