Dust optical properties over North Africa and Arabian Peninsula derived from the AERONET dataset

Kim, D.; Chin, Mian; Yu, Hongbin; Eck, T. F.; Sinyuk, A.; Смирнов, А. И.; Holben, B. N.

doi:10.5194/acp-11-10733-2011

Cited by 125 publications

(126 citation statements)

References 35 publications

Supporting

Mentioning

110

Contrasting

Order By: Relevance

“…This screening process is not identical to the CALIPSO screening process for dust, since CALIOP measures depolarization, whereas AERONET retrieves it. However, we note that the average refractive indices obtained with the AERONET depolarization screening are nearly identical to the average refractive indices presented by Kim et al (2011) at the same AERONET sites; Kim et al (2011) required Angstrom exponents of less than 0.2 for their dust classification.…”

Section: Aeronet Lidar Ratios Using the Calipso Definition Of Dustsupporting

confidence: 67%

Comparison of CALIPSO aerosol optical depth retrievals to AERONET measurements, and a climatology for the lidar ratio of dust

et al. 2012

View full text Add to dashboard Cite

Abstract. We compared CALIPSO column aerosol optical depths at 0.532 µm to measurements at 147 AERONET sites, synchronized to within 30 min of satellite overpass times during a 3-yr period. We found 677 suitable overpasses, and a CALIPSO bias of −13 % relative to AERONET for the entire data set; the corresponding absolute bias is −0.029, and the standard deviation of the mean (SDOM) is 0.014. Consequently, the null hypothesis is rejected at the 97 % confidence level, indicating a statistically significant difference between the datasets. However, if we omit CALIPSO columns that contain dust from our analysis, the relative and absolute biases are reduced to −3 % and −0.005 with a standard error of 0.016 for 449 overpasses, and the statistical confidence level for the null hypothesis rejection is reduced to 27 %. We also analyzed the results according to the six CALIPSO aerosol subtypes and found relative and absolute biases of −29 % and −0.1 for atmospheric columns that contain the dust subtype exclusively, but with a relatively high correlation coefficient of R = 0.58; this indicates the possibility that the assumed lidar ratio (40 sr) for the CALIPSO dust retrievals is too low. Hence, we used the AERONET size distributions, refractive indices, percent spheres, and forward optics code for spheres and spheroids to compute a lidar ratio climatology for AERONET sites located in the dust belt. The highest lidar ratios of our analysis occur in the non-Sahel regions of Northern Africa, where the median lidar ratio at 0.532 µm is 55.4 sr for 229 retrievals. Lidar ratios are somewhat lower in the African Sahel (49.7 sr for 929 retrievals), the Middle East (42.6 sr for 489 retrievals), and Kanpur, India (43.8 sr for 67 retrievals). We attribute this regional variability in the lidar ratio to the regional variability of the real refractive index of dust, as these two parameters are highly anti-correlated (correlation coefficients range from −0.51 to −0.85 for the various regions). The AERONET refractive index variability is consistent with the variability of illite concentration in dust across the dust belt.

show abstract

Section: Aeronet Lidar Ratios Using the Calipso Definition Of Dustsupporting

confidence: 67%

Comparison of CALIPSO aerosol optical depth retrievals to AERONET measurements, and a climatology for the lidar ratio of dust

et al. 2012

View full text Add to dashboard Cite

show abstract

“…due to the Mie scattering curve, it is possible for one value of scattering to correspond to more than one particle diameter). We present results assuming values of 1.53 for n, and 0.001 and 0.003 for k. Size distributions were also corrected using a range of other refractive indices (n = 1.42, 1.58; k = 0.006) reflective of those in the literature (Wagner, 2012;Otto et al, 2009;McConnell et al, 2010;Johnson and Osborne, 2011;Petzold et al, 2009;Kim et al, 2011). However, results presented in Sect.…”

Section: Correction Of Size Distribution For Refractive Indexmentioning

confidence: 99%

Optical properties of Saharan dust aerosol and contribution from the coarse mode as measured during the Fennec 2011 aircraft campaign

et al. 2013

View full text Add to dashboard Cite

Abstract. New in-situ aircraft measurements of Saharan dust originating from Mali, Mauritania and Algeria taken during the Fennec 2011 aircraft campaign over a remote part of the Sahara Desert are presented. Size distributions extending to 300 µm are shown, representing measurements extending further into the coarse mode than previously published for airborne Saharan dust. A significant coarse mode was present in the size distribution measurements with effective diameter (d eff ) from 2.3 to 19.4 µm and coarse mode volume median diameter (d vc ) from 5.8 to 45.3 µm. The mean size distribution had a larger relative proportion of coarse mode particles than previous aircraft measurements. The largest particles (with d eff > 12 µm, or d vc > 25 µm) were only encountered within 1 km of the ground. Number concentration, mass loading and extinction coefficient showed inverse relationships to dust age since uplift. Dust particle size showed a weak exponential relationship to dust age. Two cases of freshly uplifted dust showed quite different characteristics of size distribution and number concentration.Single Scattering Albed (SSA) values at 550 nm calculated from the measured size distributions revealed high absorption ranging from 0.70 to 0.97 depending on the refractive index. SSA was found to be strongly related to d eff . New instrumentation revealed that direct measurements, behind Rosemount inlets, overestimate SSA by up to 0.11 when d eff is greater than 2 µm. This is caused by aircraft inlet inefficiencies and sampling losses. Previous measurements of SSA from aircraft measurements may also have been overestimates for this reason. Radiative transfer calculations indicate that the range of SSAs during Fennec 2011 can lead to underestimates in shortwave atmospheric heating rates by 2.0 to 3.0 times if the coarse mode is neglected. This will have an impact on Saharan atmospheric dynamics and circulation, which should be taken into account by numerical weather prediction and climate models.

show abstract

“…While AOD provides the overall solar extinction effect of aerosols, α characterizes the AOD spectral variation, which is related to the aerosol median size (Kaufman et al, 1994). High α values indicate fine particle predominance, while low α values are related to coarse particles (Kaufman et al, 1994;Kim et al, 2011). Figure 2 illustrates an example of AOD-α distributions, showing the daily AOD time series at 500 nm labelled with the corresponding daily α values since AERONET records are available at IZO (2004 onwards).…”

Section: Description Of Site and Aerosol Conditionsmentioning

confidence: 99%

Aerosol optical depth retrievals at the Izaña Atmospheric Observatory from 1941 to 2013 by using artificial neural networks

García

Cuevas

et al. 2016

Atmos. Meas. Tech.

View full text Add to dashboard Cite

Abstract. This paper presents the reconstruction of a 73-year time series of the aerosol optical depth (AOD) at 500 nm at the subtropical high-mountain Izaña Atmospheric Observatory (IZO) located in Tenerife (Canary Islands, Spain). For this purpose, we have combined AOD estimates from artificial neural networks (ANNs) from 1941 to 2001 and AOD measurements directly obtained with a Precision Filter Radiometer (PFR) between 2003 and 2013. The analysis is limited to summer months (July-August-September), when the largest aerosol load is observed at IZO (Saharan mineral dust particles). The ANN AOD time series has been comprehensively validated against coincident AOD measurements performed with a solar spectrometer Mark-I (1984Mark-I ( -2009 and AERONET (AErosol RObotic NETwork) CIMEL photometers (2004)(2005)(2006)(2007)(2008)(2009) at IZO, obtaining a rather good agreement on a daily basis: Pearson coefficient, R, of 0.97 between AERONET and ANN AOD, and 0.93 between Mark-I and ANN AOD estimates. In addition, we have analysed the long-term consistency between ANN AOD time series and long-term meteorological records identifying Saharan mineral dust events at IZO (synoptical observations and local wind records). Both analyses provide consistent results, with correlations > 85 %. Therefore, we can conclude that the reconstructed AOD time series captures well the AOD variations and dust-laden Saharan air mass outbreaks on shortterm and long-term timescales and, thus, it is suitable to be used in climate analysis.

show abstract

Dust optical properties over North Africa and Arabian Peninsula derived from the AERONET dataset

Cited by 125 publications

References 35 publications

Comparison of CALIPSO aerosol optical depth retrievals to AERONET measurements, and a climatology for the lidar ratio of dust

Comparison of CALIPSO aerosol optical depth retrievals to AERONET measurements, and a climatology for the lidar ratio of dust

Optical properties of Saharan dust aerosol and contribution from the coarse mode as measured during the Fennec 2011 aircraft campaign

Aerosol optical depth retrievals at the Izaña Atmospheric Observatory from 1941 to 2013 by using artificial neural networks

Contact Info

Product

Resources

About