[MUSIC] Let's talk about the Mediterranean now. The Mediterranean is a very curious area, meteorologically speaking, it is a closed sea, a sea that changes much its temperature in winter and in summer, and, in addition, that also has very changing weather conditions throughout the year. And, therefore, weather, meteorological phenomena, since they are quite characteristic of every season of the year. Let's try to talk about three periods. The first is summer, summer in the Mediterranean, typically, it is a situation of high pressures, of barometric swamp. Remember that the barometric swamp was that area where we do not have, practically, isobaric gradient, the whole area is at a similar pressure and, therefore, there would be no tendency to wind, caused by the direction of the isobars. What then affects the wind? The difference between the temperature between sea water and the coast, and the temperature on the whole continental zone. And there we will talk about the breezes, or what is also called the "virazón". But to understand the phenomenon of breezes, let's talk about a phenomenon called the Hadley cell, that is, how does the temperature change under the hours of the day and also by virtue of the direction and strength of the winds. Note that if we are in an area, that we have land and sea, I will first draw the earth in black. and in blue we will draw the sea. When the radiation arrives, the energy that comes from the sun, when the energy that comes from the sun reaches the sea, what it does is penetrate, and that energy will be distributed among the whole mass of sea water. Therefore, the temperature of the sea will cost more to rise, because it will see more volume than it will have to change temperature. While when sunlight hits the ground, basically what does is heat the first part, the first portion of the soil, perhaps a few millimeters from the soil surface. That is why, when we go to the beach and touch the sand with our foot, We burn, but if we put the foot a little below, then it is cold, Because only the first line warms up, we could say, of small pebbles from the sand of the earth. Therefore, it will raise the temperature greatly in the area of land, it is going to raise the temperature a lot with the advent of solar radiation, while in sea water the temperature is going to remain stable. This increase in temperature is going to cause this air that is just in contact with the surface to rise. As here this air is leaving a vacuum just in the line of the ground, what will happen is that it will generate a current that goes from the cold air, from the sea, to the land area, from the sand, and there it will fill that void. This air rises up, here a vacuum is generated because, as this air is flowing to earth, this void will fill with air that will have a tendency to descend from the higher areas, from the layer that is above of the water of the sea, and here in general it is going to form a... Let see if this works... We paint it in blue, in red. A cell that is called the simple Hadley cell, that is, an air having a tendency to ascend in the zone heated by radiation from sun and descend in this area in the sea. What happens is that we have, as always, the Coriolis force here in the Mediterranean, it is a force that will, as the wind goes more intense, it is going to spin, remember the rule, going to spin, and, therefore, the wind will follow the position of the sun. Therefore, on the Mediterranean coast, typically, the wind begins by rising, right in the zone of sunrise, and is turning towards the west or the southwest during the hours of the day. It is increasing its strength, because, as the difference between the temperature of the soil and the sea is increasing, the marinade, Which is called here, or this breeze, is gaining intensity and is also getting more and more in. A similar thing happens when it is night. Notice that if we re-draw the sea and the earth. When the night comes, the radiation of the sun is finished and that is why the ground cools, you touch the sand of the beach and it is cold right away. While sea water, as the heat has been mixed by the effect of the waves and because the water is a liquid, because there the temperature of the sea is going to remain constant. Therefore, the temperature typically of the surface of the sea will be higher than the sand. What's going to happen there? Well, we're going to have something opposite from what happened to us during the day, There will be a certain tendency of the air that is in contact with the water from the sea to ascend, while from the ground will arrive a small breeze that is going to come from land to the sea, and here it will be re-formed this small Hadley cell, which is much smaller than the diurnal one. This in Catalonia is called "terral", wind coming from the ground, from land to sea, terral, which is in the opposite direction, but that only takes a small portion of the soil and the sea. That is why, if you sail at night in situations of anticyclone with safety it is good to stick to the shore, because there you can find a portion of that wind which comes from land to sea and that can propel you, while a little forward there'll be lulls and you will not be able to sail, you will remain becalmed. This, how does it work? Early in the morning, calm wind, when the sun rises, from nine o'clock, at ten o'clock in the morning, the wind begins to blow. Perhaps the maximum of the daytime breeze, is around the time of the maximum temperature, therefore, around 4-5-6 in the afternoon. That would be the maximum sea breeze, from sea wind to earth. Then during the afternoon entrance, they go limp, when the sun sets, sea breeze stops, and then, in the first hours of the night begins to blow in the opposite direction, And he would go back to bed with the sunrise. Therefore, it is a cycle in one direction and another, and notice that, If you fly a hand glider or paraglider, you would see that up to 200, 300, 500 meters, will depend on the shape of the coast and will depend Also of this cell, you would find wind in the opposite direction. That is, on the surface is a direction, but at 300, 400 meters high, the wind would be in the opposite direction. We have seen this situation that is classic, typical of summer, Practically all summer we would be in this same situation. But what are perhaps the most dangerous situations, we could say, that we have in the Mediterranean? Those that take place in autumn. In autumn, if you remember, when we talked about the world, I told you the world is a ball, and here. We have cold polar air. In summer, the polar cold air tends to remain above in the pole, almost as if sheltered of the heat that moves in practically all temperate zones. But when autumn arrives this air begins to gain ground, and what it does is has a tendency to behave as if they are bubbles, that are falling to him. Finally these bubbles sometimes break and are separated in the form of a small ball, a small portion of polar cold air, which is disengaged from the cold polar air that is in the highest latitudes. These balls typically begin to move across the Atlantic. And where do they fall? Note that if we draw a map of Europe, this would be France, This would be the Iberian peninsula and here begins Africa, these balls have a size similar to what would be the Bay of Biscay, or here in the Gulf of Cali. Therefore, these typical balls of the month of September, which October, that are of polar cold air, therefore this to 500 hectopascales would have to have temperatures of minus 25, minus 30 degrees. That's cold air, which worries meteorologists, this is put here or put here. And let's try to see what happens when these cold air balls cross the Iberian Peninsula. If this ball of cold air, if this kind of storm coming of the pole is placed in this position, here we have cold air. What is going to happen? In surface a storm is generated that has a similar form to this one, I will draw you in black, I have this storm here. That will start giving us winds from the south, entering through the Gulf of Cadiz. But we are in autumn, this area of sea water is hot, and this air from here, we have remained that it was, perhaps, to 30 or even 35 degrees Below zero to 500 hectopascals, are between 5000 and 6000 meters in height. Therefore, we have very cold air at 5000 meters, and warm, very humid air on the surface, what is happening here? We have maritime component wind, Do you remember that we spoke in the first lessons of the abdomen? When we have a wet advection, gives us the amount of precipitation that can fall from that situation. As here we have a wet advection, it is very wet, because it is very warm and very full of humidity, here may be, There is a lot of water, it comes in and in height we have cold air, it is generated here a wind input of the southern component, here are mountain areas and here is formed. A very intense precipitation, very abundant, that are called the winds or clandestine, are called so in Andalusia because this is the situation Classic and typical of large floods in the area of the Gulf of Cadiz. And the sea situation is not very complicated because the fetch is not very but it is very complicated in terms of accumulations of precipitation. The next position of the storm, if this storm is move and continue circulating, notice that later will be placed here. Wait, let's draw it again. We re-draw the peninsula, you draw the storm here. We continue to have very cold air in height, do you remember that here? Here we still have the cold air. What happens to us now? The storm is moving and what we are having is a southeast wind entrance that affects the eastern zone of Andalusia, Murcia, and also all the coast of Valencia. And here also also the Balearic Islands. This is a southeastern storm, which is accompanied by you by sea more and more moved and by abundant, intense precipitations, which affect especially here, In Alacant, there is an area of mountains, many precipitations are generated here important, very abundant, with the situation of the southeast. And, finally, the storm has just passed. Once it has crossed the Iberian Peninsula, is perhaps the most complicated situation because once it gets here. With cold air again. Do you remember that I was? Here. This is what we call temporary of Levant, is one of the temporary harder than there may be on the Mediterranean coast, because the fetch, here I have very south-east, sometimes the isobars are a little more Levant. The longer the journey of these isobars over the sea, this area in that generates the wave is going to be bigger and the waves are going to be higher. And here, sometimes we have waves that surpass the three meters, even, in the high sea could have received four meters of height. You know that for those who navigate in areas that have a large wave it seems not nothing, but the Mediterranean has a wave that is shorter, has a longer period short, is a slightly more complicated wave of those great, which are oceanic. That, from what I've been told they have a slightly more noble behavior than the waves of the Mediterranean. Here a very important temporal is generated, this, again the firing effect of the cold air of the height generates very abundant, intense precipitations, In all the coast of Catalonia and also of the north of Valencia, and sometimes precipitation accumulates on the 400 liters per square meter. I think these sections are complicated on land and also very complicated in the framework with maritime storm of the east, is always very difficult to navigate, is a rather complex wave situation. That would be, perhaps, one of the most dangerous Mediterranean situations. We have said that it could also come by the Bay of Cadiz, Biscay, do you remember? If the storm passes through the north, if the storm is here, it has a step on the oceans, with respect to the seas, that it will not be so complex, because you notice that in this case the wind leaves the southwest by the zone Of the Bay of Biscay, so there is not going to give us a particularly remarkable storm. Even the sea will be very quiet, but the presence of cold air in height it will generate storms and there is a situation of marked instability, Therefore, with variation of the winds. And what does end up happening, when it crosses in the north of the peninsula, is there also heavy rain or major storms, But basically it is a land situation, it is a complicated situation. In the area of the Pyrenees and in the mountain areas of the north of the peninsula Iberian, therefore, by the sea, would not be a particularly complex situation. Let's see another of the classic and typical situations, that would be the winter situations, in fact, the whole year, which would be the step of a front. Let's draw the step of a front, look at you. This is a front that approaches the Iberian peninsula, a cold front. This will happen practically anywhere in the world, all the cold fronts are accompanied by a groove in the isobars. Do you remember the furrow, which was this kind of V? Of this kind of form, v-shaped, that they have, you are the isobars like the isohips. Therefore, we see that on the front of the front, what we have is going to be southwestern wind. While, by the rear of the front we will have winds from the north, northwest. Note therefore that we have this difference marked in the direction of the winds, just with the passage of the front. The front, we will have the warm sector of the squall, here is going to be an entrance, an advection of southwestern winds, which are going to get warmer, more humid and with worse visibility. because these are, typically, more tropical, more marine airs and so they have visibility a little less clear. Behind us come polar airs, cooler airs, which will have lowering of temperatures, lowering of humidity and improved visibility. Step to the front, it approaches the here. The day before the front step, we have winds from the southwest and temperatures rise. The wind, the day after the passage of the front, we will have within the value that will be reinforced, and decrease to the temperature. Once the front passes, imagine that the front you are here. And I redraw the isobars that accompany it. Note that once crossing the coast of the Iberian peninsula, Behind the north wind continues, what happens is that here. We have the Pyrenees, and here the Alps begin, in Italy. And here the river Rhone descends, which is a river that comes from the north. When the north wind enters, all this mass of air that was in France wants to pass, But to pass you can not because it has the Pyrenees here and you have the Alps here. It has to groove, it has to enter by the hole left by the Rhone valley, and here it is greatly strengthened. This is what was called the entrance to the tramontane, it is a windy situation Very marked, very strong, affecting the area of the Gulf of Genoa. It is a wind, perhaps in this case, more north-west on the ground, on land it is more of the northwest, and also when it affects the coast of a south zone, It is also a bit more northwest, but here, right in the Gulf of Leon area, Is a complicated and complex situation. Here, again, this entry that goes down with great force can generate temporary maritime hard, with waves exceeding four and a half meters, And sometimes five meters that reach Menorca, is very curious because, here if we mark a meridian. The three degrees is where it gives the shelter, the wind of the north, the Pyrenees give shelter to the wind, above the three degrees is when it blows with force. If you ever go out, maybe you can be deceived by the Barcelona wind, leaving some places of the central coast does not notice the tramontane, because here there is a leeward effect. There is even what is called, a low leeward that, even on the coast of Barcelona, as here a high pressure is generated by the pressure of the wind when it arrives at the Pyrenees, here a small low pressure is generated, which even makes the winds, when there are tramontane in the central coast of Catalonia, southwest or southeast. Here is an erroneous perception of the wind situation. If you leave Barcelona and you go there without having sought your notice of tramontane, without having looked for a warning of wind, you can find, Once you pass the three degrees, that here you are in a situation of hard weather, with very high hours and very complicated for navigation. And in fact, the entire Gulf of Leon is an area of shipwrecks, that is, Be very careful with this situation. It is curious because one of the effects of the tramontane is that it lasts, it is said, three days or six days, it's always like a multiple of three, why? Well it has to do with the configuration of the orography. Note that if this is the Iberian Peninsula, here would be Italy and here is Greece. When the front passes, the first day, It is the first day of tramontane. Once passed behind, the groove. Generate the tramontane, we have the first day. The second day, the front reaches Italy. And here is the gulf of Genoa and remember that we had the Alps here. Here a rotation is generated, when it passes to the front, here winds of the southwest, Here north-west winds. Here you notice that this gives a shape as rounded, and here, In the Gulf of Genoa, a small storm is formed. this storm. Let's erase it again... Here would be The Alps. Here a storm is formed, tiny, but enough for, the front is moving away, the front you would be around. This storm would give the second day, and once the front moves away, this storm is dissipated, it would be a tramontane on the third day. This, the area is in the Gulf of Genoa, perhaps it is one of the areas of the world with more cyclogenesis, that is called, because after the passage of each front, here is formed a small squall, which is what drives this north wind situation that lasts three days. Why would it last six? If it were the case, if it were the case of six, it would be because this storm has increased, that is to say, it has not been provoked simply by the passage of a front, but has remained here, situated on Italy. Then, in truth you are not six days, you are not three days, but the perception of the people is that it lasts up to three, six. But this of the three is very true because it happens every time, happens every time you cross a frontal line.
