scholarly journals Quantifying the uncertainties of aerosol indirect effects and impacts on decadal-scale climate variability in NCAR CAM5 and CESM1

2014 ◽  
Author(s):  
Sungsu Park
Keyword(s):  
Climate Variability ◽  
Indirect Effects ◽  
Aerosol Indirect Effects ◽  
Decadal Scale

Common summertime total cloud cover and aerosol optical depth weekly variabilities over Europe: Sign of the aerosol indirect effects?

2015 ◽  
Vol 153 ◽  
pp. 59-73 ◽  
Author(s):  
A.K. Georgoulias ◽  
K.A. Kourtidis ◽  
G. Alexandri ◽  
S. Rapsomanikis ◽  
A. Sanchez-Lorenzo
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Indirect Effects ◽  
Cloud Cover ◽  
Total Cloud Cover ◽  
Aerosol Indirect Effects

scholarly journals Exploiting the weekly cycle as observed over Europe to analyse aerosol indirect effects in two climate models

2009 ◽  
Vol 9 (21) ◽  
pp. 8493-8501 ◽  
Author(s):  
J. Quaas ◽  
O. Boucher ◽  
A. Jones ◽  
G. P. Weedon ◽  
J. Kieser ◽  
...  
Keyword(s):  
Indirect Effects ◽  
General Circulation ◽  
Climate Models ◽  
General Circulation Models ◽  
Cloud Microphysics ◽  
Liquid Water Path ◽  
Large Variability ◽  
Aerosol Indirect Effects ◽  
Weekly Cycle ◽  
Model Control

Abstract. A weekly cycle in aerosol pollution and some meteorological quantities is observed over Europe. In the present study we exploit this effect to analyse aerosol-cloud-radiation interactions. A weekly cycle is imposed on anthropogenic emissions in two general circulation models that include parameterizations of aerosol processes and cloud microphysics. It is found that the simulated weekly cycles in sulfur dioxide, sulfate, and aerosol optical depth in both models agree reasonably well with those observed indicating model skill in simulating the aerosol cycle. A distinct weekly cycle in cloud droplet number concentration is demonstrated in both observations and models. For other variables, such as cloud liquid water path, cloud cover, top-of-the-atmosphere radiation fluxes, precipitation, and surface temperature, large variability and contradictory results between observations, model simulations, and model control simulations without a weekly cycle in emissions prevent us from reaching any firm conclusions about the potential aerosol impact on meteorology or the realism of the modelled second aerosol indirect effects.

scholarly journals Inconsistent decadal variations between surface and free tropospheric nitrogen oxides over United States

2017 ◽  
Author(s):  
Zhe Jiang ◽  
Helen Worden ◽  
John R. Worden ◽  
Daven K. Henze ◽  
Dylan B. A. Jones ◽  
...  
Keyword(s):  
United States ◽  
Air Quality ◽  
Nitrogen Oxides ◽  
Climate Variability ◽  
Long Range ◽  
North American ◽  
Long Range Transport ◽  
Substantial Impact ◽  
Decadal Scale ◽  
Range Transport

Abstract. Decreases in surface emissions of nitrogen oxides (NOx = NO + NO2) in North America have led to substantial improvements in air-quality over the last several decades. Here we show that satellite observations of tropospheric nitrogen dioxide (NO2) columns over the contiguous United States (US) do not decrease after about 2009, while surface NO2 concentrations continue to decline through to the present. This divergence, if it continues, could have a substantial impact on surface air quality due to mixing of free-tropospheric air into the boundary layer. Our results show only limited contributions from local effects such as fossil fuel emissions, lightning, or instrument artifacts, but we do find a possible relationship of NO2 changes to decadal climate variability. Our analysis demonstrates that the intensity of transpacific transport is stronger in El Niño years and weaker in La Niña years, and consequently, that decadal-scale climate variability impacts the contribution of Asian emissions on North American atmospheric composition. Because of the short lifetime, it is usually believed that the direct contribution of long-range transport to tropospheric NOx distribution is limited. If our hypothesis about transported Asian emissions is correct, then this observed divergence between satellite and surface NOx could indicate mechanisms that allow for either NOx or its reservoir species to have a larger than expected effect on North American tropospheric composition. These results therefore suggest more aircraft and satellite studies to determine the possible missing processes in our understanding of the long-range transport of tropospheric NOx.

scholarly journals Investigation of aerosol indirect effects on monsoon clouds using ground-based measurements over a high-altitude site in Western Ghats

2016 ◽  
Author(s):  
V. Anil Kumar ◽  
G. Pandithurai ◽  
P. P. Leena ◽  
K. K. Dani ◽  
P. Murugavel ◽  
...  
Keyword(s):  
High Altitude ◽  
Indirect Effects ◽  
Cloud Droplet ◽  
Droplet Size Distribution ◽  
Liquid Water Content ◽  
Number Concentration ◽  
Effective Radius ◽  
Aerosol Indirect Effects ◽  
Cloud Droplet Number Concentration ◽  
Aerosol Effects

Abstract. The effect of aerosols on cloud droplet number concentration and droplet effective radius are investigated from ground-based measurements over a high-altitude site where in clouds pass over the surface. First aerosol indirect effect AIE estimates were made using i) relative changes in cloud droplet number concentration (AIEn) and ii) relative changes in droplet effective radius (AIEs) with relative changes in aerosol for different LWC values. AIE estimates from two different methods reveal that there is systematic overestimation in AIEn as compared to that of AIEs. Aerosol indirect effects (AIEn and AIEs) and Dispersion effect (DE) at different liquid water content (LWC) regimes ranging from 0.05 to 0.50 gm-3 were estimated. The analysis demonstrates that there is overestimation of AIEn as compared to AIEs which is mainly due to DE. Aerosol effects on spectral dispersion in droplet size distribution plays an important role in altering Twomey’s cooling effect and thereby changes in climate. This study shows that the higher DE in the medium LWC regime which offsets the AIE by 30%.

Aerosol Indirect Effects in Marine Stratocumulus: The Importance of Explicitly Predicting Cloud Droplet Activation

2019 ◽  
Vol 46 (6) ◽  
pp. 3473-3481 ◽  
Author(s):  
I. Bulatovic ◽  
A. M. L. Ekman ◽  
J. Savre ◽  
I. Riipinen ◽  
C. Leck
Keyword(s):  
Indirect Effects ◽  
Cloud Droplet ◽  
Marine Stratocumulus ◽  
Aerosol Indirect Effects ◽  
Droplet Activation

scholarly journals Cloud-resolving modelling of aerosol indirect effects in idealised radiative-convective equilibrium with interactive and fixed sea surface temperature

2013 ◽  
Vol 13 (8) ◽  
pp. 4133-4144 ◽  
Author(s):  
M. F. Khairoutdinov ◽  
C.-E. Yang
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Indirect Effects ◽  
Hydrological Cycle ◽  
Cloud Microphysics ◽  
Sea Surface ◽  
Aerosol Indirect Effects ◽  
Cloud Forcing ◽  
Wide Range ◽  
Aerosol Effects

Abstract. The study attempts to evaluate the aerosol indirect effects over tropical oceans in regions of deep convection applying a three-dimensional cloud-resolving model run over a doubly-periodic domain. The Tropics are modelled using a radiative-convective equilibrium idealisation when the radiation, turbulence, cloud microphysics and surface fluxes are explicitly represented while the effects of large-scale circulation are ignored. The aerosol effects are modelled by varying the number concentration of cloud condensation nuclei (CCN) at 1% supersaturation, which serves as a proxy for the aerosol amount in the environment, over a wide range, from pristine maritime (50 cm−3) to polluted (1000 cm−3) conditions. No direct effects of aerosol on radiation are included. Two sets of simulations have been run: fixed (non-interactive) sea surface temperature (SST) and interactive SST as predicted by a simple slab-ocean model responding to the surface radiative fluxes and surface enthalpy flux. Both sets of experiments agree on the tendency of increased aerosol concentrations to make the shortwave cloud forcing more negative and reduce the longwave cloud forcing in response to increasing CCN concentration. These, in turn, tend to cool the SST in interactive-SST case. It is interesting that the absolute change of the SST and most other bulk quantities depends only on relative change of CCN concentration; that is, same SST change can be the result of doubling CCN concentration regardless of clean or polluted conditions. It is found that the 10-fold increase of CCN concentration can cool the SST by as much as 1.5 K. This is quite comparable to 2.1–2.3 K SST warming obtained in a simulation for clean maritime conditions, but doubled CO2 concentration. Assuming the aerosol concentration has increased from preindustrial time by 30%, the radiative forcing due to indirect aerosol effects is estimated to be −0.3 W m−2. It is found that the indirect aerosol effect is dominated by the first (Twomey) effect. Qualitative differences between the interactive and fixed SST cases have been found in sensitivity of the hydrological cycle to the increase in CCN concentration; namely, the precipitation rate shows some tendency to increase in fixed SST case, but robust tendency to decrease in interactive SST case.

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