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WAVE Team Responses
Atmospheric gravity waves are oscillating disturbances that form in the atmosphere when buoyancy displaces air upward, and gravity pulls it back down. We perceive the oscillation as a wave.
Gravity waves transport momentum from one region of the atmosphere to another, thereby connecting different parts of the atmosphere. For instance, a storm at the surface can cause changes in the ionosphere far above the surface, potentially affecting the transmission of GPS signals between satellites and the earth’s surface.
Since we can’t see air, we can’t really see an atmospheric gravity wave. But we can see the effects of atmospheric gravity waves. When air rises it cools, which can cause clouds to form. When air comes back down it heats up, which can cause clouds to evaporate. So when we look up at the sky, gravity waves are most apparent as wave-like patterns in clouds. There are also many instruments, both on the ground and in space, that can “see” atmospheric gravity waves by measuring oscillations in various parameters such as temperature or the density of certain atoms, molecules, and even electrons.
Gravity waves can range in size from meters to hundreds of kilometers, depending on their source and location in the atmosphere. The “size” here refers to the horizontal “wavelength”, which is the distance between adjacent wave crests (or troughs). Gravity waves tend to have several wave crests before they dampen out and disappear.
NO! The term “gravity wave” refers to oscillations in planetary fluids (like the earth’s atmosphere) that are triggered by weather disturbances such as thunderstorms. The term “gravitational wave”, on the other hand, refers to ripples in the space-time continuum that are triggered by cataclysmic events in the universe on cosmic scales of time and space. The two phenomena are quite different, but unfortunately the terms are often confused.
Yes, gravity waves can be a source of turbulence for aircraft. Mostly likely you have experienced turbulence when flying through dark clouds on an airplane, but you can also experience turbulence when there are no clouds at all. This is called clear air turbulence and it can be caused by breaking gravity waves that are generated by air moving over mountains. This source of clear air turbulence is an active area of research.
Absolutely! On September 2, 2018 an unmotorized glider (Airbus Perlan 2) found lift by following the rising phase of a mountain wave over the Andes to achieve an altitude above 76,000 feet, which is in the stratosphere. This was a record not only for a glider but the Perlan flight broke the previous altitude record held by the U-2 reconnaissance plane.
Unfortunately, yes there is. For example, the well respected Science Magazine reported that ionospheric plasma bubbles, which are ionospheric disturbances that interfere with radio communications, were a likely cause of a military helicopter crash in Afghanistan in 2002 that cost seven lives (https://www.science.org/
NASA defines space weather as “the dynamic conditions in the Earth’s outer space environment…Space weather includes any and all conditions and events on the sun, in the solar wind, in near-Earth space and in our upper atmosphere that can affect space-borne and ground-based technological systems and through these, human life and endeavor” (https://www.nasa.gov/mission_pages/sunearth/spaceweather/index.html#q11). The WAVE DRIVE center investigates the waves that connect weather in the lower atmosphere to “space” weather in the upper atmosphere. By “upper” atmosphere we’re referring to the mesosphere, thermosphere and ionosphere, or about 60 km (~37 miles) and higher above the earth’s surface.
Yes! The main way weather at the earth’s surface affects space weather is through the transfer of momentum by atmospheric gravity waves and their interactions with other waves. For example, atmospheric gravity waves are created by convective updrafts in thunderstorms when the air in those updrafts reaches and overshoots the tropopause (around 6-8 miles above the Earth’s surface). The sloshing up and down of the air at the tropopause creates these waves. Most of these waves break below where space weather occurs, similar to ocean waves breaking on a beach; but some reach much higher and contribute to space weather! In addition, the gravity waves that break at lower heights create new sets of “secondary” gravity waves, which then travel up to the ionosphere, and contribute to space weather. Both of these waves can seed plasma bubbles and other ionospheric instabilities, which can cause outages for satellite communication.
Possibly. A warming climate will bring more water vapor into the air and trigger more severe weather. More convection (e.g., from thunderstorms), can launch more gravity waves.
Yes, gravity waves affect the ozone layer. For example, since gravity waves lead to oscillating temperatures, polar stratospheric clouds (PSCs) can form when and where the waves cause cooling. Chemical reactions on the surface of PSCs initiate a complex process that leads to depletion of the ozone layer. Gravity waves also affect atmospheric winds, and this can change how many ozone-destroying molecules are transported into the polar stratosphere where most of the ozone depletion occurs.