Final Technical Report for Collaborative Research: CRI-EaSM Multiscale Modeling Aerosol Indirect Effects on Decadal Timescales

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.

Download Full-text

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

10.5194/acp-2015-1057 ◽

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%.

Download Full-text

Processes limiting the emergence of detectable aerosol indirect effects on tropical warm clouds in global aerosol-climate model and satellite data

Tellus B ◽

10.3402/tellusb.v66.24054 ◽

2014 ◽

Vol 66 (1) ◽

pp. 24054 ◽

Cited By ~ 15

Author(s):

Karsten Peters ◽

Johannes Quaas ◽

Philip Stier ◽

Hartmut Graßl

Keyword(s):

Satellite Data ◽

Indirect Effects ◽

Climate Model ◽

Aerosol Indirect Effects

Download Full-text

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

Geophysical Research Letters ◽

10.1029/2018gl081746 ◽

2019 ◽

Vol 46 (6) ◽

pp. 3473-3481 ◽

Cited By ~ 3

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

Download Full-text

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

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-4133-2013 ◽

2013 ◽

Vol 13 (8) ◽

pp. 4133-4144 ◽

Cited By ~ 11

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.

Download Full-text