scholarly journals Influence of thermodynamic state changes on surface cloud radiative forcing in the Arctic: A comparison of two approaches using data from AFLUX and SHEBA

2021 ◽  
Author(s):  
Johannes Stapf ◽  
André Ehrlich ◽  
Manfred Wendisch
Keyword(s):  
Radiative Forcing ◽  
The Arctic ◽  
Cloud Radiative Forcing ◽  
Thermodynamic State ◽  
State Changes ◽  
Using Data

scholarly journals Sensitivity of Arctic sulfate aerosol and clouds to changes in future surface seawater dimethylsulfide concentrations

2019 ◽  
Vol 19 (9) ◽  
pp. 6419-6435 ◽  
Author(s):  
Rashed Mahmood ◽  
Knut von Salzen ◽  
Ann-Lise Norman ◽  
Martí Galí ◽  
Maurice Levasseur
Keyword(s):  
Sea Ice ◽  
Radiative Forcing ◽  
Arctic Region ◽  
Sulfate Aerosol ◽  
The Arctic ◽  
Surface Seawater ◽  
Cloud Radiative Forcing ◽  
Future Global Warming ◽  
Arctic Surface ◽  
The Arctic Region

Abstract. Dimethylsulfide (DMS), outgassed from ocean waters, plays an important role in the climate system, as it oxidizes to methane sulfonic acid (MSA) and sulfur dioxide (SO2), which can lead to the formation of sulfate aerosol. Newly formed sulfate aerosol resulting from DMS oxidation may grow by condensation of gases, in-cloud oxidation, and coagulation to sizes where they may act as cloud condensation nuclei (CCN) and influence cloud properties. Under future global warming conditions, sea ice in the Arctic region is expected to decline significantly, which may lead to increased emissions of DMS from the open ocean and changes in cloud regimes. In this study we evaluate impacts of DMS on Arctic sulfate aerosol budget, changes in cloud droplet number concentration (CDNC), and cloud radiative forcing in the Arctic region under current and future sea ice conditions using an atmospheric global climate model. Given that future DMS concentrations are highly uncertain, several simulations with different surface seawater DMS concentrations and spatial distributions in the Arctic were performed in order to determine the sensitivity of sulfate aerosol budgets, CDNC, and cloud radiative forcing to Arctic surface seawater DMS concentrations. For any given amount and distribution of Arctic surface seawater DMS, similar amounts of sulfate are produced by oxidation of DMS in 2000 and 2050 despite large increases in DMS emission in the latter period due to sea ice retreat in the simulations. This relatively low sensitivity of sulfate burden is related to enhanced sulfate wet removal by precipitation in 2050. However simulated aerosol nucleation rates are higher in 2050, which results in an overall increase in CDNC and substantially more negative cloud radiative forcing. Thus potential future reductions in sea ice extent may cause cloud albedos to increase, resulting in a negative climate feedback on radiative forcing in the Arctic associated with ocean DMS emissions.

scholarly journals Radiative energy budget and cloud radiative forcing in the daytime marginal sea ice zone during Arctic spring and summer

2021 ◽  
Author(s):  
Johannes Stapf ◽  
André Ehrlich ◽  
Christof Lüpkes ◽  
Manfred Wendisch
Keyword(s):  
Boundary Layer ◽  
Sea Ice ◽  
Energy Budget ◽  
Radiative Forcing ◽  
The Arctic ◽  
Radiative Energy ◽  
Cloud Radiative Forcing ◽  
Airborne Measurements ◽  
Marginal Sea ◽  
The Impact

Abstract. Airborne measurements of the surface radiative energy budget (REB) collected in the area of the marginal sea ice zone (MIZ) close to Svalbard (Norway) during two campaigns conducted in early spring and and early summer are presented. From the data, the cloud radiative forcing was derived. The analysis is focussed on the impact of changing atmospheric thermodynamic conditions on the REB and on the linkage of sea ice properties and cloud radiative forcing (CRF). The observed two-mode longwave net irradiance frequency distributions above sea ice are compared with measurements from previous studies. The transition of both states (cloudy and cloud-free) from winter towards summer and the associated broadening of the modes is discussed as a function of the seasonal thermodynamic profiles and the surface type. The influence of cold air outbreaks (CAO) and warm air intrusions on the REB is illustrated for several case studies, whereby the source and sink terms of REB in the evolving CAO boundary layer are quantified. Furthermore, the role of thermodynamic profiles and the vertical location of clouds during on-ice flow is illustrated. The sea ice concentration was identified as the main driver of the shortwave cooling by the clouds. The longwave warming of clouds, estimated to about 75 W m−2, seems to be representative for this region, as compared to other studies. Simplified radiative transfer simulations of the frequently observed low-level boundary layer clouds and average thermodynamic profiles represent the observed radiative quantities fairly well. The simulations illustrate the delicate interplay of surface and cloud properties that modify the REB and CRF, and the challenges in quantifying trends in the Arctic REB induced by potential changes of the cloud optical thickness.

scholarly journals The effect of aerosol on surface cloud radiative forcing in the Arctic

2005 ◽  
Vol 5 (5) ◽  
pp. 9039-9063 ◽  
Author(s):  
R.-M. Hu ◽  
J.-P. Blanchet ◽  
E. Girard
Keyword(s):  
Radiative Forcing ◽  
Climate Models ◽  
Climate Model ◽  
Regional Climate ◽  
High Surface ◽  
The Arctic ◽  
Cloud Radiative Forcing ◽  
Cloud Forcing ◽  
Aerosol Forcing ◽  
Albedo Effect

Abstract. Cloud radiative forcing is a very important concept to understand what kind of role the clouds play in climate change with thermal effect or albedo effect. In spite of that much progress has been achieved, the clouds are still poorly described in the climate models. Due to the complex aerosol-cloud-radiation interactions, high surface albedo of snow and ice cover, and without solar radiation in long period of the year, the Arctic strong warming caused by increasing greenhouse gases (as most GCMs suggested) has not been verified by the observations. In this study, we were dedicated to quantify the aerosol effect on the Arctic cloud radiative forcing by Northern Aerosol Regional Climate Model (NARCM). Major aerosol species such as Arctic haze sulphate, black carbon, sea salt, organics and dust have been included during our simulations. By inter-comparisons with the Atmospheric Radiation Measurement (ARM) data, we find surface cloud radiative forcing (SCRF) is −22 W/m2 for shortwave and 36 W/m2 for longwave. Total cloud forcing is 14 W/m2 with minimum of −35 W/m2 in early July. If aerosols are taken into account, the SCRF has been increased during winter while negative SCRF has been enhanced during summer. Our estimate of aerosol forcing is about −6 W/m2 in the Arctic.

scholarly journals Reassessment of the common concept to derive the surface cloud radiative forcing in the Arctic: Consideration of surface albedo – cloud interactions

2019 ◽  
Author(s):  
Johannes Stapf ◽  
André Ehrlich ◽  
Evelyn Jäkel ◽  
Christof Lüpkes ◽  
Manfred Wendisch
Keyword(s):  
Radiative Forcing ◽  
Surface Albedo ◽  
Global Climate Models ◽  
Cooling Effect ◽  
The Arctic ◽  
Radiative Energy ◽  
Cloud Radiative Forcing ◽  
Airborne Measurements ◽  
Solar Cooling ◽  
Snow And Ice

Abstract. The concept of cloud radiative forcing (CRF) is commonly used to quantify the warming or cooling effect due to clouds on the radiative energy budget (REB). In the Arctic, radiative interactions between micro- and macrophysical properties of clouds and the surface influence the CRF and complicate its estimate obtained from observations or models. In this study the individual components and processes related to the surface CRF are analysed separately using simulations and measurement from low-level airborne observations of the REB in the heterogeneous springtime marginal sea ice zone (MIZ). The measurements were obtained during the Arctic CLoud Observations Using airborne measurements during polar Day (ACLOUD) campaign. The effect of changing surface albedo, due to the presence of clouds, and its dependence on cloud optical thickness was found to be relevant for the estimation of the solar CRF. A method to correct this albedo effect by retrieving the cloud-free surface albedo from observations under cloudy conditions is proposed. The application of this new concept to ACLOUD data shows, that the estimated average solar cooling effect by clouds almost doubles over snow and ice covered surfaces (−63 W m−2 instead of −33 W m−2), if surface albedo-cloud interactions are considered. Concerning the seasonal cycle of the surface albedo, this effect would potentially enhance solar cooling in periods where cold snow and ice dominate the surface and weaken the cooling by optical thin clouds and surface albedos commonly found during the summertime Arctic melting season. These findings suggest, that the surface albedo-cloud interaction needs to be represented in global climate models and in long-term observations to obtain a realistic estimate of the solar CRF and a reasonable representation of cloud radiative feedback mechanisms in the Arctic and to quantify the role of clouds in Arctic amplification.

scholarly journals Sensitivity of Arctic sulfate aerosol and clouds to changes in future surface seawater dimethylsulfide concentrations

2018 ◽  
Author(s):  
Rashed Mahmood ◽  
Knut von Salzen ◽  
Ann-Lise Norman ◽  
Martí Galí ◽  
Maurice Levasseur
Keyword(s):  
Sea Ice ◽  
Radiative Forcing ◽  
Arctic Region ◽  
Sulfate Aerosol ◽  
The Arctic ◽  
Surface Seawater ◽  
Cloud Radiative Forcing ◽  
Future Global Warming ◽  
Arctic Surface ◽  
The Arctic Region

Abstract. Dimethylsulfide (DMS), outgassed from ocean waters, plays an important role in the climate system, as it oxidizes to methane sulfonic acid (MSA) and sulfur dioxide (SO2), which can lead to the formation of sulfate aerosol. Newly formed sulfate aerosol resulting from DMS oxidation may grow by condensation of gases, in-cloud oxidation, and coagulation to sizes where they may act as cloud condensation nuclei (CCN) and influence cloud properties. Under future global warming conditions, sea-ice in the Arctic region is expected to decline significantly, which may lead to increased emissions of DMS from the open ocean and changes in cloud regimes. In this study we evaluate impacts of DMS on Arctic sulfate aerosol budget, changes in cloud droplet number concentration (CDNC), and cloud radiative forcing in the Arctic region under current and future sea ice conditions using an atmospheric global climate model. Given that future DMS concentrations are highly uncertain, several simulations with different surface seawater DMS concentrations and spatial distributions in the Arctic were performed in order to determine the sensitivity of sulfate aerosol budgets, CDNC, and cloud radiative forcing to Arctic surface seawater DMS concentrations. For any given amount and distribution of Arctic surface seawater DMS, similar amounts of sulfate are produced by oxidation of DMS in 2000 and 2050 despite large increases in DMS emission in the latter period due to sea ice retreat in the simulations. This relatively low sensitivity of sulfate burden is related to enhanced sulfate wet removal by precipitation in 2050. However simulated aerosol nucleation rates are higher in 2050, which results in an overall increase in CDNC and substantially more negative cloud radiative forcing. Thus potential future reductions in sea ice extent may cause cloud albedos to increase, resulting in a negative climate feedback on radiative forcing in the Arctic associated with ocean DMS emissions.

scholarly journals Reassessment of shortwave surface cloud radiative forcing in the Arctic: consideration of surface-albedo–cloud interactions

2020 ◽  
Vol 20 (16) ◽  
pp. 9895-9914 ◽  
Author(s):  
Johannes Stapf ◽  
André Ehrlich ◽  
Evelyn Jäkel ◽  
Christof Lüpkes ◽  
Manfred Wendisch
Keyword(s):  
Sea Ice ◽  
Radiative Forcing ◽  
Surface Albedo ◽  
The Arctic ◽  
Radiative Energy ◽  
Cloud Radiative Forcing ◽  
Airborne Measurements ◽  
Ice Surfaces ◽  
The Impact ◽  
Snow And Ice

Abstract. The concept of cloud radiative forcing (CRF) is commonly applied to quantify the impact of clouds on the surface radiative energy budget (REB). In the Arctic, specific radiative interactions between microphysical and macrophysical properties of clouds and the surface strongly modify the warming or cooling effect of clouds, complicating the estimate of CRF obtained from observations or models. Clouds tend to increase the broadband surface albedo over snow or sea ice surfaces compared to cloud-free conditions. However, this effect is not adequately considered in the derivation of CRF in the Arctic so far. Therefore, we have quantified the effects caused by surface-albedo–cloud interactions over highly reflective snow or sea ice surfaces on the CRF using radiative transfer simulations and below-cloud airborne observations above the heterogeneous springtime marginal sea ice zone (MIZ) during the Arctic CLoud Observations Using airborne measurements during polar Day (ACLOUD) campaign. The impact of a modified surface albedo in the presence of clouds, as compared to cloud-free conditions, and its dependence on cloud optical thickness is found to be relevant for the estimation of the shortwave CRF. A method is proposed to consider this surface albedo effect on CRF estimates by continuously retrieving the cloud-free surface albedo from observations under cloudy conditions, using an available snow and ice albedo parameterization. Using ACLOUD data reveals that the estimated average shortwave cooling by clouds almost doubles over snow- and ice-covered surfaces (−62 W m−2 instead of −32 W m−2), if surface-albedo–cloud interactions are considered. As a result, the observed total (shortwave plus longwave) CRF shifted from a warming effect to an almost neutral one. Concerning the seasonal cycle of the surface albedo, it is demonstrated that this effect enhances shortwave cooling in periods when snow dominates the surface and potentially weakens the cooling by optically thin clouds during the summertime melting season. These findings suggest that the surface-albedo–cloud interaction should be considered in global climate models and in long-term studies to obtain a realistic estimate of the shortwave CRF to quantify the role of clouds in Arctic amplification.

scholarly journals The Arctic Temperature Response to Global and Regional Anthropogenic Sulfate Aerosols

2021 ◽  
Vol 9 ◽  
Author(s):  
Acharya Asutosh ◽  
Suvarna Fadnavis ◽  
M. Nuncio ◽  
Rolf Müller ◽  
Sarat C. Tripathy
Keyword(s):  
Radiative Forcing ◽  
Dominant Role ◽  
Winter Season ◽  
Temperature Response ◽  
Summer Season ◽  
The Arctic ◽  
Sulfate Aerosols ◽  
Surface Cooling ◽  
Cloud Radiative Forcing ◽  
High Level

The mechanisms behind Arctic warming and associated climate changes are difficult to discern. Also, the complex local processes and feedbacks like aerosol-cloud-climate interactions are yet to be quantified. Here, using the Community Earth System Model (CAM5) experiments, with emission enhancement of anthropogenic sulfate 1) five-fold globally, 2) ten-times over Asia, and 3) ten-times over Europe we show that regional emissions of sulfate aerosols alter seasonal warming over the Arctic, i.e., colder summer and warmer winter. European emissions play a dominant role in cooling during the summer season (0.7 K), while Asian emissions dominate the warming during the winter season (maximum ∼0.6 K) in the Arctic surface. The cooling/warming is associated with a negative/positive cloud radiative forcing. During the summer season increase in low–mid level clouds, induced by sulfate emissions, favours the solar dimming effect that reduces the downwelling radiation to the surface and thus leads to surface cooling. Warmer winters are associated with enhanced high-level clouds that induce a positive radiative forcing at the top of the atmosphere. This study points to the importance of international strategies being implemented to control sulfate emissions to combat air pollution. Such strategies will also affect the Arctic cooling/warming associated with a cloud radiative forcing caused by sulfate emission change.

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