scholarly journals Correlation between present-day model simulation of Arctic cloud radiative forcing and sea ice consistent with positive winter convective cloud feedback

2012 ◽  
Vol 4 (3) ◽  
pp. n/a-n/a ◽  
Author(s):  
Benjamin D. Leibowicz ◽  
Dorian S. Abbot ◽  
Kerry Emanuel ◽  
Eli Tziperman
Keyword(s):  
Sea Ice ◽  
Radiative Forcing ◽  
Model Simulation ◽  
Convective Cloud ◽  
Cloud Feedback ◽  
Cloud Radiative Forcing

scholarly journals Improving the Simulation of Tropical Convective Cloud-Top Heights in CAM5 with CloudSat Observations

2018 ◽  
Vol 31 (13) ◽  
pp. 5189-5204 ◽  
Author(s):  
Mingcheng Wang ◽  
Guang J. Zhang
Keyword(s):  
Radiative Forcing ◽  
Model Simulation ◽  
Convective Cloud ◽  
Model Atmosphere ◽  
Convective Precipitation ◽  
Cloud Radiative Forcing ◽  
Convective Clouds ◽  
Community Atmosphere Model ◽  
Cloud Tops ◽  
Main Factor

Using 4 years of CloudSat data, the simulation of tropical convective cloud-top heights (CCTH) above 6 km simulated by the convection scheme in the Community Atmosphere Model, version 5 (CAM5), is evaluated. Compared to CloudSat observations, CAM5 underestimates CCTH by more than 2 km on average. Further analysis of model results suggests that the dilute CAPE calculation, which has been incorporated into the convective parameterization since CAM4, is a main factor restricting CCTH to much lower levels. After removing this restriction, more convective clouds develop into higher altitudes, although convective clouds with tops above 12 km are still underestimated significantly. The environmental conditions under which convection develops in CAM5 are compared with CloudSat observations for convection with similar CCTHs. It is shown that the model atmosphere is much more unstable compared to CloudSat observations, and there is too much entrainment in CAM5. Since CCTHs are closely associated with cloud radiative forcing, the impacts of CCTH on model simulation are further investigated. Results show that the change of CCTH has important impacts on cloud radiative forcing and precipitation. With increased CCTHs, there is more cloud radiative forcing in tropical Africa and the eastern Pacific, but less cloud radiative forcing in the western Pacific. The contribution to total convective precipitation from convection with cloud tops above 9 km is also increased substantially.

scholarly journals Transmission of Solar Radiation by Clouds over Snow and Ice Surfaces. Part II: Cloud Optical Depth and Shortwave Radiative Forcing from Pyranometer Measurements in the Southern Ocean

2005 ◽  
Vol 18 (22) ◽  
pp. 4637-4648 ◽  
Author(s):  
Melanie F. Fitzpatrick ◽  
Stephen G. Warren
Keyword(s):  
Solar Radiation ◽  
Southern Ocean ◽  
Sea Ice ◽  
Optical Depth ◽  
Radiative Forcing ◽  
Surface Albedo ◽  
Cloud Droplet ◽  
Frequency Distributions ◽  
Cloud Optical Depth ◽  
Cloud Radiative Forcing

Abstract Downward solar irradiance at the sea surface, measured on several voyages of an icebreaker in the Southern Ocean, is used to infer transmittance of solar radiation by clouds. Together with surface albedo estimated from coincident hourly sea ice reports, instantaneous cloud radiative forcing and effective cloud optical depth are obtained. Values of “raw cloud transmittance” (trc), the ratio of downward irradiance under cloud to downward irradiance measured under clear sky, vary from 0.1 to 1.0. Over sea ice, few values of trc were observed between 0.8 and 1.0, possibly due to the threshold nature of the aerosol-to-cloud-droplet transition. This sparsely populated region of transmittances is referred to as the Köhler gap. The instantaneous downward shortwave cloud radiative forcing is computed, as well as the time-averaged net forcing. The net forcing at a solar zenith angle of 60° is typically −250 W m−2 over open ocean, but only half this value over sea ice because of the higher surface albedo and less frequent occurrence of clouds. “Effective” optical depths τ (for a radiatively equivalent horizontally homogeneous cloud) are classified by season and surface type. The frequency distributions of τ are well fitted by decaying exponentials, giving a characteristic optical depth of 15 at 47°S, increasing to 24 in the region of maximum cloud cover at 58°S, and decreasing to 11 at 67°S near the coast of Antarctica.

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 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 Estimation of Asian dust aerosol effect on cloud radiation forcing using Fu-Liou radiative model and CERES measurements

2008 ◽  
Vol 8 (10) ◽  
pp. 2763-2771 ◽  
Author(s):  
◽  
P. Minnis ◽  
◽  
◽  
◽  
...  
Keyword(s):  
Direct Effect ◽  
Radiative Forcing ◽  
Model Simulation ◽  
Radiant Energy ◽  
Asian Dust ◽  
Dust Aerosol ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Cloud Radiative Forcing ◽  
The Impact

Abstract. The impact of Asian dust on cloud radiative forcing during 2003–2006 is studied by using the Clouds and Earth's Radiant Energy Budget Scanner (CERES) data and the Fu-Liou radiative transfer model. Analysis of satellite data shows that the dust aerosol significantly reduced the cloud cooling effect at TOA. In dust contaminated cloudy regions, the 4-year mean values of the instantaneous shortwave, longwave and net cloud radiative forcing are −138.9, 69.1, and −69.7 Wm−2, which are 57.0, 74.2, and 46.3%, respectively, of the corresponding values in pristine cloudy regions. The satellite-retrieved cloud properties are significantly different in the dusty regions and can influence the radiative forcing indirectly. The contributions to the cloud radiation forcing by the dust direct, indirect and semi-direct effects are estimated using combined satellite observations and Fu-Liou model simulation. The 4-year mean value of combination of dust indirect and semi-direct shortwave radiative forcing (SWRF) is 82.2 Wm−2, which is 78.4% of the total dust effect. The dust direct effect is only 22.7 Wm−2, which is 21.6% of the total effect. Because both first and second indirect effects enhance cloud cooling, the aerosol-induced cloud warming is mainly the result of the semi-direct effect of dust.

scholarly journals Estimation of Asian dust aerosol effect on cloud radiation forcing using Fu-Liou radiative model and CERES measurements

2008 ◽  
Vol 8 (1) ◽  
pp. 2061-2084 ◽  
Author(s):  
J. Su ◽  
J. Huang ◽  
Q. Fu ◽  
P. Minnis ◽  
J. Ge ◽  
...  
Keyword(s):  
Direct Effect ◽  
Radiative Forcing ◽  
Model Simulation ◽  
Radiant Energy ◽  
Asian Dust ◽  
Dust Aerosol ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Cloud Radiative Forcing ◽  
The Impact

Abstract. The impact of Asian dust on cloud radiative forcing during 2003–2006 is studied by using the Clouds and Earth's Radiant Energy Budget Scanner (CERES) data and the Fu-Liou radiative transfer model. Analysis of satellite data shows that the dust aerosol significantly reduced the cloud cooling effect at TOA. In dust contaminated cloudy regions, the 4-year mean values of the instantaneous shortwave, longwave and net cloud radiative forcing are −138.9, 69.1, and −69.7 Wm−2, which are 57.0, 74.2, and 46.3%, respectively, of the corresponding values in pristine cloudy regions. The satellite-retrieved cloud properties are significantly different in the dusty regions and can influence the radiative forcing indirectly. The contributions to the cloud radiation forcing by the dust direct, indirect and semi-direct effects are estimated using combined satellite observations and Fu-Liou model simulation. The 4-year mean value of combination of indirect and semi-direct shortwave radiative forcing (SWRF) is 82.2 Wm−2, which is 78.4% of the total dust effect. The direct effect is only 22.7 Wm−2, which is 21.6% of the total effect. Because both first and second indirect effects enhance cloud cooling, the aerosol-induced cloud warming is mainly the result of the semi-direct effect of dust.

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.

Using CloudSat observations to evaluate cloud top heights from convection parameterization

2017 ◽  
Vol 2 (2) ◽  
Author(s):  
Guang Jun Zhang ◽  
Mingcheng Wang
Keyword(s):  
Radiative Forcing ◽  
Model Simulation ◽  
Convective Cloud ◽  
Radiation Budget ◽  
Convective Clouds ◽  
Average Temperature ◽  
Community Atmosphere Model ◽  
Convection Parameterization ◽  
Cloud Ice ◽  
The Tropics

How high convective clouds can go is of great importance to climate. Cloud ice and liquid water that detrain near the top of convective cores are important for the formation of anvil clouds and thus impact cloud radiative forcing and the Earth’s radiation budget. This study uses CloudSat observations to evaluate convective cloud top heights in the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM5). Results show that convective cloud top heights in the tropics are much lower than observed by CloudSat, by more than 2 km on average. Temperature and moisture anomalies from climatological means are composited for convective clouds of different heights for both observations and model simulation. It is found that convective environment is warmer and moister, and the anomalies are larger for clouds of higher tops. For a given convective cloud top height, the corresponding atmosphere in CAM5 is more convectively unstable than what the CloudSat observations indicate, suggesting that there is too much entrainment into convective clouds in the model.

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