Strait and currents. Studies and TIPS. Lo Stretto di Messina is a unique and fascinating place of special chaotic phenomena such as vortices (the mouths of Charybdis), the scales of sea, the oil stains.
These phenomena are due to a combination of factors related to tidal currents peculiar to this area and meeting / clash between two seas, the Tyrrhenian and Ionian seas with chemical and physical properties (salinity, temperature and density) different .
The Strait of Messina constitutes the link between the Tyrrhenian and Ionian basin, the first of the second deepest.
Morphologically similar to a funnel that reaches twice the minimum width along the joining Ganzirri -Punta Pezzo which is about 3.4 km. The water of the Ionian and the Tyrrhenian Sea have tides opposite the central part of the Strait is a anfitromico.
The Tyrrhenian Sea is on average colder and less salty Ionian even if, all along the coast between Giardini Naxos and Messina, the phenomena of "upwelling" by bringing water to the surface deep, which determine the ionic waters in the Strait are considerably colder than those occurring in the same share in other sites of the Ionian basin. In the summer surface water temperature differences are included in the Strait on average between 4 and 10 ° C. The transit through the Strait of Messina of different water masses, according to the current regime, therefore results in the meeting of the waters between them is not immediately miscible. Since only a part of the waters that are able to pass on the saddle in the basin adjacent to these and a large part, losing speed, parked on the edge of the Strait to return again with the next flow, you may experience frequent water bodies that , changing basin, are filled at different levels from the original function un nuovo equilibrio dinamico negli strati d’acqua del bacino ricevente.
Nella parte nord dello Stretto di Messina, nel bacino del Tirreno, fino al Golfo di Sant’Eufemia è stata notata la presenza di onde interne e, in conseguenza di ciò la circolazione di acque nello stretto può essere schematizzata nel modo seguente:
- al prevalere della corrente ionica (direzione nord-sud), acque ioniche profonde vengono sospinte dai moti di marea e risalgono la scarpata meridionale affiorando nella parte centro-settentrionale, questo è il cosiddetto fenomeno dell’upwelling;
- al prevalere della corrente tirrenica, le acque di questo bacino transitano verso sud, ma a causa della minore densità si dispongono esclusivamente in superficie; al di sotto dei trenta metri invece il bilancio è a favore dell’acqua ionica che, invadendo il bacino tirrenico, si colloca a profondità di circa 200-300 m.
Le correnti stazionarie a livello della sella sottomarina fluiscono verso Sud dalla superficie a 30 metri ed in senso inverso da questa profondità fino al fondo, con velocità che possono raggiungere anche i 50 cm/sec in particolari situazioni meteo-marine. La co-oscillazione delle masse Strait of water with the tides of the seas adjacent to the original tidal currents which, with nearly opposite phase and equal amplitude, are added to those stationary. The relative speeds can reach along the section of the saddle Ganzirri - Punta Pezzo, maximum values \u200b\u200bof 200 cm / sec in both the flow towards the north (the current "post"), and in the south (the current "going down"), involving all 'about the same intensity with the mass of water in its entirety. The most recent measurements indicate that the rate of movement of water in the Straits can reach, in particular times and thanks to the coincidence of several components, to to a maximum of 20 km / h.
When the Tyrrhenian Sea has a low tide on the northern edge of Strait, the adjacent Ionian Sea is at high tide and the other is the next change of tide. The difference in height (up to 27 cm) that is created which periodically determines the waters of both the basin may flow back into the adjacent space. More specifically, during the current "going down" the water flow on the Tyrrhenian lighter ion heavier until the whole central part of the Strait is filled with these flowing waters to the south contrast with the predominance of power " pillar, increasingly heavy water will affect the center of the Tyrrhenian basin sinking lighter than water, previously occupied the Straits to pour into the Tyrrhenian Sea and then once past the saddle. The meeting of two bodies of water (Ionian and Tyrrhenian) determines the onset of a whole series of phenomena that are attributable to instability dynamic that is created and dispersed in the well-known spectacular manifestations of turbulence, these " disorders "may arise with the current development horizontally (in the case of" cuts "and" scale of sea ") or vertical (in the case of" Garofalo "," bastards " and "oil spots"). For the phenomena of the first kind is of real waves, similar to those occurring at a rate of tidal estuaries, which develop when, in the case of the mast, the heavier water of the Ionian Sea rush against lighter water Tyrrhenian in a recession or when, in the case of descending, the waters of the Tyrrhenian slide quickly on those heavier ion, already present in the basin. These waves of discontinuity will grow at particular points ( Ganzirri , Torre Faro and Punta Pezzo) extending into the central part of the Strait , sometimes widen and intensify the action of strong winds pushing a type of water to another. With regard, however, the phenomena of vertical development is real eddies formed by the meeting of opposing currents and favorites by the irregularity of the fund. The main eddies are formed, however, in certain points with the current post.
is the mythological "Charybdis", south of Cape Pelorus . A big "Garofalo" format instead of the current going down is located between Punta S. Entrance of the port of Messina Raineri. I "Garofalo" have a cyclonic rotation and in the waters they lie heavy on the lighter ones stemming from turbulent motions. In the case of "oil spots" but the movement is anticyclonic and waters emerge at the center of the vortex showing a calm surface of oily appearance. As for the "bastards" they are the currents that develop along the coasts, with intensity proportional and opposite to the main flow, but variable from area to area.
Such high speeds and the huge volumes of water involved (over 750,000 m3 per second for a current of 200 cm / s), when compared to the means of navigation of the times omerici, indicano chiaramente perché lo stretto venisse considerato abitato da mostri in grado di ingoiare le imbarcazioni o farle naufragare nel volgere di poco tempo, come l’immane Cariddi: il mostro senza volto che risucchiava le navi dagli abissi producendo vortici e gorghi.
Uno dei fenomeni più interessanti legati al ritmo generale e locale delle correnti messinesi è rappresentato da un periodico ribollimento delle acque lungo le linee ad andamento trasversale che viene designato dai rivieraschi col nome "taglio", che ha origine nella zona di Capo Peloro . Ogni inversione di corrente, in ogni singola zona, suole essere accompagnata dal passaggio della linea del taglio. Il fenomeno dura pochi minuti manifestando un ribollimento, un’agitazione nel settore interessato. Questo settore si presenta cosparso di piccoli vortici rotanti rapidamente attorno ad un definito centro di risucchio. In seguito la striscia di mare agitato si sposta e percorre lo Stretto recando ovunque le stesse apparenze superficiali.