Implications of different aerosol species to direct radiative forcing and atmospheric heating rate

Abstract. Sixteen years of analysis of clear-sky direct aerosol radiative forcing is presented for the Amazon region, with calculations of AERONET network, MODIS sensor and MERRA-2 reanalysis data. The results showed that MERRA-2 reanalysis is an excellent tool for calculating and providing the spatial distribution of aerosol direct radiative forcing. In addition, the difference between considering the reference state of the atmosphere without aerosol loading and with natural aerosol to obtain the aerosol direct radiative forcing is discussed. During the dry season, the monthly average direct forcing at the top of atmosphere varied from −9.60 to −4.20 Wm−2, and at the surface, it varied from −29.81 to −9.24 Wm−2, according to MERRA-2 reanalysis data and the reference state of atmosphere without aerosol loading. Already with the state of reference being the natural aerosols, the average direct forcing at the top of atmosphere varied from −5.15 to −1.18 Wm−2, and at the surface, it varied from −21.28 to −5.25 Wm−2; this difference was associated with the absorption of aerosols.

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Impact of Desert Dust Radiative Forcing on Sahel Precipitation: Relative Importance of Dust Compared to Sea Surface Temperature Variations, Vegetation Changes, and Greenhouse Gas Warming

Journal of Climate ◽

10.1175/jcli4056.1 ◽

2007 ◽

Vol 20 (8) ◽

pp. 1445-1467 ◽

Cited By ~ 234

Author(s):

Masaru Yoshioka ◽

Natalie M. Mahowald ◽

Andrew J. Conley ◽

William D. Collins ◽

David W. Fillmore ◽

...

Keyword(s):

Surface Temperature ◽

Sea Surface Temperature ◽

North Africa ◽

Radiative Forcing ◽

Sea Surface ◽

Desert Dust ◽

Direct Radiative Forcing ◽

Sahel Region ◽

Precipitation Reduction ◽

Sahel Precipitation

Abstract The role of direct radiative forcing of desert dust aerosol in the change from wet to dry climate observed in the African Sahel region in the last half of the twentieth century is investigated using simulations with an atmospheric general circulation model. The model simulations are conducted either forced by the observed sea surface temperature (SST) or coupled with the interactive SST using the Slab Ocean Model (SOM). The simulation model uses dust that is less absorbing in the solar wavelengths and has larger particle sizes than other simulation studies. As a result, simulations show less shortwave absorption within the atmosphere and larger longwave radiative forcing by dust. Simulations using SOM show reduced precipitation over the intertropical convergence zone (ITCZ) including the Sahel region and increased precipitation south of the ITCZ when dust radiative forcing is included. In SST-forced simulations, on the other hand, significant precipitation changes are restricted to over North Africa. These changes are considered to be due to the cooling of global tropical oceans as well as the cooling of the troposphere over North Africa in response to dust radiative forcing. The model simulation of dust cannot capture the magnitude of the observed increase of desert dust when allowing dust to respond to changes in simulated climate, even including changes in vegetation, similar to previous studies. If the model is forced to capture observed changes in desert dust, the direct radiative forcing by the increase of North African dust can explain up to 30% of the observed precipitation reduction in the Sahel between wet and dry periods. A large part of this effect comes through atmospheric forcing of dust, and dust forcing on the Atlantic Ocean SST appears to have a smaller impact. The changes in the North and South Atlantic SSTs may account for up to 50% of the Sahel precipitation reduction. Vegetation loss in the Sahel region may explain about 10% of the observed drying, but this effect is statistically insignificant because of the small number of years in the simulation. Greenhouse gas warming seems to have an impact to increase Sahel precipitation that is opposite to the observed change. Although the estimated values of impacts are likely to be model dependent, analyses suggest the importance of direct radiative forcing of dust and feedbacks in modulating Sahel precipitation.

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Uncertainties in anthropogenic aerosol concentrations and direct radiative forcing induced by emission inventories in eastern China

Atmospheric Research ◽

10.1016/j.atmosres.2015.06.021 ◽

2015 ◽

Vol 166 ◽

pp. 129-140 ◽

Cited By ~ 10

Author(s):

Wenyuan Chang ◽

Hong Liao ◽

Jinyuan Xin ◽

Zhengqiang Li ◽

Donghui Li ◽

...

Keyword(s):

Radiative Forcing ◽

Eastern China ◽

Emission Inventories ◽

Anthropogenic Aerosol ◽

Direct Radiative Forcing

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Aerosol optical and hygroscopic properties during TexAQS‐GoMACCS 2006 and their impact on aerosol direct radiative forcing

Journal of Geophysical Research Atmospheres ◽

10.1029/2008jd011604 ◽

2009 ◽

Vol 114 ◽

Cited By ~ 52

Author(s):

P. Massoli ◽

T. S. Bates ◽

P. K. Quinn ◽

D. A. Lack ◽

T. Baynard ◽

...

Keyword(s):

Radiative Forcing ◽

Hygroscopic Properties ◽

Direct Radiative Forcing

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Aerosol's optical and physical characteristics and direct radiative forcing during a shamal dust storm, a case study

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-3751-2014 ◽

2014 ◽

Vol 14 (7) ◽

pp. 3751-3769 ◽

Cited By ~ 21

Author(s):

T. M. Saeed ◽

H. Al-Dashti ◽

C. Spyrou

Keyword(s):

Optical Thickness ◽

Dust Storm ◽

Radiative Forcing ◽

Longwave Radiation ◽

Aerosol Optical Thickness ◽

Radiative Heating ◽

Dust Layer ◽

Surface Level ◽

Maximum Value ◽

Direct Radiative Forcing

Abstract. Dust aerosols are analyzed for their optical and physical properties during an episode of a dust storm that blew over Kuwait on 26 March 2003 when the military Operation Iraqi Freedom was in full swing. The intensity of the dust storm was such that it left a thick suspension of dust throughout the following day, 27 March. The synoptic sequence leading to the dust storm and the associated wind fields are discussed. Ground-based measurements of aerosol optical thickness reached 3.617 and 4.17 on 26 and 27 March respectively while the Ångstrom coefficient, α870/440, dropped to −0.0234 and −0.0318. Particulate matter concentration of 10 μm diameter or less, PM10, peaked at 4800 μg m−3 during dust storm hours of 26 March. Moderate Resolution Imaging Spectroradiometer (MODIS) retrieved aerosol optical depth (AOD) by Deep Blue algorithm and Total Ozone Mapping Spectrometer (TOMS) aerosol index (AI) exhibited high values. Latitude–longitude maps of AOD and AI were used to deduce source regions of dust transport over Kuwait. The vertical profile of the dust layer was simulated using the SKIRON atmospheric model. Instantaneous net direct radiative forcing is calculated at top of atmosphere (TOA) and surface level. The thick dust layer of 26 March resulted in cooling the TOA by −60 Wm−2 and surface level by −175 Wm−2 for a surface albedo of 0.35. Slightly higher values were obtained for 27 March due to the increase in aerosol optical thickness. Radiative heating/cooling rates in the shortwave and longwave bands were also examined. Shortwave heating rate reached a maximum value of 2 K day−1 between 3 and 5 km, dropped to 1.5 K day−1 at 6 km and diminished at 8 km. Longwave radiation initially heated the lower atmosphere by a maximum value of 0.2 K day−1 at surface level, declined sharply at increasing altitude and diminished at 4 km. Above 4 km longwave radiation started to cool the atmosphere slightly reaching a maximum rate of −0.1 K day−1 at 6 km.

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