Unusual weather may have helped Ukrainian military sink Russian warship

On 13 April 2022, explosions wracked the Russian guided missile cruiser Moskva as it sailed the Black Sea more than 100 kilometers south of the Ukrainian city of Odesa. The vessel, the flagship of Russia’s Black Sea fleet, sank hours later as it was being towed to port, and Ukraine claimed it had hit the cruiser with missiles. But, how did Ukrainian forces target a vessel they normally couldn’t spot so far over the horizon?

New modeling, published this month in the Bulletin of the American Meteorological Society , suggests they caught a lucky break : Anomalous atmospheric conditions may have greatly extended the range of their missile radar.

“The thorough analysis shows that militaries really need to beware of such anomalies,” says Lt. Col. Andreas Grantinger, a meteorologist with the Swedish Armed Forces weather service who was not involved in the study. Such conditions, he notes, are common in the Mediterranean and occur from time to time in other regions.

Russian sources initially claimed the explosions aboard the Moskva resulted from an accident. Ukraine asserted it had sunk the ship with a pair of R-360 Neptune antiship missiles fired from a coastal battery east of Odesa. But the Moskva was about three times farther out than the range of the system’s targeting radar.

Analysts speculated that a U.S. military aircraft might have pointed Ukraine to the Moskva . “At that time, it would have been quite a big step for the U.S. to have shared that information,” says the new study’s lead author, Lars Norin, a space physicist at the Swedish Defence Research Agency (FOI). Russia would have viewed such assistance as the U.S. military’s direct involvement in the conflict—a major escalation the United States was seeking to avoid.

In December 2022, the Ukrainian newspaper Ukrainska Pravda reported that unusual weather conditions had allowed the Neptune’s Mineral-U search-and-track radar to register an unexpected blip in the Black Sea. Targeters concluded it was the Moskva . The report raised eyebrows at FOI, which in the early 1990s had begun to develop a wave propagation model that could be used to test the Ukrainian claims.

The claims especially intrigued Norin, who during a previous stint in Sweden’s meteorological bureau had been working on a problem that bedeviled weather radars on the country’s Baltic Sea coast. On occasion, the shorelines of Estonia and other countries across the sea would light up on radar, even though Earth’s curvature should have put them outside the radar’s range. Low-lying clouds and precipitation, they realized, were refracting echoes from the shoreline back to the radar, much as a glass lens bends the path of visible light. “We were trying to correct for that,” Norin says.

The refraction effect is nothing new. Because of it, radars generally see somewhat beyond the geometric horizon. And during the Cold War, the United States, Russia, and other nations built huge, high-powered radar stations that operated at relatively low frequencies of 3 to 30 megahertz, at which radio waves are refracted more strongly in the ionosphere. Such over-the-horizon systems can detect objects at distances of 3000 kilometers or more. However, they cannot pinpoint the location of something as small as a ship precisely enough to target it. What’s more, an over-the-horizon early-warning system the Soviet Union built in Ukraine in 1976 had been shuttered by the end of the Cold War.

Norin and his colleagues used his agency’s Detvag wave propagation model to explore whether a similar phenomenon had revealed the Moskva to Ukrainian forces. At 186 meters long and 20 meters tall, the half-century old ship presented a substantial cross section for radio waves to ping off. Although the Mineral-U radar’s specifications are not publicly known, those of a similar Russian radar are. Assuming the Mineral-U radar uses radio waves in the range of 8 to 12 gigahertz, the Swedish team calculated that under normal atmospheric conditions and from an estimated shoreline position of 45 meters above sea level, Mineral-U could detect the Moskva as far as 46 kilometers offshore—about 6 kilometers farther than the distance at which the ship would begin to poke above the horizon. Ukrainska Pravda claimed the Moskva was 120 kilometers out to sea; more conservatively, the Swedish team assumed it was 135 kilometers out.

But could atmospheric conditions bend the radar’s radio waves and the returning echoes that far over the horizon? That day, northerly cyclonic winds swept warm and dry continental air over a moist, cooler boundary layer on the Black Sea. The resulting temperature inversion drew in low-level clouds along the line of sight between the radar and the warship. The thick clouds allowed the radar’s pulses and pings to hug Earth’s curvature over a longer distance than usual. Based on parameters plugged into the Detvag model, the Mineral-U radar “would easily have been able to detect the warship in the afternoon and evening on 13 April 2022, but not earlier (or later) in the day,” Norin’s team concludes in its paper. The targeting, the scientists write, “seems to have occurred as soon as the atmospheric propagation conditions allowed for detection.”

Neither Norin nor Grantinger is aware of other instances of anomalous atmospheric conditions allowing radar to target a military object so far over the horizon. But the phenomenon is common enough that militaries account for weather in their communications. “You wouldn’t want to transmit when you believe your enemy can hear you,” Norin says.

A related phenomenon at optical wavelengths—mirages—has wreaked havoc in past conflicts, especially in desert warfare. And climate change is bound to pose new riddles for military meteorologists, Grantinger says. “We’ll have to keep up with that.”