scholarly journals Linearity of Climate Response to Increases in Black Carbon Aerosols

2013 ◽  
Vol 26 (20) ◽  
pp. 8223-8237 ◽  
Author(s):  
Salil Mahajan ◽  
Katherine J. Evans ◽  
James J. Hack ◽  
John E. Truesdale
Keyword(s):  
Black Carbon ◽  
Radiative Forcing ◽  
Global Climate ◽  
Temperature Response ◽  
Ocean Model ◽  
Climate Response ◽  
Global Average ◽  
High Level ◽  
Carbon Aerosols ◽  
Black Carbon Aerosols

Abstract The impacts of absorbing aerosols on global climate are not completely understood. This paper presents the results of idealized experiments conducted with the Community Atmosphere Model, version 4 (CAM4), coupled to a slab ocean model (CAM4–SOM) to simulate the climate response to increases in tropospheric black carbon aerosols (BC) by direct and semidirect effects. CAM4-SOM was forced with 0, 1×, 2×, 5×, and 10× an estimate of the present day concentration of BC while maintaining the estimated present day global spatial and vertical distribution. The top-of-atmosphere (TOA) radiative forcing of BC in these experiments is positive (warming) and increases linearly as the BC burden increases. The total semidirect effect for the 1 × BC experiment is positive but becomes increasingly negative for higher BC concentrations. The global-average surface temperature response is found to be a linear function of the TOA radiative forcing. The climate sensitivity to BC from these experiments is estimated to be 0.42 K W−1 m2 when the semidirect effects are accounted for and 0.22 K W−1 m2 with only the direct effects considered. Global-average precipitation decreases linearly as BC increases, with a precipitation sensitivity to atmospheric absorption of 0.4% W−1 m2. The hemispheric asymmetry of BC also causes an increase in southward cross-equatorial heat transport and a resulting northward shift of the intertropical convergence zone in the simulations at a rate of 4° PW−1. Global-average mid- and high-level clouds decrease, whereas the low-level clouds increase linearly with BC. The increase in marine stratocumulus cloud fraction over the southern tropical Atlantic is caused by increased BC-induced diabatic heating of the free troposphere.

Black carbon aerosols over a high altitude station, Mahabaleshwar: Radiative forcing and source apportionment

2020 ◽  
Vol 11 (8) ◽  
pp. 1408-1417
Author(s):  
M.P. Raju ◽  
P.D. Safai ◽  
S.M. Sonbawne ◽  
P.S. Buchunde ◽  
G. Pandithurai ◽  
...  
Keyword(s):  
High Altitude ◽  
Black Carbon ◽  
Source Apportionment ◽  
Radiative Forcing ◽  
Carbon Aerosols ◽  
Black Carbon Aerosols

Distribution and direct radiative forcing of black carbon aerosols over Korean Peninsula

2012 ◽  
Vol 58 ◽  
pp. 45-55 ◽  
Author(s):  
Min Young Kim ◽  
Seung-Bok Lee ◽  
Gwi-Nam Bae ◽  
Seung Shik Park ◽  
Kyung Man Han ◽  
...  
Keyword(s):  
Black Carbon ◽  
Korean Peninsula ◽  
Radiative Forcing ◽  
Direct Radiative Forcing ◽  
Carbon Aerosols ◽  
Black Carbon Aerosols

scholarly journals The Semidirect Aerosol Effect: Comparison of a Single-Column Model with Large Eddy Simulation for Marine Stratocumulus

2005 ◽  
Vol 18 (1) ◽  
pp. 119-130 ◽  
Author(s):  
B. T. Johnson
Keyword(s):  
Boundary Layer ◽  
Black Carbon ◽  
Radiative Forcing ◽  
General Circulation ◽  
Radiative Properties ◽  
Aerosol Effect ◽  
Large Eddy ◽  
Single Column ◽  
Carbon Aerosols ◽  
Black Carbon Aerosols

Abstract Large eddy simulations (LES) show that the presence of black carbon aerosols in marine boundary layers leads to a marked reduction of stratocumulus liquid water path (LWP) by heating the cloud layer and suppressing convection in the boundary layer. The reduction of LWP leads to a positive radiative forcing known as the semidirect effect. In this study LES results are compared with results from the National Center for Atmospheric Research (NCAR) Single-Column Community Climate Model (SCCM). The SCCM represents clouds and boundary layer processes through simple parameterization schemes that are typical of general circulation models (GCMs) used for climate experiments. In a case study in which black carbon aerosols were introduced in a stratocumulus-capped boundary layer the SCCM gave a semidirect aerosol radiative forcing that was a factor of 5 smaller than the value obtained from the LES. The cloud response to absorbing aerosols was underestimated because of the way that cloud cover and cloud radiative properties were parameterized in the SCCM. Furthermore, the SCCM gave a poor representation of processes, such as entrainment and boundary layer decoupling, that are crucial to determining stratocumulus LWP. This study shows that GCMs may not include all the physical processes necessary to adequately capture the semidirect aerosol effect. Previous GCM estimates of the semidirect effect that have incorporated simple cloud parameterizations should, therefore, be treated with some caution.

scholarly journals Black carbon fractal morphology and short-wave radiative impact: a modelling study

2011 ◽  
Vol 11 (8) ◽  
pp. 23103-23137
Author(s):  
M. Kahnert ◽  
A. Devasthale
Keyword(s):  
Optical Properties ◽  
Fractal Dimension ◽  
Black Carbon ◽  
Radiative Forcing ◽  
Homogeneous Sphere ◽  
Radiative Impacts ◽  
Radiative Impact ◽  
Sphere Approximation ◽  
Carbon Aerosols ◽  
Black Carbon Aerosols

Abstract. We investigate the impact of the morphological properties of freshly emitted black carbon aerosols on optical properties and on radiative forcing. To this end, we model the optical properties of fractal black carbon aggregates by use of numerically exact solutions to Maxwell's equations within a spectral range from the UVC to the mid-IR. The results are coupled to radiative transfer computations, in which we consider six realistic case studies representing different atmospheric pollution conditions and surface albedos. The spectrally integrated radiative impacts of black carbon are compared for two different fractal morphologies, which brace the range of recently reported experimental observations of black carbon fractal structures. We also gauge our results by performing corresponding calculations based on the homogeneous sphere approximation, which is commonly employed in climate models. We find that at top of atmosphere the aggregate models yield radiative impacts that can be as much as 2 times higher than those based on the homogeneous sphere approximation. An aggregate model with a low fractal dimension can predict a radiative impact that is higher than that obtained with a high fractal dimension by a factor ranging between 1.1–1.6. Although the lower end of this scale seems like a rather small effect, a closer analysis reveals that the single scattering optical properties of more compact and more lacy aggregates differ considerably. In radiative flux computations there can be a partial cancellation due to the opposing effects of differences in the optical cross sections and asymmetry parameters. However, this cancellation effect can strongly depend on atmospheric conditions and is therefore quite unpredictable. We conclude that the fractal morphology of black carbon aerosols and their fractal parameters can have a profound impact on their radiative forcing effect, and that the use of the homogeneous sphere model introduces unacceptably high biases in radiative impact studies. We emphasise that there are other potentially important morphological features that have not been addressed in the present study, such as sintering and coating of freshly emitted black carbon by films of organic material.

scholarly journals Distinct surface response to black carbon aerosols

2021 ◽  
Author(s):  
Tao Tang ◽  
Drew Shindell ◽  
Yuqiang Zhang ◽  
Apostolos Voulgarakis ◽  
Jean-Francois Lamarque ◽  
...  
Keyword(s):  
Wind Speed ◽  
Surface Energy ◽  
Surface Temperature ◽  
Black Carbon ◽  
Temperature Response ◽  
Energy Redistribution ◽  
Carbon Aerosols ◽  
Enhanced Stability ◽  
Reduced Surface ◽  
Black Carbon Aerosols

Abstract. For the radiative impact of individual climate forcings, most previous studies focused on the global mean values at the top of the atmosphere (TOA) and less attention has been paid to surface processes, especially for black carbon aerosols. In this study, the surface radiative responses to five different forcing agents were analyzed by using idealized model simulations. Our analyses reveal that for greenhouse gases, solar irradiance and scattering aerosols, the surface temperature changes are mainly dictated by the changes of surface radiative heating, but for BC, surface energy redistribution between different components plays a more crucial role. Globally, when a unit BC forcing was imposed at TOA, the net shortwave radiation at the surface decreased by 5.09 ± 1.80 W m−2 (averaged over global land), which is partially offset by increased downward longwave radiation (1.67 ± 0.24 W m−2) from the warmer atmosphere, causing a net decrease in the incoming downward surface radiation of 3.42 ± 0.51 W m−2. Despite a reduction in the downward radiation energy, the surface air temperature still increased by 0.14 ± 0.05 K because of less efficient energy dissipation, manifested by reduced surface sensible (2.53 ± 0.37 W m−2) and latent heat flux (1.30 ± 0.27 W m−2), as well as a decrease of Bowen ratio (0.18 ± 0.05). Such reductions of turbulent fluxes can be largely explained by enhanced air stability (0.06 ± 0.01 K), measured as the difference of the potential temperature between 925 hPa and surface, and reduced surface wind speed (0.05 ± 0.01 m s−1). The enhanced stability is due to the faster atmospheric warming relative to the surface whereas the reduced wind speed can be partially explained by enhanced stability and reduced equator-to-pole atmospheric temperature gradient. These rapid adjustments under BC forcing exerted a “top-down” impact on the surface energy redistribution and thus, surface temperature response, which is not observed under greenhouse gas or scattering aerosols. Our study provides new insights into the impact of absorbing aerosols on surface energy balance and surface temperature response.

scholarly journals A Standardized Global Climate Model Study Showing Unique Properties for the Climate Response to Black Carbon Aerosols

2015 ◽  
Vol 28 (6) ◽  
pp. 2512-2526 ◽  
Author(s):  
M. Sand ◽  
T. Iversen ◽  
P. Bohlinger ◽  
A. Kirkevåg ◽  
I. Seierstad ◽  
...  
Keyword(s):  
Black Carbon ◽  
Radiative Forcing ◽  
Climate Model ◽  
Kernel Method ◽  
Global Climate ◽  
Global Climate Model ◽  
Climate Response ◽  
Air Concentration ◽  
Surface Warming ◽  
The Difference

Abstract The climate response to an abrupt increase of black carbon (BC) aerosols is compared to the standard CMIP5 experiment of quadrupling CO2 concentrations in air. The global climate model NorESM with interactive aerosols is used. One experiment employs prescribed BC emissions with calculated concentrations coupled to atmospheric processes (emission-driven) while a second prescribes BC concentrations in air (concentration-driven) from a precalculation with the same model and emissions, but where the calculated BC does not force the climate dynamics. The difference quantifies effects of feedbacks between airborne BC and other climate processes. BC emissions are multiplied with 25, yielding an instantaneous top-of-atmosphere (TOA) radiative forcing (RF) comparable to the quadrupling of atmospheric CO2. A radiative kernel method is applied to estimate the different feedbacks. In both BC runs, BC leads to a much smaller surface warming than CO2. Rapid atmospheric feedbacks reduce the BC-induced TOA forcing by approximately 75% over the first year (10% for CO2). For BC, equilibrium is quickly re-established, whereas for CO2 equilibration requires a much longer time than 150 years. Emission-driven BC responses in the atmosphere are much larger than the concentration-driven. The northward displacement of the intertropical convergence zone (ITCZ) in the BC emission-driven experiment enhances both the vertical transport and deposition of BC from Southeast Asia. The study shows that prescribing BC concentrations may lead to seriously inaccurate conclusions, but other models with less efficient transport may produce results with smaller differences.

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