GNSS shows how volcanic eruptions cause disturbances in the ionosphere


On January 15, the uninhabited volcanic island of Hunga Tonga-Hunga Haapai in the Tonga archipelago in the South Pacific erupted with great force, shattering ocean waters halfway around the globe.

GNSS engineers also discovered its impact hundreds of miles higher in the ionosphere. The GNSS community is now moving from such fact-finding to real-time monitoring using NASA’s Global Differential GPS (GDGPS), the team said. Section of tracking systems and applications at NASA’s Jet Propulsion Laboratory (JPL) in Southern California.

“We tracked in real time four GNSS satellite constellations from many stations around the world using the GDGPS network. In particular, the three closest stations to the volcano are in Samoa, Fiji and Tahiti, ”said doctoral student Leo Martir. “We could see extremely high and strong signals in the ionosphere, which is very unusual. Depending on the radial distance from the eruption, the first detected ionospheric perturbation probably arose directly from the explosion. Then we see patterns that propagate over increasing distances with different radial velocities. ”

Monitoring such events adds information to a catalog of signals from natural hazards, said Siddhart Krishnamurti, a research technologist who manages the JPL GUARDIAN tsunami warning system in near real time, which is currently under development. “This is useful because in the future, if you want to be able to spot natural hazards and issue alerts, you need to know what the signal looks like. There have been reports of a tsunami in Tonga due to this event, so we will consider possible signs of a tsunami in the ionosphere. We are trying to get to the place where we catch such a signal, and we can say: “This is a tsunami that is spreading at such a speed and in this direction.”

Diagram: Jet Propulsion Laboratory

Before being detected in the ionosphere, signals of natural hazards must travel all the way from the surface. For a tsunami it usually takes more than 10-20 minutes, but a volcanic eruption took only a couple of minutes to reach the ionosphere because it rose up. “We do not yet know, based on observations, how the various events on the surface caused by natural hazards are combined with the atmosphere,” said research technologist Panagiotis Vergadas. “Each event is unique in its spectral properties.”

The event did not affect the quality of GNSS GDGPS positions or orbits because dual-frequency measurements eliminate significant ionospheric effects. “Instead of looking at the direct impact on the position of our available reference stations, which makes our traditional real-time monitoring and which was basically insignificant, imagine connections from each of these stations to a dozen or more satellites,” he said. . Larry Romance, GDGPS chief technologist. “Whenever one of these many links enters the ionosphere, we can monitor this signal for ripples as the waves pass. So this is an incredibly powerful method for viewing violations, just in terms of data density. This is very complementary to monitoring position-based natural hazards because the data is much richer. ”

In addition to volcanoes and tsunamis, some other natural events, such as earthquakes and very large thunderstorms, also cause these effects. “These natural influences cause large-scale low-frequency pressure shocks that tend to rise and be visible in the ionosphere,” Krishnamurti said. “There are also perturbations of the ionosphere due to events outside the Earth, such as solar flares or the impact of fireballs.”

Many of these shocks begin in the troposphere, which is 10 km to 15 km high, including hurricanes that cross gravitational waves all the way to the ionosphere, and heat waves that have been observed to reach 600 km. said Vergadas. “There are also geomagnetic storms and sub-storms that can change the ionization of the ionosphere during electronic precipitation. Thus, the combination can occur both below and above, or simultaneously, and then the effect can be greatly enhanced.

Most perturbations that come from below have the nature of pressure – that is, they begin as mechanical waves – while most of those that come from above are electromagnetic. “Apart from nuclear explosions, very large chemicals, such as the explosion in Beirut in 2020, are also causing a signature in the ionosphere because they create very large pressure waves,” Krishnamurti said.

Photo: Tongan Meteorological Service, Tongan Government

Photo: Tongan Meteorological Service, Tongan Government

GNSS shows how volcanic eruptions cause disturbances in the ionosphere

Source link GNSS shows how volcanic eruptions cause disturbances in the ionosphere