Inertial gravity wave of atmospheric fluctuation

The fluctuation formed by gravity and Coriolis force in a stratified atmosphere. Like gravity wave, it can also be divided into inertial gravity external wave and inertial gravity internal wave. Their wave velocities are respectively

F is the Coriolis parameter. Inertial gravity external wave and inertial gravity internal wave are dispersive waves, and their group velocities are respectively

Inertial gravity internal wave is the main fluctuation in the process of atmospheric mesoscale motion (the horizontal scale L is about 102 km), and many mesoscale weather phenomena are closely related to the activity of inertial gravity internal wave.

Long-wave atmospheric fluctuation caused by the change of Coriolis parameter f with latitude when the airflow in the westerlies is disturbed from north to south. Because this kind of fluctuation in the earth's atmosphere was first studied by Swedish meteorologist C.-G. Rosby, it is also called Rosby wave. The horizontal scale of this wave is equivalent to radius of the earth, so it is also called planetary wave. The main parameter that reveals the characteristics of planetary waves is called Rossby parameter, which represents the variation of Coriolis parameter f with latitude (RE is the average radius of the earth, ω is the angular velocity of the earth's rotation, φ is the latitude). Planetary waves are mainly generated under the action of β: according to the principle of conservation of absolute vorticity (see atmospheric dynamics equation), suppose that the initial vertical vorticity ξ of the air mass at point O (Figure 2) is zero, the north-south component of the air mass velocity is V, and it moves slightly northward after being disturbed (v >；); 0) In the process of moving to point A, f(=2ωsinφ) increases; However, due to the conservation of absolute vorticity, ξ will change from 0 to a negative value, making the trajectory of the gas block form an anticyclonic bend. The air mass moved northward again, and the anticyclone vorticity reached the maximum when it reached point B. At this time, v=0, the air mass could not continue to move northward, but moved southward (V

This huge arrow-shaped cloud structure can be clearly seen in this image taken by NASA's Cassini detector, which is located in the equatorial region of Titan. It shows the seasonal changes on Saturn's largest moon. The arrowhead cloud visible in the figure extends over 1200 km from east to west and over 1500 km from north to south.

According to a new research result, the mystery of the mysterious arrow-shaped structure observed in Titan's clouds may have been solved. It seems that this may be caused by waves sweeping through Titan's atmosphere. The researchers said that this result will help scientists better understand similar phenomena in the earth's atmosphere, especially in such a period of climate change, which is more valuable.

In 20 10, NASA's Cassini Saturn spacecraft first observed this strange cloud structure on Titan. This cloud is very large, extending over 1500 km. In order to find out how such a strange cloud is formed, Jonathan Mitchell, a planetary scientist at UCLA, and his colleagues deduced Titan's atmospheric motion pattern with the help of a computer three-dimensional climate model.

Mysterious fluctuations

They found that shock waves near Titan's equator can cause clouds of this shape to appear. If you want to understand how this shock wave appears more vividly, please imagine a wine glass making a pure * * * vibration.

Michelle told reporters: "The vibration of the wine glass is limited by its internal structure, so it can only make a specific sound, and so can Titan." He said: "This is the natural vibration of the whole system, and this strange arrow-shaped cloud is only an inevitable reflection in response to this characteristic vibration wave."

This abnormal cloud structure will lead to heavy rainfall 20 times stronger than conventional precipitation, which plays a key role in shaping the surface process of Titan. A lot of "rain" has caused serious erosion, which can explain some broad erosion valleys on Titan's surface. But the "rain" on Titan is not water, but hydrocarbons.

More mysterious clouds?

As for the future research direction, Michelle said that we can integrate the data collected by the entire Cassini project and find other unique cloud structures: "It is very likely that we can find similar cloud structures again and repeat the analysis, thus further deepening our understanding of Titan's climate model."

At the same time, these studies from Titan can also inspire the earth, because Titan is very similar to the earth in essence. Scientists have found that some characteristics of Titan's atmosphere are very similar to the tropical atmosphere in the equatorial part of the earth. It's just that the phenomenon confined to tropical areas on earth seems to have spread to the global scope on Titan.

"This global fluctuation forms a violent rain cloud on Titan, which is very similar to the process of storms in the tropical atmosphere of the earth, although this process is not as obvious on Earth as on Titan," Michelle said. "I hope that the study of Titan will eventually help us understand the weather patterns that appear in the earth's climate change."