金星 6,000 公里巨型雲牆之謎解開，由最大規模水躍現象引起 | 科技新報 – LINE TODAY

Researchers from the University of Tokyo and other institutions have identified the physical mechanism driving the massive, 6,000-kilometer-long atmospheric waves observed at the equator of Venus. The study reveals that these giant cloud walls are caused by a hydraulic jump, marking the largest known occurrence of this phenomenon within the solar system.

The atmospheric disturbances were first captured in August 2016 by the near-infrared camera aboard Japan’s Akatsuki probe. The imagery showed bow-shaped cloud waves, resembling a giant smile, that repeatedly swept across the Venusian equator. While these structures were clearly visible, their origin remained a mystery to scientists for several years due to the immense scale of the disturbance.

Venus is characterized by a dense cover of clouds and the potential for sulfuric acid rain. A defining feature of its atmosphere is the extreme speed of the cloud layers, which move at approximately 60 times the planet’s own rotational speed.

The research team determined that the 6,000-kilometer cloud walls are the result of a hydraulic jump. In fluid dynamics, a hydraulic jump occurs when a high-velocity liquid flow enters a low-velocity region, causing the flow to suddenly decelerate. This transition shifts the liquid from a shallow, fast state to a deep, slow state, converting a portion of the kinetic energy into potential energy, while some energy is dissipated as heat through turbulence.

On Venus, this process manifests in the mid-to-low cloud layers. When an eastward-moving atmospheric wave becomes unstable, a hydraulic jump occurs, leading to a sharp drop in wind speed. This deceleration creates a powerful localized updraft that pushes sulfuric acid vapor into the higher levels of the atmosphere.

Once the vapor reaches the upper atmosphere, it condenses into clouds. These clouds are then dragged behind the wave, forming the spectacular cloud walls that can encircle the entire planet.

Takeshi Imamura, an astronomer at the University of Tokyo, noted that the dynamics of the lower and middle cloud layers of Venus have historically been poorly understood. The identification of the hydraulic jump is significant because it provides a link between large-scale horizontal phenomena, such as atmospheric waves, and strong local vertical phenomena, such as intense updrafts.

This integrated understanding differs from previous fluid dynamics models, which predicted these horizontal and vertical movements separately. According to the research, this specific process also contributes to the maintenance of the super-rotation of the Venusian atmosphere.

The researchers suggest that the physical mechanisms responsible for these cloud walls may not be unique to Venus. Under certain conditions, the atmosphere of Mars may also possess the necessary environment for hydraulic jumps to occur. Developing more accurate atmospheric models based on these findings could improve future missions to Mars.