Atmospheric Gravity Waves

Last updated on September 16, 2023

Atmospheric Gravity Waves: Exploring the Phenomenon

When we drop a stone into a pool of water, we observe the formation of ripples that spread outwards. These ripples are known as gravity waves. Interestingly, similar waves can also be found in the Earth's atmosphere, occurring between stable layers of fluids with different densities. These waves, known as atmospheric gravity waves or buoyancy waves, play a significant role in shaping the dynamics of our atmosphere.

Gravity waves in the atmosphere are most prominently observed in the stable density layering of the upper atmosphere. Their effects can be visually witnessed in various atmospheric phenomena. For instance, the curls of nacreous clouds in the stratosphere, the moving patterns of noctilucent clouds in the mesosphere, and the shifting bands of airglow in the thermosphere are all manifestations of the influence of these gravity waves.

The question arises: what triggers these atmospheric gravity waves? The disturbances that initiate these waves typically originate far below in the troposphere. Wind flow over mountain ranges, violent thunderstorms, jet stream shear, and even solar radiation are some of the sources that can create these disturbances. While initially small in amplitude at the tropopause, these waves increase in height as they propagate upward. Eventually, they break in the mesosphere and lower thermosphere, contributing to the dynamic behavior of these atmospheric layers.

The wavelengths of atmospheric gravity waves can span a vast range, extending up to thousands of kilometers. Similarly, their periods can vary from just a few minutes to several days. This wide range allows for a diverse array of wave patterns and behaviors within the atmosphere.

Beyond their aesthetic value, atmospheric gravity waves serve a vital role in the transfer of energy, momentum, and chemical species between different atmospheric layers. These transfers have significant implications for various atmospheric phenomena, including upper atmosphere winds, turbulence, temperature distribution, and chemical composition.

To summarize the key points about atmospheric gravity waves:

• They are similar to the ripples formed when a stone is dropped into water.
• Gravity waves occur between stable layers of fluids with different densities in the atmosphere.
• They are visible in phenomena such as nacreous clouds, noctilucent clouds, and airglow.
• Disturbances in the troposphere, such as wind flow over mountains and thunderstorms, trigger these waves.
• Jet stream shear and solar radiation are other sources of disturbances.
• Atmospheric gravity waves increase in amplitude as they propagate upward, eventually breaking in the mesosphere and lower thermosphere.
• Their wavelengths can span thousands of kilometers, while their periods range from minutes to days.
• These waves play a crucial role in transferring energy, momentum, and chemical species between atmospheric layers.
• They significantly influence upper atmosphere winds, turbulence, temperature distribution, and chemistry.

Understanding the behavior and impact of atmospheric gravity waves is essential for comprehending the complex dynamics of our atmosphere. By studying these waves, scientists gain valuable insights into the intricate processes that shape our planet's weather and climate systems. The ongoing research in this field continues to unravel the mysteries of atmospheric gravity waves and their far-reaching consequences.

Drop a stone into a pool of water. The spreading ripples are gravity waves. The waves occur between any stable layers of fluids of different density. When the fluid boundary is disturbed, buoyancy forces try to restore the equilibrium. The fluid returns to its original shape, overshoots and oscillations then set in which propagate as waves. Gravity or buoyancy is the restoring force hence the term - gravity waves.

These waves (internal gravity or buoyancy waves) abound in the stable density layering of the upper atmosphere. Their effects are visibly manifest in the curls of the stratosphere’s nacreous clouds, in the moving skein-like and billow patterns of the mesosphere’s noctilucent clouds and in the slowly shifting bands of the thermosphere’s airglow.

What triggers them? The ‘stones into the pond’ are disturbances far below in the troposphere, for example, wind flow over mountain ranges and violent thunderstorms. Jet stream shear and solar radiation are other sources. An initial small amplitude at the tropopause increases with height until the waves break in the mesosphere and lower thermosphere. Their wavelengths can range up to thousands of kilometres. Their periods range from a few minutes to days.

They do more than give clouds interesting shapes. They are vital in their role of transferring energy, momentum and chemical species between the different atmospheric layers and in the subsequent influence on upper atmosphere winds, turbulence, temperature and chemistry.

Images:

Nacreous clouds, Antarctica - Cherie Ude

Noctilucent clouds, England - Chris Terran

Airglow, Kansas - Doug Zubenel

Note: this article has been automatically converted from the old site and may not appear as intended. You can find the original article here.

Reference Atmospheric Optics

If you use any of the definitions, information, or data presented on Atmospheric Optics, please copy the link or reference below to properly credit us as the reference source. Thank you!