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.
We identified a canonical pattern of the diurnal cycle (DC) of precipitation on tropical islands, with exceptions for small and very large islands, using an 18-year climatology of satellite estimates. Medium-to-large islands receive more precipitation than the surrounding ocean with superenhancement of precipitation in their center respective to their periphery. Differential heating of the island surface generates a sea breeze front (SBF) propagating inland in the afternoon, triggering precipitation. SBF segments from different coasts meet in the island center, further invigorating precipitation. Small islands exhibit neither DC nor precipitation enhancement most likely because ventilation prevents the genesis of the land-sea breeze circulation. On the largest islands, the SBFs decay after sunset before reaching the center; hence, the superenhancement is not significant, also precipitation lasts longer and cloud remnants delay the DC on the next day, which we attribute to the presence of high mountains.Plain Language Summary Satellite estimates of rainfall show that medium-to-large tropical islands receive more rain than the surrounding ocean, and rainfall amounts are even higher at the center of these islands. The increased precipitation is caused by the surface and atmospheric diurnal cycle. Land heats faster than the ocean in the morning, and a sea breeze develops. The sea breeze lifts the warm and moist air over the island and the rising air condenses as it cools with ascent, forming clouds and thus rainfall. The sea breeze penetrates inland during the afternoon and meets the sea breeze from other coasts of the island in its center which further enhances rainfall. Small islands do not exhibit this behavior most likely because the wind transports warm surface air away from the island and brings cool air from the sea, preventing the sea breeze formation and the development of a diurnal cycle. The largest islands are too big for the sea breeze segments to meet in their center before sunset; thus, no superenhancement of rainfall occurs in the center of these islands.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.