Meteotsunami or Meteorological Tsunami

A meteotsunami or meteorological tsunami is a type of ocean or lake wave that forms due to rapid atmospheric disturbances, such as changes in air pressure or wind speed, rather than seismic activity. These disturbances generate waves that behave similarly to tsunamis, traveling across large bodies of water and potentially causing significant coastal flooding and damage.

Key Points

• What is a meteotsunami? A meteotsunami is a tsunami caused by weather rather than a seismic disturbance.
• How big is a meteotsunami? While generally smaller than a tsunami, a meteotsunami reaches heights over 6.6 feet (2 meters), with rare events reaching 20 feet (6 meters).
• Are meteotsunamis dangerous? Yes. Meteotsunamis are dangerous because they move quickly, predicting them is challenging, and the cause coastal flooding. In some cases, they cause deaths.

How Meteotsunamis Work

Meteotsunamis form when a sudden atmospheric disturbance transfers energy to a body of water. This energy propagates large waves through the ocean or large lakes, sometimes with devastating effects along coastlines. The speed and intensity of the meteotsunami depend on how well the atmospheric disturbance matches the natural frequency of the body of water it affects. If the atmospheric conditions and the water’s natural oscillation align, wave heights increase significantly through resonance, amplifying the energy transferred to the water.

Here’s how it works:

1. Atmospheric Pressure Changes
   Sudden changes in atmospheric pressure generate meteotsunamis. These changes come from fast-moving weather systems, such as thunderstorms, squalls, or frontal passages. The air pressure disturbances create a direct force on the water surface.
2. Low and High Pressure Effects
   • Low Pressure Systems: When air pressure drops rapidly, there is less atmospheric force pushing down on the water surface. This causes the water to “rise” in response, similar to how a vacuum pulls on air. This local rise in water level begins the formation of a wave.
   • High Pressure Systems: Conversely, a sharp increase in air pressure pushes down on the water surface, creating a depression or lowering of the water level. This also contributes to wave formation as the water rushes in to fill the depression.
3. Energy Transfer to the Water
   Whether it’s low pressure lifting water or high pressure pushing it down, the disturbance initiates a horizontal movement of water. If the pressure change occurs over a wide area, this movement is sustained and grows into a wave. Strong winds accompanying these systems further enhance the transfer of energy to the water, amplifying the wave size.
4. Resonance and Amplification
   A key aspect of meteotsunami formation is resonance. If the speed of the atmospheric disturbance matches the natural frequency of wave oscillation in the body of water (a phenomenon known as Proudman resonance), the wave’s amplitude increases significantly, forming larger waves. This is especially likely in semi-enclosed basins or coastal areas where the waves reflect off the shoreline and further intensify.
5. Wave Propagation
   Once formed, the wave behaves like a tsunami, traveling across the ocean or lake. As it approaches the shallower waters near the coast, the wave grows in height due to the decreasing depth of the seafloor.

Even though meteotsunamis are associated with storms, the wave can arrive in clear weather. The wave forms over the water, some distance from the land, where conditions may be quite different.

Characteristics of Meteotsunamis

• Wave Height: Typically, meteotsunamis generate waves ranging from a few centimeters to several meters in height. A large meteotsunami reaches a height over 2 meters (6.6 feet), posing a threat to coastal infrastructure and human lives. In rare instances, the wave height is even higher.
• Wavelength: The wavelength of a meteotsunami is similar to that of a seismic tsunami, often stretching tens to hundreds of kilometers.
• Wave Speed: Meteotsunamis travel at speeds proportional to the water’s depth, usually between 10 and 100 km/h (6 to 62 mph).
• Duration: The duration of a meteotsunami event varies from minutes to several hours, depending on the scale of the atmospheric disturbance and the size of the body of water.
• Frequency: Meteotsunamis can occur multiple times a year, particularly in regions with frequent atmospheric pressure changes or storms.

Where Meteotsunamis Are Common

Meteotsunamis occur worldwide, but they are most common in semi-enclosed bodies of water where atmospheric conditions are more likely to resonate with water movements. Key regions include:

• Mediterranean Sea: One of the most well-known meteotsunamis occurred in the Balearic Islands in 2006, with waves reaching over 4 meters.
• Great Lakes (U.S. and Canada): The Great Lakes experience meteotsunamis during periods of intense thunderstorms or pressure changes. In 1954, a meteotsunami struck Chicago, causing significant damage and claiming seven lives.
• East Coast of the United States: Meteotsunamis have been recorded along the eastern seaboard, especially in the Gulf of Maine and Massachusetts Bay.
• Adriatic Sea: A notable meteotsunami occurred in Vela Luka, Croatia, in 1978, reaching 6 meters in height.

Differences Between Meteotsunamis and Tsunamis

Meteotsunamis and tsunamis share many similarities, including their resonance behavior and the potential for causing coastal flooding, but their origins are different:

Meteotsunami vs Seiche

Meteotsunamis and seiches are both types of water oscillations in response to atmospheric or other disturbances, but they differ in how they form and behave.

• In a meteotsunami, an atmospheric disturbance forms a wave that proceeds toward the shoreline of the ocean, a lake, or a partially-enclosed body of water.
• A seiche is a standing wave that forms in an enclosed or partially-enclosed body of water, like a lake, swimming pool, or bay. The driving force can be wind, pressure changes, or seismic activity. While the wave of a meteotsunami only moves inland, the waves of a seiche oscillate back and forth.

So, a meteotsunami is essentially a tidal wave that moves toward land, while a seiche involves an ebb and flow of water from one side of a body to another. In some cases, a meteotsunami and seiche occur together.

Meteotsunamis vs. Storm Surge

Meteotsunamis are often confused with storm surges, as both involve coastal flooding. However, the mechanisms behind their formation are different.

• A meteotsunami forms when a sudden change in barometric pressure produces a wave offshore that then grows in height due to resonance.
• Storm surge forms when wind pushes water toward the shore. When storm surge adds to the height of a tide, it is called storm tide.

Dangers and Risks of Meteotsunamis

Meteotsunamis can be highly dangerous, especially in regions where they are unpredictable and infrequent. The most common dangers include:

• Coastal Flooding: Like tsunamis, meteotsunamis rapidly flood coastal areas, damaging infrastructure and threatening lives.
• Strong Currents: The rapid arrival of waves often creates strong currents that are hazardous for swimmers and boats.
• Property Damage: In severe cases, meteotsunamis damage buildings, piers, and other coastal infrastructure.
• Loss of Life: While not as deadly as tsunamis, meteotsunamis sometimes claim lives.

Assessing the risk of meteotsunamis depends on the location. Coastal regions near semi-enclosed seas or lakes, where resonance is more likely, are at higher risk.

Prediction and Detection of Meteotsunamis

Predicting a meteotsunami is challenging because they depend on rapidly changing atmospheric conditions. However, advances in meteorological and oceanographic technology have improved prediction capabilities:

• Atmospheric Pressure Sensors: Sudden drops in atmospheric pressure signal the potential for a meteotsunami.
• Ocean Buoys and Tide Gauges: These devices monitor sea level changes and detect unusual wave activity early.
• Weather Forecasting: Thunderstorms, squalls, and sharp pressure systems in specific areas indicate a meteotsunami risk.

What to Do in the Event of a Meteotsunami Warning

If a meteotsunami warning is issued, it’s essential to take the following precautions:

1. Move to Higher Ground: As with a tsunami, evacuating low-lying coastal areas is critical.
2. Stay Informed: Listen to weather updates, and pay attention to local authorities’ warnings.
3. Avoid the Shoreline: Strong currents and rapid waves occur without warning, making coastal areas dangerous.

Climate Change and Meteotsunamis

Changing global weather patterns influence the frequency and intensity of meteotsunamis:

1. Increased Storm Intensity
   Climate change is expected to lead to more frequent and intense storms, including thunderstorms and squalls. These atmospheric disturbances generate meteotsunamis, so a rise in storm activity may result in more frequent meteotsunamis in certain regions.
2. Shifts in Atmospheric Pressure Patterns
   Climate change alters atmospheric circulation patterns, leading to more extreme variations in air pressure. Rapid drops in pressure are a known trigger for meteotsunami formation. Coastal areas that have previously been less affected by meteotsunamis may see an increase in risk as atmospheric patterns change.
3. Sea-Level Rise
   Rising sea levels increase the baseline water level along coastlines, making coastal communities more vulnerable to flooding from waves of all types, including meteotsunamis.

Comparison with Other Rare Coastal Phenomena

In addition to meteotsunamis, there are other rare coastal phenomena that cause unexpected waves or water movements, often with similarly dangerous consequences:

• Rogue Waves
  Rogue waves are unusually large and sudden ocean waves that appear seemingly out of nowhere, often in deep water. Unlike meteotsunamis, rogue waves result from the constructive interference of multiple wave systems, making them extremely dangerous for ships. While rogue waves occur in deep water, meteotsunamis primarily affect coastlines and shallow bodies of water.
• Microseisms
  Microseisms are faint, continuous seismic waves caused by ocean waves. While microseisms themselves do not cause flooding or coastal damage, they indicate strong storm activity far offshore. These seismic waves sometimes provide early warnings of large oceanic events, including meteotsunamis.
• Sneaker Waves
  Sneaker waves are larger-than-expected waves that suddenly surge up the shore, often without warning, sweeping people and objects into the water. They result from wave interactions and local topography rather than atmospheric disturbances. Though sudden like meteotsunamis, sneaker waves typically occur along open coastlines rather than in enclosed seas or lakes.

References

• Bailey, Kathleen; DiVeglio, Christopher; Welty, Ashley (November 2014). “An Examination of the June 2013 East Coast Meteotsunami Captured By NOAA Observing Systems (NOAA Technical Report NOS CO-OPS 079)“. NOAA.gov. National Oceanic and Atmospheric Administration.
• Monserrat, S.; Vilibić, I.; Rabinovich, A. B. (2006). “Meteotsunamis: atmospherically induced destructive ocean waves in the tsunami frequency band”. Natural Hazards and Earth System Sciences. 6 (6): 1035–1051. doi:10.5194/nhess-6-1035-2006
• Oskin, Becky (December 2012). “Freak ‘Meteotsunamis’ Can Strike on a Sunny Day“. Huffington Post.