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.
“We’re seeing waves propagating radially and upward, in a cone-like shape,” said Joan Alexander, senior research scientist at NorthWest Research Associates. Alexander was surprised to see well-defined waves in the mesospheric airglow above the storm. Winds in the upper atmosphere can dissipate the waves before they reach such high altitudes, Alexander explained, but relatively light stratospheric winds at the storm’s latitude in April 2026 may have helped preserve them.
A relatively low amount of moonlight was fortuitous, as well. The VIIRS day-night band is sensitive to airglow in the mesosphere but also observes reflected moonlight. …