[MUSIC] Let's draw the world again, here we will draw the Equator again. Notice that we have said that the northern hemisphere, the trade winds were from the northeast, and in the south they were from the southeast. That is to say the local weather phenomena that we are seeing here, or we are seeing a zone of convergence. The wind enters, therefore what is going to happen to this wind is that it will have a tendency to ascend. What we are going to see there is what is called, the zone of intertropical convergence, caused by the trade winds that converge the zone of the Equator and that generate an upward movement. Notice then that this area of here is going to be marked by the storms or you remember that we had left storms in the general atmospheric circulation, but at the same weather the engine of these storms is the surface convergence. And that's why this line of intertropical convergence zone is called. This moves throughout the year, goes eight or ten degrees north in summer, and to the south about five degrees in winter, the sun follows. Therefore, this zone of convergence, if we go through in summer, we will find squalls relative to the north with respect to the Equator. If we go through in winter, they will be south with respect to Equator. But this is a living area, this line would have to be drawn every day because this would be which would mark us the reason of the changes of weather in that Equatorial zone. At the North Pole, we have said that there was cold air, is a desert area of cold air. We call this the mass of polar air. The pole is an area of cold air, and cold air, the air is made up of air masses. The air does not mix with one another, Therefore, this zone of the cold air of the North Pole, or the equivalent. From the South Pole are two polar air caps that are in the two ends of the Earth, and here is what we call tropic air. This polar area in winter gains ground, and in summer it remains as smallest here in the zone of the North Pole. And now, let me draw something else: I will draw the tropopause. As you know the Earth is not round, but in fact it is like a a revolving ovoid. Well, the air above that land is also a revolving ovoid. It means that it is a little flattened by the poles and longer in Equator. And although it would seem that the thing has to be uniform, it is not true. Actually, the tropopause is drawn like this. Forgive me... let me... It is higher in Equator, it is lower in the poles. In fact, here in Equator can measure up to 15 kilometers The number was not very well, and here about nine kilometers. But, this height increase is not a uniform thing but there are a kind of places of rupture. Here, it is what we call the polar jet. This is an "o". Jet polar [LAUGH] Looks like an "r". Notice that this area of cold air, you remember when we talked about the engines of local weather that were the fronts? Well look, here this area here would be the warm front. This area has a warm air that is getting into the cold air, while here would be the cold air. These ripples of the polar air as they move, generate warm fronts and cold fronts, And this kind of bubble that is coming down moves, this is cold air therefore, here is the cold air, here is the polar front. And this one that is getting upwards is the warm air, So this would be the warm front. This would be the area of polar air, and right on the end of the zone of polar air, here in height there is a wind current, Literally a wind river with forces of 100 knots, 150 knots wind that runs in the form of a river but discontinuous. Sometimes ascending, sometimes descending. This would be the wind current that accompanies the movements of the polar air. This is the polar jet. And finally here right in the middle is another jet called subtropical jet stream. This looks awful, but [LAUGH] The tropical sub jet. What is the tropical sub jet? Well, it is another current similar to this that breaks the continuity of the tropopause, of the height of the air on the surface of the earth. And that is a strong wind that appears in these middle latitudes. Look, here we have said, wind that converges on surface, this was the motor of the weather of the convergence in surface, generates the inter-tropical convergence zone. Here at height what we are seeing is a very strong current. What will generate this? Divergence in height. In height the air passes very fast, very strong, therefore, here we are going to generate a kind of vacuum and what is going to happen to us is a suction is generated. That is going to provoke us to rise in the subtropical latitudes around 20, 30 degrees north or south latitude, the motor of the weather gives us the subtropical jet. And it is basically a divergence in height, by effect of the wind in height will generate ascent from above, and that will generate from below ascents that are going to provoke cloudiness or types of weather, storms, squalls, whatever, in this area here. Here the wind is surface, it is generating height, ascents. From the surface, here it is generated by divergence in height, and here, in middle latitudes, we would be talking about many things put together at the same weather. Because to notice that we have difference of cold air and warm air, therefore, the fronts. Divergence in height, because we also have the polar jet, we could also have confluence on the surface. We can here in the middle latitudes, we really have an important sum of factors that will give us the weather, but above all, that difference between the temperatures between the polar air and the tropical air. In subtropical latitudes, the motor of weather is the subtropical jet, that divergence in height, and in the Equator zone what we see is that the engine of weather, is going to be the convergence in surface that give us the trade winds.
