Satellites observed striking upper-atmosphere phenomena generated by an intensifying tropical cyclone.
Atmospheric gravity waves generated by Super Typhoon Sinlaku are visible via mesospheric airglow in this nighttime image acquired with the VIIRS (Visible Infrared Imaging Radiometer Suite) on the NOAA-20 satellite on April 12, 2026, Universal Time (April 13 local time).
NASA Earth Observatory/Michala Garrison

Image of the Day for June 1, 2026
NASA Earth Observatory

Jun 01, 2026

In mid-April 2026, Super Typhoon Sinlaku churned across the North Pacific Ocean and brought heavy rain and flooding to the Mariana Islands. The storm reached “violent typhoon” status—the highest intensity on the scale used by the Japan Meteorological Agency and roughly equivalent to a category 5 storm on the Saffir-Simpson wind scale. Sinlaku was one of only a handful of tropical cyclones of that intensity known to have occurred so early in the year in the region, meteorologists noted.

Sinlaku rapidly intensified over the ocean before its impacts reached land. Around the time of this strengthening, satellites began to detect that the typhoon’s effects also extended upward, into the upper atmosphere.

The nighttime image above, acquired with the VIIRS (Visible Infrared Imaging Radiometer Suite) on the NOAA-20 satellite, shows atmospheric gravity waves radiating from the typhoon. These waves, resembling ripples on a pond, were made visible to the sensor via airglow in the mesosphere. Airglow occurs when atoms and molecules, excited by sunlight during the day, later emit light to release excess energy.

The release of latent heat near the eyewalls of tropical cyclones is known to drive convection and the formation of tall cumulonimbus clouds. These “hot towers” can rise out of the troposphere, the lowest layer of the atmosphere, and generate waves that propagate into the stratosphere and mesosphere above. An analysis of past tropical cyclones revealed that gravity waves often occur around the time that storms are intensifying. Indeed, in the 24 hours prior to the acquisition of the image above, Sinlaku had strengthened from a category 2 to a category 5 storm.

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Observing atmospheric gravity waves, particularly those caused by tropical cyclones, goes beyond scientific curiosity. Practical implications could include improved monitoring of storm development. “We’d like to use gravity waves to tell us if a storm is intensifying,” Alexander said, “which can be difficult to know, especially over the open ocean.” A geostationary satellite with the proper infrared imager would be able to observe gravity waves and track tropical cyclone evolution, she and colleagues have argued.

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