scholarly journals Total aerosol effect: radiative forcing or radiative flux perturbation?

2010 ◽  
Vol 10 (7) ◽  
pp. 3235-3246 ◽  
Author(s):  
U. Lohmann ◽  
L. Rotstayn ◽  
T. Storelvmo ◽  
A. Jones ◽  
S. Menon ◽  
...  
Keyword(s):  
Global Warming ◽  
Radiative Forcing ◽  
Climate Models ◽  
Radiative Flux ◽  
Radiative Forcings ◽  
Microphysical Properties ◽  
Aerosol Effect ◽  
Precipitation Formation ◽  
Aerosol Radiative ◽  
Flux Perturbation

Abstract. Uncertainties in aerosol radiative forcings, especially those associated with clouds, contribute to a large extent to uncertainties in the total anthropogenic forcing. The interaction of aerosols with clouds and radiation introduces feedbacks which can affect the rate of precipitation formation. In former assessments of aerosol radiative forcings, these effects have not been quantified. Also, with global aerosol-climate models simulating interactively aerosols and cloud microphysical properties, a quantification of the aerosol forcings in the traditional way is difficult to define properly. Here we argue that fast feedbacks should be included because they act quickly compared with the time scale of global warming. We show that for different forcing agents (aerosols and greenhouse gases) the radiative forcings as traditionally defined agree rather well with estimates from a method, here referred to as radiative flux perturbations (RFP), that takes these fast feedbacks and interactions into account. Based on our results, we recommend RFP as a valid option to compare different forcing agents, and to compare the effects of particular forcing agents in different models.

scholarly journals Total aerosol effect: radiative forcing or radiative flux perturbation?

2009 ◽  
Vol 9 (6) ◽  
pp. 25633-25661 ◽  
Author(s):  
U. Lohmann ◽  
L. Rotstayn ◽  
T. Storelvmo ◽  
A. Jones ◽  
S. Menon ◽  
...  
Keyword(s):  
Global Warming ◽  
Radiative Forcing ◽  
Climate Models ◽  
Radiative Flux ◽  
Radiative Forcings ◽  
Microphysical Properties ◽  
Aerosol Effect ◽  
Rain Formation ◽  
Aerosol Radiative ◽  
Flux Perturbation

Abstract. Uncertainties in aerosol radiative forcings, especially those associated with clouds, contribute to a large extent to uncertainties in the total anthropogenic forcing. The interaction of aerosols with clouds and radiation introduces feedbacks which can affect the rate of rain formation. In former assessments of aerosol radiative forcings, these effects have not been quantified. Also, with global aerosol-climate models simulating interactively aerosols and cloud microphysical properties, a quantification of the aerosol forcings in the traditional way is difficult to properly define. Here we argue that fast feedbacks should be included because they act quickly compared with the time scale of global warming. We show that for different forcing agents (aerosols and greenhouse gases) the radiative forcings as traditionally defined agree rather well with estimates from a method, here referred to as radiative flux perturbations (RFP), that takes these fast feedbacks and interactions into account. Based on our results, we recommend RFP as a valid option to compare different forcing agents, and to compare the effects of particular forcing agents in different models.

scholarly journals Development of prognostic aerosol–cloud interactions combining a chemistry transport model and a regional climate model

2015 ◽  
Vol 8 (2) ◽  
pp. 897-933
Author(s):  
M. A. Thomas ◽  
M. Kahnert ◽  
C. Andersson ◽  
H. Kokkola ◽  
U. Hansson ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Climate Models ◽  
Climate Model ◽  
Transport Model ◽  
Regional Climate ◽  
Cloud Droplet ◽  
Microphysical Properties ◽  
Aerosol Effect ◽  
Aerosol Cloud Interactions ◽  
Set Up

Abstract. To reduce uncertainties and hence, to obtain a better estimate of aerosol (direct and indirect) radiative forcing, next generation climate models aim for a tighter coupling between chemistry transport models and regional climate models and a better representation of aerosol–cloud interactions. In this study, this coupling is done by first forcing the Rossby Center regional climate model, RCA4 by ERA-Interim lateral boundaries (LBCs) and SST using the standard CDNC (cloud droplet number concentration) formulation (hereafter, referred to as the "stand-alone RCA4 version" or "CTRL" simulation). In this simulation, the CDNCs are assigned fixed numbers based on if the underlying surface is land or oceanic. The meteorology from this simulation is then used to drive the chemistry transport model, MATCH which is coupled online with the aerosol dynamics model, SALSA. CDNC fields obtained from MATCH-SALSA are then fed back into a new RCA4 simulation. In this new simulation (referred to as "MOD" simulation), all parameters remain the same as in the first run except for the CDNCs provided by MATCH-SALSA. Simulations are carried out with this model set up for the period 2005–2012 over Europe and the differences in cloud microphysical properties and radiative fluxes as a result of local CDNC changes and possible model responses are analyzed. Our study shows substantial improvements in the cloud microphysical properties with the input of the MATCH-SALSA derived 3-D CDNCs compared to the stand-alone RCA4 version. This model set up improves the spatial, seasonal and vertical distribution of CDNCs with higher concentration observed over central Europe during summer half of the year and over Eastern Europe and Russia during the winter half of the year. Realistic cloud droplet radii (CD radii) values have been simulated with the maxima reaching 13 μm whereas in the stand-alone version, the values reached only 5 μm. A substantial improvement in the distribution of cloud liquid water path was observed when compared to the satellite retrievals from MODIS for the boreal summer months. The median and SD values from the "MOD" simulation are closer to observations than those obtained using the stand-alone RCA4 version. These changes resulted in a significant decrease in the total annual mean net fluxes at the top of the atmosphere (TOA) by −5 W m−2 over the domain selected in the study. The TOA net fluxes from the "MOD" simulation show a better agreement with the retrievals from CERES instrument. The aerosol indirect effects are evaluated based on 1900 emissions. Our simulations estimated the domain averaged annual mean total radiative forcing of −0.64 W m−2 with larger contribution from the first indirect aerosol effect than from the second indirect aerosol effect.

scholarly journals Atmospheric Lifetimes, Infrared Absorption Spectra, Radiative Forcings and Global Warming Potentials of NF<sub>3</sub> and CFC-115

2016 ◽  
Author(s):  
Anna Totterdill ◽  
Tamás Kovács ◽  
Wuhu Feng ◽  
Sandip Dhomse ◽  
Christopher J. Smith ◽  
...  
Keyword(s):  
Global Warming ◽  
Cross Sections ◽  
Infrared Absorption ◽  
Radiative Forcing ◽  
Climate Model ◽  
Radiative Forcings ◽  
Atmospheric Window ◽  
Infrared Absorption Spectra ◽  
Global Warming Potentials ◽  
Good Agreement

Abstract. Fluorinated compounds such as NF3 and C2F5Cl (CFC-115) are characterised by very large global warming potentials (GWPs) which result from extremely long atmospheric lifetimes and strong infrared absorptions in the atmospheric window. In this study we have experimentally determined the infrared absorption cross-sections of NF3 and CFC-115, calculated the radiative forcing and efficiency using two radiative transfer models and identified the effect of clouds and stratospheric adjustment. The infrared cross sections are in good agreement with previous measurements, whereas the resulting radiative forcings and efficiencies are, on average, around 10 % larger. A whole atmosphere chemistry-climate model was used to determine the atmospheric lifetimes of NF3 and CFC-115 to be (616 ± 34) years and (492 ± 22) years, respectively. The GWPs for NF3 are estimated to be 14 600, 19 400 and 21 400 over 20, 100 and 500 years, respectively. Similarly, the GWPs for CFC-115 are 6120, 8060 and 8630 over 20, 100 and 500 years, respectively.

scholarly journals Including the efficacy of land ice changes in deriving climate sensitivity from paleodata

2019 ◽  
Vol 10 (2) ◽  
pp. 333-345 ◽  
Author(s):  
Lennert B. Stap ◽  
Peter Köhler ◽  
Gerrit Lohmann
Keyword(s):  
Climate Sensitivity ◽  
Radiative Forcing ◽  
Climate Models ◽  
Co2 Concentration ◽  
Global Temperature ◽  
Maximum Temperature ◽  
Radiative Forcings ◽  
The Impact ◽  
The Last Glacial

Abstract. The equilibrium climate sensitivity (ECS) of climate models is calculated as the equilibrium global mean surface air warming resulting from a simulated doubling of the atmospheric CO2 concentration. In these simulations, long-term processes in the climate system, such as land ice changes, are not incorporated. Hence, climate sensitivity derived from paleodata has to be compensated for these processes, when comparing it to the ECS of climate models. Several recent studies found that the impact these long-term processes have on global temperature cannot be quantified directly through the global radiative forcing they induce. This renders the prevailing approach of deconvoluting paleotemperatures through a partitioning based on radiative forcings inaccurate. Here, we therefore implement an efficacy factor ε[LI] that relates the impact of land ice changes on global temperature to that of CO2 changes in our calculation of climate sensitivity from paleodata. We apply our refined approach to a proxy-inferred paleoclimate dataset, using ε[LI]=0.45-0.20+0.34 based on a multi-model assemblage of simulated relative influences of land ice changes on the Last Glacial Maximum temperature anomaly. The implemented ε[LI] is smaller than unity, meaning that per unit of radiative, forcing the impact on global temperature is less strong for land ice changes than for CO2 changes. Consequently, our obtained ECS estimate of 5.8±1.3 K, where the uncertainty reflects the implemented range in ε[LI], is ∼50 % higher than when differences in efficacy are not considered.

scholarly journals Role of black carbon mass size distribution in the direct aerosol radiative forcing

2019 ◽  
Vol 19 (20) ◽  
pp. 13175-13188 ◽  
Author(s):  
Gang Zhao ◽  
Jiangchuan Tao ◽  
Ye Kuang ◽  
Chuanyang Shen ◽  
Yingli Yu ◽  
...  
Keyword(s):  
Size Distribution ◽  
Black Carbon ◽  
Radiative Forcing ◽  
Climate Models ◽  
Radiative Effects ◽  
Aerosol Radiative Forcing ◽  
Mass Size Distribution ◽  
Mass Size ◽  
Mixing States ◽  
Aerosol Radiative

Abstract. Large uncertainties exist when estimating radiative effects of ambient black carbon (BC) aerosol. Previous studies about the BC aerosol radiative forcing mainly focus on the BC aerosols' mass concentrations and mixing states, while the effects of BC mass size distribution (BCMSD) were not well considered. In this paper, we developed a method of measuring the BCMSD by using a differential mobility analyzer in tandem with an Aethalometer. A comprehensive method of multiple charging corrections was proposed and implemented in measuring the BCMSD. Good agreement was obtained between the BC mass concentration integrated from this system and that measured in the bulk phase, demonstrating the reliability of our proposed method. Characteristics of the BCMSD and corresponding radiative effects were studied based on a field measurement campaign conducted in the North China Plain by using our own measurement system. Results showed that the BCMSD had two modes and the mean peak diameters of the modes were 150 and 503 nm. The BCMSD of the coarser mode varied significantly under different pollution conditions with peak diameter varying between 430 and 580 nm, which gave rise to significant variation in aerosol bulk optical properties. The direct aerosol radiative forcing was estimated to vary by 8.45 % for different measured BCMSDs of the coarser mode, which shared the same magnitude with the variation associated with assuming different aerosol mixing states (10.5 %). Our study reveals that the BCMSD as well as its mixing state in estimating the direct aerosol radiative forcing matters. Knowledge of the BCMSD should be fully considered in climate models.

scholarly journals Radiative forcing bias of simulated surface albedo modifications linked to forest cover changes at northern latitudes

2015 ◽  
Vol 12 (7) ◽  
pp. 2195-2205 ◽  
Author(s):  
R. M. Bright ◽  
G. Myhre ◽  
R. Astrup ◽  
C. Antón-Fernández ◽  
A. H. Strømman
Keyword(s):  
Radiative Forcing ◽  
Surface Albedo ◽  
Forest Cover ◽  
Climate Models ◽  
Open Area ◽  
Data Set ◽  
Radiative Forcings ◽  
Open Forest ◽  
Northern Latitudes ◽  
Analytical Time

Abstract. In the presence of snow, the bias in the prediction of surface albedo by many climate models remains difficult to correct due to the difficulties of separating the albedo parameterizations from those describing snow and vegetation cover and structure. This can be overcome by extracting the albedo parameterizations in isolation, by executing them with observed meteorology and information on vegetation structure, and by comparing the resulting predictions to observations. Here, we employ an empirical data set of forest structure and daily meteorology for three snow cover seasons and for three case regions in boreal Norway to compute and evaluate predicted albedo to those based on daily MODIS retrievals. Forest and adjacent open area albedos are subsequently used to estimate bias in top-of-the-atmosphere (TOA) radiative forcings (RF) from albedo changes (Δα, Open–Forest) connected to land use and land cover changes (LULCC). As expected, given the diversity of approaches by which snow masking by tall-statured vegetation is parameterized, the magnitude and sign of the albedo biases varied considerably for forests. Large biases at the open sites were also detected, which was unexpected given that these sites were snow-covered throughout most of the analytical time period, therefore eliminating potential biases linked to snow-masking parameterizations. Biases at the open sites were mostly positive, exacerbating the strength of vegetation masking effects and hence the simulated LULCC Δα RF. Despite the large biases in both forest and open area albedos by some schemes in some months and years, the mean Δα RF bias over the 3-year period (November–May) was considerably small across models (−2.1 ± 1.04 Wm−2; 21 ± 11%); four of six models had normalized mean absolute errors less than 20%. Identifying systematic sources of the albedo prediction biases proved challenging, although for some schemes clear sources were identified.

scholarly journals Ice water content of arctic, midlatitude, and tropical cirrus – Part 2: Extension of the database and new statistical analysis

2012 ◽  
Vol 12 (11) ◽  
pp. 29443-29474 ◽  
Author(s):  
A. E. Luebke ◽  
L. M. Avallone ◽  
C. Schiller ◽  
C. Rolf ◽  
M. Krämer
Keyword(s):  
Water Content ◽  
Radiative Forcing ◽  
Climate Models ◽  
Distribution Functions ◽  
Formation Mechanisms ◽  
Mean Values ◽  
Microphysical Properties ◽  
Ice Water Content ◽  
Ground Based Lidar ◽  
Ice Water

Abstract. Ice clouds are known to be major contributors to radiative forcing in the Earth's atmosphere, yet describing their microphysical properties in climate models remains challenging. Among these properties, the ice water content (IWC) of cirrus clouds is of particular interest both because it is measurable and because it can be directly related to a number of other radiatively important variables such as extinction and effective radius. This study expands upon the work of Schiller et al. (2008), extending a climatology of IWC by combining datasets from several European and US airborne campaigns and ground-based lidar measurements over Jülich, Germany. The relationship between IWC and temperature is further investigated using the new merged dataset and probability distribution functions (PDFs). A PDF-based formulation allows for representation of not only the mean values of IWC, but also the variability of IWC within a temperature band. The IWC-PDFs are found to be bimodal over the whole cirrus temperature range, which might be attributed to different cirrus formation mechanisms such as heterogeneous and homogeneous freezing. The PDFs of IWC are further compared to distributions of cirrus ice crystal number and mass mean radius, which show that the general relationship between IWC and temperature appears to be influenced much more by particle number than by particle size.

scholarly journals Aerosol radiative forcings induced by substantial changes in anthropogenic emissions in China from 2008 to 2016

2021 ◽  
Vol 21 (8) ◽  
pp. 5965-5982
Author(s):  
Mingxu Liu ◽  
Hitoshi Matsui
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Radiative Forcing ◽  
Eastern China ◽  
Radiation Budget ◽  
Anthropogenic Emissions ◽  
Radiative Forcings ◽  
The Past ◽  
Positive Direct ◽  
Aerosol Radiative

Abstract. Anthropogenic emissions in China play an important role in altering the global radiation budget. Over the past decade, the strong clean-air policies in China have resulted in substantial reductions of anthropogenic emissions of sulfur dioxide (SO2) and primary particulate matter, and air quality in China has consequently improved. However, the resultant aerosol radiative forcings have been poorly understood. In this study, we used an advanced global climate model integrated with the latest localized emission inventory to quantify the aerosol radiative forcings by the changes of anthropogenic emissions in China between 2008 and 2016. By comparing with multiple observation datasets, our simulations reproduced the considerable reductions of sulfate and black carbon (BC) mass loadings reasonably well over eastern China (the key region subject to stringent emission controls) during the period and accordingly showed a clear decline in both aerosol optical depth and absorption aerosol optical depth. The results revealed a regional annual mean positive direct radiative forcing (DRF) of +0.29 W m−2 at the top of the atmosphere (TOA) due to the reduction of SO2 emissions. This positive aerosol radiative forcing was comprised of diminished sulfate scattering (+0.58 W m−2), enhanced nitrate radiative effects (−0.29 W m−2), and could be completely offset by the concurrent reduction of BC emissions that induced a negative BC DRF of −0.33 W m−2. Despite the small net aerosol DRF (−0.05 W m−2) at the TOA, aerosol–radiation interactions could explain the surface brightening in China over the past decade. The overall reductions in aerosol burdens and associated optical effects mainly from BC and sulfate enhanced the regional annual mean downward solar radiation flux at the surface by +1.0 W m−2 between 2008 and 2016. The enhancement was in general agreement with a long-term observational record of surface energy fluxes in China. We also estimated that aerosol effects on cloud radiative forcings may have played a dominant role in the net aerosol radiative forcings at the TOA in China and over the northern Pacific Ocean during the study period. This study will facilitate more informed assessment of climate responses to projected emissions in the future as well as to sudden changes in human activities (e.g., the COVID-19 lockdown).

scholarly journals Atmospheric lifetimes, infrared absorption spectra, radiative forcings and global warming potentials of NF<sub>3</sub> and CF<sub>3</sub>CF<sub>2</sub>Cl (CFC-115)

2016 ◽  
Vol 16 (17) ◽  
pp. 11451-11463 ◽  
Author(s):  
Anna Totterdill ◽  
Tamás Kovács ◽  
Wuhu Feng ◽  
Sandip Dhomse ◽  
Christopher J. Smith ◽  
...  
Keyword(s):  
Global Warming ◽  
Cross Sections ◽  
Infrared Absorption ◽  
Radiative Forcing ◽  
Climate Model ◽  
Intergovernmental Panel ◽  
Radiative Forcings ◽  
Radiative Efficiency ◽  
Atmospheric Window ◽  
Global Warming Potentials

Abstract. Fluorinated compounds such as NF3 and C2F5Cl (CFC-115) are characterised by very large global warming potentials (GWPs), which result from extremely long atmospheric lifetimes and strong infrared absorptions in the atmospheric window. In this study we have experimentally determined the infrared absorption cross sections of NF3 and CFC-115, calculated the radiative forcing and efficiency using two radiative transfer models and identified the effect of clouds and stratospheric adjustment. The infrared cross sections are within 10 % of previous measurements for CFC-115 but are found to be somewhat larger than previous estimates for NF3, leading to a radiative efficiency for NF3 that is 25 % larger than that quoted in the Intergovernmental Panel on Climate Change Fifth Assessment Report. A whole atmosphere chemistry–climate model was used to determine the atmospheric lifetimes of NF3 and CFC-115 to be (509 ± 21) years and (492 ± 22) years, respectively. The GWPs for NF3 are estimated to be 15 600, 19 700 and 19 700 over 20, 100 and 500 years, respectively. Similarly, the GWPs for CFC-115 are 6030, 7570 and 7480 over 20, 100 and 500 years, respectively.

scholarly journals Role of black carbons mass size distribution in the direct aerosol radiative forcing

2019 ◽  
Author(s):  
Gang Zhao ◽  
Jiangchuan Tao ◽  
Ye Kuang ◽  
Chuanyang Shen ◽  
Yingli Yu ◽  
...  
Keyword(s):  
Size Distribution ◽  
Radiative Forcing ◽  
Climate Models ◽  
Field Measurements ◽  
Radiative Effects ◽  
Aerosol Radiative Forcing ◽  
Mass Size Distribution ◽  
Mass Size ◽  
Mixing States ◽  
Aerosol Radiative

Abstract. Large uncertainties exist when estimating radiative effects of ambient black carbon (BC) aerosol. Previous studies about the BC aerosol radiative forcing mainly focus on the BC aerosols’ mass concentrations and mixing states, while the effects of BC mass size distribution (BCMSD) were not well considered. In this paper, we developed a method by measuring the BCMSD by using a differential mobility analyzer in tandem with an aethalometer. A comprehensive method of multiple charging corrections is proposed and implemented in measuring the BCMSD. Good agreement is obtained between the BC mass concentration integrated from this system and that measured in bulk phase, demonstrating the reliability of our proposed method. Characteristics of the BCMSD and corresponding radiative effects are studied based on field measurements conducted in the North China Plain by using our own designed measurement system. Results show that the BCMSD have two modes and the mean peak diameters of the two modes are 150 nm and 503 nm respectively. The BCMSD of coarser mode varies significantly under different pollution conditions with peak diameter varying between 430 nm and 580 nm, which gives rise to significant variation in aerosol buck optical properties. The aerosol direct aerosol radiative forcing is estimated to vary by 22.5 % for different measured BCMSDs, which shares the same magnitude to the variation associated with assuming different aerosol mixing states (21.5 %). Our study reveals that the BCMSD matters as well as their mixing state in estimating the direct aerosol radiative forcing. Knowledge of the BCMSD should be fully considered in climate models.

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