Global Clear-Sky Aerosol Speciated Direct Radiative Effects over 40 Years (1980–2019)

Abstract

We assess the 40-year climatological clear-sky global direct radiative effect (DRE) of five main aerosol types using the MERRA-2 reanalysis and a spectral radiative transfer model (FORTH). The study takes advantage of aerosol-speciated, spectrally and vertically resolved optical properties over the period 1980–2019, to accurately determine the aerosol DREs, emphasizing the attribution of the total DREs to each aerosol type. The results show that aerosols radiatively cool the Earth’s surface and heat its atmosphere by 7.56 and 2.35 Wm−2, respectively, overall cooling the planet by 5.21 Wm−2, partly counterbalancing the anthropogenic greenhouse global warming during 1980–2019. These DRE values differ significantly in terms of magnitude, and even sign, among the aerosol types (sulfate and black carbon aerosols cool and heat the planet by 1.88 and 0.19 Wm−2, respectively), the hemispheres (larger NH than SH values), the surface cover type (larger land than ocean values) or the seasons (larger values in local spring and summer), while considerable inter-decadal changes are evident. These DRE differences are even larger by up to an order of magnitude on a regional scale, highlighting the important role of the aerosol direct radiative effect for local and global climate.

Modification of Temperature Lapse Rates and Cloud Properties during a Spatiotemporally Extended Dust Aerosol Episode (16–18 June 2016) over the Mediterranean Basin Based on Satellite and Reanalysis Data

“…The 3-D temperature profiles used in the present analysis are obtained from the "M2I3NVASM" 3-h instantaneous product, which is available at the aforementioned 72 model levels. The AOD and DOD vertical profiles used in the present study are calculated using MERRA-2 vertically resolved (in 72 layers), 3-h instantaneous aerosol mixing ratios, and spatiotemporally collocated relative humidity data, both taken from the "M2I3NVAER" product, along with look-up-tables providing the extinction efficiency per aerosol type, size bin and relative humidity [4,42].…”

“…This can be attributed to the dust aerosol semi-direct effect [9,10], taking into account the considerable absorptivity of DA [53]. Indeed, DA significantly absorb solar radiation over North Africa, especially during summer (up to 33.9 W/m 2 [4]), resulting in local heating, thereby reducing RH, lowering supersaturation, and leading to cloud dissipation. Similar characteristics, in terms of similarity between the spatial patterns of DOD and CF, are also observed in the subsequent and last day (D-3, 18 June 2016) of the DAEC.…”

“…This modification arises from the interaction, through scattering and absorption, of dust aerosols with the radiation (both short and longwave). In general, dust is known to induce a SW cooling/warming effect at the top-of-atmosphere (TOA), depending on properties such as the dust loading (DOD) and absorptivity, the underlying surface albedo, and a SW cooling effect at the Earth's surface [4,[58][59][60][61], as well as a LW warming effect either at the TOA and at the Earth's surface [62,63]. The corresponding dust radiative temperature effects in the atmosphere are more complicated.…”

“…Through their interaction with radiation, aerosols affect the Earth's radiation budget, modifying the atmospheric temperature structure and driving to temperature inversions [2]. Aerosols tend to cool the surface and warm the atmosphere, inducing a cooling effect at the top of the atmosphere (TOA) [3,4]. Apart from their direct radiative effect (DRE), aerosols also exert an indirect effect on climate.…”

“…Dust aerosols (DA) is one of the most significant aerosol types in terms of their loading in the atmosphere 1700 Tg/yr [12]. They also play a significant role in aerosol-radiation and aerosol cloud interactions since they strongly absorb and scatter shortwave and longwave radiation [4] while being effective IN [6] and CCN [13][14][15]. Indeed, on an annual basis, insoluble mineral dust contributes up to 40% to the CCN in cloud-forming areas, and coatings with hygroscopic salts double the dust contribution to CCN [16].…”