14 November 2023

Did the weather help sink Russia's warship Moskva?

Did an atmospheric phenomenon known as anomalous propagation play a key role when Ukrainian missiles hit and sank the Russian warship Moskva in April 2022? Using publicly available weather data researchers from FOI can now prove that it was possible for a ground-based Ukrainian radar to detect Moskva, despite the ship being located far beyond the normal radar horizon.

The distance at which any given radar system can detect a target near the surface is usually limited by the Earth's horizon. To calculate the distance to the horizon certain assumptions about the prevailing atmospheric conditions are usually made.

In the case of Mineral-U, the ground-based and mobile radar system most likely used by the Ukrainian military to detect the Russian warship, the detection distance is about 50 kilometres.

So questions were raised on 13 April 2022, when the Ukrainian military claimed two of its missiles had hit Moskva, given that the ship was located about 135 kilometres out at sea.

“The problem with the usual way of estimating the radar horizon is that it does not consider the varying atmospheric conditions that can be present,” says Lars Norin, from the Department of Radar Electronic Warfare Systems at FOI.

Temperature, pressure and humidity can vary a lot from day to day and from different layers of the atmosphere and these parameters can have a significant impact on the propagation of electromagnetic waves, which are emitted by radar systems.

“Anomalous propagation happens when certain gradients in temperature, pressure and humidity in the atmosphere cause electromagnetic waves to be refracted back toward Earth’s surface,” Norin explains. “This phenomenon can allow a radar system such as Mineral-U to reach far beyond the normal horizon.”

Recently analysed weather data suggest the right conditions for anomalous propagation did occur in the afternoon of 13 April 2022, and that this could explain how Moskva showed up on Ukrainian radar.

Using data from the European Centre for Medium-Range Weather Forecasts along with satellite images of the area, Norin, together with FOI-colleague Niklas Wellander and Abhay Devasthale, researcher at the Swedish Meteorological and Hydrological Institute, could more precisely determine the atmospheric conditions throughout the day on 13 April last year.

This in turn made it possible to more accurately calculate the actual reach of the radar system for every hour of the day.

“Our research shows that from 4 pm to 9 pm local time, the Mineral-U radar would have been able to detect a target far beyond the horizon,” Niklas Wellander explains. “Given our estimated size of Moskva we found that the radar would easily have been able to detect it, but only within that window of time.”

The findings were recently published by The Bulletin of the American Meteorological Society. External link, opens in new window.