[MUSIC] Well, in this chapter we are going to talk, again, of instability but of planetary scale or large scale. Recall that we have previously dealt with inertial oscillations and scale and mesoscale, as disturbances affecting the course of the currents causing oscillations. Now we are going to see scale oscillations of an entire ocean basin. In the specific case, let's go a bit, remember that the planet we have, is a planet full of water and this vision, is the vision of the Pacific Ocean, where practically water is everywhere. There is a bit of land here in New Zealand, a little here on the east coast of Australia and a little bit in South America around here, a little North America around here, but it's practically a huge ocean, a huge basin. Then there, any disturbance can give rise to oscillations of a much higher scale and, therefore also, of a longer duration. And here we have this, typical cases that is what is called El Niño. El Niño Southern Oscillation is a phenomenon known since antiquity and which particularly affects the South American area. This is a scheme of the Pacific, and we have the normal conditions here we have, on the one hand we have America, this imagine is a block, And here we have another section. Here we have, this is the equator, here we have the Australian coast, New Guinea and, in general, the situation that is usually given is that we have here is an area of low pressure, an area of hot water in its surface low pressures here that cause instability in the atmosphere, which cause rains in motion, rise air giving formation of large clouds, typical, the typical conditions of the equatorial situation. Generally it is the cycle, it comes back here and in this zone of here, we have a rather anticyclonic area, is of the zones a little exceptional in the equatorial zone, but the area is relatively quiet at high pressures. And what we have, therefore, is the atmospheric circulation goes in this direction. The marine circulation is also following Ecuador in this sense, and what we have is that this causes an inclination of the Isopycnals and the thermocline zone, deeper in this area, obviously, in the area where there is more warming and where there is a precipitation that is the area of the Eastern Pacific, but of the Western Pacific, the coasts, the Asian coast and Eastern Australia. This is the normal contrast and, these, normal conditions. What happens when there is a Niño? For this usually oscillates between a Niño and a Niña. It is called Niño when we have a system reversal this heating zone moves to the east. What it does is that the area of storms and formation of torrents are also moves east, until arriving at the American coast. So here we have high pressures and here we have low pressures. Therefore we have more precipitation here and here we have an increase of the surface mixing layer, the thermocline stays lower and here it rises. And, in addition, here we have an area here we have an important drought where there is not, these important rain zones cease to function. And at the same time, also this interrupts the outcrop we had on the coast. Here possibly because the waters are surface, which are hotter are somehow plugging the outcrop area. Let's go a little while back, to see here, here we have an area clearly, the thermocline, here is in the most coastal area, we have the outcrop area, remember the outcrop. Somehow this chapter is what it does is encompass a little several concepts that we have been seeing. Here we have the trade winds of the southern hemisphere, on the coast of Peru and Chile that cause an important coastal outcrop in the Peruvian and Chilean zone. And here these conditions what it does is, of course, the thermocline is very shallow and it is deeper here, but that is the inclination, while in the situation of the Niño this goes ironing in some way and what is the Niña? La Niña is a bit of a step, but we went from stopping in the other direction. That is, it is a normal situation, to such an extent that hot water concentrates much more here, this deepens the thermocline much more, here there is practically no surface mixing layer, this area is very intense, on the coast here. Normally, things go like this, Niños and Niñas alternating with more or less force, that is, here we have important Niños, that is the surface water temperature on the American Pacific coast. And the high values, obviously, correspond to Niños, The low values correspond to Niñas or normal situations. That is, and this would be the average, the average we have here. This seems to me that these temperatures are measured in Galapagos, if I remember correctly, or near, maybe Ecuador. Well, we have these episodes of Important Kids here. It is called Niño, because normally this phenomenon occurs in the middle of the Southern Hemisphere summer, which is the Christmas season, that is, the time of December and is called Niño for obvious reasons as it is a phenomenon that occurs during the Christmas season. It is simply a diagram of how the mechanism in general, but in this case it is between the Ecuador and 30 degrees. Let's see a little as well how we have the mechanisms of compensation of the sea. That is, we are doing one thing when we move to one side, then we have an oscillation and that oscillation can be triggered with any thing, because, in general, there is no need for a large phenomenon that is in a situation of a precarious balance and that anything causes an oscillation. And here a few years ago theory appeared, that was a bit of a recharge system, it's like saying, charge and discharge, charge and discharge. We have here cold water and hot water, how a layer of hot water is distributed, a layer of cold water and how it is going from one situation to another. We have a Niño, passes the unloading situation, passes the situation of Niña and goes to the situation of the recharged state again, is a way of talking about the system this. Here we practically have you without water from the superficial area and here we have a deeper layer. Here is an animation of the different phases of the Pacific oscillation, normal conditions, conditions with Niño, conditions with Niña. We have here, at this moment, as it is the view, those conditions of Niño, but let's see how it goes to normal conditions. Under normal conditions we start from high pressures here, low pressures here. We have some trade winds that move in this sense and here very low pressures, the air has a tendency to rise. The air has a tendency to rise, causing condensation, which produces tropical rains. The air above travels dry and, naturally, it tends to go down in the antyciclonic zone. At the same time, we find that we have the cold Humboldt that is coming here, that follows the American Pacific coast. And, of course, this outcropping and therefore bottom water, the cooler water that rises to the surface here and is expanding in area following the coastal zone. With which we have that here the thermocline is deeper, here less deep, here it practically is not, we have the outcrop of water rising to the surface here. And here we have very stratified water, these conditions of the Niño. We have rains in the area of Indonesia, the northern area of Australia and dry weather in very cold surface water. We will see from here how the conditions of a Niño develop. What about the Niño? Well let's see how, little by little, we find that the wind has changed and now the wind is reversed. With this, it moves this layer of water warmer, the displacement towards the east and, of course, here causes a low pressure and here a high surface pressure is present. What's up? That in every circuit the air is reversed, we now have major torrential rains in the eastern part of the domain, circulation from the top also has changed and we have low pressures but high pressures here. We have major rains here, the homogeneous thermocline, practically at the same depth on the American coast which on the east coast of Australia and, of course, the outcropping has been blocked. You do not have outcrop of this area here, upside down, we have rains and we have hot waters on the surface of the coast. What about the Niña? With La Niña, what we have is that this situation is increased, this jet is given more importance in this sense, this causes an intensification of the rains, the outcrop expands, increases and the area covered by cold water is spread much further into the Pacific Ocean. With which we have practically no thermocline in a good part of the eastern zone of the South Pacific. And here we have an intensification of the thermocline and the identification of the hot zone with intensification of the rains. And this, somehow, this animation allows you to see how one thing is developed from the next, and how the beginning really, where it starts, is something that is not yet known exactly because it can be anything. That at a given moment causes a change in conditions and then changes everything. This year, for example, there has been an unimportant Niño, But there has been a Niño who until December still had doubts whether it would be Niño or not, And in the end it seems that with this we finished.
