Simulation of Optical Properties and Direct and Indirect Radiative Effects of Smoke Aerosols Over Marine Stratocumulus Clouds During Summer 2008 in California With the Regional Climate Model RegCM

Abstract

The regional climate model RegCM has been modified to better account for the climatic effects of biomass‐burning particles. Smoke aerosols are represented by new tracers with consistent radiative and hygroscopic properties to simulate the direct radiative forcing (DRF), and a new parameterization has been integrated for relating the droplet number concentration to the aerosol concentration for marine stratocumulus clouds (Sc). RegCM has been tested during the summer of 2008 over California, when extreme concentration of smoke, together with the presence of Sc, is observed. This work indicates that significant aerosol optical depth (AOD) (~1–2 at 550 nm) is related to the intense 2008 fires. Compared to Ozone Monitoring Instrument (OMI) and Moderate Resolution Imaging Spectroradiometer, the regional pattern of RegCM AOD is well represented although the magnitude is lower than satellite observations. Comparisons with Polarization and Directionality of Earth Reflectances (POLDER) above‐clouds aerosol optical depth (ACAOD) show the ability of RegCM to simulate realistic ACAOD during the transport of smoke above the Pacific Ocean. The simulated single scattering albedo is ~0.90 (at 550 nm) near biomass‐burning sources, consistent with OMI and POLDER, and smoke leads to shortwave heating rates ~1.5–2°K d−1. RegCM is not able to correctly resolve the daily patterns in cloud properties notably due to its coarse horizontal resolutions. However, the changes in the sign of the DRF at top of atmosphere (TOA) (negative to positive) from clear‐sky to all‐sky conditions is well simulated. Finally, the “aerosol‐cloud” parameterization allows simulating an increase of the cloud optical depth for significant concentrations, leading to large perturbations of radiative fluxes at TOA.

Simulation of the transport, vertical distribution, optical properties and radiative impact of smoke aerosols with the ALADIN regional climate model during the ORACLES-2016 and LASIC experiments

“…This positive sign (warming) of the DRE is mainly due to the presence of highly reflective stratocumulus (Sc) clouds over the SAO. Although such a positive DRE is occasionally observed over other regions, such as the northeast Pacific during extreme summertime biomass burning events in continental North America (Mallet et al, 2017), the SAO clearly represents the main region at the global scale where such positive forcings can be observed every year at a seasonal timescale. Indeed, this significant radiative forcing is due to the persistent biomass burning emissions over central Africa during the July-August-September-October (JASO) period.…”

“…At very high humidity (RH > 99 %), maximum thresholds of 8.5 and 16.9 m 2 g −1 are considered for fresh and aged smoke, in order to avoid unrealistic values of MEE. In a similar way, we have also implemented a dependence of smoke SSA on RH using the same relationship as (Mallet et al, 2017). The values of α have been fixed to 0.015 (0.02) for aged (fresh) smoke to rep-resent the variations of SSA with RH, as reported in Bellouin et al (2011).…”

APIFLAME v2.0 trace gas and aerosol emissions from biomass burning: application to Portugal during the summer of 2016 and evaluation against satellite observations of CO (IASI) and AOD (MODIS)

“…The ability of the model to provide useful information for the simulation of the impact of biomass burning on air quality using a CTM has been demonstrated in various previous studied (Rea et al, 2015;Mallet et al, 2017;Menut et al, 2018;Majdi et al, 2019). It is illustrated here for the case of the forest fires in Portugal during the summer of 2016 using the CHIMERE CTM.…”

“…A full description of the model in its first version is provided in Turquety et al (2014) with an application to fire emissions in Europe and the Mediterranean area. It has been successfully used in different studies looking at the impact of fires on regional atmospheric composition over Europe (Rea et al, 2015;Majdi et al, 2019), Australia (Rea et al, 2016), California (Mallet et al, 2017) or Africa (Menut et al, 2018).…”

Inferring Fine-Mode and Coarse-Mode Aerosol Complex Refractive Indices from AERONET Inversion Products over China

“…Atmospheric aerosol plays an important role in the Earth-Ocean-Atmosphere system because it changes the radiance balance of the system via both direct effects, such as absorption and scattering of shortwave solar radiation and longwave earth radiation, and indirect effects, such as acting as cloud condensation nuclei [1,2]. The complex refractive index is a fundamental parameter in determining the absorption and scattering properties of atmospheric aerosols and is the basis for calculating the earth's radiative budget and assessing the aerosol climate effect [3][4][5]. The complex refractive index can be mathematically described as m = n + ki, where the real part n represents the light scattering capacity of aerosol particles, while the imaginary part k is related to the light absorption capacity [6][7][8][9].…”