Our results highlight the generation of terrain-induced downslope winds in response to the transition of the atmospheric flow from a subcritical to supercritical state in all three cases.
We revisit the Harmattan dust storm of 2 March 2004, the Saudi dust storm of 9 March 2009, and the Bodélé Depression dust storm of 8 December 2011 and use high-resolution WRF modeling to assess the dynamical processes during the onset of the storms in more depth. We performed detailed mesoscale observational analyses and Weather Research and Forecasting (WRF) model simulations to study the terrain-induced downslope winds that generated dust-emitting winds at the beginning of three strong subtropical dust storms in three distinctly different regions of North Africa and the Arabian Peninsula. Subtropical Dust Storms and Downslope Wind Events During the 1996-1997 " storm" two strong earthquakes occurred (Potenza and Colfiorito) - and (maybe) in 2002 also the Molise earthquake can be reckoned to this " storm". Then, a quiet period occurred from 2002 until, when a new "crustal storm" started, and by the end of 2009 it is still on. During 1996-1997 a "crustal storm" was on, maybe elapsing until 2002 (we lack information for the period 1998-2001). Concerning the case histories that are here discussed, the lithospheric slab is identified with the Italian peninsula. A "crustal storm" lasts typically few years, eventually involving several destructive earthquakes that hit at different times, at different sites, within that given lithospheric slab. An earthquake responds to strictly local rheological features of the crust, which are eventually activated, and become crucial, on the occasion of a "crustal storm". In general, it cannot be easily reckoned to any specific seismic event. Unlike a seismic event, which involves a much limited focal volume and therefore affects a restricted area on the Earth's surface, a "crustal storm" typically involves some large slab of lithosphere and crust. This results to be an effective check for validating the physical interpretation. The same effect ought to be detected being time-delayed, when referring to progressively lower frequencies. AE is an effective tool for diagnosing the state of some wide slab of the Earth's crust, and for monitoring its evolution, by means of AE of different frequencies. A few case histories are discussed, all dealing with the Italian peninsula, and with the different behaviour shown by the AE records in the Cephalonia island (Greece), which is characterized by a different tectonic setting. We call them " storms of crustal stress" or, briefly "crustal storms". Ventrice, G.Īcoustic emission (AE) displays violent paroxysms preceding strong earthquakes, observed within some large area (several hundred kilometres wide) around the epicentre. " Storms of crustal stress" and AE earthquake precursors
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