Do you know why there are so few typhoons in the southeastern Pacific and South Atlantic?

Large areas of warm sea water. The energy of typhoons mainly comes from the latent heat of condensation released during the formation of typhoon clouds. The horizontal scale of a typhoon can be hundreds or even thousands of kilometers, and the wind speed is as high as 50-60m/s. The energy required to maintain such a huge weather system must rely on the underlying surface

A steady supply is provided to sustain. And the only such source is a warm ocean.

Warm seawater continues to evaporate, supplying a large amount of water vapor. The water vapor condenses into clouds during its rise and releases a large amount of heat (water evaporation will absorb

heat as the reverse of evaporation. process, condensation will release an equal amount of heat), causing the air block to expand, and the density of the expanded air will decrease, which will accelerate its rise and attract more moist air below to fill it up, thus forming a positive feedback process : The air rises and condenses at an accelerated rate, and the ocean evaporates at an accelerated rate. Over tropical oceans, this process generates massive convective clouds.

1. Warm seawater provides the heat required for the formation of typhoons. As you will see later, the maintenance of typhoons not only requires warm seawater, but also requires warm seawater to maintain a certain thickness.

, a large number of convective clouds provide embryos for the formation of typhoons in the next step. Usually, the sea temperature reaching 26.5℃ is the critical value for typhoon generation.

With warm sea water, will typhoons definitely be generated? Don't get too close to the equator. This is because, as a huge vortex structure, the formation of a typhoon requires geostrophic deflection.

Otherwise, the air will flow directly into the convection system, causing convection congestion. A certain geostrophic deflection force can make the air entering the convective system spin

to form a vortex, which will prevent the convective system from quickly filling up, which is conducive to the generation of typhoons.

< p>Usually, sufficient geostrophic deflection can only be provided in areas beyond 5° north and south latitude. Therefore, despite strong convection in the warm equatorial ocean, the geostrophic deflection force is 0, it is difficult to generate a typhoon.

If the above two conditions are met, will a typhoon be sure to form? The answer is still no. , the atmosphere cannot have significant wind shear. This is easily overlooked by many people. The so-called wind shear, in layman's terms, means that the wind directions in the lower atmosphere and the upper atmosphere are inconsistent. After a typhoon forms, a large amount of latent heat released by the condensation of low-level moist air will flow to the upper levels with the rising air, heating the middle and upper atmosphere. The heated middle and upper atmosphere accelerates its expansion and rise, attracting the inflow of low-level moist air. This kind of The mechanism is conducive to the maintenance of the typhoon structure.

2. In reason one, I mentioned the important role played by the latent heat of condensation in maintaining the convection system. A typhoon is essentially a huge heat engine. It absorbs a large amount of warm and humid air from the lower levels, and the warm and humid air rises to high altitudes (in the process, water vapor condenses and releases a large amount of water vapor.

latent heat, heated air), flows out at high altitude, and sinks outside the typhoon, forming a cycle. Among them, the process of rising low-level moist air is particularly important, because during this process, a large amount of latent heat in the moist air is released to heat the typhoon itself, and this is what

The driving force behind the formation and maintenance of typhoons. According to calculations by meteorologists, more than 90% of the energy used to sustain typhoons comes from the release of latent heat of condensation.

At this time, a question arises. How to ensure that the heat heats the typhoon itself without being lost to the outside? The answer is that heat cannot be taken away in large quantities at high altitudes. Wind shear can do this. If the wind speed at high altitude is high and the direction is inconsistent with the wind direction at middle and low levels, then as the convective clouds develop upward, the latent heat brought up can be carried away by the high-altitude wind. In this way, a large amount of heat cannot be retained In a convective system, the system cannot accumulate enough energy to develop into a typhoon.

When a typhoon moves to high latitudes, it will usually transform into an extratropical cyclone and eventually weaken and dissipate. One of the reasons is that the westerly wind belt maintained at high altitudes all year round will The heat inside the typhoon system moving northward is quickly taken away.

The necessary conditions for the generation of typhoons are now clear. Next, we will see the underlying reasons why typhoons are difficult to generate in the South Pacific and South Atlantic.

3. From the above global ocean surface sea temperature distribution map, we can see that compared with the tropical western Pacific and tropical Indian Ocean, the surface sea temperatures in the southeastern Pacific and

South Atlantic Ocean are Not high enough.

The direct consequence of the low sea temperature is that the oceans in these two areas cannot provide enough energy to the atmosphere above them. Even if there is convection,

the scale will not be large enough. If it develops into a typhoon, even if it develops into a typhoon embryo, the ocean surface will no longer be able to provide enough energy to sustain its growth.

The cause of lower sea temperatures in the southeastern Pacific and South Atlantic is mainly the influence of the Peruvian Cold Current and the Benguela Cold Current. In addition, the accelerated evaporation of seawater

by trade winds is also one of the reasons. .

Not only are the sea temperatures in the southeastern Pacific not high, but the warm water layer is also thin. The situation in the South Atlantic is similar. This is what matters most.

Friends who have a little knowledge of oceanography will know that in the ocean, the temperature usually decreases with increasing depth. This is due to the low temperature in the polar regions.

The sea water is cold and sinks to the world. Caused by ocean floor diffusion. In tropical areas, because the sea surface water temperature is high and the deep water temperature is similar to that in high latitudes, the trend of water temperature decreasing with depth is particularly obvious.

The reason why I mention this is that the maintenance of typhoons not only requires a large area of ??warm sea water, but also requires that the thickness of this layer of warm water should not be too thin.

This is because typhoons are low-pressure systems with low central air pressure. Under the action of this, the center of the sea surface where the typhoon passes will be slightly raised, which will make

the typhoon pass through the sea area. The surface water appears to be upturned.

4. If the warm water layer is too thin, the cold water below will rise to the sea surface.

The sea temperature will be lowered, so that the typhoon will not get enough heat, and then it will quickly weaken.

Therefore, no matter from the perspective of surface sea temperature or the thickness of the warm water layer, the southeastern Pacific and South Atlantic do not have the conditions for the generation and maintenance of typhoons

. At the same time, because the guiding airflow in the middle of the atmosphere at low latitudes often points to the west, typhoons mostly move in a westward direction. Very few external typhoons enter the southeastern Pacific. Even if they do, they will be affected by sea temperature restrictions. Rapidly weakens and dissipates. As for the South Atlantic,

firstly, it is because the cyclones in the North Atlantic cannot overcome the limitation of geostrophic deflection and cross the equator, and secondly, because the vast and towering African continent blocks

the southern Indian Ocean. As the cyclone moves westward, it becomes more difficult for tropical cyclones to enter.

In the tropical southeastern Pacific and South Atlantic, the prevailing wind at low altitude is the southeast trade wind, while the prevailing wind at high altitude is westerly

wind. Affected by the Walker circulation, westerly winds prevail in the upper altitudes of the South Pacific (the same applies to the South Atlantic), which is different from many other tropical areas where easterly winds prevail at upper altitudes.

As a result, there is a 180° difference in the high and low altitude wind directions in these two areas. Such significant wind shear can easily nip the budding tropical cyclone embryos in the two places in their cradle. For the southeastern Pacific, if a tropical cyclone comes from the west (which is rare), it will quickly weaken and disappear due to wind shear.

For the above reasons, typhoons (tropical cyclones) are extremely rare in the southeastern Pacific and South Atlantic.