Direct observations of clear‐sky aerosol radiative forcing from space during the Indian Ocean Experiment

Rajeev, K.; Ramanathan, V.

doi:10.1029/2000jd900723

Cited by 66 publications

(51 citation statements)

References 27 publications

(10 reference statements)

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“…Furthermore, observational PM data in different Spanish sites have also shown a decreasing trend in the 2000s (e.g., Barmpadimos et al, 2012;Cusack et al, 2012;Pey et al, 2013;Bennouna et al, 2014;Mateos et al, 2014). This fact can be understood by the effect of the current economic crisis and the implementation of new environmental laws to control the pollution (e.g., Querol et al, 2014). In addition, recent studies have shown that natural aerosols have also decreased in the last decade.…”

Section: Analysis Of Aerosol Properties Over the Iberian Peninsulamentioning

confidence: 99%

“…This is a key quantity in the determination of climate change (e.g., Hansen et al, 1998). Most studies dealing with ARE have focused on discrete wavelengths, whole shortwave (SW) solar radiation spectrum (e.g., Rajeev and Ramanathan, 2001;García et al, 2008;di Sarra et al, 2008;Foyo-Moreno et al, 2014;Mateos et al, 2013a), longwave (LW) radiation (e.g., Panicker et al, 2008;di Sarra et al, 2011;Antón et al, 2014), ultraviolet (UV) interval (e.g., Hatzianastassiou et al, 2004;Kazadzis et al, 2009;Nikitidou et al, 2013), and visible (VIS) range (e.g., Jayaraman et al, 1998;Horvath et al, 2002;Bush and Valero, 2003;Meloni et al, 2003). With regards to surface SW radiative effect (ARE SW ), Di obtained the maximum radiative daily effects for different aerosol types in the central Mediterranean in the period [2004][2005][2006][2007]: −61 W m −2 (desert dust aerosols), −26 W m −2 (urban/industrial-biomass burning aerosols), and −43 W m −2 (mixed aerosols).…”

Section: Introductionmentioning

confidence: 99%

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Aerosol radiative effects in the ultraviolet, visible, and near-infrared spectral ranges using long-term aerosol data series over the Iberian Peninsula

et al. 2014

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Abstract.A better understanding of aerosol radiative properties is a crucial challenge for climate change studies. This study aims at providing a complete characterization of aerosol radiative effects in different spectral ranges within the shortwave (SW) solar spectrum. For this purpose, longterm data sets of aerosol properties from six AERONET stations located in the Iberian Peninsula (southwestern Europe) have been analyzed in terms of climatological characterization and inter-annual changes. Aerosol information was used as input for the libRadtran model in order to determine the aerosol radiative effect (ARE) at the surface in the ultraviolet (ARE UV ), visible (ARE VIS ), near-infrared (ARE NIR ), and the entire SW range (ARE SW ) under cloudfree conditions. Over the whole Iberian Peninsula, yearly aerosol radiative effects in the different spectral ranges were found to be −1.1 < ARE UV < −0.7, −5.7 < ARE VIS < −3.5, −2.6 < ARE NIR < −1.6, and −8.8 < ARE SW < −5.7 (in W m −2 ). Monthly means of ARE showed a seasonal pattern with larger values in spring and summer. The aerosol forcing efficiency (AFE), ARE per unit of aerosol optical depth, has also been evaluated in the four spectral ranges. AFE exhibited a dependence on single scattering albedo as well as a weaker one on the Ångström exponent. AFE is larger (in absolute value) for small and absorbing particles. The contributions of the UV, VIS, and NIR ranges to the SW efficiency varied with the aerosol types. The predominant aerosol size determined the fractions AFE VIS /AFE SW and AFE NIR /AFE SW . The AFE VIS was the dominant contributor for all aerosol types, although non-absorbing large particles caused more even contribution of VIS and NIR intervals. The AFE UV / AFE SW ratio showed a higher value in the case of absorbing fine particles.

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Section: Analysis Of Aerosol Properties Over the Iberian Peninsulamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Aerosol radiative effects in the ultraviolet, visible, and near-infrared spectral ranges using long-term aerosol data series over the Iberian Peninsula

et al. 2014

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“…21. These strong gradients, including the sharp gradient across the ITCZ, were first noted in measurements made on the pre-INDOEX and INDOEX ship cruises (e.g., Rhoads et al, 1997;Moorthy et al, 1997;Jayaraman et al, 1998Jayaraman et al, , 1999Jayaraman et al, , 2001Satheesh et al, 1998;Naja et al, 1999;Stehr et al, 2002;Quinn et al, 2002;Chand et al, 2001Chand et al, , 2003Kamra et al, 2003;Norman et al, 2003;Nair et al, 2004;Naja et al, 2004), as well as in aircraft observations during INDOEX (e.g., Ramanathan et al, 2001;Reiner et al, 2001;Gabriel et al, 2002a;Pelon et al, 2002;de Reus et al, 2002), and shortly thereafter were corroborated to be a general feature of the broader region based on numerous pieces of evidence, including further in situ observations, satellite retrievals and model simulations (e.g., Rajeev et al, 2000Rajeev et al, , 2004Rajeev and Ramanathan, 2001;Collins et al, 2001Collins et al, , 2002de Laat et al, 2001a, b;Lelieveld et al, 2001;Lawrence et al, 2003a;Minvielle et al, 2004a, b;Moorthy et al, 2005a;Satheesh et al, 2006a, b;Vinoj et al, 2007;Verma et al, 2008). In addition to this generally strong gradient of pollutants in the SAW-ABC, these observations and modeling studies have also shown a very abrupt transition between the polluted NH air masses and more pristine SH air in the MBL at the ITCZ, which can be considered a "chemical ITCZ" …”

Section: Transit Times Lofting In the Itcz And Interhemispheric Exchmentioning

confidence: 99%

Atmospheric pollutant outflow from southern Asia: a review

2010

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Abstract. Southern Asia, extending from Pakistan and Afghanistan to Indonesia and Papua New Guinea, is one of the most heavily populated regions of the world. Biofuel and biomass burning play a disproportionately large role in the emissions of most key pollutant gases and aerosols there, in contrast to much of the rest of the Northern Hemisphere, where fossil fuel burning and industrial processes tend to dominate. This results in polluted air masses which are enriched in carbon-containing aerosols, carbon monoxide, and hydrocarbons. The outflow and long-distance transport of these polluted air masses is characterized by three distinct seasonal circulation patterns: the winter monsoon, the summer monsoon, and the monsoon transition periods. During winter, the near-surface flow is mostly northeasterly, and the regional pollution forms a thick haze layer in the lower troposphere which spreads out over millions of square km between southern Asia and the Intertropical Convergence Zone (ITCZ), located several degrees south of the equator over the Indian Ocean during this period. During summer, the heavy monsoon rains effectively remove soluble gases and aerosols. Less soluble species, on the other hand, are lifted to the upper troposphere in deep convective clouds, and are then transported away from the region by strong upper tropospheric winds, particularly towards northern Africa and the Mediterranean in the tropical easterly jet. Part of the pollution can reach the tropical tropopause layer, the gateway to the stratosphere. During the monsoon transition periods, the flow across the Indian Ocean is primarily zonal, and strong pollution plumes originating from both southeastern Asia and from Africa spread across the central Indian Ocean. This paper provides a review of the current state of knowledge based on the many observational and modeling studies over the last decades that have examined the southern AsianCorrespondence to: M. G. Lawrence (mark.lawrence@mpic.de) atmospheric pollutant outflow and its large scale effects. An outlook is provided as a guideline for future research, pointing out particularly critical issues such as: resolving discrepancies between top down and bottom up emissions estimates; assessing the processing and aging of the pollutant outflow; developing a better understanding of the observed elevated pollutant layers and their relationship to local sea breeze and large scale monsoon circulations; and determining the impacts of the pollutant outflow on the Asian monsoon meteorology and the regional hydrological cycle, in particular the mountain cryospheric reservoirs and the fresh water supply, which in turn directly impact the lives of over a billion inhabitants of southern Asia.

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“…This, along with weaker absorption by dust than by pollution, results in a more negative TOA DRE in May (Satheesh and Srinivasan, 2002). The aerosol direct solar effect also has large spatial variations over the tropical Indian Ocean (Rajeev and Ramanathan, 2001). The observed TOA solar effect north of the equator is about a factor of 2 greater than that south of the equator, with the minimum effect occurring around the Inter-Tropical Convergence Zone (ITCZ).…”

Section: E Arabian Sea and Northern Indian Oceanmentioning

confidence: 99%

A review of measurement-based assessments of the aerosol direct radiative effect and forcing

et al. 2006

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Abstract. Aerosols affect the Earth's energy budget directly by scattering and absorbing radiation and indirectly by acting as cloud condensation nuclei and, thereby, affecting cloud properties. However, large uncertainties exist in current estimates of aerosol forcing because of incomplete knowledge concerning the distribution and the physical and chemical properties of aerosols as well as aerosol-cloud interactions. In recent years, a great deal of effort has gone into improving measurements and datasets. It is thus feasible to shift the estimates of aerosol forcing from largely model-based to increasingly measurement-based. Our goal is to assess current observational capabilities and identify uncertainties in the aerosol direct forcing through comparisons of different methods with independent sources of uncertainties. Here we assess the aerosol optical depth (τ ), direct radiative effect (DRE) by natural and anthropogenic aerosols, and direct climate forcing (DCF) by anthropogenic aerosols, focusing on satellite and ground-based measurements supplemented by global chemical transport modelCorrespondence to: H. Yu (hyu@climate.gsfc.nasa.gov) (CTM) simulations. The multi-spectral MODIS measures global distributions of aerosol optical depth (τ ) on a daily scale, with a high accuracy of ±0.03±0.05τ over ocean. The annual average τ is about 0.14 over global ocean, of which about 21%±7% is contributed by human activities, as estimated by MODIS fine-mode fraction. The multiangle MISR derives an annual average AOD of 0.23 over global land with an uncertainty of ∼20% or ±0.05. These high-accuracy aerosol products and broadband flux measurements from CERES make it feasible to obtain observational constraints for the aerosol direct effect, especially over global the ocean. A number of measurement-based approaches estimate the clear-sky DRE (on solar radiation) at the top-of-atmosphere (TOA) to be about −5.5±0.2 Wm −2 (median ± standard error from various methods) over the global ocean. Accounting for thin cirrus contamination of the satellite derived aerosol field will reduce the TOA DRE to −5.0 Wm −2 . Because of a lack of measurements of aerosol absorption and difficulty in characterizing land surface reflection, estimates of DRE over land and at the ocean surface are currently realized through a combination of satellite Published by Copernicus GmbH on behalf of the European Geosciences Union. 614H. Yu et al.: Measurement-based aerosol direct forcing retrievals, surface measurements, and model simulations, and are less constrained. Over the oceans the surface DRE is estimated to be −8.8±0.7 Wm −2 . Over land, an integration of satellite retrievals and model simulations derives a DRE of −4.9±0.7 Wm −2 and −11.8±1.9 Wm −2 at the TOA and surface, respectively. CTM simulations derive a wide range of DRE estimates that on average are smaller than the measurement-based DRE by about 30-40%, even after accounting for thin cirrus and cloud contamination.A number of issues remain. Current estimates of the aerosol direct effect ...

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Direct observations of clear‐sky aerosol radiative forcing from space during the Indian Ocean Experiment

Cited by 66 publications

References 27 publications

Aerosol radiative effects in the ultraviolet, visible, and near-infrared spectral ranges using long-term aerosol data series over the Iberian Peninsula

Aerosol radiative effects in the ultraviolet, visible, and near-infrared spectral ranges using long-term aerosol data series over the Iberian Peninsula

Atmospheric pollutant outflow from southern Asia: a review

A review of measurement-based assessments of the aerosol direct radiative effect and forcing

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