A climatology of dust episodes in the broader Mediterranean Basin using satellite MODIS C6.1 and OMI OMAERUV data

2020 ◽  
Author(s):  
Nikos Hatzianastassiou ◽  
Maria Gavrouzou ◽  
Antonis Gkikas ◽  
Nikos Mihalopoulos
Keyword(s):  
Optical Depth ◽  
Mediterranean Basin ◽  
Cloud Condensation Nuclei ◽  
Longwave Radiation ◽  
Threshold Value ◽  
Mean Value ◽  
Dust Transport ◽  
Cloud Properties ◽  
The Mediterranean ◽  
The Mediterranean Basin

<p>Aerosols, due to their interaction primary with the shortwave, but also with the longwave radiation, constitute a significant climate component, and at the same time an important, but still uncertain, factor of the contemporary climatic change. Apart from radiation, aerosols also interact with clouds, acting as Cloud Condensation Nuclei (CCN) and/or Ice Nuclei (IN), modifying the cloud optical and physical properties like cloud albedo, extent, lifetime or precipitation producing ability. Hence, it is also expected that high loads of specific aerosol types, such as desert dust, can induce even stronger effects on the above mentioned cloud properties.</p><p>More specifically, dust aerosols, which are inserted in the atmosphere mainly from the great world deserts, represent the major global aerosol component. These aerosols can remain suspended in the air and travel for several days, reaching areas far away from their sources. The Mediterranean Basin (MB), which is one of the most responsive regions to climate change, due to its location (nearby the Sahara desert in North Africa and the deserts of Middle East), is frequently affected from massive and extended dust transport. Because of the potentially significant role of these dust episodes, and their seasonal and inter-annual variability, they are worth to be studied and monitored through time.</p><p>In the present study, a modified version of a satellite algorithm, which is fully described by Gavrouzou et al. in another study of this conference, is used for the determination of strong and extreme dust episodes in the Mediterranean Basin over the period 2005-2018. The algorithm, using MODIS C6.1 spectral Aerosol Optical Depth (AOD) and OMI OMAERUV Aerosol Index (AI) as input data, ran on a daily and an 1°x1° pixel level basis and determined the occurrence and intensity of dust episodes whenever the AI is greater than 1 and the Angstrom Exponent (AE), which is calculated from spectral AOD data, is lower than 0.4. Any day is characterized as an episodic one when the dust optical depth (DOD) exceeds a computed threshold value (mean value plus two or four standard deviations for strong and extreme episodes, respectively) on at least 30 pixels of the study area. According to the algorithm results, 148 dust episode days (104 strong and 44 extreme) are found during the 2005-2018 period in the Mediterranean Basin. Most of the episodes occur in July (27 strong- and 3 extreme-episode days) and April (25 strong- and 6 extreme-episode days) while dust episodes are not detected at all in November and December. It is also found that in April, March and May take place the highest number of extreme MB episodes (23 out of the total 44 ones).</p>

scholarly journals Quantitative Aerosol Optical Depth Detection during Dust Outbreaks from Meteosat Imagery Using an Artificial Neural Network Model

2019 ◽  
Vol 11 (9) ◽  
pp. 1022 ◽  
Author(s):  
Stavros Kolios ◽  
Nikos Hatzianastassiou
Keyword(s):  
Neural Network ◽  
Artificial Neural Network ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Mediterranean Basin ◽  
Pearson Correlation ◽  
Ann Model ◽  
Artificial Neural ◽  
The Mediterranean ◽  
The Mediterranean Basin

This study presents the development of an artificial neural network (ANN) model to quantitatively estimate the atmospheric aerosol load (in terms of aerosol optical depth, AOD), with an emphasis on dust, over the Mediterranean basin using images from Meteosat satellites as initial information. More specifically, a back-propagation ANN model scheme was developed to estimate visible (at 550 nm) aerosol optical depth (AOD550 nm) values at equal temporal (15 min) and spatial (4 km) resolutions with Meteosat imagery. Accuracy of the ANN model was thoroughly tested by comparing model estimations with ground-based AOD550 nm measurements from 14 AERONET (Aerosol Robotic NETwork) stations over the Mediterranean for 34 selected days in which significant dust loads were recorded over the Mediterranean basin. Using a testbed of 3076 pairs of modeled and measured AOD550 nm values, a Pearson correlation coefficient (rP) equal to 0.91 and a mean absolute error (MAE) of 0.031 were found, proving the satisfactory accuracy of the developed model for estimating AOD550 nm values.

scholarly journals Modelling Saharan dust transport into the Mediterranean basin with CMAQ

2013 ◽  
Vol 70 ◽  
pp. 337-350 ◽  
Author(s):  
David de la Paz ◽  
Michel Vedrenne ◽  
Rafael Borge ◽  
Julio Lumbreras ◽  
Juan Manuel de Andrés ◽  
...  
Keyword(s):  
Mediterranean Basin ◽  
Saharan Dust ◽  
Dust Transport ◽  
The Mediterranean ◽  
The Mediterranean Basin

scholarly journals North African dust transport toward the western Mediterranean basin: atmospheric controls on dust source activation and transport pathways during June–July 2013

2016 ◽  
Vol 16 (22) ◽  
pp. 14147-14168 ◽  
Author(s):  
Kerstin Schepanski ◽  
Marc Mallet ◽  
Bernd Heinold ◽  
Max Ulrich
Keyword(s):  
Mediterranean Basin ◽  
Dust Emission ◽  
Western Mediterranean ◽  
North African ◽  
Atmospheric Dust ◽  
Dust Source ◽  
Dust Transport ◽  
The Mediterranean ◽  
The Mediterranean Basin ◽  
Heat Low

Abstract. Dust transported from north African source region toward the Mediterranean basin and Europe is a ubiquitous phenomenon in the Mediterranean region. Winds formed by large-scale pressure gradients foster dust entrainment into the atmosphere over north African dust source regions and advection of dust downwind. The constellation of centers of high and low pressure determines wind speed and direction, and thus the chance for dust emission over northern Africa and transport toward the Mediterranean. We present characteristics of the atmospheric dust life cycle determining dust transport toward the Mediterranean basin with focus on the ChArMEx (Chemistry-Aerosol Mediterranean Experiment) special observation period in June and July 2013 using the atmosphere–dust model COSMO-MUSCAT (COSMO: COnsortium for Small-scale MOdeling; MUSCAT: MUltiScale Chemistry Aerosol Transport Model). Modes of atmospheric circulation are identified from empirical orthogonal function (EOF) analysis of the geopotential height at 850 hPa and compared to EOFs calculated from 1979–2015 ERA-Interim reanalysis. Two different phases are identified from the first EOF, which in total explain 45 % of the variance. They are characterized by the propagation of the subtropical ridge into the Mediterranean basin, the position of the Saharan heat low and the predominant Iberian heat low, and discussed illustrating a dipole pattern for enhanced (reduced) dust emission fluxes, stronger (weaker) meridional dust transport, and consequent increased (decreased) atmospheric dust concentrations and deposition fluxes. In the event of a predominant high-pressure zone over the western and central Mediterranean (positive phase), a hot spot in dust emission flux is evident over the Grand Erg Occidental, and a reduced level of atmospheric dust loading occurs over the western Mediterranean basin. The meridional transport in northward direction is reduced due to prevailing northerly winds. In case of a predominant heat low trough linking the Iberian and the Saharan heat low (negative phase), meridional dust transport toward the western Mediterranean is increased due to prevailing southerly winds resulting in an enhanced atmospheric dust loading over the western Mediterranean. Altogether, results from this study illustrate the relevance of knowing dust source location and characteristics in concert with atmospheric circulation. The study elaborates on the question of the variability of summertime dust transport toward the Mediterranean and Europe with regard to atmospheric circulation conditions controlling dust emission and transport routes of Saharan dust, exemplarily for the 2-month period of June–July 2013. Ultimately, outcomes from this study contribute to the understanding of the variance in dust transport into a populated region.

scholarly journals 15-year variability of desert dust optical depth on global and regional scales

2021 ◽  
Vol 21 (21) ◽  
pp. 16499-16529
Author(s):  
Stavros-Andreas Logothetis ◽  
Vasileios Salamalikis ◽  
Antonis Gkikas ◽  
Stelios Kazadzis ◽  
Vassilis Amiridis ◽  
...  
Keyword(s):  
Optical Depth ◽  
Mediterranean Basin ◽  
Arabian Peninsula ◽  
Geometric Mean ◽  
Dust Particles ◽  
Gobi Desert ◽  
Seasonal Trends ◽  
The Mediterranean ◽  
Bodele Depression ◽  
The Mediterranean Basin

Abstract. This study aims to investigate global, regional and seasonal temporal dust changes as well as the effect of dust particles on total aerosol loading using the ModIs Dust AeroSol (MIDAS) fine-resolution dataset. MIDAS delivers dust optical depth (DOD) at fine spatial resolution (0.1∘×0.1∘) spanning from 2003 to 2017. Within this study period, the dust burden increased across the central Sahara (up to 0.023 yr−1) and Arabian Peninsula (up to 0.024 yr−1). Both regions observed their highest seasonal trends in summer (up to 0.031 yr−1). On the other hand, declining DOD trends are encountered in the western (down to −0.015 yr−1) and eastern (down to −0.023 yr−1) Sahara, the Bodélé Depression (down to −0.021 yr−1), the Thar (down to −0.017 yr−1) and Gobi (down to −0.011 yr−1) deserts, and the Mediterranean Basin (down to −0.009 yr−1). In spring, the most negative seasonal trends are recorded in the Bodélé Depression (down to −0.038 yr−1) and Gobi Desert (down to −0.023 yr−1), whereas they are in the western (down to −0.028 yr−1) and the eastern Sahara (down to −0.020 yr−1) and the Thar Desert (down to −0.047 yr−1) in summer. Over the western and eastern sector of the Mediterranean Basin, the most negative seasonal trends are computed at summer (down to −0.010 yr−1) and spring (down to −0.006 yr−1), respectively. The effect of DOD on the total aerosol optical depth (AOD) change is determined by calculating the DOD-to-AOD trend ratio. Over the Sahara the median ratio values range from 0.83 to 0.95, whereas in other dust-affected areas (Arabian Peninsula, southern Mediterranean, Thar and Gobi deserts) the ratio value is approximately 0.6. In addition, a comprehensive analysis of the factors affecting the sign, the magnitude and the statistical significance of the calculated trends is conducted. Firstly, the implications of the implementation of the geometric mean instead of the arithmetic mean for trend calculations are discussed, revealing that the arithmetic-based trends tend to overestimate compared to the geometric-based trends over both land and ocean. Secondly, an analysis interpreting the differences in trend calculations under different spatial resolutions (fine and coarse) and time intervals is conducted.

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